Record Lows Saturday and Sunday

Courtesy of Pro Music

 The high temperature at Fairbanks Saturday of 35ºF is the lowest so late in the season and the latest date of record with a high in the 30s, breaking the previous record of May 17, 1964. The low of 23ºF Sunday morning was not a record for the date for Fairbanks: record for the 19th is still 20ºF in 1918. Temperatures Sunday morning were coolest in areas with snowpack, including 13ºF at Keystone Ridge and Wickersham Dome and 15ºF at Goldstream Creek, were there is still patchy snow cover.
Photo Sunday afternoon showing ice floes running in the Chena River downtown.



Here are some more records, though I've edited this NWS Fairbanks statement to correct erroneous data in the original:

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE FAIRBANKS AK
1149 AM AKDT SUN MAY 19 2013

...TEMPERATURE RECORDS CONTINUE TO FALL IN INTERIOR ALASKA...

STRONG COLD AIR FROM THE ARCTIC PUSHED TEMPERATURES DOWN ACROSS
THE INTERIOR THE LAST FEW DAYS TO RECORD LEVEL. TEMPERATURES WILL
BE ON THE RISE TODAY THOUGH A FEW RECORDS COULD FALL TODAY BEFORE
THE COLD AIR EXITS THE STATE.

RECORD MINIMUM HIGH TEMPERATURES ON SATURDAY MAY 18TH...
                                       MAX
                                   TEMPERATURE    PREVIOUS RECORD
FAIRBANKS...............................35            44 (1918)
TANANA..................................34            41 (1918)
COLLEGE OBSERVATORY AT UAF..............32            37 (1964)
BETTLES.................................27            35 (1975)
EAGLE COOPERATIVE OBSERVER..............32            40 (1992)
DELTA JUNCTION..........................29            39 (1992)
EIELSON AFB.............................34            42 (1992)
NORTHWAY................................33            38 (1992)
DENALI PARK Headquarters................36            39 (1992)
NORTH POLE (KJNP).......................35            43 (1992)
MCGRATH.................................36            52 (1993)

RECORD LOW TEMPERATURES FOR MAY 19TH...

EIELSON AFB.............................23            29 (1966)
NORTHWAY................................21            25 (1966)
TANANA..................................14            18 (1975)
BETTLES.................................10            14 (1975)
COLLEGE OBSERVATORY AT UAF..............20            26 (1983)
MCGRATH.................................19            28 (1985)
NORTH POLE (KJNP).......................21            25 (1996)
DELTA JUNCTION..........................19            30 (1999)

Updated Fairbanks Temperatures

Interior Alaska's long cold spell will come to and end this week, so here's an update on daily temperatures (through Saturday, May 18th).

As regular reader Richard pointed out, every day in Fairbanks since April 3rd has had a daily mean temperature below normal (the mean on May 11th was one degrees below normal). This appears to be the longest consecutive streak of below normal daily mean temperatures of record, regardless of the base period normals used.

Record Low Temperatures

1030am May 18th, courtesy of the Nenana Ice Classic

I will not be able to keep track of them all, but here are some low temperatures records from the Interior the past day or so:

McGrath (since 1940)
daily record low May 17th of 19ºF
low temperature of May 18th of 15ºF is (by far) coldest so late in the season

Fairbanks (since 1905)
daily record low temp May 18th of 24ºF (might go lower by midnight)

College Observatory ( since 1948)
low of 21ºF coldest so late in the season

Tanana (few gaps, since 1901)
low temp May 18th of 18ºF coldest (barely) so late in the season.

Denali National Park HQ (since 1923)

daily record low May 18th 14ºF, not the coldest so late in the season

Coldest Airmass so Late in the Season is on the Way

As previously mentioned, the coldest airmass so late in the season is moving into Fairbanks-land. This is based on the period of record for upper air soundings, which is this case is since 1948. The WB/NWS in Fairbanks has taken has upper air data since the late 1930s but I've been unable to locate the actual observations from before 1948.

