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.