The End of the Snowpack

Amazing what sunshine and temperatures in the 60s and 70s (and lows near 50ºF) will do to a snowpack. By Sunday evening the snow pack here on Keystone Ridge, which on Wednesday was still near 100% coverage, was reduced to patches. Of course, with the melting snow and warm temperatures came the first mosquitoes of the season, which were surprisingly pesky.  Down at Denali Park HQ, the meltout date of May 25th was one day short of the 1992 record of May 26th. 

Spring Temperature Anomalies

The cold spring over Interior Alaska is fading into the past now as "insta-summer is upon us: the high was 77ºF at Fairbanks on Saturday and snow is melting fast at higher elevations. This has pushed rivers draining the uplands well up, though so far no flooding on the Chena or Salcha.

For the spring as a whole (Mar-Apr-May), the anomalies are not especially remarkable, and will be even less so by the end of the month. Low level temperature anomalies from the NCEP/NCAR Reanalysis through May 24th, are depicted below for Alaska and vicinity, The warm anomaly over the Arctic Ocean north of Wrangel Island is much more impressive than the cold anomalies over Alaska.

Courtesy of NCEP/NCAR Reanalysis

The cold temperatures show up in this short loop of weekly temperature anomalies (ºC) since March 1st:

Fairbanks Finally Above Normal

Fairbanks topped out at 71ºF Friday, the first day the temperature has been 70 or higher since August 30th. With a morning low of 40ºF, the daily mean of 56ºF was 3 degrees above normal. Here's a plot of daily temperatures this spring.

The long streak of below normal daily means ran from April 4th until May 23, for 49 consecutive days. Using the normals that were effect at the time, the longest consecutive anomaly streak I can find is Oct 18 to Dec 10, 2002, 53 consecutive days with above normal daily means. That streak was bounded by two days that were right at normal (departures of 0ºF). That autumn there were 88 consecutive days between days with a daily average temperature below normal. This spring there were 50 days (April 3-May 23) between above normal days.

More Snow to Go

Reader Richard asked about snowmelt on Keystone Ridge. Here's a photo from Wednesday evening, May 22nd. As you can see, there is still plenty of snow yet to melt, though it's going fast now. As of Thursday evening I was calling the depth 15" and coverage at about 90%. The snow-free areas under the trees are starting to coalesce but have not spread much yet. However, with lows in the past three days in the 40s and dew points now around 30ºF, it will not take more than a few days more to reduce the snow to patches.


Denali National Park Headquarters was down to 12" of snow on the ground as of Thursday morning. The latest meltouts of the winter snowpack there is May 26, 1964 and May 25, 1992, so this year will be close.

Update: Here's a couple of photos from Friday evening, May 24th:

Tanana River at Nenana…A New Record Late Break-Up

Courtesy of the Nenana Ice Classic

At 1142pm AKST (1241pm AKDT) Monday the tripod on the Tanana River at Nenana was still standing (as seen in this photo) making this now the latest break-up of the winter ice of record (since 1917). The previous record was 1141 AKST May 20, 1964. The tripod fell three hours later, at 341pm AKDT as the ice began running.

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.