Disappearing Halloween Snow

Rick Thoman pointed out today on Twitter that this Sunday will - in all likelihood - be the 5th Halloween in the past 6 years to have less than an inch of snow on the ground in Fairbanks.  For a span of 75 years - 1941 through 2015 - only one year managed the same feat.  (Incidentally, that year was 1962, which bears more than a passing resemblance to this year in terms of alignment of various aspects of the global climate system.  Interesting.)

The disappearance of Fairbanks snowcover at Halloween is consistent with a downward trend in October 31 snow depth that seems to have started more than two decades ago; it's been 24 years since more than 6 inches was on the ground, but prior to 2000 about a third of all years had at least that much snow.

Here's Rick's excellent graphic:

Total October snowfall in Fairbanks also shows the same kind of decline.  Before 2009 it was quite normal to have 10" or more of snowfall in October; this happened in nearly 50% of all years.  But amazingly it hasn't happened for the last 13 consecutive years.  Based on the 1930-2008 climate, and assuming each year is independent of the last, the chance of less than 10" happening 13 straight times is less than 1 in 1000.  So this appears to be a highly statistically significant change.

Interestingly the ERA5 reanalysis captures the preponderance of low snow accumulations in October over the last 12 years; the map below uses a 1951-2010 median as the baseline "normal".  According to this data, the anomaly has been most significant over the Bering Sea, but it extends across southern Alaska to the Canada's west coast and northwestern regions.

The lack of October snow does not principally reflect dry weather, at least not in the Bering Sea region; ERA5 actually shows more wet than dry weather in this area, and since 2009 Fairbanks has seen above-median liquid-equivalent precipitation in 5 of 13 years, including 4 very wet Octobers (2012, 2017, 2019, and this year).

Rising temperatures are a much more plausible explanation for the loss of snow; the ERA5 map below uses a 1951-2010 average for the climatological baseline.  In Fairbanks, all but 2 of the last 12 Octobers have been warmer than the 1930-2008 mean, and more than half have been over 5°F warmer than the old normal.

Alaska isn't the only place to have seen a paucity of October snow in the past decade or so.  Here's the ERA5 map for a global domain: note the similar low-snow signal from eastern Canada across the northern North Atlantic and in much of Russia.

Sun and Snow

Remarkable warmth has continued to build over eastern and southern Alaska, under the influence of a tremendous ridge of high pressure aloft.  Yesterday the southern Panhandle community of Klawock reached 75°F, the earliest on record for such a high temperature anywhere in the state.

Fairbanks saw 64°F yesterday, close to a record for the date, and this was with plenty of snow still on the ground.  Brian Brettschneider spotted that it was actually the warmest on record for such a substantial snow pack; the figure below illustrates this point.  There have been warmer spring days with a lesser snow cover, but none so warm with more than a foot remaining.

Here's the early evening scene on the UAF campus today:

And here is yesterday afternoon's 500mb analysis, courtesy of Environment Canada.  We've seen a lot of this in recent years, and it's amazing how the pattern flipped right back to its multi-year default after the excessive cold of 10 days ago.  Notice too the northerly flow rushing down the other side of the ridge into western Canada and the Lower 48; folks down south are wondering where their spring disappeared to.

Lots of Water

Interior Alaska is finally escaping the grip of winter, with snow disappearing quickly and break-up beginning to advance on some rivers.  Remarkably abundant snowfall in late winter combined with recent rains has led to an excess of run-off and the potential for flooding if temperatures rise too high too quickly.  Here's the NWS flood potential map from last week:

Fairbanks is already down to a snow depth of only 4 inches, but the snow pack remaining in the hills is quite monumental: the Munson Ridge SNOTEL site at 3100' elevation near Fairbanks is reporting 15" of liquid equivalent water.  That's a lot of water to come down the creeks and rivers in the next month.

According to the SNOTEL instrument, 6.8" of liquid-equivalent precipitation has fallen on the hill since March 1 - this is quite remarkable for the (usually dry) time of year.  It's believable too; here's a chart of recent precipitation at the top-quality CRN site (1140' elevation).

The massive influx of melt water will almost certainly bring forward the date of break-up at the Nenana tripod, owing to the increased stress caused by high water.  There's some evidence of this effect in the history of the Nenana break-up; the chart below shows that when precipitation is very high after March 1, the heat input (thawing degree days) required to reach break-up tends to be lower than normal.

