Windy and Colder...or Warmer

Colder air began pouring into the Fairbanks area Wednesday afternoon. The 4am Thursday surface analysis shows big high pressure extending from the Beaufort Sea southeast through the Yukon and western Northwest Territories, and broad low pressure in the Gulf of Alaska. Northeast winds gusted to  41 mph at the Fairbanks area during the late afternoon and early evening Wednesday.

Courtesy of Environment Canada

The winds diminished mid-evening but never went calm overnight. This prohibited any inversion from forming, as seen in the sounding plotted on the left. The wind speeds above the ground, plotted on the right side of the lower chart, are not excessive. Rather, with enough sunshine now to completely break the valley based inversion, once the winds started up Wednesday afternoon the winds were strong enough (enough momentum transport) to keep an inversion from developing, even under completely clear skies.

The result was that temperatures on the valley floor were considerably higher than the last couple of nights even as hills were much cooler. At Fairbanks International, the low temperature Thursday morning was 9 below, which was 13 degrees warmer than Wednesday. At Keystone Ridge, the low Thursday morning of  11 below was 17 degrees colder than the morning before. 

Updated Fairbanks Temperatures

Here's an updated plot of daily mean temperatures and the associated standardized departures at the Fairbanks Airport. Since October 1st, four percent of days have been more than 1.5 standard deviation above the mean, but 14 percent have been above the daily mean.  

The Cooling Snowpack

Courtesy of IARC

Here's a plot of temperatures at the Smith Lake met station near UAF West Ridge the past couple of  days. What caught my eye here was the one meter temperature yesterday during the afternoon (inside the magenta box). Notice that at one meter the temperature spiked around noon, but then fell back to right around freezing even as the 2, 4 and 8 meter high sensors remained in the upper 30s and lower 40s. Presently the one meter sensor is less than half a meter above the surface of the snowpack, and it looks as though on Friday the air just above the snow surface was isolated and kept cool in part by sublimation. This is much less evident on Saturday, when there was evidently better mixing, and the different between the 1 meter temperature and higher levels was mostly only a couple degrees.

Mild Day in Fairbanks

Courtesy of the FAA

UPDATED FOR FINAL HIGH TEMPS:

Friday was the mildest day in Fairbanks since October 10th with a high of 42F at Fairbanks Airport.
Other high temperatures in the area included:
40F at Keystone Ridge
42F at UAF West Ridge
43F at Eielson AFB,
44F at Fort Wainwright, Gilmore Creek and College Hills,
46F at Aurora
48F at North Pole

The warm weather was due to a storm in the Bering Sea that brought warm air across the Alaska Range. The photo above from Ester Dome on Friday afternoon shows some lenticular structure due to the strong southerly winds across the mountains.

February Summary

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
733 PM AKST FRI MAR 1 2013

...FEBRUARY WEATHER SUMMARY FOR FAIRBANKS ALASKA...

FEBRUARY WAS A FAIRLY QUIET MONTH IN FAIRBANKS. MILD WEATHER
EARLY IN THE MONTH AND AGAIN THE LAST COUPLE OF DAYS ALMOST
EXACTLY BALANCED OUT A SPELL OF COLD WEATHER AFTER MID-MONTH. AT
THE FAIRBANKS AIRPORT...THE AVERAGE HIGH TEMPERATURE FOR FEBRUARY
WAS 10 ABOVE AND THE AVERAGE LOW WAS 13 BELOW. THE MONTHLY AVERAGE
OF 1.4 BELOW WAS ALMOST EXACTLY NORMAL. THE HIGH FOR THE MONTH
WAS 29 DEGREES ON THE 9TH...WHILE THE LOWEST TEMPERATURE AT THE
AIRPORT WAS 43 BELOW ON THE 19TH.

FOR THE FOUR MONTHS OF NOVEMBER THROUGH FEBRUARY...THE AVERAGE
TEMPERATURE AT THE FAIRBANKS AIRPORT WAS 7.7 BELOW...NEARLY FIVE
DEGREES BELOW NORMAL. THIS WAS THE COLDEST NOVEMBER THROUGH FEBRUARY
SINCE 1998-99. THERE WERE A TOTAL OF 15 DAYS WITH A LOW
TEMPERATURE OF 40 BELOW OR LOWER...A BIT ABOVE THE LONG TERM
AVERAGE OF 11 SUCH DAYS BUT TWO LESS THAN LAST WINTER. IN
CONTRAST...THE AVERAGE TEMPERATURE FOR THE FIRST TWO MONTHS OF
2013 WAS 2.1 BELOW...WHICH IS MORE THAN TWO DEGREES ABOVE NORMAL.

SNOWFALL WAS LIGHT BUT FREQUENT THE FIRST THREE WEEKS OF THE
MONTH. TOTAL SNOWFALL WAS 10.7 INCHES...OVER A THIRD MORE THAN
NORMAL FOR FEBRUARY. THE SNOW MELTED DOWN TO 0.48 INCHES OF
WATER...WHICH IS ABOUT 15 PERCENT ABOVE NORMAL. SNOW DEPTHS AT THE
AIRPORT ROSE TO AN EVEN TWO FEET ON THE 22ND BEFORE SETTLING BACK
TO 22 INCHES BY MONTHS END. AS OF THE END OF FEBRUARY...TOTAL
SNOWFALL FOR THE WINTER STOOD AT 50.5 INCHES...WHICH IS ABOUT SIX
INCHES BELOW NORMAL.

LOOKING AHEAD TO MARCH...TEMPERATURES CLIMB SHARPLY AS THE SUN
RISES HIGHER AND HIGHER IN THE SKY EACH DAY. AVERAGE DAILY HIGH
TEMPERATURES INCREASE FROM 18 DEGREES ON THE FIRST TO 34 DEGREES BY 
THE 31ST. AVERAGE LOW TEMPERATURES START OFF MARCH AT 9 BELOW BUT
RISE ABOVE ZERO BY THE 21ST...AND THEN UP TO 8 ABOVE BY THE 31ST.
OVER THE PAST 108 YEARS MARCH TEMPERATURES IN FAIRBANKS HAVE
RANGED FROM 56 ABOVE IN 1994 TO 56 BELOW IN 1911. MARCH IS...ON
AVERAGE...THE DRIEST MONTH OF THE YEAR. NORMAL PRECIPITATION IS
0.25 INCHES OF LIQUID FROM AN AVERAGE OF 4.9 INCHES OF SNOW. IN
SOME YEARS THE WINTER SNOWPACK BEGINS TO MELT DURING THE LAST WEEK
OF MARCH IN URBAN AREAS...THOUGH TYPICALLY THAT DOES NOT OCCUR
UNTIL APRIL.