There are numerous ways to assess the temperature of an airmass. In general it's best to use thickness, as this is proportional to the mean temperature through a given layer of the atmosphere. This time of year though it's simplest to use the 850mb temperature (roughly 4000' MSL), since the atmosphere is usually pretty well mixed from the ground up to that level.

For the second half of May and early June, here are the lowest 850 mb temperatures at Fairbanks after May 15th (since 1948). Notice the coldest is an estimate from the high resolution North American Regional Reanalysis as the RAOB was missed that day. 

May 17 1992 00Z: -12.5C (RAOB missed, estimated from NARR)
May 16 1992 00Z: -11.7C
May 16 1992 12Z: -10.9C
May 19 1975 12Z: -10.9C
May 18 1964 12Z: -10.9C
May 18 1964 00Z: -10.5C
Jun 04 2006 12Z: -9.4C

Here is a plot of the GFS forecasted 850mb temperature from the Friday morning run:

As you can see, the GFS is forecasteing 850mb temperatures colder than -12.5C for about 36 hours. For what it's worth, the GFS forecasted an 850mb temperature Friday afternoon at McGrath of -16.3C, and the RAOB came in with -16.7C, by far the coldest so late in the season there.

Updated:

Here's the same model forecast with the verification (through Sunday afternoon) plotted. Fairbanks (-14.3C) and Anchorage (-10.9C) both set records for lowest 850mb temps so late in the season.

Comparing Cold and Colder Springs in Fairbanks

Long time Fairbanksians have been comparing this spring to 1992. That spring was much snowier than this year, but this year is colder. So I thought it would be interesting to compare temperatures this spring, not to the average, but to the coldest springs. So of course I have to make a chart, and here it is:

The heavy black line is this year (through Wednesday, May 15th), and the lighter lines are some representative prior years. The dotted line is the average of eight cold April-May periods (1924, 1931, 1945, 1948, 1964, 1985, 1992 and 2002) not including this year (which is certain to be in the top three). So in the "typical" cold spring, the average daily temperature does not get above freezing to stay until about May 4th. Well, we missed that this year by nearly a week. In the typical cold the daily mean exceeds 40ºF about May 10th. While we have had a few days that warm, with the coldest airmass so late in the spring poised for the weekend (more on that in a coming post), we are not going to keep daily means above 40ºF until early next week, nearly two weeks later than normal even for a "cold spring".

Record Cold Again in the Interior

Lots of record lows and record low max temperatures in the Interior Monday and Tuesday. Here's some records (slightly reworded) from the NWS statements:

Fairbanks set a new record low max temperature May 13th when the high only reached 37 degrees. The previous low max  temperature was 40 degrees in 1937. The low temperature on the 13th of 22 degrees was also a record, breaking the previous record of 26 degrees set in 1928. 

Bettles set a new record low temperature May 12th with a low of 15 degrees. The old record low was 20 degrees set in 2007. Bettles again set records May 13th as temperatures dropped to 11 degrees and only climbed to 27 degrees. The previous record  low for this day was 22 low in 1986 and the old record low max was 34 degrees in 1986. 

College Observatory on UAF West Ridge tied the old record low of 22 low on May 12th. The previous occurrence at this temperature 
was in 1954. On May 13th a new low was set with temperature dropping to 21 above. The old record was set at 24 low in 1964. 

 Eielson AFB set a new record low of 22 low May 12th. The old record was 26 low in 1965. May 13th temperatures set a new low of 22 low breaking the old record of 26 set in 1954. The high temperature on May 13th only reached 38 degrees setting a new record  low max that of 40 degrees that was set in 1992. 

Galena broke two records May 13th. A new record low temperature of 13 low when the old record was 16 low in 1965. A new low  max temperature of 31 degrees breaks the old record of 34 degrees in 1965. 

Tanana set a new record low max temperature May 13th when highs only reached 34 degrees. the previous record low max was  37 degrees set in 1918. Denali National Park Headquarters recorded a low temperature of 14 degrees the morning of the 13th. This broke the previous record of 17 set in 1957.  