This year Fairbanks has seen 2.86" of precipitation since March 1, which is the highest on record for March 1 - April 21.  The previous record for this period was in 1967, which happens to be the year of the great August flood in Fairbanks (hmm...)

Here's the latest break-up summary from the NWS.

HYDROLOGIC OUTLOOK
NWS ALASKA PACIFIC RIVER FORECAST CENTER
ANCHORAGE AK
1 PM AKDT WED APR 22 2020

..SPRING BREAKUP OUTLOOK FOR ALASKA...

Breakup Update: The Forty Mile river upstream of the Taylor Highway
has broken up as well as the Kuskokwim River near Nikolai. The Tozitna
River has broken up with an ice jam forming and releasing. The Aniak
River is reported to have broken up dynamicaly and is mostly open at
the confluence with the Kuskokwim. Ice is beginning to lift on the
Kuskokwim, Yukon and Koyukuk Rivers.

The 2020 Alaska Spring Breakup flood potential is forecast to be
generally above average south of the Brooks Range and average flood
potential for the North Slope. The Flood Potential forecast is based on
observed snowpack, ice thickness reports, and long-range temperature
forecasts and focuses on the Kuskokwim, Tanana , Yukon, Koyukuk,
Copper, and North Slope rivers. Recent observed and forecast
temperatures suggest a generally earlier than normal, more dynamic
type breakup for locations statewide.

Timing of breakup statewide is expected to be several days earlier
than normal. Breakup along the Yukon River upstream of Fairbanks
is expected to be 1 to 3 days earlier than median dates; generally 3 days
earlier at locations downstream from Fairbanks to Anvik; and 3 to 5 days
earlier at locations downstream from Anvik to the mouth. Breakup along the
Kuskokwim River at Nikolia downstream to Tuluksak are expected to be 1
to 2 days earlier than median dates and 2 to 5 days earlier downstream
from Tuluksak to the mouth.

Temperatures - Statewide, temperatures over the past few weeks generally
have been normal to below normal. However, temperatures over the next
several weeks are expected to be normal in areas north of the Brooks
Range and above normal for the remaining parts of the state. Statewide,
temperatures for April and May are expected to be above normal.

Ice - The April 1st ice thickness data indicate that ice thickness is near
normal across the state. A few measurements across interior Alaska
ranged from 32 inches at Galena, which is 82% of average; 33 inches
at Nenana, which is 80% of average; 48 inches at Eagle, which is
117% of average.

Snow - April 1st snowpack by the Natural Resources Conservation Service
(NRCS) indicates greater than normal snowpack across interior Alaska
ranging from 117% in the central Yukon Basin to 197% of average in
the Kuskokwim Basin. The Yukon government is also reporting greater
than normal snowpack across the Upper Yukon River Basin in Canada.
The snowpack is near normal along the North Slope and below normal along
the Gulf Coast and throughout Southeast Alaska.

Climate Outlook:

April and May weather is the most important factor determining the severity
of river ice breakup. Dynamic breakups have a high potential for ice jam
flooding and typically require cooler than average temperatures during March
and into the first few weeks of April followed by an abrupt transition to
warmer than normal temperatures in late April to early May. Thermal breakups
have a low potential for ice jam flooding as river ice generally rots in place.

The Climate Outlook for Spring 2020 suggests a more dynamic type breakup this
year. Observed temperatures in March thru the first week of April were generally
below normal to normal. The second and third weeks of April were generally
warmer than normal.  Temperature forecasts for the last week in April
indicate near normal temperatures statewide with equal chances for above and
below normal for early may. The mid-March 3-month Climate outlook
indicates increased chances of above average temperatures throughout Alaska.

Further information can be found at the following web sites:
Weather-
https://www.weather.gov/aprfc/AGAK78PACR

Snow-
https://www.weather.gov/aprfc/nrcs_ak_swe
https://www.weather.gov/aprfc/snow_depth
https://www.wcc.nrcs.usda.gov/snow/

Ice thickness-
https://www.weather.gov/aprfc/icethickness

Climate prediction-
http://www.cpc.ncep.noaa.gov/

River Ice Breakup Flood Threat:

The two generalized types of river ice breakup are dynamic (mechanical)
and thermal. A dynamic breakup moves from the headwaters of a river
downstream in a somewhat linear fashion. Ice jam flooding occurs more often
during a dynamic type breakup than a thermal type. A thermal type breakup
results in the river ice rotting in place primarily due to gradual to rapid
warm ups and little snowmelt runoff. Thermal type breakups usually result
in fewer ice jams and less chance of flooding.