DURING MARCH...POSSIBLE SUNSHINE INCREASE BY NEARLY SEVEN MINUTES
EVERY DAY...AND REACHES 13 HOURS AND 33 MINUTES BY THE END OF THE
MONTH.  

THE FORECAST FOR MARCH FROM THE CLIMATE PREDICTION CENTER CALLS
FOR INCREASED CHANCES OF SIGNIFICANTLY BELOW NORMAL TEMPERATURES
AND SLIGHTLY INCREASED CHANCES OF ABOVE NORMAL PRECIPITATION.

$$
RT MAR 13

Winter Temperature Recap For Fairbanks

February 2013 is in the books, so here is an updated plot of temperatures this winter in Fairbanks. The frequently above normal temperatures since late December were not enough to offset the deep cold early in that month, resulting in an average temperature for core winter, December through February of -7.3ºF. This is significantly below normal but several winters recently have been colder. The departure of -4.9ºF for the November through February is more much significant. This is the coldest such period since 1998-1999 and  third coldest since the 1976 PDO shift (1989-90, which also featured a very cold November, is the coldest Nov-Feb period since 1976, at -9.0ºF).

Sunshine Gaining…but not quite there yet

Here's a plot of the Fairbanks soundings from Sunday and Monday afternoons. The primary item of interest here is that both days featured lots of sunshine and very little wind. Monday especially was almost cloud free. This nicely illustrates that even though the maximum solar elevation is now above 15 degrees, it's still not enough to mix out the boundary layer. Another week to ten days should do it.

Seasonal Snowfall Creeping Up

Here's an update on seasonal snowfall in the Fairbanks area (KERA2=Keystone Ridge, PAFA=Fairbanks International).

Thanks to frequent light snows, snowfall is above normal now in Fairbanks area for February, and is getting back toward normal for the season. Snow depths are generally near or slightly more than two feet in the area.

Colder Early Winters in Fairbanks?

Were only a month away from the vernal equinox now, with possible sunshine increasing at nearly seven minutes a day. Nonetheless, today we'll look back to the dark days of early winter. Fairbanks has had a run of cold early winters, or maybe better, early winters the past few years have featured more cold weather than before that. Is this something new? One way to assess this is simply to examine the number of cold days. Here I've plotted the numbers of days October through December with low temperatures of 20 below or lower. I chose 20 below because temperature that "warm" should not be impacted too much by the urban heat island growth. 

 

What we see here is this past early winter, with 36 days of lows of 20 below or lower before New Years Day, was the third highest total since 1930. The red line represents the 5-year running median, which is now back up to values common in the mid 1990s and during the past negative PDO phase (transitions between phases marked by the black lines). The plot of lowest absolute temperature during early winter does not paint the same picture:

This clearly shows that absolute low temperatures have been increasing. Prior to 1980, temperatures of 50 below or lower did not occur every early winter, but were by no means uncommon. Since 1980…just one year, 1999. This however must, in part, be attributable to increase in urban effect, which is greatly amplified by the formation of ice fog at temperatures colder than -35F. 

Cold Airmass over Fairbanks-Land

It's a chilly airmass over Fairbanks, with afternoon temperatures barely cracking 10 below after morning lows in the 20s and 30s below. Here are the Monday soundings from the Fairbanks Airport. Notice that the temperature only varies by about three degrees Celsius in the lowest kilometer, with not much of a surface inversion. On the up side, it was a bright and sunny day.

Fairbanks Winter Temperature Update

Here's an update on Fairbanks temperatures thus far this winter. Reader Gary asked for a plot showing relative magnitude of the daily departures, and after some fiddling around with Excel I came up with this plot:

The daily mean temperatures are the values at the end of the bars, with above and below normal values colored accordingly. Just eyeballing this you can see that early winter was consistently chilly, while since the last days of December it has been mostly mild except for the few days of deep cold late in January. The actual means are:

Oct 01 to Feb 16 Mean Temp: -1.1F which is 4.0 degrees below the 1981-2010 normals
Dec 01 to Feb 16 Mean Temp: -7.5F which is 2.0 degrees below the 1981-2010 normals
Jan 01 to Feb 16 Mean Temp: -1.1F which is 5.3 degrees above the 1981-2010 normals

Sunshine but not much Heating…Yet

Courtesy of the FAA

The sun rises over Fairbanks-land Thursday to a reasonably sharp inversion. Valley temperatures are just below zero while hillsides are in the 20s above. The inversion held Wednesday, with the high temperature at both Fairbanks Airport and Goldstream Creek of +7F, while Keystone Ridge had a low temperature Wednesday of +13F.

Daytime Inversion Still Holds

The sun is getting higher in the sky every day, but at solar noon the sun is still only 12 degrees above the horizon. This is still not enough to break the inversion without some clouds and/or wind help, as Wednesday afternoon's sounding shows. Temperatures in most places on the valley floor never got out of the single digits, while higher elevations were in the low 20s.

Post-Frontal Sunshine

Courtesy of Alaska Climate Research Center

As sometimes happens, especially with storms moving northwestward from the North Pacific into the Bering Sea, the occluded front has fractured, with the high clouds out-racing and becoming disassociated with the surface front. When this happens, what low level moisture there is stripped out crossing the Alaska Range and a large area of temporarily clear skies develops. That's what happen Saturday afternoon, resulting in a sunny and mild weekend day for Fairbanks, with temperatures in all but the lowest spots jumping up into the upper 20s and lower 30s.

Snow Slowly Catching Up

While the Northeast digs out, here in Fairbanks we plod along, "nickel and diming" our way to near normal snowfall. Here's an updated plot of cumulative snowfall for the season. The big snow in December continues to be the highlight, being (practically) the only significant snow in the two months from early November through early January. Since early January snowfall has been more regular, and the Airport is now up to 90% of normal for the season.

The Sun is Shining, But...