Winter Lives in the Brooks Range

Courtesy of the FAA

The sun might shining 20+ hours a day now in the Brooks Range, but winter lives. Some of the higher elevation stations are below zero this Monday morning. Lows through 5am AKDT include:

North Side:
Killik Pass RAWS (3000' MSL): -6ºF
Atigun Pass (4800' MSL): -3ºF
Imnaviak Creek (3100' MSL): -2ºF

South Side:
Ram Creek RAWS (3000' MSL): -4ºF
Chimney Creek (3100' MSL): -2ºF

The Fairbanks Snowpack: Going...Going...

The remaining winter snowpack was down to 1" as of late Saturday evening at the Fairbanks Airport. Here's a plume diagram of springtime daily snow depth at the Airport since 1985.

The outstanding feature of this plot is that this year, unlike other recent years with very late meltouts, the mid-spring snow depth was not unusual. Even 1985 started off considerably more snow on the ground in March. Because meltout is uneven and the remaining snow cover is patchy, there is an element of subjectivity in putting down a single number for snow depth. But for this year, at the Airport, even with the turn back to cooler temperatures cooling, the end of the snow pack is near.

Fairlbanks Temperatures…Warming but Still Cool

Here's an update of daily mean temperatures in Fairbanks for 2013. As usual, the gray shading is plus or minus one standard deviation from the 1981-2010 mean. Although Wednesday was the warmest day of the year thus far, with the first 50ºF max temperature since October 7th and a  daily mean of 36ºF, this was still 1.6 standard deviations below normal. The 215 days with a high less than 50ºF is the fourth longest such streak, although more than two weeks shorter than the 1963-64 record.

Snow Melt…Up High There's A Long Way to Go

The pattern is definitely changing and spring is on the way to Fairbanks-land this week.

Here's the 500mb heights from the Sunday morning ECMWF (12Z 05 May 2013) run valid at 4am AKDT Friday 10 May: I've drawn in the ridge extending northwest from the big high over Washington. The green colors reflect higher than average clustering of the various ensemble members, which increases  confidence in this forecast. This would be a mild, but not overly warm, pattern for Interior Alaska. Given how high normal temperatures are now, this will get snow melt and break-up going full swing. The snow cover will go pretty quickly in town, helped out by 18 hours of sunshine. But at elevation it will take a while.

Here's a plot of daily snow depth here on Keystone Ridge for each spring the past 17 years. I've highlighted some of the notable years.

Obviously there is nothing like this year in any spring since 1997, and this is undoubtedly the greatest snow depth this late in the season here on the ridge since 1992. The current high value will decrease several inches simply due to compaction of the flurry snow that fell this past week. However, that still leaves a lot of snow that needs plenty of heat input to turn into water.

So what will the date of meltout* be this spring on Keystone Ridge? I'll go for 24 May, assuming a curve somewhere between the rapid decline in 2002 and the much slower rate in 2000, but note it's never a quasi-linear decline to zero: once the snow depth gets down to 10-12", it goes fast. 

*Meltout is defined here as the date when the snow depth fall to zero or trace. In practice, this means the date when the snow-free area in the vicinity of the weather station increases to greater than 50 percent coverage.

Big Snowfall and Precip Differences Across Area This Week

Amidst  the cold temperatures, this week has been persistently snowy, at least in parts of the area. This morning's view from Keystone Ridge sure looks like winter.

With temperatures getting above freezing each afternoon at low elevations it's not really possible to get consistent measurements. That said, here are some totals for Monday April 29th through Saturday morning, May 4th.