Statewide, breakup this year is expected to lean generally to the dynamic
type. Temperatures statewide over the past few weeks generally have been
normal to below normal. However, temperatures over the next several weeks
are expected to be normal in areas north of the Brooks Range with above
normal temperatures for the remaining parts of the state. Temperatures
statewide for April and May are expected to be above normal. South of
the Brooks Range, the expected more dynamic type breakup, above normal
temperatures, and above average snowpack has increased the potential for
flooding this year to above average, while flooding potential north of the
Brooks Range is expected to be average.

THE FOLLOWING TABLE GIVES AN ESTIMATION OF FLOOD POTENTIAL FOR
VARIOUS LOCATIONS AROUND THE STATE AND BASIN RUNOFF VOLUMES.
---------------------------------------------------------------------
SNOWMELT RUNOFF VOLUME...EXPECTED WATER VOLUME FROM SNOWMELT DURING
                         THE MELT SEASON.

FLOOD POTENTIAL...THE LIKELIHOOD OF FLOODING FROM SNOWMELT AND/OR
                  ICE JAMS.  THIS IS INITIALLY CALCULATED BASED ON THE FLOOD
                  FREQUENCY FOR THE 2000 TO 2019 HISTORICAL RECORD AND ADJUSTED
                  TO REFLECT CURRENT CONDITIONS.

*  MEDIAN BREAKUP DATES ARE FOR THE PERIOD 1980 THROUGH 2019 AND ARE
      CALCULATED FOR LOCATIONS WITH AT LEAST 5 YEARS OF DATA.
** ACTUAL BREAKUP DATE FOR THIS YEAR
---------------------------------------------------------------------

                      SNOWMELT    FLOOD     MEDIAN  NO. OF  FORECAST
RIVER - REACH          RUNOFF    POTENTIAL  BREAKUP  YEARS   BREAKUP
                       VOLUME                DATE*    USED    DATE
-------------         ---------- ---------  -------  ------  --------
SOUTHEAST PANHANDLE     ABOVE

KENAI RIVER            AVERAGE    LOW       OPEN TO SKILAK LAKE

ANCHOR RIVER            BELOW     LOW       MOSTLY OPEN

MATANUSKA RIVER       ABOVE AVERAGE  LOW

SUSITNA RIVER         ABOVE AVERAGE
  GOLD CREEK                      MOD
  SUNSHINE                      LOW-MOD     05/02     31  04/26-05/02

YENTNA RIVER          ABOVE AVERAGE
  LAKE CREEK                    LOW-MOD     04/30     29  04/27-05/03

SKWENTNA RIVER        ABOVE AVERAGE
  SKWENTNA                      LOW-MOD     04/29     25  04/23-04/29

COPPER RIVER BASIN     AVERAGE
  GAKONA RVR @ HWY                LOW       04/29     32  04/23-04/29
  GULKANA RVR @ HWY               LOW       04/29     30  04/23-04/29

CHENA RIVER           ABOVE AVERAGE
  CHENA LAKES PROJECT             MOD
  FAIRBANKS                       LOW       04/25     27    OPEN

TANANA RIVER          ABOVE AVERAGE
  CHISANA @ NORTHWAY             LOW-MOD    04/26     27  04/17-04/23
  SALCHA                         LOW-MOD
  FAIRBANKS                      LOW-MOD    04/28     19  04/26-04/02
  NENANA                         LOW-MOD    04/29     40  04/24-04/30
  MANLEY                         LOW-MOD    05/02     29  04/26-05/02

KUSKOKWIM RIVER       ABOVE AVERAGE
  NIKOLAI                        LOW-MOD    04/22     34   **04/21
  MCGRATH                          MOD      05/04     40  04/30-05/06
  STONY RIVER                    LOW-MOD    05/01     32  04/27-05/03
  SLEETMUTE                        MOD      05/01     31  04/27-05/03
  RED DEVIL                        MOD      05/03     34  04/28-05/04
  CROOKED CREEK                    MOD      05/03     34  04/29-05/05
  ANIAK                            MOD      05/04     37  04/29-05/05
  KALSKAG                        LOW-MOD    05/04     31  04/30-05/06
  TULUKSAK                       LOW-MOD    05/06     28  05/01-05/07
  AKIAK                          LOW-MOD    05/08     34  05/01-05/07
  KWETHLUK                         MOD      05/03      8  04/30-05/06
  BETHEL                         LOW-MOD    05/09     40  05/01-05/07
  NAPAKIAK                       LOW-MOD    05/10     25  05/03-05/09