The sun is shining these days at Barrow, but there is not much heating yet. At 4pm Thursday the temperature fell to 34 below as winds shift to the south, which is an overland trajectory at Barrow. This is the lowest temperature so far this winter at Barrow.

Courtesy of the FAA

More Winter Temperatures

Here is a plot of daily mean temperatures so far this winter at the Fairbanks Airport along with the 1981-2010 normal. Recall that the shaded area represents one standard deviation from normal, so actual temperatures that are inside the gray area could be considered as "near normal". 

Cold Still Reigns…For Now

Here's an update of Fairbanks standardized daily temperature anomalies thus far this winter. For those keeping score at home, the average temperature December 1st through February 3rd at the Fairbanks Airport is -9.4F, a substantial 3.4 degrees F below normal. October 1st through February 3rd the mean temperature is -1.4F, a whooping 4.9 degrees F below normal. The 1 to 2 week forecast from the Climate Forecast System has been consistent in keeping most of Alaska quite mild in the mean…so I expect that those impressive seasonal anomalies will decrease during the course of this month. 

Gina Puffin Feeder

Here's a link to a website I just learned about yesterday: the GINA Puffin Feeder site. GINA is a group at UAF that is involved with capturing and distributing Alaska and high latitude imagery from a wide variety of sources.  I've used GINA's Swath Viewer for some years, but yesterday I saw a presentation on the GINA Puffin Feeder website that is distributing imagery from the new VIIRS polar orbiter satellite. It has a variety of interesting images, including true color, landform and a low light visible channel.

Here's the low light visible image taken at 4am Friday. This is unprocessed by me; this is as-is on the website. Look at that detail! The bright swirl on the upper left hand side of the image is aurora, and the lights of Prudhoe Bay, Anchorage and Fairbanks are all clearly visible.

Fairbanks January Summary

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
835 AM AKST FRI FEB 1 2013

...JANUARY MONTHLY WEATHER SUMMARY FOR FAIRBANKS ALASKA...

JANUARY 2013 WAS A ROLLER COASTER OF INTERESTING WEATHER.

THE MONTH OF JANUARY BEGAN UNSEASONABLY WARM...OVER 30 DEGREES
ABOVE NORMAL ON THE 1ST OF THE MONTH. TEMPERATURES FELL BACK TO
NEAR NORMAL GRADUALLY THROUGH THE 10TH OF THE MONTH...UNTIL
UNSEASONABLY WARM SOUTHERLY FLOW PUSHED BACK INTO THE INTERIOR BY
THE 12TH. THE WARM AIR PLATEAUED ON JANUARY 14TH WHEN THE
FAIRBANKS AIRPORT REACHED 37 DEGREES. THE WARM AIR WAS ACCOMPANIED BY A
SWATH OF RAIN AND SNOW WHICH CAUSED WIDESPREAD TRAVEL HEADACHES
THROUGHOUT THE FAIRBANKS AREA. AT THE AIRPORT...0.15 INCHES OF
RAIN FELL...THE GREATEST JANUARY RAINFALL SINCE 1963. IN THE NORTH
POLE AREA...SOME PLACES RECEIVED OVER ONE THIRD OF AN INCH OF
RAIN...AND THROUGHOUT THE AREA MANY ROADS REMAINED ICE COVERED AT
MONTHS END. FOLLOWING THE RAIN...TEMPERATURES COOLED BUT REMAINED
ABOVE NORMAL MOST DAYS UNTIL STAGNANT ARCTIC AIR MOVED IN ON THE
25TH. THE THERMOMETER PLUMMETED TO THE 40S BELOW FOR THE FIRST
TIME OF 2013 ON JANUARY 25TH. THE COLD SPELL OF LATE JANUARY DID
NOT LAST LONG BUT THERE WERE SEVERAL DAYS WHERE AIR QUALITY
EXCEEDED THE EPA HEALTH LIMITS FOR FINE PARTICULATE
POLLUTION...AIDED BY THE USUAL STEEP TEMPERATURE INVERSIONS IN THE
FAIRBANKS BOWL.

OVERALL...THE AVERAGE JANUARY TEMPERATURE WAS 2.7 BELOW. THIS IS
5.2 DEGREES ABOVE NORMAL AND MADE THIS THE MILDEST JANUARY IN
FAIRBANKS SINCE 2002. THE MAXIMUM TEMPERATURE FOR THE MONTH
OCCURRED ON THE 14TH WHEN THE FAIRBANKS AIRPORT REACHED 37
DEGREES. THE MINIMUM TEMPERATURE OF 48 BELOW WAS REACHED ON
JANUARY 27TH...WHICH TIES THE 48 BELOW REACHED ON DECEMBER 17TH
FOR THE LOWEST TEMPERATURE OF THE WINTER SO FAR.

JANUARY ENDS WITH A TOTAL OF 14 DAYS WITH TEMPERATURES OF 40
BELOW OR LOWER AT THE FAIRBANKS AIRPORT. FAIRBANKS HAS NOT REACHED
50 BELOW THIS YEAR...THOUGH SOME TYPICALLY COLDER PLACES
HAVE...INCLUDING LOWS OF 54 BELOW IN TWO RIVERS...52 BELOW AT
NORTH POLE AND 50 BELOW AT GOLDSTREAM CREEK.

PRECIPITATION FOR THE MONTH OF 0.79 INCHES WAS 0.21 INCHES ABOVE
NORMAL FOR THE MONTH OF JANUARY. DESPITE THE ABOVE NORMAL
PRECIPITATION AMOUNTS...SNOWFALL FOR JANUARY OF 9.9 INCHES WAS
ALMOST EXACTLY NORMAL. SNOW DEPTH INCREASED TO 19 INCHES BY THE END
OF JANUARY.

WITH THE CLIMATOLOGICALLY COLDEST PART OF WINTER BEHIND...FEBRUARY
PROMISES TO DELIVER MORE NOTICEABLE DIURNAL TEMPERATURE RANGES AS
THE MONTH PROGRESSES AND THE REGION GAINS OVER 3 HOURS OF POSSIBLE SUNSHINE
BETWEEN THE 1ST TO THE 28TH. AVERAGE TEMPERATURES INCREASE FROM 6
BELOW TO 4 ABOVE BY THE END OF THE MONTH. THOUGH ONLY A 10 DEGREE
AVERAGE INCREASE...THE NORMAL HIGH TEMPERATURES BY THE END OF THE
MONTH IS 17 ABOVE. NORMAL SNOWFALL IN FEBRUARY IS 8.1 INCHES...THOUGH
HISTORICALLY FAIRBANKS HAS OCCASIONALLY RECEIVED DAILY SNOWFALLS
IN EXCESS OF TEN INCHES...MOST RECENTLY IN FEBRUARY 1996 AND
2011.