Updated with additional info:

Keystone Ridge (1600' MSL): 0.89" precip and 17.5" snow
Gilmore Creek CRN (1184' MSL): 0.30" precip NA snow
East Farmers Loop (705' MSL): 0.36" precip and 4.8" snow
UAF West Ridge (610' MSL): 0.34" precip and 5.3" snow
Goldstream Valley Bottom (580' MSL): 0.33" precip and 6.9" snow
North Pole (475' MSL): 0.16" precip and 0.5" snow
Aurora (450' MSL): 0.40" precip and 1.2" snow
Fairbanks Midtown (445' MSL): 0.28" precip and 3.8" snow
Fairbanks Airport (434' MSL): 0.35" precip and 4.8" snow

Obviously it would be nice to have more info from elevation, but notice that the CRN at Gilmore Creek has had only a third of liquid as Keystone. This is probably a function of the southwest flow aloft and borderline downslope flow (at least of Friday).  Unfortunately the SNOTEL data appears to be corrupt for at least some of the sites at the NCRS website.

Why So Cold in April in Fairbanks

Here's a try at an explanation of why it was so cold in April in Fairbanks and much of Alaska.

First, here's the mean 500 mb heights and anomalies:

Courtesy of NCEP.NCAR Reanalysis

The most notable features are the big high over the northwest Bering Sea, with a mean height anomaly for the month of over 200 gpm. The other feature is the trough from the western Canadian Arctic across mainland Alaska, though the heights are not especially low, with the 50 gpm anomaly just reaching Alaska near Eagle. The weakness in the contours over Interior Alaska reflect the frequent closed low that was found over the area, especially early in the month.

This pattern is reflected in the April anomaly of the meridional (north-south) component of  the 700 mb (roughly 10,000ft)  wind flow:

Courtesy of NCEP.NCAR Reanalysis

The blues and purples show more northerly wind component in the 700 mb wind than is usual in April over nearly all of mainland Alaska, with more southerly than average flow over Kamchatka, the Sea of Okhotsk and most of eastern Siberia. 

Finally, the mean April near surface (1000mb) temperature anomalies are about what you'd expect with this transport pattern:

Courtesy of NCEP.NCAR Reanalysis

April was extremely warm over the East Siberian Sea and quite warm over all over eastern Siberia and Chukotka, with the cold over most Alaska (extending southeast thru the Canadian Praise Provinces and into the upper Midwest). The northwest North Slope and Bering Straits region were not so nearly so cold, being closer to the high aloft and, for the Slope, getting occasional warm pushes from the west.

I'll anticipate regular reader Gary and suggest the following to the question "why this  particular pattern at this time?" The high aloft over the Bering sea and anomalous northerly flow are signature features of the negative PDO phase of North Pacific sea surface temperatures, which as been the case since 2010. This was amplified by only limited deep tropical convection in the western Pacific (in jargon, a not especially active MJO). This allowed a favored negative PDO pattern to persist.

April 2013 in Fairbanks

There is a lot of Alaska weather going on...but we'll try and take it one piece at time.

So, for Fairbanks for April, the mean temperature of 18.0ºF makes this solidly the coldest April since 1924 and the third coldest of record. Only 1924 (14.8ºF) and 1911 (17.4ºF) are colder. For all Interior locations with data from 1924, that month is still the coldest April of record.

The high temperature for the month of 48ºF makes this the first April since 1972 when the temperature failed to get to 50ºF or higher. Two daily record lows were set: 15 below on the 12th and 2 above on the 28th. The record on the 28th was especially notable as only twice as the temperature been lower than this so late in the season. The monthly low of 21 below on the 11th was not a daily record, but was the lowest April temperature since 1992. Daily mean temperatures were below normal every day after the 3rd. Which of course calls for a standardized anomaly plot:

Eight April days had daily anomalies 2.5 or more standard deviations below normal, and the monthly mean of 18.0ºF is a whopping 2.8 standard deviations below the 1981-2010 mean. The mean temperature for March and April combined of 12.5ºF is the coldest since 1972.

Snowfall totaled 9.9", while well above normal, made this only the 4th snowiest April since 1990. Far more unusual was the snowpack; outside of urban areas the snowpack has compacted some but has not really started to melt out at all. At the Airport, the snow depth of 18" on the 30th was the greatest end of April snow cover since 1937. This is not too surprising considering that the accumulated thaw degrees through the end of April is a paltry 3, fewer even than 1924 and 1911; 1937 had just one thaw degree day through the end of April, the lowest of record.