YUKON RIVER (UPPER)   ABOVE AVERAGE
  DAWSON, YT                     LOW-MOD    05/03     40  04/29-05/05
  EAGLE                            MOD      05/03     40  04/28-05/04
  CIRCLE                         MOD-HIGH   05/07     36  05/02-05/08
  FORT YUKON                       MOD      05/10     36  05/04-05/10
  BEAVER                         LOW-MOD    05/09     24  05/04-05/10
  STEVENS VILLAGE                LOW-MOD    05/10     23  05/05-05/11
  RAMPART                        LOW-MOD    05/10     25  05/04-05/10

YUKON RIVER (MIDDLE)   ABOVE AVERAGE
  TANANA                         LOW-MOD    05/07     35  05/01-05/07
  RUBY                           LOW-MOD    05/08     34  05/02-05/08
  GALENA                           MOD      05/10     39  05/04-05/10
  KOYUKUK                          MOD      05/08     14  05/04-05/10
  NULATO                           MOD      05/10     23  05/04-05/10
  KALTAG                         LOW-MOD    05/11     34  05/05-05/11
  ANVIK                          LOW-MOD    05/13     32  05/07-05/13

YUKON RIVER (LOWER)    ABOVE AVERAGE
  HOLY CROSS                     LOW-MOD    05/14     33  05/06-05/12
  RUSSIAN MISSION                LOW-MOD    05/14     34  05/06-05/12
  MARSHALL                         MOD      05/14     28  05/06-05/12
  PILOT STATION                  LOW-MOD    05/13     23  05/07-05/13
  MOUNTAIN VILLAGE               LOW-MOD    05/15     33  05/08-05/14
  ALAKANUK/EMMONAK                 MOD      05/20     32  05/12-05-18

KOYUKUK RIVER          ABOVE AVERAGE
  BETTLES                        LOW-MOD    05/09     38  05/01-05/07
  ALLAKAKET                      LOW-MOD    05/09     33  05/03-05/09
  HUGHES                           MOD      05/10     33  05/03-05/09

SEWARD PENINSULA       ABOVE AVERAGE
  BUCKLAND                         MOD      05/15     30  05/09-05/15

KOBUK RIVER            ABOVE AVERAGE
  KOBUK                            MOD      05/13     36  05/07-05/13
  SHUNGNAK                       LOW-MOD    05/16     29  05/10-05/16
  AMBLER                         LOW-MOD    05/16     35  05/10-05/16

NOATAK RIVER           ABOVE AVERAGE
  NOATAK                         LOW-MOD    05/13     23  05/17-05/19

BROOKS RANGE - NORTH     AVERAGE
  COLVILLE @ UMIAT               LOW-MOD    05/24     19  05/16-05/22
  COLVILLE @ COLVILLE            LOW-MOD    06/02     22  06/26-06/01

SAGAVANIRKTOK RIVER      AVERAGE
  DALTON HWY                     LOW-MOD


For more detail and to see a Flood Potential Map, refer to our Website
at https://www.weather.gov/aprfc/FLOODPOTENTIAL

The next Spring Breakup Outlook is scheduled at 2PM AKDT Friday April 24th, 2020

Still No Snow

With rain and very mild temperatures today (up to 48°F so far), Fairbanks is moving further into uncharted territory in terms of the lack of any wintry weather so far this season.  Today the airport has reported 0.05" of rain and no snow, there's zero snow on the ground, and the temperature seems very likely to stay above freezing through midnight.

Putting aside the lack of snow on earlier dates, there are only two other days in Fairbanks history that meet these conditions at this late date in the autumn: October 23, 1981, and October 28, 2013.  In 1981 several inches of snow had fallen earlier in the month and then melted out; the situation in 2013 was more similar to this year, but even then there had been hints of winter's approach with occasional light snow in both September and October.  Here's my post from late October 2013: http://ak-wx.blogspot.com/2013/10/record-warmth-again.html

Here are some non-wintry webcam views from Fairbanks-land this afternoon.

Cleary Summit (2200' elevation) on the Steese Highway:

UAF's webcam on the West Ridge of campus:

Ester Dome:

In view of the bare ground, an interesting question to ask is, "How cold can it get without snow cover?"  The quick answer is, of course, "Pretty cold"; in December 1934, after the great chinook melted Fairbanks' snow cover, the temperature dropped to -29°F on Christmas Eve with only a trace of snow reported on the ground.