THE FORECAST FOR FEBRUARY FOR FAIRBANKS FROM THE CLIMATE
PREDICTION CENTER CALLS FOR INCREASED CHANCES OF SIGNIFICANTLY
ABOVE NORMAL TEMPERATURES. 

$$

JM/RT

Elevated Inversion

Here's the Fairbanks sounding from Wednesday afternoon, showing a nice elevated inversion. Temperatures were up into the upper teens to around 20 degrees above 2200' MSL, while zero to 10 above at lower elevations.

Nip in the Air

Courtesy of the FAA

Ice fog was quite dense this morning in Fairbanks  but had almost completely burned off by mid-afternoon, as evidenced by these two views from Ester Dome, the top one from 1138am AST and the bottom one four hours later.  Temperatures are rapidly warming aloft now and winds have picked up at elevation and channeled valleys.

Here are some low temperatures reported the past couple days:

Chicken Co-op: 62 below
Eagle Co-op: 57 below
Two Rivers: 54 below
Eielson AFB: 52 below
North Pole: 52 below
Fort Wainwright: 51 below
Fairbanks Airport: 48 below
Aurora: 45 below
Gilmore Creek: 45 below
UAF West Ridge: 44 below
Keystone Ridge: 29 below

Pacific Decadal Oscillation and Interior Alaska

I often mention the Pacific Decadal Oscillation and Interior Alaska climate, and I've written about it before, but it's so important to understanding climate variability for most of Alaska (except the North Slope), that it's worth updating. 

To start with, below is the classic PDO anomaly diagram from the University of Washington. The color field is the sea surface temperature anomalies and the arrows are the surface wind anomalies. On the left is the positive phase of the PDO and the right is the negative phase. Note that from the North Pacific-wide perspective the phases are misnamed: the positive phase features a huge area of cooler than normal temperatures from Asia to about 155W, and the negative  phase a similarly place warm anomaly. The surface wind anomalies are southerly into mainland Alaska during the positive phase and northerly during the negative phase.  

Courtesy of the U. of Washington

Next is an updated plot of the PDO Index. I constructed this by taking the monthly PDO index page at the UW website and constructed four non-overlapping seasonal means per year (effectively a course low pass filter). The heavy black line is the ten year (40 season) centered running mean. Using a centered mean preserves the timing of the phase transitions.

The phase changes in 1946 and 1976 are pretty clear in the ten year mean, while the early 20th and  21st century transitions are less obvious. At least the 21st century transitions is a little clearer in the even smoother annual averages (note I've used a July to June year in order to capture as a unit the Northern Hemisphere winter):

Since the 2005-06 year, only once (2009-10) has the annual mean PDO been above zero, and even that just barely, and the negative values have been repeatedly lower than any time since the 1976 transition. This is why I place the positive to negative phase PDO transition at 2007.

Deeper Cold

It's colder this Sunday morning across Fairbanks-land, and it's a deep cold. Here's a temperature trace from the early morning sounding. Unlike my usual fashion, this one is for the lowest five kilometers of the atmosphere. This is quite a cold troposphere: the warmest temperature in the entire atmosphere over Fairbanks is just -27.5C. Note too that the inversion right at the at the time of the sounding was not all  sharp: the surface was only about 4C cooler than 400 meters up. Since then the inversion has sharped some as valley temperatures are now well down in the 40s below.

Some low temperatures reported so far (through 9am AST) include:

Fort Wainwright: 51 belo
Eielson AFB: 50 below
Goldstream Creek: 49 below (through 6am) 
Fairbanks Airport: 48 below
UAF West Ridge: 42 below
Keystone Ridge: 28 below
Clearly Summit: 22 below

In the eastern Interior it's, as usual, even colder:

Chicken Co-op: 60 below
Eagle Co-op: 57 below
Fort Yukon: 56 below
Eagle Airport: 55 below
Dawson, YT: 54 below
Circle Hot Springs: 52 below
Northway: 51 below

It's a Cold One

Courtesy of the FAA

It's a cold Saturday in Fairbanks-land. The dawn view from atop Ester Dome shows thin ice fog covering much of the flats. Low temperatures so far this morning include:

Eielson AFB: 49 below
Fort Wainwright: 47 below
Goldstream Creek: 45 below (thru 6am)
Fairbanks Airport: 44 below
UAF West Ridge: 40 below
Keystone Ridge: 25 below
Cleary Summit: 18 below

Extreme Wind Chill in Atigun Pass

Deep cold air is pouring across the central and eastern Brooks Range this morning, creating extremely low wind chills. The NRCS SNOTEL at the top of Atigun Pass (4800' MSL), the highest point on the Dalton Highway, at 7am AST Friday was reporting a temperature of 36 below with sustained winds of 36 mph, gusting to 45 mph. That's a wind chill of 77 below. Farther west, at Anatuvuk Pass at 9am AST it was 24 below with winds 28 gusting 35 mph, a wind chill of 58 below.

No Inversion Morning

Lest you think there's always a surface based inversion in Fairbanks during mid-winter, here's a rare example from this morning with no inversion and no significant snow falling. The wind from the surface right up through 1000 meters AGL was 10 to 15 knots. By late morning wind chills were getting nippy in exposed higher elevations: the Caribou Peak RAWS north of the Chatanika at 2500' at noon was down to 15 below with sustained 14 mph winds. Not up to North Slope standards, but enough to notice.

Ted Fathauer (1946-2013)

My friend, colleague and former boss Ted Fathauer unexpectedly died late Sunday evening at his home in Fairbanks, just three weeks after retiring from the Weather Service. For those on Facebook,  here is the NWS Alaska Region Facebook Tribue to Ted:

http://www.facebook.com/rthomanjr/posts/428668320537438?ref=notif&notif_t=like

RIP Ted

Barrow Sunrise

The sun is back at Barrow: FAA webcam image sequence starting about 11am AST  through 115pm Tuesday. Temperature at sunrise a pleasant 7 below with east winds 30 gusting 35 knots. Images  courtesy of the FAA.

