December 1955 Storm in the Southern Mainland

This is a narrative I started working on a few weeks ago regarding the impressive snow totals that I notice every year on the daily climate summary for Anchorage at the end of December. While not having anything to do with Interior Alaska, it might be an interesting read for some of you.

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Anchorage Snow Event: December 28-29, 1955

On December 28 and 29, 1955, Anchorage, Alaska, endured the greatest snow event since record-keeping began. A remarkable 29 inches fell on those two calendar days. When looking at a four day period, 35.5 inches fell. This discussion focuses on the 2-day period where 29 inches fell since it represents a clearly definable, discrete event in the climate record.

The Datasets

This analysis utilizes several National Oceanographic and Atmospheric Administration (NOAA) databases that are available to the general public. They include: 1) the National Climate Data Center's (NCDC) GHCN summary of daily conditions, 2) the Earth System Research Laboratory (ESRL) reanalysis data, 3) the NCDC DS3505 hourly observation database, and finally, we use clippings from two Anchorage newspapers.

The Surface Setup

December 1955 was fairly cold in Anchorage with a typical amount of snow through the first 27 days of the month. The average high temperature was 16°F and the average low temperature was 0°F. Through December 27, 10.1 inches of snow fell, which is slightly lower than normally occurs during that time period. However, a brief pattern change was about to take place ('brief,' because the first half of the following month was extremely cold and dry).

A substantial high pressure system moved into the Bering Sea during late December as an existing high pressure center strengthened in British Columbia. This resulted in a massive trough of low pressure between the two high pressure centers. Figure 1 shows the ESRL Reanalysis surface pressure pattern and Figure 2 shows the track of the low pressure center.

   

Fig. 1. ESRL surface air pressure estimates for Dec. 27 (left), Dec. 28 (middle), and Dec. 29 (right), 1955. The units are in millibars of mercury and the contour interval is 3 millibars.



Fig. 2. ESRL estimate of the storm path between Dec. 26, 1955, and Jan. 3, 1956. Each black dot represents a new 24-hour position. The Dec. 30 and Dec. 31 positions are identical.

The Upper Air Setup

A look at the ESRL 500 mb geopotential height map shows a deep H5 trough of low pressure centered over the high Arctic with a trough axis developing and extending past the central Aleutian Islands. This type of upper air pattern is not uncommon in Alaska during the winter but the magnitude is somewhat atypical. Figure 3 shows the geopotential heights at the 500mb pressure level. In general, lower heights represent upper level low pressure and high heights represent upper level high pressure. Since winds are geostrophic at this level, the winds move parallel to the isolines.

   

Fig. 3. ESRL upper air pressure estimates at the 500mb geopotential height level for Dec. 27 (left), Dec. 28 (middle), and Dec. 29 (right), 1955. Units are meters. Purple represents low heights and orange represents high heights. The scale is 5000m to 5700m.

The upper level pressure and wind pattern formed a classical pineapple express that took aim on southern Alaska. A long southerly fetch of moisture-laden air traveled along the 150th meridian originating near the Hawaiian Islands. The upstream focus of this plume of moisture extended from as far west as Cook Inlet and eastward to include all of Prince William Sound and much of the Panhandle. Figure 4 shows the ESRL Reanalysis estimate of precipitable water.

   

Fig. 4. ESRL precipitable water anomaly estimates for Dec. 27 (left), Dec. 28 (middle), and Dec. 29 (right), 1955. Units are kg/m². Purple represents low precipitable water amounts (<0.15 inches) and red represents high precipitable water amounts (>1.0 inches).

Weather balloon soundings have been recorded twice daily at the Anchorage International Airport ever since the program was initiated in 1948. In 1955, the balloons were launched at 6 a.m. and 6 p.m. local Standard time (3Z and 15Z). Figure 5 shows the temperature profile for four balloon soundings during the heavy precipitation event. There is a noticeable warm layer between 400m and 1000m on several of the soundings. The wind component at the 700mb and 500mb level (not shown) varied between south and southwest on all soundings. Unfortunately there is no data for moisture (dew point, mixing ratio, vapor pressure, etc.) so we cannot directly compute precipitable water, vorticity, or many other useful variables.



Fig. 5. Upper air temperature profile for four consecutive soundings at the Anchorage International Airport beginning at 6 a.m. (15Z) on December 28, 1955.