A more comprehensive search for cold conditions with no snow cover is complicated by the fact that Alaska's cooperative observers have often reported zero snow depth in error (instead of new snow amount, for example), and missing snow depth is often recorded as zero.  I did find a couple of interesting examples, though.  Just a couple of years ago (Nov 2016) the Fort Yukon SNOTEL site reported -36°F with a zero-inch snow depth, and the Fort Yukon RAWS saw -34°F the same day.  I don't really trust the snow depth number, however; I suspect there could easily have been an inch or two on the ground.

Perhaps a more credible instance is November 11, 1984, at Chandalar Lake in the Brooks Range, when -33°F was reported with only a trace of snow on the ground.  However, in this case a "trace" may just mean "less than an inch", as preceding conditions suggest there might have been a very thin but continuous snow cover.

I haven't investigated to see what Alaska's lowest reported temperature is with zero snow on the ground - if anyone has an idea, please leave a comment!

Snow Piling Up

Fairbanks has seen something of a snow onslaught in the past week, with a remarkable 19" of snow over six days, taking the seasonal snowfall total to 78".  This is the highest in over 20 years.

The entire month of February normally only brings about 6" of snow, as the weather usually becomes increasingly dry in late winter.  On average, the heaviest 1-day snowfall in February is 2.5", but Fairbanks just saw 4 consecutive days with more than 2".  Interestingly this has only happened 8 times before since 1930, and never after mid-January.

Another interesting factoid: the months of December through February brought 15 calendar days with at least 2" of snow in Fairbanks this winter, and that's the highest on record; the previous record was 13 such days in December 1936 through February 1937.

The map below shows reported snow depths today.  A remarkable aspect to me is how high the valley-level snow depths are from the Fairbanks area down to Nenana; the snow depths are no greater at some of the elevated Snotel sites northeast of Fairbanks.  Keystone Ridge is reporting 35" on the ground - barely more than Fairbanks airport (32").

The percent of normal snow water equivalent at the long-term Snotel sites ranges from 112% at Mt Ryan to 198% at Monument Creek.

Here's a chart showing the seasonal snowfall totals and maximum snow depth in Fairbanks for each winter since 1930-31; the long-term median values are indicated with dotted lines.  For as unusual as the snow has seemed this winter, the season as a whole is nowhere near some of the extraordinary winters of the past; but what has been very unusual is the concentration of snowfall in the past three months.

Cold Kusko 300

The Kuskokwim 300 sled dog race occurred over the weekend, with the teams running from Bethel to Aniak and back.  The race is quite notorious for volatile weather conditions, which of course is not surprising as southwestern Alaska is subject to Bering Sea storminess and often experiences highly variable temperatures during winter.

This year the race was a cold one, with temperatures as low as -31°F in Bethel - normally the warmest location on the trail - and as low as -45°F in Aniak.  Looking back at past years, and without accounting for wind chill, this may in fact have been the coldest race in the 38-year history of the Kuskokwim 300.

The chart below shows the average temperature and wind chill in Bethel for each race from 1986-present, based on the 48 hours ending 3pm on the day when the first-place team returned to Bethel.  (I wasn't able to find the dates for the early races from 1980-1985).  Based on conditions in Bethel, this year's race was the coldest, with an average temperature of -25°F.  Mercifully, however, winds were relatively light this year, so the wind chill was not terribly low; the lowest wind chill occurred in 1989, when the race start was postponed 3 days to avoid even worse conditions during the severe cold spell of that January.

Perhaps the most striking aspect of the chart is the change in snow conditions that has occurred over the past few decades; it's been more than 10 years since the race has occurred with more than 10" of snow on the ground in Bethel, but this was common in the 1990s.  However, a quick look at the longer term history suggests that the 1970s and early 1980s also generally saw low snow depths in late January, so the increased snow in the 1990s may have been more of a decadal-scale anomaly than a reflection of a different climate in the past.

Snow Cover - Will It Last

A fair portion of the interior now has at least a little snow on the ground after yesterday's modest snowfall.  Half an inch of accumulation was reported at Fairbanks airport, but the snow depth was rounded up to 1".  It's little more than a dusting of snow, so what are the odds that it will last and prove to be the start of the winter snow pack?

An analysis from a couple of years ago (see here) indicates that we're now late enough in October that there is less than a 20% chance that a one-inch snow cover will melt out to a trace or less.  This suggests that this year is likely to be one of the 10% or so in which the first measurable snowfall doesn't melt out.  On the other hand, the forecast for next week looks warm, with major storminess in the Bering Sea importing warm air over interior Alaska.  About half of all years reach 40°F or warmer after October 25 in Fairbanks, so if it doesn't snow any more - which looks likely in the short-term - then I'd say there's a fair chance of seeing bare ground again.