One More Round of Interior Alaska Seasons

Okay, before moving on to actual numbers, here's my personal "integrated" seasonal definitions for Fairbanks-land. By integrated, I mean this takes into account astronomics, climate and events.

• Early Winter: establishment of the permanent winter snow cover in October until mid-November. Roads are regularly icy and skies often quite cloudy. Most precipitation is snow but drizzle or very light rain from shallow clouds not that uncommon.
• Core Winter: the dark time of year, mid-November until the end of January: potential for extreme inversion and of course deep cold. 
• Late Winter: February through very early March: more sunshine, less snow. Daytime inversions weaken from the rapidly increasing solar heating but do not completely break without other forcing.
• Early Spring: very early March until sustained melting commences, typically early April. Often clear for days on end and breezy even in town. The time of year to get out and "play in the snow".
• Late Spring: early April until early to early to mid May: active snow melt and break-up. Ends at green-up. The sloppy season; crud emerges from the snow. Not the finest time in Fairbanks, but all the daylight is a delight after the dark winter.  Precipitation of any kind uncommon.
• Early Summer: green-up until start of the deep convective season, typically early to mid May until very early June. Very light brief showers common.
• High Summer: peak of the convective season, very early June until early-mid July. Highest frequency of hot days, and often all the rain comes as showers or thunderstorms.
• Late Summer: the stratiform rain season, typically mid July to mid-late August. Often condensed to "August" in general conversation in Fairbanks, i.e. "it always rains for the Fair". Highest frequency of fog.
• Early Autumn: late August until mid-late September: return of darkness at night, colors in trees and undergrowth. Ran frequency drops way down from late summer. The quintessential "crisp frosty nights and gorgeous sunny days" time of year (my personal favorite these days, just ahead of Late Winter).
• Late Autumn: mid to late September until establishment of permanent winter snow cover. Changeable weather, most common time for "snow in the hills, rain in the valley" kind of weather. Increasing darkness yet all is brown: harder to see moose by the road without some snow cover.

So obviously these definition are generalizations and in some years differ. For example, in 2004 there never was a late summer in that a sustained period with regular stratiform rain never occurred. The super high aloft help almost all month and helped keep the record wildfire season going until in snowed in September.

Seasonal Defintions in Interior Alaska

Continuing on the topic of what are "seasons" in Interior Alaska, I thought it might be useful lay out some definitions that crop up or that I have used on occasion. Feel free to chime in with more.

• Fixed dates with "Equal" Length Seasons:
• Traditional: Winter begins at Winter Solstice, Spring begins at Vernal Equinox, etc. I don't know the history of this definition, but it it can't be completely rooted in northwestern European tradition: witness Shakespeare's 'A Midsummer Night's Dream' which takes place around Summer Solstice. The inappropriateness of this definition in Interior Alaska, at least in relation to climate, natural history, etc. is obvious. 
• Astronomical: Winter is the quarter of the year with the least possible sunshine, i.e. the darkest quarter and summer the quarter of the year with the most possible sunshine. So, Winter is Nov 6-Feb 5, Spring Feb 6-May 5, Summer May 5-Aug 5 Autumn Aug 6 to Nov 5.  This is certainly better than the traditional definition. 
• Meteorological: by long standing convention, Winter is Dec-Feb, Spring Mar-May, etc.  Mostly commonly used in analysis and certainly captures the core season in Interior Alaska, i.e. winter is the (on average) three coldest calendar months and summer the warmest.  A variation of this would be the two-season definition of winter (cold season) as Oct-Mar and summer (warm season) May-Sep.

• Fixed Dates with Variable Length Seasons
• Winter is coldest third of the mean daily temperature variation and summer the warmest third (spring and autumn the middle third), So for Fairbanks, the mean daily temperatures (1981-2010 normals) range from -9F in mid January to 64F for a couple weeks in late June and early July, for a range of 73F. So the coldest third of the temperature range is -9F to +15 F and summer is 40F to 64F. So for Fairbanks this yields a winter season of Oct 26-Mar 24 and a summer season of Apr 26-Sep 25. This is a much better fit to many residents' intuition that spring and autumn are functionally much shorter than winter and summer.
• A two-season definition with Winter as the Mean Snow Cover Season, for Fairbanks something like Oct 16-Apr 22. Summer is the rest of the year.

• Phenomena based Yearly Variable Dates (including single season definitions)
• Winter begins when the first day that the 5 or 7-day running mean temperature is below freezing and ends when the running mean goes above freezing (for Fairbanks typically in Oct and Apr). Summer begins the first day when the 5 or 7-day running mean temperature is above 55F or 60F (depending on application, typically later May to late Aug in Fairbanks). Spring and autumn in between.
• Winter begins when the permanent winter snow cover is established. For Fairbanks, this almost always in October and ends when the snow is gone (for Fairbanks April or early May). 
• Autumn starts when deciduous tree leaves turn color (late August or very early September).
• Summer begins on the date of green-up
• Summer begins with river ice break-up and winter begins with river freeze-up

Sunny...But not Much Warming

Courtesy of Alaska Climate Research Center

The sun is getting higher each day but still is not  high enough to do much to break the surface inversion. The webcam photo from the Alaska Climate Research Center on UAF West Ridge was taken at exactly solar noon. 2pm temperatures are in the 20s and 30s below in the lowest areas, including 30 below at Woodsmoke, 27 below at Goldstream Creek and 23 below at Fairbanks International. In contrast, higher elevation temperatures at 2pm include 6 below at Keystone Ridge and 4 below at Wickersham Dome and Clearly Summit.

Average Winter Temperatures: The Long View

Reader Gary asked about Fairbanks-land temperatures over the course of the entire winter. Now what winter means in Fairbanks is an interesting question, but obviously simplistic definitions like Solstice to Equinox (Dec 21-Mar 20) are not very helpful (How is December 15th not winter in Fairbanks but March 19th is winter?). An easy way is simply to split the year in half, a cold season (Oct-Mar) and a warm season (Apr-Sep). This roughly corresponds to the snow cover season, so is a useful "first crack".

Here's a plot of cold season mean temperatures. I've included data from the Experiment Station back to the winter of 1918-19 to highlight the correlation of temperatures on the Pacific Decadal Oscillation phases (the transitions are marked). 