The Hourly Observations

There were 40 consecutive hours between 7 a.m. on December 28 and 10 p.m. on December 29 where snow was observed and the visibility was 2.5 miles or less. A few hours either side of those 40 hours saw light snow with visibilities between 7 and 10 miles. It is reasonable to assume that at least 27 of the 29 inches recorded on those two days fell during the 40-hour period. Figure 6 shows the temperature, snow intensity, wind chill, and visibility for the two calendar days. The wind during the entire two-day period originated from the north and northeast at speeds between 7 and 10 miles per hour (mph). This represents a classic down-Inlet, cold air advection flow that frequently causes enhanced meso-scale lift.



Fig. 6. Hourly observations for Anchorage International Airport on December 28, and December 29, 1955. The dots at each hour show the snow intensity. No hourly precipitation or snow rates are indicated in the database.

The daily summary for Anchorage International Airport is shown in Table 1. Both days recorded high and low temperature values that are typical for the date. However, the precipitation and snow values are extremely high.



Table 1. Daily summary for Anchorage International Airport on Dec. 29 and Dec. 30, 1955. The values are from midnight to midnight.

The 13.4 inches on December 28 represents the 6th largest calendar day snow in Anchorage and the 15.6 inches on December 29 represents the 2nd largest calendar day snowfall. Table 2 shows the largest calendar day snow observations for Anchorage.



Table 2. The six largest daily snowfall observations at the official Anchorage climate station. Snow records began in 1939.

A review of the Anchorage Times and the Anchorage Daily News provides a little more insight into the conditions within the city and the region. In addition to stories about people being stuck, busses not moving, stores closed, and the constant sound of snow plows, there is a reference to 24-hour snowfall measurements. Specifically, they mention that 17.2 inches fell between 8 a.m. on December 29 and 8 a.m. on December 30th (see Figure 7). While this value does not eclipse the March 2002 event, it is larger than the currently listed calendar day total.



Fig. 7. Portion of Anchorage Times story December 30, 1955. The paragraph states that 10.5 inches was recorded between 8 a.m. on Dec. 28 and 8 a.m. on Dec. 29 and that the following 24-hour period saw 17.2 inches of snow.

Regional Impact

Unlike the March 2002 snow event in Anchorage, the December 1955 storm produced record rain and snow over an area from the Susitna River basin to the Panhandle. Story headlines from the Anchorage Times regarding the impacts to Cordova and to Yakutat are shown in Figure 8.



Fig. 8. Portion of Anchorage Times stories from December 30, 1955. The stories describe the damage caused by heavy rain in both Cordova and Yakutat.

Areas that normally receive heavy precipitation, like Valdez, Cordova, and Yakutat, lived up to their reputations. Both Cordova and Valdez recorded their wettest calendar day in their respective climate histories. Cordova observed 17.77 inches of mostly rain during a 2-day period. The 14.13 inches on December 29th was a single-day record for Alaska at the time. Thompson Pass, which by some measures is the snowiest location in Alaska, recorded their greatest single day snowfall in the 25-year record of that station. An amazing 62.0 inches was observed on December 29 1955 to follow the 26.4 inches that fell on December 28th. On December 30th, an additional 58.6 inches fell bringing the three-day total to 147 inches. Figure 9 shows the 2-day precipitation for stations surrounding Prince William Sound and Figure 10 shows the 2-day snow amounts for those same stations.



Fig. 9. Total precipitation observed (inches) on Dec. 28 and Dec. 29 1955. All data is from the NCDC GHCN database.



Fig. 10. Total snowfall observed (inches) on Dec. 28 and Dec. 29 1955. All data is from the NCDC GHCN database.

Conclusion

A majority of heavy snow events in Anchorage occur when a large plume of moisture follows a low pressure into western Prince William Sound. This setup allows for northerly winds that advect cold air down Cook Inlet which provides a meso-scale forcing mechanism to enhance the synoptic-scale forcing. In addition, the flow minimizes the downsloping that is typical with a more easterly component to the wind; therefore, the moisture streaming from the Tropics flows unimpeded over the Chugach Mountains. Based on all available information, the December 1955 storm appeared to follow this well-established pattern that has been repeated many times since - except on a much larger scale. Given the synoptic and meso-scale features, I suspect that were this storm to materialize in 2014, it would be well forecasted several days in advance.