The chart below shows the number of days with zero or trace snow cover occurring after the first measurable snowfall, versus the date of the first snowfall on the horizontal axis.  Obviously the earlier the first snow occurs, the more subsequent snow-free days there tend to be before winter sets in.  But it's interesting to see that very late first snows do tend to melt out - which makes sense if the weather pattern is unusually warm in those years.

The outlier on the lower left is from the infamous early winter onset of 1992 - the only time the winter snow pack was established in September, and mid-September at that.

Snowpack Meltout

Despite a few hours of accumulating snow yesterday morning in Fairbanks, today's climate report shows only a "trace" of snow on the ground, which means the winter snowpack has officially melted out.  In practice it means that less than half of the ground area was snow-covered at midnight last night in the vicinity of the upper-air observation site at the airport.

The chart below shows the date of meltout for Fairbanks since 1930.  As Rick Thoman noted on this blog at meltout 5 years ago, there is no long-term trend.  There have been decadal-scale variations, such as periods of early meltout in the early decades and late meltout around the 1960s, but recent decades have not been unusually early on the whole.  The only possibly noteworthy aspect of the past 20 years is how few years have been very anomalous: only 2 years have seen meltout before April 16, and only 2013 was later than May 2.

The absence of a long-term trend is surprising in view of satellite indications that Northern Hemisphere spring snow extent has decreased in recent decades.  See, for example, the following articles:

https://nsidc.org/cryosphere/sotc/snow_extent.html

https://www.climate.gov/news-features/understanding-climate/climate-change-spring-snow-cover

It's also surprising that Fairbanks meltout dates have remained steady when we consider that spring temperatures increased substantially in the 20th century (with the main increase occurring at the 1976 PDO phase change).  The chart below illustrates this and also provides at least part of the answer for the meltout mystery: late winter snow depths have also increased over time.  It seems that increasing temperatures have been offset by greater snowpack depth, and so there's been no significant change in the timing of spring snowpack elimination.

Deep Snow Above Fairbanks

I'll have more on the topic of "snowiest place in the interior" soon - and thanks to readers for comments - but today I just wanted to point out the remarkable accumulation of snow that's been reported from Keystone Ridge in recent weeks.

As of Wednesday evening, the cooperative observer on Keystone Ridge reported 32" of snow on the ground, which is greater than a normal winter's peak snow depth of 28".  Only 5 previous winters (in 1996-present) produced a snow depth greater than 32", and the all-time record is 48".

It's worth pointing out that the Keystone Ridge coop station changed hands this summer; the new location is about 3/4 mile west of the old location, but the elevation is nearly identical and both locations are close to the ridgeline, so it seems unlikely that there would be significant systematic differences in snowfall.  The November to-date liquid equivalent precipitation is 2.85", which is the highest on record for the month of November and therefore consistent with the record snow depth.

By way of explanation, I would point to the anomalous west-southwesterly flow that has affected interior Alaska this month.  The normal 850mb flow direction is southeasterly at this time of year (first figure below), but this year there has been a pronounced westerly anomaly bringing moist air inland (second figure below).

Recent Snowfall

Frequent light snowfall over the past 12 days has brought the snow depth up to 6 inches in Fairbanks, which while still modest, is actually above the long-term normal of 5" for this date.  A more substantial snowpack is in place now in the hills; for example, the Keystone Ridge COOP (1600' elevation) is reporting 16" on the ground, which is the most for this date since 2004.  The SNOTEL sites to the northeast of Fairbanks are reporting between 11" and 20", as seen in the map below (click to enlarge and view the small icons).

Farther afield, McGrath also has 6" (normal 4") and Bettles has 14" (normal 9").

The onset of relatively snowy weather in the interior is not too surprising in view of the highly positive phase of the North Pacific Mode.  The NPM index in October was the second highest on record since 1900, and according to station data since 1950, a positive NPM phase tends to bring above-normal precipitation to interior Alaska.  The map below shows the percentage of years with above-normal precipitation in October through December when the October NPM index was strongly positive.  More details on the NPM influence can be found in the slideshow from my UAF talk back in September:

https://accap.uaf.edu/sites/default/files/The_BLOB_AK_Weather.pdf

[Update November 10: another 2.3" of snow yesterday brings the snow depth to 7" in Fairbanks as of midnight.  This is now the snowiest start to November since 1990, and 4th snowiest on record.  The season-to-date snowfall of 33.5" is the 3rd highest on record.]