Gary also asked if there was any correlation between winter temperatures and the following summer. The short answer, using just the half year seasonal means is no, none at all (correlation =0.04).

Yes, It Has been Warm

NOAK49 PAFG 162304
PNSAFG
AKZ222-171115-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
204 PM AKST WED JAN 16 2013

...VERY WARM START TO JANUARY IN FAIRBANKS...

THE AVERAGE TEMPERATURE THE FIRST HALF OF JANUARY IN FAIRBANKS WAS
7.1 ABOVE. THIS IS 15 DEGREES WARMER THAN NORMAL AND THE 9TH
WARMEST START TO JANUARY IN 108 YEARS OF WEATHER RECORDS IN THE
GOLDEN HEART CITY. THE LAST TIME THE FIRST HALF OF JANUARY WAS WARMER
THAN THIS YEAR WAS IN 2002.

$$
RT JAN 13

The Bottom has been Reached

For those looking forward to the end of winter, here's another piece of encouragement: the bottom of the normal temperature curve in Fairbanks has been reached. To the left is a plot of the NCDC 1981-2010 normal daily temperatures. The inflection point is today and tomorrow. Thereafter it's up, up up til early July. Combined with the 30% increase in possible sunshine since solstice, can springtime, Interior style be far away?

Storm Summary

I'll update this has I have time, but some preliminary numbers:

For Monday 13 Jan 2013

Fairbanks Airport: 0.22" precip and 0.4" snow. Estimated 0.17" of the preci total was rain.
This is easily the biggest January rain since 1963.

North Pole (KJNP): 0.36" rain, trace snow
Woodsmoke (near North Pole): 0.37" rain and 0.2" snow. 
UAF West Ridge: 0.22" and 0.8" snow (9am Mon-9am Tue) and 0.01" precip Monday morning.
 

Courtesy of IARC at UAF

The Arctic front moved through the area late Monday evening, as vividly illustrated on the temperature plot from Smith Lake, just west of the Experimental Farm at UAF. 

Greatest January Rain in 50 years

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
353 PM AKST MON JAN 14 2013

...BIGGEST JANUARY RAIN IN FAIRBANKS SINCE 1963...

RAINFALL AT THE FAIRBANKS AIRPORT BETWEEN MIDNIGHT AND 3PM AKST
MONDAY TOTALED 0.10 INCHES. THIS IS THE MOST RAIN IN THE MONTH
OF JANUARY AT THE FAIRBANKS AIRPORT SINCE JANUARY 19-20 1963...WHEN
0.52 INCHES OF RAIN FELL. 

$$
RT JAN 13
 

Record Warmth

The chinook broke through most of the upper Tanana Valley. Delta Junction/Fort Greely set a record high of 47F Monday afternoon,. The old record for January 14th was 40F set in 2002. At Tok the all time record high for January is 43F, and Tok #2, which is not the Tok climate station of record, has been up to 42F so far. 

Rain Has Arrived

Fairbanks-land got a little bit of rain Sunday evening and more Monday morning. Temperatures are in the mid to upper 30s in the hills and near freezing in the valleys. The 9am AST Monday POES infrared image shows the big ridge over the Gulf of Alaska with deep subtropical moisture into South-Central and eastern Alaska.

Courtesy of NWS Alaska Region

The 3am AST Monday 500mb analysis from Environment Canada shows the deep southerly fetch:

Courtesy of Environment Canada

The morning sounding from Fairbanks, which was launched between showers, showed above freezing temperatures through almost the entire lowest kilometer of the atmosphere, excepting the lowest 50 meters:

The good news is that colder air is already into southwest Alaska (you can see this on the GOES image) and will more quickly eastward, and Fairbanks area should get some snow later Monday and Monday evening, which hopefully will help with traction on roads. 

Here It Comes…

The stage has been set for the upcoming ice event. Here is the 11am AST Saturday GOES infrared image. The high aloft is obvious over the eastern Gulf of Alaska, with the deep plume of subtropical moisture on the west side of the high.

Courtesy NWS Alaska Region

The 500mb analysis for 3am Saturday shows the ridge extending from the eastern Pacific across Alaska and phasing with the high near the Pole that has been around in some form for nearly a month.

Courtesy Environment Canada

Fairbanks-land remains right on the edge of the chinook shadow. ANY rain will create very icy roads, and a 12-24 hour period of above freezing temperatures will not help. The numerical guidance is in agreement on driving colder air back into the Interior Monday night. Any ice that accumulates on roads will certainly be with us until spring.

Not Quite Like 2010…But Still…

Here's a composite graphic showing 500mb heights for the November 2010 rain event and the Friday morning GFS forecast valid Sunday 3pm. They patterns are similar, with huge ridge in the Gulf of Alaska, subtropical origin of the flow on the west side of the ridge and a shortwave trough turning northeast near the west end of the Alaska Peninsula. The most important difference for Fairbanks-land is that in the 2010 event there was no significant chinook as the winds were way around to WSW. This case will be much closer to the downslope edge, though at this point my take is that it IS going to rain some in Fairbanks Sunday/Monday. Quite unlikely to be as much rain as November 2010, but I'm banking on roads being terrible early next week.

Then and Now

As we await the ridge of doom, here's a comparison of daily mean temperatures for Fairbanks between last winter and this winter. The most noticeable difference (so far) is there have been no prolonged periods of well above normal temperatures has we had for the first three weeks of December 2011 and again much of February.

Update on Rain Threat

Here's the Thursday 18Z GFS forecast for 3pm AST Sunday. This is a forecaster's nightmare. The ridge access is barely east of Fairbanks (farther west than yesterday) and heights are higher. If it precipitates out of this it's hard to see how there isn't some rain. Could be a calamity.

Rain, Rain, Go Away…

Courtesy NCEP

I don't want to say it, but here it is: the numerical models are increasingly suggesting the threat of rain in Fairbanks-land Sunday into Monday. Here is the GFS forecast from Wednesday valid 3pm AST Sunday. Notice the flow from just northwest of Hawai'i right into Interior Alaska. Now it will be a close shave on whether the flow aloft will be southerly enough allow for chinook drying in Fairbanks: that scenario is likely in Delta, or if it will stay just cold enough for the precipitation to be mostly or wholly snow as is likely at, say, Tanana. Stay tuned.