Tomorrow I'll try and gin a some analysis of why it was so cold in April.

Cold is Not the New Normal

There will be a lot to write about once April is in the books, but for now here's something to chew on. April is going to finish up as the coldest in Fairbanks since 1924. Following on the cold December and the cold January 2012, I thought I'd look at thermally "extreme" months in recent years.

In the past decade, 2003-2012 plus the first four months of this year, here are the number of times a given month was in either the top ten warmest or coldest in the Weather Bureau/NWS era (since 1930). So red is the "warm month" count and blue the "cold month" count.

The total count is: since January 2003, 21 month have been in the warmest ten and 10 have been in the coldest ten. Interestingly, only two months in the warm season (April 2013 and September 2004) have been in the cold column. while 11 months have been in the warmest ten.

Significant Record Low at Fairbanks

Courtesy of Pro Music, Fairbanks

Updated with additional observations and faciods…

Temperatures dropped to near zero overnight. The low temperature at the Fairbanks Airport of +2ºF easily broke the previous record of 8 above set in 1924, and is among the coldest temperatures so late in the season (more below). Other low temperatures include:

Chena Hot Springs: -8ºF
Goldstream Creek: -6ºF
Woodsmoke CWOP: -3ºF
Mile 43 Steese: -2ºF
Fort Wainwright: -1ºF
Eielson AFB: +1ºF
UAF West Ridge: +2ºF
Wickersham Dome: +6ºF
Keystone Ridge: +8ºF

The low of +2F at the airport makes this among the lowest temperatures so late in the season. The only lower temperatures later than April 28th are a low of 0ºF on May 3, 1945 and the -1ºF on May 9, 1964. At UAF West Ridge and Eielson, with obs since the 1940s, these are the lowest temperatures of record this late in the season.

Obviously the sustained cold  weather has kept break-up at bay. The photo from Pro Music Sunday morning, looking south across the Chena River, hardly even shows any frozen melt water on top of the ice.

Fairbanks Standardized Temperature Departures: Blue Edition

Here's the standardized daily mean temperature departures updated through Thursday. Fairbanks is definitely headed toward a top five coldest Aprils of record, and that's no surprise given all that blue on the chart. 19 days so far this month have been 1.0 or more standard deviations below normal, while only the first three days of the month were above average at all.

A Record Falls, Another Remains

Courtesy of the FAA

The average daily temperature on Tuesday at Fairbanks was 32ºF, which means that 2013 is now the latest in the spring that Fairbanks has ever gone with zero accumulated thaw degree days.  The high Wednesday has been 39ºF (early morning right with the cold frontal passage), and the low through 7pm AKDT has been just 32ºF. However, it is possible that the temperature could get down to 25ºF by midnight, so the streak might continue.

The inch of snow today is not a record for April 24th. That remains 1.9" in 1941.

Fairbanks Staying Cool

Here's an update of temperatures through Saturday, April 20th.  In this plot, in addition to trying out new software, I've plotted the daily mean temperatures along with the 1981-2010 mean ± 0.43 standard deviations (the grey area).

This basically corresponds to the Climate Prediction Center's tercile categories, with red colors showing temperatures in the CPC "much above" tercile and blue showing temperatures in the "much below" tercile. Of course, you don't need a weatherman to tell you that mild weather has been short supply for quite a while now.

Fairbanks Snow Melt…Getting There…But Not Quite Yet

Milder weather has come to Fairbanks-land, and so the long process of snow melt and river ice break-up will, after a couple week delay, get underway. Here was the view on Smith Lake, at the west end of the University of Alaska Fairbanks campus on Thursday afternoon (April 18th), when trail conditions were still "perfect".

Courtesy of Ed Plumb

Temperatures finally cracked freezing early Friday afternoon and we now look to be into the thaw-freeze diurnal cycle, with mild days and clear cool nights. This will allow for slow ripening the snow pack, a necessary step in before substantial runoff can commence. One measure of how this process is progressing are thaw degree days, which are simply the sum of daily mean temperatures above freezing. Below is a plot of cumulative thaw degrees at Fairbanks through April 20th for each of the last 108 years, expressed as the difference from the mean.