The storm of late December 1955 is one for the record books. Not only was an incredibly large amount of snow and rain observed, but the spatial extent was larger than other storms with similar synoptics. The Unites States Weather Bureau collected excellent information that enabled this post-storm discussion nearly 60 years after the fact. Many thanks should be given to the numerous people who collected this, and all other climate data.



Fig. 11. Headlines and photograph from Anchorage Times (left) and Anchorage Daily News (right) on December 30, 1955.

December Anomalies

The maps below show the December climate anomalies for most of the first order observing stations in Alaska; as usual, the area of each circle indicates how unusual the month's conditions were, as measured by the anomaly in standard deviations for temperature and the percentile rank for precipitation (based on the 1981-2010 normals).

It was another warm and wet month in western and southwestern Alaska, and Cold Bay was anything but cold as it experienced its warmest December on record.  The annual average temperature for 2013 was also the warmest on record in Cold Bay.  However, December was colder than normal in the eastern half of the interior and in the southeast.  Fairbanks was relatively warmer and wetter than several other interior locations.

Barrow experienced an extraordinarily wet month again and broke the previous record for December precipitation by over 50%; in fact, December was the wettest calendar month ever observed in Barrow between November and February (inclusive).  Remarkably, three individual days in the month recorded precipitation greater than would normally be expected for the entire month of December.  2013 ended as the third warmest and third wettest year on record for Barrow.

 

Fairbanks Temperature Update

Reader "citizenschallenge" asked about recent temperatures in Fairbanks, so here is a quick update on the comparison to seasonal norms.  The chart below shows that temperatures have continued on quite a roller coaster, with both significant warmth and cold relative to normal occurring in the past several weeks.  Lately, of course, it's been warmth, with surface temperatures reaching 20 °F or higher for three days at the airport, and above-freezing air being observed aloft on January 1st, 5th, and 6th.  However, a cooling trend is already underway, and much colder conditions will soon emerge once again.

2013 Review (NOAA)

Here's a nice summary of 2013 weather in Fairbanks, courtesy of the National Weather Service.  All in all, an extraordinary year from a meteorological perspective.

...2013 FAIRBANKS WEATHER REVIEW...

2013 WAS A HIGHLY VARIABLE YEAR WITH LARGE SWINGS IN TEMPERATURE
AND MOISTURE. FOR EXAMPLE JANUARY STARTED OFF WITH THE
TEMPERATURE REACHING 37 DEGREES ABOVE ON THE 14TH BUT FALLING TO A
BONE CHILLING 48 BELOW ON THE 27TH WHICH WAS THE COLDEST
TEMPERATURE AT THE FAIRBANKS AIRPORT IN 2013. FEBRUARY WAS THE
ONLY MONTH FROM JANUARY TO JUNE THAT ENDED UP AVERAGE OR WARMER.
MARCH BROUGHT A RETURN TO MUCH BELOW NORMAL TEMPERATURES AND ABOVE
NORMAL SNOWFALL. APRIL WAS EXCEPTIONALLY COLD AND SNOWY AND RANKED
AS THE 3RD COLDEST APRIL OF 108 YEAR ON RECORD. APRIL WAS ALSO THE
8TH SNOWIEST WITH THE SNOW PACK REACHING 25 INCHES ON THE NINTH.
MAY WAS AN EXCEPTIONAL MONTH THAT TRANSITIONED FROM ONE OF THE
COLDEST AND SNOWIEST SPRINGS IN RECENT MEMORY. IN FACT THE PERIOD
FROM THE 3RD OF APRIL TO THE 7TH OF MAY WAS THE COLDEST 5 WEEK
PERIOD FOR THAT PERIOD IN THE RECORDED IN HISTORY. THE SNOWPACK ON
THE 1ST OF MAY MEASURED IN AT A HEALTHY 17 INCHES AND REMAINED
THROUGH THE 12TH. WINTER WAS NOT QUITE DONE WITH FAIRBANKS AS
NEARLY ONE HALF INCH SNOW WAS MEASURED AGAIN ON THE 17TH AND 18TH.
MAY ENDED UP BEING OVER 5 DEGREES BELOW NORMAL DESPITE THE
TEMPERATURES SHOOTING INTO THE THE UPPER 70S AND MID 80S DURING
THE LAST WEEK WITH A DAILY RECORD OF 84 DEGREES SET ON THE 30TH.