Different Paths to Low Snow

Here's a plot of cumulative seasonal snowfall at Fairbanks for the past two winters through January 7th: I've taken the liberty of assuming that snowfall today will be trace or less. The totals are almost exactly the same, just about 30". Last winter though was typical of the "nickel and dime" snow that Fairbanks so frequently gets, while this winter 60% of the snow (so far) fell in one week.

Relative Inversion Strength

It seems like for the past couple weeks inversions have been mostly pretty strong in Fairbanks-land, stronger than normal anyway. So I've been toying with an easy way to quantify that.

Here's an attempt that uses the daily difference in standardized mean daily temperature anomaly for Fairbanks International Airport and Keystone Ridge. This accounts for the "normal inversion" as reflected in the daily means and adjusts for variance (the standardized part) that differs between hills and valleys (valleys have significantly larger variations in temperature). This differences is the relative inversion strength (RIS). I've plotted the daily anomalies for both sites in the background for reference.

The purple line is constructed so the positive values reflect stronger inversions than average, zero would be average and negative RIS are weaker than average. Positive RIS has indeed been the rule since late November, with the only extended exception the snowy week in mid-December.

Open Water Offshore Barrow

Strong east winds have been blowing for a couple of days now over the North Slope and have opened up quite a break in the ice west of Barrow, as seen in this NOAA-18 infrared image from Sunday early afternoon. This is not the usual lead beyond the shorefast ice that typically forms in this scenario. That kind of fracture typically runs basically parallel to the shore. I wonder if some of this is flooded ice, i.e. ice covered with sea water.

More Sun

Courtesy of the FAA

The first sunrise of the year at Barrow is still two weeks away, but it is getting lighter around noon now, per the 114pm AST Sunday image at the right (this is close to solar noon at Barrow).

January 6th marks the end of the darkest month of the year (the 31 days centered on winter solstice).  Here in Fairbanks we've already gained almost 40 minutes of sunshine since Solstice.

Accessing Deep Cold in Fairbanks

Reader Gary asked about quantifying deep cold in Fairbanks, i.e. when it's cold enough to require extra effort by hardly Fairbanks folk to stay warm and keep things running. Monthly mean temperatures only hint at the question, since means, by definition, smooth out the day to day variation. So here's an effort at addressing this question.

I start by calculating a "Bitter Degree Day" (BDD) statistic for each day. I've chosen a daily mean of -30F as the threshold, based on my own experience: daily means colder than -30f require some extra work. Recall that the daily mean is simply the average of the high and low, so a day with a high of- 30F and a low of -40F would have a mean of -35F. Like most degree day calculations, values outside of the threshold are set to zero: there are no negative degree days. So for each day in the winter, if the mean temperature is ≥ -30F, the BDD is zero. If the mean is less than -30F then I subtract -30 from that value and the remainder is the BDD.
Doing this uncovers some interesting nuggets. For example, this past December, there were 73 BDD, a smidgen more than the 70 BDD in December 1980, even though the monthly mean last month was nearly 7 degrees warmer than December 1980. This reflects the fact that the coldest days this past month were colder than in December 1980 AND the cold snap broke after Solstice last month, but not til the 30th in 1980. In fact, the January correlation between monthly mean temperature and BDD is a less than might be expected 0.69: good, but not great (the correlation of, say, mean temperature and conventional Heating Degrees Days would be 1.00, since the daily mean is always less than 65F in January). 
 
Winter totals have ranged from none eight times to 570 in 1933-34. In the past 30 years the highest total is 172 in 188-89, all of which were in that memorable January. Here is a plot of the winter (Oct-Mar) totals for each winter 1929-30 through this winter (thus far):   

This plot reveals that almost 20% of winters have very few (or no) BDDs, while very few (and none since 1971) have had more than 200. Except for the outlier high values, there is not much of trend, though the positive PDO phase (1977-2007), with many very BDD totals, is evident.

Since 1929-30, the monthly BDD median and maximum values are:

Nov:  0, 18 in 1994
Dec: 6, 237 in 1961
Jan: 24, 369 in 1934
Feb: 0, 84 in 1950
Mar: 0, 8 in 1956 (only March with >0 BDD)


Now the daily BDD is a measure of the mean temperature on the coldest days, and there is no doubt that the growth of the Fairbanks urban area and modern transportation have impacted very cold temperatures (mostly by providing water vapor for ice fog development). So instead of total BDD, how about number of days with a daily mean of <-30f: p="p">

The correlation between number of days and the seasonal total is quite good: 0.91 for the whole period, and still 0.88 since 1977, which can arguably be considerable the modern era of Fairbanks urban influences on temperatures.

So, this little exercise demonstrates that a focused statistic (like BDD) can get context specific information: climatology has a lot more to offer the informed user than just averages and normals.

Sharp Inversion

Here's a plot of the temperature in the lowest 500 meters of the Fairbanks sounding from 3am Wednesday. The surface temperature +7F, while 75 meters up the temperature was above freezing. Not bad. Temperatures around town were quite variable, even on the valley floor. At 9am AST Fairbanks Airport was +12Fwhile fort Wainwright, with an 8 mph downriver breeze, was 28F. At higher elevations temperatures are in the mid 20s to lower 30s. Similarly in the North Pole area, Woodsmoke PWS was +7F and Eielson AFB 27F.

December in Perspectve

Here is a scatter plot of mean temperature in December over the past 84 years. I've marked the year of the change in phase of the Pacific Decadal Oscillation (PDO), a long term variation in sea surface temperatures in the central and eastern Pacific Ocean. December 2010 and 2012 were unremarkable for a negative PDO phase.

December and 2012 Summary

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
1128 AM AKST TUE JAN 1 2013

...DECEMBER WEATHER SUMMARY AND 2012 REVIEW FOR FAIRBANKS ALASKA...

MOST OF DECEMBER WAS COLD AND TRANQUIL...BUT A SNOWY WEEK MID-MONTH
AN A BIG WARM-UP THE LAST DAYS OF THE MONTH TOOK THE EDGE OFF THE
BELOW NORMAL TEMPERATURES.