Disappearing Snow

With last week's snow all but gone in Fairbanks, it's interesting to see where snow is hanging on across the interior and north.  We can get a broad sense of this from the SNPP satellite landcover imagery.  The images below were taken at about the same time mid-afternoon yesterday (top) and today (bottom); blue is indicative of snow and ice cover.  The Brooks Range and North Slope are pretty well snow-covered, except for patches of the western North Slope inland from Wainwright, and south of Point Lay.  In the interior, the Tanana valley, the middle and lower Koyukuk, and the Yukon Flats and upper Yukon valley clearly have little snow; but the high terrain is snowy throughout the interior.  Note also the lack of sea ice so far in the southern Beaufort and Chukchi Seas.

A quick tour of SNOTEL sites and FAA webcams confirms that last week's snow is mostly gone at low levels, but plenty remains at elevation.  Here are a few snow depths as of last report:

Eagle COOP: 0"

Chicken COOP: 1"

Fort Yukon SNOTEL: 1"

Bettles SNOTEL: 3"

Coldfoot SNOTEL: 4"

Fairbanks airport (as of midnight): 1"

Upper Nome Creek SNOTEL (2520' MSL): 10"

Munson Ridge SNOTEL (3100' MSL): 11"

Here are a few webcam shots for good measure.

Snow Remaining at Elevation

Higher elevations in the interior now have a modest but unequivocal snow cover as a result of the chilly, wet conditions of the past week.  I was able to hike most of the way up Wickersham Dome this afternoon, but found myself wishing for snowshoes and eventually gave up on post-holing through a good 12" of snow, and more in places.  There were some patches of snow at 1900' elevation, a more-or-less continuous cover above about 2500', and then the depth increased rapidly above 2700'.  Interestingly very light snow was falling over the hill, although the cloud base was fairly high and visibility was good.

Including today, Fairbanks has remained below 50°F for 7 consecutive days, which is rather unusual for this early in the season; it happened before in 1935, 1987, and of course 1992.  Is it possible that Fairbanks won't reach 50°F again this year?  Yes, it's possible, though unlikely.  It probably won't get there in the next week, and the CPC 8-14 day forecast is decidedly cool.  However, there's still about a 65% chance of reaching 50°F in October or later.

Here is CPC's 6-10 day forecast:

and the 8-14 day forecast is below.  It seems like a long time since decidedly cool weather has persisted over Alaska.

More on Snow Conditions

I've spent a bit of time in the past couple of days putting together a simple website for realtime monitoring of Alaska snow conditions.  It's not quite ready for me to provide a link yet, but a screenshot of a map for south-central Alaska illustrates the dire lack of snowpack this spring - see below (click to enlarge).  The map shows today's percent of normal snow water equivalent (SWE) at SNOTEL sites.

The deficits are very large at most of the sites, for example:

0.3" SWE vs 10.8" normal at the Anchorage Hillside site (elevation 2080')
0.7" vs 12.3" normal at Cooper Lake SNOTEL (1200') in the central Kenai Peninsula
0.1" vs 16.4" normal at Grouse Creek Divide SNOTEL (700') just north of Seward
10.5" vs 39.8" normal at Turnagain Pass SNOTEL (1880')

Looking at the Cooper Lake history, the May 1 SWE has varied from 31.1" in 1988 to 0.4" after the very warm winter of 2002-2003.  Several other sites that I examined also had comparable deficits in 2003, so the current situation is not entirely unprecedented (although Anchorage is on track for their least snowy winter on record).

As we noted the other day, there is still plenty of snow on the ground in the hills of the eastern interior, although the substantial snowpack is now becoming confined to elevations above 2000 feet.  (The Chicken COOP observer reported melt-out yesterday.)  SWE is above normal at the Mt Ryan and Monument Creek SNOTEL sites, see below.

Melt-Out Progress

The valley-level snowpack melted out to a trace 10 days ago in Fairbanks, but higher elevations near Fairbanks still have a significant depth of snow on the ground, as do many other interior locations.  The photos below were taken at about 6pm AKDT yesterday on Keystone Ridge; the snow depth measurement was 13 inches.