2013 WILL BE REMEMBERED FOR ITS RECORD BREAKING WARM AND DRY
SUMMER. A REMARKABLE HEAT WAVE BAKED THE INTERIOR BEGINNING ON
THE 14TH OF JUNE AND CONTINUING WELL INTO JULY. THE WEEK OF 23RD
TO 29TH OF JUNE WAS THE WARMEST WEEK EVER RECORDED AT THE
FAIRBANKS AIRPORT AND MAY BE THE WARMEST WEEK OF RECORD AT ANY
LOCATION IN ALASKA. THE MERCURY SOARED TO 92 DEGREES BOTH ON THE
25TH AND THE 26TH. THE LOW TEMPERATURE OF 70 DEGREES ON THE 25TH
SET A MAXIMUM LOW TEMPEATRURE RECORED AND MAY BE THE HIGHEST
RELIABLE CALENDAR DAY LOW TEMPERATURE EVER RECORDED IN ALASKA.
JUNE RANKED AS THE 10TH DRIEST OF 101 YEARS OF RECORD. JULY
REMAINED HOT AND DRY AND HAMPERED FIRE FIGHTING EFFORTS ON SEVERAL
WILD FIRES ACROSS THE INTERIOR. THE METEOROLOGICAL SUMMER WHICH
IS THE 3 MONTH PERIOD FROM JUNE THROUGH AUGUST WAS THE SECOND
WARMEST ON RECORD AND THE 17TH DRIEST. THE MERCURY HIT 80 DEGREES
OR WARMER ON 36 DAYS DURING THE SUMMER OF 2013 SHATTERING THE
AVERAGE OF 11 DAYS. THE MERCURY REACHED 85 DEGREES ON 14 DAYS AND
REACHED 90 OR ABOVE ON TWO DAYS.

TEMPERATURES IN AUGUST WERE ABOVE AVERAGE AND REMAINED VERY DRY
HOWEVER A SIGNIFICANT PATTERN CHANGE IN THE MIDDLE OF THE MONTH
BROUGHT A WELCOME BREAK FROM THE HOT TEMPERATURES AND DRY
CONDITIONS AND BROUGHT MUCH MORE FAVORABLE CONDITIONS FOR
FIREFIGHTERS FIGHTING THE MANY FIRES ACROSS THE LOCAL AREA. THE
FLIP FROM HOT AND DRY TO COLD AND WET WAS SIGNIFICANT AS MANY
OUTLYING AREAS REPORTED A HARD FREEZE WITH TEMPERATURES FALLING
INTO THE MIDDLE AND UPPER TWENTIES. THE LOW TEMPERATURE AT THE
AIRPORT FOR AUGUST WAS 34 DEGREES ON THE 25TH. COLD AND WET AND
YES SNOWY CONDITIONS REMAINED THROUGH SEPTEMBER. THE FIRST
SNOWFALL OF THE SEASON AT THE AIRPORT FELL ON THE MORNING OF THE
18TH WHICH WAS ABOUT 2 WEEKS EARLY. THE 123 DAYS BETWEEN THE LAST
SNOWFALL OF THE SPRING ON THE 17TH OF MAY AND THE 18TH OF
SEPTEMBER WAS THE 4TH SHORTEST SNOW FREE PERIOD AT THE FAIRBANKS
AIRPORT. ANOTHER SIGNIFICANT PATTERN CHANGE OCCURRED EARLY IN
OCTOBER WITH VERY WARM DRY CHINOOK CONDITIONS DOMINATING THE
MONTH. OCTOBER 2013 WILL BE REMEMBERED FOR ITS LACK OF SNOW FALL
AND LACK OF SNOW PACK ON THE GROUND. ONLY A TENTH OF AN INCH OF
SNOW HAD FALLEN AT THE AIRPORT THROUGH THE MORNING OF THE 31ST
WITH ONLY TRACE AMOUNTS FALLING AND MELTING ON SEVEN DAYS IN
OCTOBER. THE SNOW DEPTH AT THE AIRPORT REMAINED ZERO UNTIL THE
EVENING OF THE 31ST WHEN 0.6 INCHES OF SNOW FELL. SNOW DEPTH IS
RECORDED IN WHOLE INCHES SO THE 0.6 INCHES ROUNDED UP TO 1 INCH OF
SNOW COVER. THE LAST MINUTE SNOWFALL PREVENTED MATCHING A LONG
STANDING SNOW DEPTH RECORD FOR THE 31ST OF OCTOBER. THE LAST TIME
SNOW DEPTH ON THE 31ST OF OCTOBER WAS ZERO IN FAIRBANKS WAS IN
1925 AND IS THE ONLY OCCURRENCE OF ZERO SNOW DEPTH IN THE CLIMATE
RECORD. THERE HAVE BEEN 5 OCCURRENCES OF A TRACE SNOW DEPTH ON THE
31ST OF OCTOBER IN THE CLIMATE RECORD...THE LATEST OCCURRING IN
1962.