OVERALL...THE AVERAGE HIGH TEMPERATURE AT THE FAIRBANKS AIRPORT WAS
9 BELOW AND THE AVERAGE LOW 26 BELOW. THE MONTHLY AVERAGE
TEMPERATURE OF 17.3 BELOW WAS MORE THAN 13 DEGREES BELOW NORMAL.
THIS WAS THE SECOND COLDEST DECEMBER IN THE PAST 30 YEARS. ONLY
DECEMBER 2010...WITH AN AVERAGE TEMPERATURE OF 17.9 BELOW...WAS
COLDER. THE HIGH TEMPERATURE FOR THE MONTH WAS 34 DEGREES ON NEW
YEARS EVE. THE LOW WAS 48 BELOW ON THE 17TH. TEN DAYS DURING THE
MONTH HAD AN DAILY LOW TEMPERATURE OF 40 BELOW OR LOWER...THE MOST
IN ANY DECEMBER SINCE 1975. LOWEST TEMPERATURES WERE SIMILAR IN
OTHER LOW LYING AREAS...INCLUDING MONTHLY LOWS OF 50 BELOW AT
NORTH POLE AND 48 BELOW AT GOLDSTREAM VALLEY BOTTOM. IN
CONTRAST...TEMPERATURES AT HIGHER ELEVATIONS DROPPED IN THE 
30S BELOW ON JUST A COUPLE OF DAYS.

AS IS TYPICAL IN MID-WINTER...STRONG INVERSIONS PREVAILED ON MANY
DAYS DURING THE MONTH...SETTING THE STAGE FOR FREQUENT AIR QUALITY
PROBLEMS.

WITH THE LOW TEMPERATURE CAME CONSIDERABLE ICE FOG IN URBAN
AREAS...AND WAS ESPECIALLY DENSE ON THE 20TH AND 21ST. OUTSIDE OF
ICE FOGGY AREAS...AURORA WERE SEEN ON SOME CLEAR NIGHTS.

SNOWFALL WAS WELL ABOVE NORMAL IN DECEMBER...BUT WAS ALMOST ALL
PACKED INTO ONE WEEK. A TOTAL OF 18.5 INCHES OF SNOW FELL AT THE
AIRPORT...ABOUT SIX INCHES ABOVE NORMAL AND THE MOST IN ANY
DECEMBER SINCE 1992. PRACTICALLY ALL THE SNOW FELL BETWEEN THE 9TH
AND 14TH. THE BIGGEST SNOW FELL ON THE 12TH...WHEN 9.5 INCHES
FELL. THIS WAS THE EIGHTH HIGHEST DECEMBER CALENDAR DAY SNOWFALL
IN FAIRBANKS WEATHER HISTORY...AND THE HIGHEST ONE DAY SNOW IN
DECEMBER SINCE 1990. THE SNOW DEPTH AT THE AIRPORT TOPPED OUT AT
20 INCHES ON THE 13TH...BUT HAD SETTLED BACK TO 14 INCHES BY NEW
YEARS EVE.

THE SNOW MELTED DOWN TO 1.19 INCHES..WHICH IS ALMOST DOUBLE NORMAL
AND MADE THIS THE WETTEST DECEMBER SINCE 1990.

AS IS USUAL IN WINTER...WIND SPEEDS WERE MOSTLY VERY LIGHT. A
TOTAL OF 18 DAYS HAD A DAILY AVERAGE WIND SPEED OF LESS THAN 
ONE MPH...AND THE PEAK DAILY WIND SPEED EXCEEDED 10 MPH ON JUST
TWO DAYS.

LOOKING AHEAD TO JANUARY...FAIRBANKS AVERAGE TEMPERATURES REACH
THE LOWEST POINT IN THE ANNUAL CYCLE MID-MONTH BEFORE BEGINNING TO
SLOWLY CLIMB. BETWEEN THE 14TH AND 20TH THE AVERAGE HIGH IS ZERO
AND THE AVERAGE LOW 18 BELOW. IN THE PAST 108 YEARS...THE HIGHEST
TEMPERATURE IN JANUARY WAS 52 DEGREES IN 2009...AND THE LOWEST
66 BELOW IN 1934. NORMAL SNOWFALL IS 10.2 INCHES...LOWER THAN ANY
EARLY WINTER MONTH. TOTAL JANUARY SNOWFALL HAS VARIED FROM A
WHOPPING 65.6 INCHES IN 1937 TO A PALTRY 0.7 INCHES IN 1966.

POSSIBLE SUNSHINE...WHILE STILL IN SHORT SUPPLY...INCREASES
QUICKLY DURING JANUARY. THE SUN WILL BE UP FOR ONLY FOUR HOURS ON
NEW YEARS DAY BUT INCREASES TO JUST UNDER SEVEN HOURS BY THE 31ST.

...2012 FAIRBANKS WEATHER REVIEW...

THE COLDEST JANUARY IN 40 YEARS AND SUSTAINED UNUSUALLY COLD
WEATHER IN NOVEMBER AND DECEMBERS MORE THAN MADE UP FOR
SIGNIFICANTLY WARMER THAN NORMAL WEATHER IN FEBRUARY AND
APRIL...FOR AN OVERALL AVERAGE TEMPERATURE AT THE FAIRBANKS
AIRPORT FOR THE YEAR OF 24.1 DEGREES. THAT MADE THIS THE COOLEST
YEAR SINCE 1999. THE HIGHEST TEMPERATURE IN 2012 WAS 86 DEGREES
ON JUNE 23RD AND THE LOWEST 51 BELOW ON JANUARY 29TH.

PRECIPITATION TOTALED 10.62 INCHES...WHICH IS ALMOST EXACTLY
NORMAL. HOWEVER...THE SUMMER WAS DRIER THAN NORMAL. THIS LEAD TO A
VERY UNUSUAL FIRE SITUATION IN MID-AUGUST...WHEN THE DRY CREEK
FIRE...WEST OF EIELSON AFB...WHICH HAD STARTED IN LATE JUNE AND
SMOLDERED AT JUST 100 ACRES...FLARED UP AND GREW TO OVER 40000
ACRES BY THE END OF AUGUST.

SIX INCH SNOWFALLS ARE UNUSUAL IN FAIRBANKS...AVERAGING JUST ONE
DAY EVERY TWO YEARS...BUT 2012 BROUGHT TWO SUCH DAYS...ONE IN
MARCH AND ONE IN DECEMBER. HOWEVER...THE 2012 ANNUAL SNOWFALL
TOTAL OF 61 INCHES IS CLOSE TO NORMAL.

$$
RT JAN 13