The Big Diurnal

Courtesy of NWS Alaska Region

So you probably have read of the big temperature swing on Thursday at Fairbanks, with a low of 24 below and a high of 31 above, for a daily temperature range of 55 degrees, the largest calendar day  temperature range in the Weather Bureau/NWS era (since Dec 1929). Slightly larger ranges were observed at other locations in the area, including 57ºF at Eielson and North Pole and 59ºF at Goldstream Creek and Woodsmoke. Meanwhile, 25 degree range here at Keystone Ridge.

On the NWS Facebook page, there are, unsurprisingly. claims of 110 and 120ºF one day temperature ranges. Considering that the US record is evidently 103 degrees at Loma Montana, that would be something. My response is: what day? My guess is that people are either telescoping changes that occurred over a few days or a simply exaggerating, which, believe or not, does happen with weather. 

So what is the Alaska record for one day temperature change? That's a good question. I'm sure it's over 70 degrees, and will update when I find some examples. If you know of any documented 70+ degrees ranges in one day, let us know.

Winter Wrapping Up…

The cold airmass that has been over the region for more ten days is on the way out, and temperatures will rebound to near normal, which will be 20 or more degrees warmer that it's been lately. Here's an updated plot of daily mean temperatures this cold season in Fairbanks. Recall that the grey area is plus of minus standard deviation from normal.

It's a Cold One…

Courtesy of FAA

Corrected old record low at Denali Park HQ.

Fairbanksians tend to be pretty jaded about cold temperatures. Take this morning: the last week of March and morning drive-time temperatures are in the 20s and 30s below. And all you here is "cold this morning, but lovin' that sunshine", as seen in this afternoon view from high atop Ester Dome.

Some lows this morning include:

Denali National Park HQ: -22F new record for March 27; old record -21F in 1938
Eielson AFB: -31F new record for March 27;  old record -26F in 2004

McGrath: -33F (record -37F in 1977)
Fairbanks Airport -30F (record -37F in 1925)

Other lows Wednesday morning included: 
Chicken: -35F
Goldstream Creek: -33F
Tanana -31F

Cold Sounding for Late March

Here's a trace of the temperature in the lowest 1000 meters from the sounding from the Fairbanks Airport Tuesday afternoon. This is quite a cold profile for this late in March (technically, 1000-850mb thickness 1192 gpm and 850 mb temperature -26.9C). Of course there's no afternoon inversion; too much solar gain for that.

Temperature held in the single digits in the valleys, and never got above zero above 1500'MSL, which highs of +5F at Fairbanks Airport, -2F here at Keystone Ridge and -5F at Munson Ridge, at 3100'MSL south of Chena Hot Springs.

Optimum Climate Normals Alaska-wide

Reader Richard was asking about the past decade's temperature anomalies Alaska-wide, so here's a sample from around the state. The departures here are again standardized, so direct station to station comparisons are valid.

There are a couple of region-wide trends, with cooler temperatures than the 1981-2010 normals having been the rule the past ten years state-wide in both January and March, while late summer and autumn are notably milder. Juneau has been slightly, but persistently cool in almost every month, reflecting the now negative phase of the PDO (the 1981-2010 normals consist mostly of positive phase PDO). Recall the negative phase of the PDO corresponds to cooler than normal sea surface temperatures near Alaska. In contrast, Barrow has been remarkably warm the latter half of year, which is definitely a direct result of the decline in Arctic sea ice.

Late Winter Cold on the North Slope

It's a sunny morning on the western North Slope as this 9am AKDT webcam from Atqasuk shows. Not atypically for this time of year, it's cold too.  Low temperatures through 9AM include:

Atasuk: -37F
Barrow: -34F
Inigok RAWS: -30F
Umiat RAWS: -29F

These are not to record low levels: the record low at Barrow today is -42F set in 1925.

Optimum Climate Normals and Fairbanks

One of the statistical tools that the Climate Prediction Center uses for monthly and longer period forecasting is called the "Optimum Climate Normals", which is simply how temperatures and precipitation have averaged in the past 10 years (15 for precipitation) compared to normal. This is potentially important because most longer term forecasts are made in reference to some "normal".

Here's a plot Fairbanks 1981-2010 normal monthly temperatures along with how the past 10 years (Mar 2003-Feb 2012) compare. Due to the very short period (10 years), I've included the decadel mean and median, which in some cases (e.g. January and October) are substantially different; this is an artificant that one extreme value can have on the mean in such a small sample.

As you can see, in the past decade January and March and November have averaged significantly below the 30 year normal, while September and especially October have averaged above.

How does this look if we standardize the differences (multiplied by 10 so scale is the same as the first chart), so that we account for the fact that temperatures have much wider ranges in winter than summer:

 

So now we see that the decline in January temperatures is not so spectacular (but March still is), but the recent warmth in May and August through October really stands out. This is a nice illustration of the power of standarization when the there are big differences in the variance in the data through the year.

Long Term High Pressure

It sure seems like high pressure has been the rule over the Arctic Ocean, and sure enough, it has been. Here's a plot of mean seal level pressure for the two months between January 15th and March 15th (the units are in Pascals: divide by 100 for millibars). That's quite a big high north of Barrow. The bottom plot shows the anomaly over the same time period. The 12 millibar anomaly is  quite substantial for a two month period..

Clear Skies

Here's a visible image from Friday afternoon from the Suomi NPP satellite. With clear skies over much of mainland Alaska, there's a lot of detail to be seen. Note the area of open water west of Barrow. It's small, but the fact that there's more  than a lead is quite remarkable for mid-March. Also note that many areas in Interior Alaska are fairly dark, which of course is simply the boreal forest. This difference in albedo on land is a major factor in show fast it warms up in the spring in Alaska.

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).