OF ALL THE WILD WEATHER IN FAIRBANKS IN 2013 THE ONE THAT WILL BE
TALKED ABOUT AND REMEMBERED THE MOST WAS THE ICE AND WIND STORM
OF 13 AND 14 NOVEMBER. A POWERFUL STORM MOVED OUT OF THE BERING
SEA AND INTO THE INTERIOR WITH VERY WARM TEMPERATURES AND
ABUNDANT MOISTURE WHICH FELL AS FREEZING RAIN AND SNOW ON THE
MORNING OF THE 13TH. WIDESPREAD FREEZING RAIN WAS REPORTED ACROSS
THE AREA CAUSING DIFFICULT DRIVING CONDITIONS AND MANY ACCIDENTS
REPORTED THE MORNING OF THE 13TH. MANY RESIDENTS REPORTED HAVING
TO PULL OVER AND SCRAPE OFF THE FREEZING RAIN THAT BONDED
INSTANTLY ON WINDSHIELDS. ICE ACCUMULATIONS OF ONE HALF INCH WERE
COMMON ACROSS THE AREA NOT ONLY ON ROAD SURFACES BUT TREES AND
POWER LINES AS WELL. 3.9 INCHES OF SNOW FELL DURING THE DAY AT
THE AIRPORT WITH 4 TO 6 INCHES OF SNOW FALLING IN THE HILLS. THE
SNOW ADDED TO HEAVY ICE LOADS ALREADY ON TREES AND POWER LINES.
THE MOST DESTRUCTIVE PORTION OF THE STORM CAME WITH THE WINDS THAT
BLASTED INTO THE AREA LATE IN THE EVENING ON THE 13TH AND
CONTINUING THROUGH THE 14TH. WINDS GUSTS PEAKED AT 55 MPH AT THE
AIRPORT AT 1239 AM ON THE 14TH AND WAS ONE OF THE STRONGEST WIND
GUSTS IN THE PAST DECADE. A WIND GUST OF 62 MPH WAS RECORDED AT
FORT WAINWRIGHT. WIND GUSTS IN THE 60 TO 70 MPH RANGE BUFFETED THE
HIGHER TERRAIN SURROUND FAIRBANKS OVERNIGHT. NUMEROUS TREES WERE
UPROOTED WITH SEVERAL REPORTS OF CAR AND ROOF DAMAGE. THE STORM
ULTIMATELY LEFT OVER 14000 PEOPLE WITHOUT POWER ACROSS THE
FAIRBANKS AREA...SOME AREAS DID NOT GET POWER BACK FOR NEARLY TWO
WEEKS. TEMPERATURES DROPPED TO 27 BELOW ON THE 19TH PROMPTING THE
OPENING OF WARMING SHELTERS FOR THOSE WITHOUT POWER ACROSS THE
FAIRBANKS AREA AND A DECLARATION OF A STATE OF DISASTER BY THE
FAIRBANKS NORTH STAR BOROUGH MAYOR ON MONDAY NOVEMBER 18TH.

Record Daily Temperatures in Alaska for 2013

** Updated on 1/6/13 *

1/6 Update Section: Due to my declining confidence in the NCDC records database, I decided to process all of the GHCN data for each station and sort the data from high to low and from low to high. The table is accurate and the 6 maps below the table represent the number of records in 2013 for 24 primary (mostly 1st order) stations across Alaska. In theory, it is a definitive list. The period of record mirrors the period of record that the NWS states in the daily climate summaries.