Through Saturday, Fairbanks has cumulative total of zero thaw degree days since March 1, 47 below the mean . How unusual is this? Well, it's not unprecedented: 1960 and 1954 also had zero thaw degree days through April 20th. However, we don't want to get too hung up on "zero". After all, "one" is not very much different than "zero. Next is a histogram of the above data:

So having accumulated very few thaw degree days at this point is not unusual;  11 percent of springs have five or less through April 20th. So, while it is unusual not to have any significant snow melt thus far, it is well within the range of past experience. If Saturday's numerical weather models are vaguely correct, we'll start to accumulate those thaw degree days pretty quickly next week and with it snow pack ripening.

Cold April in Context

The average temperature the first half of April in Fairbanks was10.8ºF. This is a remarkable 16.3 degrees below normal and the fourth coldest of record (second coldest in the WB/NWS era). The chart plots the mean temperature the first half of April and the 10-year running mean.

The years with coldest first half of April and the mean temperatures are:

1911:  4.4ºF

1985:  9.8ºF
1924:  9.9ºF
2013: 10.8ºF
1986: 11.0ºF

The 10 year running mean shows nicely that there has been little trend in April temperatures over the past 50 years except for the decade or so of warm Aprils in the 1990s. This year is a good example of an "outlier" that we have no reason to think is tied to a larger pattern (unlike say, Barrow temperatures in October).

Here's a link to the NWS Alaska Region Facebook graphic showing how the cold weather this month is distributed across Alaska. Northwest and Southeast Alaska have not been notably cold but in between it sure has been.

The Cold April week

Updated with Saturday, April 13th stats

Fairbanks has chilled through the coldest April week since the 1920s. The average temperature Saturday, April 6th through Friday, April 12th was +2.6ºF. This is the coldest week wholly within April (no end-of-March days) since April 2-8, 1927, when the average temperature was also 2.6ºF. The coldest April week was in 1924, when the average temperature April 1-7 was -1.5ºF. If we include the last couple of days of March, then this is the coldest "mostly April" week since March 30-April 5, 1985, when the average temperature was 1.7ºF. This was not quite the coldest week so late in the season: April 7-13, 1911 had an average temperature of 1.0ºF.

Update: Saturday came in with a high of 25ºF and a low of -13ºF. So, the week of April 7-13th is now the coldest (and this should be the bottom), with an average temperature of +2.2ºF.  This the coldest April week since April 3-9, 1924, when the average temperature was +1.9ºF.  

The lowest temperature this week was 21 below on the 10th, the lowest April temperature since 1992. The only daily record temperature set was the low of 15 below on the 11th, which broke the previous record of 12 below set in 1936.

From my favored standardized anomaly viewpoint, the average daily temperature on Thursday, April 10 was 3.0 standard deviations below normal. This is the largest daily negative anomaly since June 4, 2006 (-3.4). However, this was only the absolute largest anomaly since May 28, 2011 (+3.1). A quick analysis of the weekly anomaly, using the full Weather Bureau/NWS era, 1930-2013 as a base comes to -2.9. This is no where close to the greatest negative weekly anomaly in April: April 20-26 1924 and 1948 both came in at -4.0.

Update: The average temperature of +2.2ºF for April 7-13 is 3.0 standard deviations below the 1930-2013 mean. 

How did this happen: cold low aloft. Here's the mean 500mb heights for April 6-12:

Courtesy NCEP/NCAR reanalysis

There have been no upper air records set or even approached. Rather, it's the duration of the cold pattern that has produced the cold April week.

Coldest Morning This Late in Two Decades

Courtsey of the FAA

I'll be posting a wrap-up of the current cold snap this weekend, but in the meantime, it's worth noting that the low (through 6am) Thursday at the Fairbanks Airport has been -20F. This is the lowest temperature this late in the season since 1992, when the temperature fell to 23 below on April 13th. It's slightly colder in the usual places, with 24 below at Goldstream Creek and the Woodsmoke CWOP near North Pole.