It's a little unusual to have this amount of snow left on the hill 10 days after valley-level melt-out, as the normal difference in melt-out dates is 11 days.  In the 18-year history of the station, only 3 years saw more snow surviving 10 days after valley melt-out.  This year's anomaly appears to be related to the warm - but not excessively warm - chinook pattern, which efficiently removed the valley-level snowpack but has not become warm enough to cause rapid melting at elevation.  Through yesterday, April 2015 is the 11th warmest April since 1930 in Fairbanks.

The list below shows the most recent snow depth measurements from various first-order and SNOTEL sites across interior and western Alaska.  If a date is included in parentheses, it indicates the 1981-2010 median melt-out date. 

Fort Yukon SNOTEL  0" as of today
Coldfoot SNOTEL  17" (May 15)
Atigun Pass SNOTEL  41"
Bettles SNOTEL  16" (May 16)
Bettles airport  10" (May 12)
Kotzebue  3"  (May 20)
Nome  4"  (May 12)
McGrath  0" (melt-out April 11, median May 4)
Eagle COOP  10" 0" (observer error reported 10" in recent days) (May 1)
Chicken COOP  4" (1997-2014 median May 1)
Granite Creek SNOTEL near Delta Junction  6" (April 27)

Other SNOTEL sites:
Little Chena Ridge 2000'  8"  (May 7)
Upper Nome Creek 2520'  23"
Upper Chena 2850'  34"
Munson Ridge 3100'  31"  (May 26)
Eagle Summit 3650'  18"

Suddenly Snowless

Chinook winds and warmth in Fairbanks eliminated the remains of the valley-level winter snowpack on Saturday, with the official daily snow depth measurement dropping from 5" to only a trace in a single day.  The last time this much snow was removed in one day was in April 2004, and for context the record 1-day decrease is 8" on several occasions (most recently April 24, 1993).  Snow removal of this efficiency is accomplished by sustained winds that allow for large heat transfer to the snow surface.

The April 18 end of the winter snowpack is 5 days earlier than the long-term median date and just barely falls within the earliest tercile of melt-out dates; so it is earlier than usual but not very much so.  The earliest melt-out in Fairbanks was on April 3, 1970, although in that year snow returned the very next day; there was a more abiding melt-out on April 6, 1965.

Is this the last of any snow cover in Fairbanks until autumn?  Not necessarily.  Almost half of all years see some accumulating snow after the first melt-out date, although only 20% of years see an inch or more of snow depth reported.  More than 1 inch of reported snow depth is rare after melt-out, so any snow that accumulates from here is very likely to be light and/or short-lived.

It's interesting to observe that the chinook warmth has also done a number on river ice in the area, and the tripod at Nenana is on its last legs (see below).  If the clock is tripped today, it will tie the all-time record for earliest breakup date (1940, 1998).  It's a remarkable turn-around from the cold spring and record late breakup of 2013.

Low Snow in the Northwest

One of the many notable climate anomalies in Alaska this winter is a lack of snowfall in many locations, and even Kotzebue in the northwest is suffering in this regard.  So far this winter, only 8.1 inches has fallen in Kotzebue, and the snow depth has been stuck at a meager 2 inches since November 27, after peaking earlier at 4 inches.

The only other winter with such a low snow depth in January was 2012-2013; that winter saw an even more extreme snow drought in the early going, but the snow depth then reached 5" on January 12 and 9" on January 15.  So this winter now has the distinction of the lowest peak snow depth through this date.  In a couple of days we'll also break the record for latest date to first reach 6" snow depth (January 14, 2013); the median date is November 17.

Here's a chart of the season-to-date snowfall and peak snow depth since 1949.  (I'm not sure how the snow depth exceeded the snow total in 1994-95 and 1999-2000, but that's what the data say.)  It's interesting to note the high volatility in snow totals in recent decades and especially in the last 5 years or so.

Why the lack of snow?  The answer is that a blocking ridge over the Arctic Ocean north of Alaska has prevented cyclonic storm systems from reaching Kotzebue.  The six maps below show the sea-level pressure anomaly (left column) and 500 mb height anomaly (right column) in October, November, and December of 2014; notice the general lack of low pressure in the north.

The recent flow pattern can be contrasted with the situation in a very snowy month: below are the maps for the snowiest early winter month in Kotzebue's history, November 2003 (46 inches):
It's interesting to note that Nome is not doing too badly for snow this winter, with 27.1" season-to-date and a current snow depth of 11".  Seasonal snowfall totals are correlated at only +0.42 between Kotzebue and Nome, so this isn't too surprising; but it does appear that Nome has done fairly well out of an unfavorable upper-air pattern.