** Updated on 1/4/13 **

1/4 Update Section: I have come to the conclusion that the NCDC records database is of marginal utility – at least for Alaska. It is useful to display patterns but not to make comparisons from station to station.

Here is a table of the primary Alaska stations and the count of records in 2013 generated by downloading the complete station histories and ranking the temperatures and precipitation values by each day of the year. The rightmost columns give the number of partial and complete years in the database.

Original post:

Using the NCDC's daily record website, I extracted all of the daily records for Alaska in 2013. The list is pretty good but not perfect. A station needs to be in existence for 30 years with at least 50% completeness of data to have a record posted to the database. Even still, some are missed. All of the Yakutat records are missing (including the all-time record last June) and the Talkeetna records from June are missing too (but their January records are there). All but one of the Cold Bay record high temperatures are missing. Maybe someone can inquire with NOAA about the discrepancies.

In any event, here are two maps showing the number of days with a record high max temperature and the number of days with a record low min temperature. There is a strong clustering of observations around Fairbanks.

Fairbanks 2013 Charts

Here are some preliminary charts depicting the 2013 year in Fairbanks. In terms of temperature, 2013 was the 20th warmest of the 84 years since 1930 with an annual temperature of 28.3°F. As will be detailed in a future post, by my chi-square metric, this was the most extreme year on record due to the very large number of days more than 2.0 standard deviations from the mean. For precipitation, the 10.65" was very near the normal and was the 41st most of the last 84 years.

Deep Freeze (Temperatures Aloft)

Last week's post about the first -40° temperature of the winter in Fairbanks provoked a bit of discussion about the causes of the long-term decline in the frequency of very cold days in Fairbanks.  As reader Gary noted, there are numerous candidates for possible drivers of the long-term change, including changes in wind, cloud cover, and air mass characteristics; we also can't exclude the possibility of an urban heat island effect or subtle station siting issues.  As a simple first step at tackling this, I looked at the 850 mb temperatures from Fairbanks balloon soundings since 1948; the chart below shows the annual (cold season) number of days with 850 mb temperatures below -26 and -32 °C; these thresholds were chosen because the long-term frequencies of occurrence are close to those for -40 and -50 °F at the surface, respectively.  Last week's chart of -40 and -50 °F frequency is also reproduced below, except with an adjusted time scale for ease of comparison between the charts.

It's plain to see that the frequency of very cold temperatures aloft has also shown a notable decrease since the mid-1970's, although the warming appears less pronounced than at the surface.  Temperatures of -32 °C or lower at 850 mb have become rare in the past decade or so, just like -50 °F temperatures at the surface.  From a first glance, then, it seems that warming aloft explains at least a significant part of the dwindling of extreme cold frequency in Fairbanks.

Viewing the data in summary form, here are the 30-year counts of the extreme temperature categories, at the surface and aloft, for 1951-1980 and 1981-2010.

Surface	1951-1980	1981-2010	Difference
-40 °F or Lower	434	224	-48%
-50 °F or Lower	106	15	-86%

850 mb	1951-1980	1981-2010	Difference
-26 °C or Lower	401	257	-36%
-32 °C or Lower	89	41	-54%

Looking at the December-February mean conditions, temperatures at 850 mb have increased substantially, and only modestly less than at the surface:

DJF mean (°F)	1951-1980	1981-2010	Difference
850 mb	8.3	11.9	+3.6
Surface	-9.1	-4.1	+5.0

As a final note, and as food for thought, the surface and upper-air data from McGrath show broadly similar trends, although the drop-off in extremely cold days is less pronounced at the surface than for Fairbanks (especially for -50 °F and below); see charts below.  Note that I used different 850 mb temperature thresholds to correspond to the long-term frequencies of the respective categories.  As an aside, it is also interesting that McGrath has a higher frequency of very cold days than Fairbanks (much higher in the modern era) despite being warmer in the mean, both at the surface and aloft.