Interior Alaska Temperature Anomalies: Hills vs. Valleys

I was talking with a colleague this past week about standardized anomalies as a way of grouping locations into broad climate regimes (e.g. the Alaska climate divisions work in Bieniek 2012).  A primary question is to what extant different elevations anomalies are correlated. This is hard to answer for Alaska because there are so few stations above their respective valley floors with long periods of record. However, I thought I'd give it a go for Fairbanks-land.

Here's a plot of the difference in monthly mean temperature standardized anomalies (anomalies computed from the NCDC 1981-2010 normals) between Keystone Ridge and Fairbanks Airport (14 miles apart) for entire period of record for Keystone Ridge (June 1996 to present). This is not an ideal test as Keystone Ridge is only 1200' higher elevation than the Fairbanks Airport. However, data for both sites are complete and there is no differing time of observations to confound the question. The way this plot is constructed, positive values indicate the higher elevation station is warmer than expected compared to the valley, and vice versa. In winter, this is straightforwardly interpretable as variations in mean monthly inversion strength. In summer, the situation is more complex but certainly differences in the number of rainy days will effect the differences in anomalies.

The overall correlation between monthly temperature anomalies at the valley and higher elevation site is an very impressive 0.94. Looking at individuals months, May and October have correlations of 0.99, while December has the lowest correlation at 0.88. In the above plot there are some interesting outliers. The largest negative anomaly is November 2003. This was a wet and cloudy month, with only minimal inversions most of the time. The largest positive anomaly is December 2005, with exceptionally strong inversions (and hardly any precipitation) prevailed the second half of the month. Just eyballing the plot, there may be some longer term signal. Since late 2007 there have been a (seemingly) large number of months with negative differences, while 2004 and 2005 had a large number of months with positive differences.


Variations in daily anomalies are greater, as the plot below since 2011 shows, I've presented a slightly different view in this case, with the actual Fairbanks Airport daily anomalies in green and the Keystone Ridge difference in red. Again, positive values indicate that Keystone Ridge is warmer than expected compared to the valley, and vice versa.

Note: it would be better to use the anomalies calculated from  means and standard deviations for the overlapping period of record (again, June 1996 to present), but it turns out that the difference from using the 1981-2010 normals is, in this case, negligible, and since I otherwise use the current NCDC normals for calculating standardized anomalies, I chose in this case to remain consistent. 

Cold April Morning

Fairbanks-land awoke Saturday to the coolest weather this late in the season in several years. A decent pressure gradient across the Interior kept winds blowing in some valley locations overnight, but where winds dropped off temperatures dipped well into the teens below. But hey, with more than 14 hours of sunshine to enjoy, I'm not complaining.






Lows Saturday morning included:

Goldstream Creek: -16F
Eielson AFB: -18F
Fort Wainright: -14F

Valley locations where winds persisted were notably milder:

Woodsmoke CWOP:  +1F (near North Pole)
Mile 42 Steese Highway: -2F
Fairbanks Airport: -3F

Higher elevations were mostly breezy and nippy:

Keystone Ridge: -3F
Wickersham Dome: -5F
Cleary Summit: -5F

Fairbanks Winter Wrap-up

It's April now, so the 2012-13 cold season is in the books. Here's how temperatures shook out: 

Unrelenting cold weather early in the season gave way to a much more mixed temperatures starting just before New Years. Overall, the average temperature from October 1 through March 31 was an even 0.0°F. This is 1.4 degrees colder than last winter and the third coldest October through March period since 1976. The first half of the winter, October through December, with an average temperature of -1.1°F was the coldest since 1961 and the third coldest in the 82 years of the Weather Bureau/NWS era. In stark contrast, the second half of the cold season, January through March, the average temperature of 1.1°F was the mildest January through March period in Fairbanks since 2006.

To mind my the highlight of the season was the dreaded ran January 14th. There are still stretches of Murphy Dome Road that are ice covered from this rain (though that is now improving rapidly).

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).