Here are the 30-year counts and DJF means:

Surface	1951-1980	1981-2010	Difference
-40 °F or Lower	481	304	-37%
-50 °F or Lower	127	83	-35%

850 mb	1951-1980	1981-2010	Difference
-26 °C or Lower	441	341	-23%
-32 °C or Lower	116	64	-45%

DJF mean (°F)	1951-1980	1981-2010	Difference
850 mb	11.4	13.3	+1.9
Surface	-7.5	-2.9	+4.6

Update: here's the McGrath 850 mb chart for the same temperature thresholds as Fairbanks:

Solar Heating Minimum

** Updated on 12/30 **

As Richard noted in a recent post, there is little to no solar energy for much of Alaska this time of year. In fact, there is no functional solar heating anywhere north of Fairbanks for the next several weeks. In looking at hourly data for Bettles from NCDC, I looked at the average hourly temperature for every day of the year to see when solar energy stopped influencing daily temperatures (n=45 years). Bettles was chosen due to its location far away from any alternate heat source (e.g., an ocean).

Though trial and error, it appears that when the sun is 3° above the horizon or less, there is no perceptible diurnal temperature difference. At 3° above the horizon, the theoretical solar energy is 9 watts/square meter. At the latitude of Bettles, that translates to a 55-day period of no solar heating. The next two charts show the annual solar elevation for Bettles and for Barrow.

The chart immediately below shows the average hourly temperature for the 55-days at Bettles where the sun is less than 3° above the horizon. Interestingly, there is a very slight bump at the equivalent of solar noon – even on days when there is no sunrise at all!

The final graphic (map) shows the number of days with no effective solar heating; i.e., to maximum solar elevation is 3° or less. The 835 GHCN stations are shown as green dots.

** Updated Section **

Here are some charts showing the hourly temperatures and sea level pressure readings for the days with no sunrise and no sunset at Bettles (Dec. 12 to Dec. 31 & June 12 to July 2 respectively). Note: Due to Leap Years and the procession of the equinoxes, the dates will be slightly different from year to year.

The final (?) chart shows the hourly temperatures for Barrow between December 1st and January 27th. December 1st was chosen to account for the variability in sea ice pack closure around Barrow. January 27th was chosen due to that being the date that the sun is still below the horizon. The local effect at Bettles disappears. When only those days when the sun was within 2 degrees of the horizon were chosen, the line was still effectively flat. Interestingly, the point at which a daily insolation pattern was established in the Spring wasn't until the sun was 5° above the horizon (~Feb. 14th).

Also, the 3-hour pattern that Eric noted is highly exaggerated for Barrow. It turns out that this is due to some days recording temperatures in 3-hour increments instead of hourly. Those occurrences are much more frequent in the earlier part of the climate record when the temperatures at Barrow were significantly colder. It will take more work to tease out those obs.

Maximum Statewide Temperature Range

There have been several references in social media the last few days  (here and here) regarding the range of temperatures across the state approaching 100 degrees. I thought it would be interesting to see what the greatest daily temperature range was in the Alaska climate record. The winner appears to be February 3rd, 1977, with a statewide temperature range of 125°F. The high temperature was +60°F at Annette Island and the low temperature was -65°F at Umiat. There are 5 or 6 days in the GHCN database with larger ranges but they all contain highly questionable values; e.g., a max high of +73°F with the second highest of +45°F. None of those instances were even marginal so they were easy to toss out. No more than 4 days have ever had a daily range of over 120°F.

I initially expected the record range day to fall in mid February to early March since the far northerly latitudes receive little insolation and the stations in Southeast Alaska receive a fair amount. What surprised me was that December and January are the months most likely to see a day with a statewide diurnal range in excess on 110°F.

Deep Freeze

The temperature at Fairbanks airport touched -40° this morning for the first time this winter.  This is very close to the long-term median date of December 28 for the first -40° reading in Fairbanks, but slightly earlier than the 1981-present median date of January 4.  The long-term median for latest -40° reading is February 10.  Note that -40° is never reached in slightly more than 10 percent of winters in Fairbanks (15 percent since 1981).

It's colder yet at many other interior Alaska stations, including -50 °F in Eagle and -58 °F in Chicken.

The chart below shows the annual number of days reaching -40 °F (total column height) and -50 °F (red columns) in Fairbanks since 1930.  The long-term decline is very noticeable, especially for -50 °F days which have become rare.  However, there was tremendous year-to-year variability prior to about 1975; some winters had few or no extreme cold days, while others had many.  Superficially, it appears that variability has decreased, but this could be an artifact of sampling a smaller portion of the climate distribution in recent decades.

Webcam photos from around Fairbanks show the clear skies and shallow ice fog that are typical in association with deep cold.