Sea Ice Forecast

It's interesting to note that NOAA's CFSv2 long-range forecast model is again predicting a very substantial increase in sea ice this summer in parts of the Arctic Ocean.  The map below shows a large positive anomaly in sea ice concentration in August stretching from the eastern Kara Sea all the way east to the Beaufort Sea.  If this was the first time we'd seen this, it would be worth paying attention, but the model produced a similar forecast in 2014, and it proved to be completely wrong (see here and here).

The CFSv2 "nowcast" for May shows a large ice deficit in the Bering Sea (see below), which is correct, so it seems the model is not developing the summer ice excess from erroneous initial conditions; the anomaly is being generated from the internal physics of the sea ice component of the CFSv2 system.  Assuming the forecast proves incorrect again, I'd say this aspect of the model needs some attention.

According to the forecast, the sea ice anomaly persists into the autumn and helps generate a really remarkable cold anomaly on this side of the Arctic - see the temperature forecast map for October, below.  It seems very unlikely indeed that anything remotely like this will happen; simply put, I think the model is "out to lunch".  But time will tell.  (As an aside, note the La Niña cold anomaly in the equatorial Pacific; this is reasonably likely to be correct.)

Here are the latest charts of observed Arctic sea ice from NSIDC; total ice extent is running close to record low levels for the time of year, and there seems to be a fair chance of a new record melt-out later this year.  Unless of course the CFSv2 is onto something.

Unending Warmth

The persistence of abnormal warmth in Alaska in the past few months has been nothing short of amazing.  A strongly positive PDO phase and strong (though now decaying) El Niño conditions have maintained a remarkably steady circulation pattern over the northeastern Pacific sector, leading to a seemingly never-ending flow of warm air into Alaska.  The maps below show the remarkable month-to-month similarity of the 500mb height anomalies so far this year:

In Fairbanks the daily mean temperature has been above normal every day since March 20, which makes 47 days in a row including today; this is the most on record for the time of year. (There have been a couple of times when above-normal conditions persisted longer in early winter.)  For the year to date, the temperature has been above normal 115 out of 126 days, which is also the most on record for this period of the year, by some margin (see chart below).  However, the year is not yet running as the warmest on record; 1981 was warmer through this date, owing to some incredible warmth in mid-winter.

Incidentally, notice in the chart above that most years within the 1981-2010 "normal" period had more than half of days above normal; the average is actually 54%.  This is because the distribution of daily temperatures is negatively skewed at this time of year; large cold anomalies are more common than warm anomalies of the same magnitude, and more than half of all days are warmer than the mean temperature.

The chart below tells the tale for Fairbanks temperatures since November and needs no comment.  I was beginning to think Fairbanks might not even see a freeze in May this year, which would have been unprecedented; but this morning's low temperature was 31°F at the airport.

Breakup Progress

Now that I'm back from my lengthy trip, the first order of business seems to be to look at how breakup is playing out.  Today's NWS breakup map (below) shows that breakup is mostly complete in the southern and eastern interior, and the Yukon River is currently in the process of breakup, with the ice having gone out at Tanana on Friday and at Fort Yukon on Saturday.  This is all considerably earlier than normal, of course.

As many readers know, the Nenana tripod moved out on April 23, which is only 1 day earlier than last year and does not match the April 20 record.  However, breakup was the earliest on record by a significant margin on the Kuskokwim River at Bethel and on the Yukon River at Dawson in Yukon, Canada.  The charts below show the annual breakup dates for the common period of record at these locations.  It's interesting to see that the variance is a lot larger at Bethel than at Dawson, and the long-term trend towards earlier breakup is somewhat less at Bethel.  Of the 3 locations, the trend is strongest at Nenana.

A scatterplot comparison of the breakup dates reveals that Bethel's breakup is rarely earlier than Nenana's (as occurred this year), although it has been as much as 11 days earlier (in 1927).

Breakup timing at Nenana is more highly correlated with Dawson than with Bethel, as might be expected based on closer proximity and a more similar (interior) environment.

Lastly, here's the final result for the chart of thawing degree days that I showed before.  Breakup at Nenana didn't occur until TDDs reached 216, which is twice as high as last year.  It's tempting to speculate that the resilience of the ice this year may have been related to the amazing lack of snow during most of the winter: a lack of insulation may have allowed the ice to become stronger than would be expected based on the mild temperatures.  However, the peak ice thickness of 40 inches at Nenana was only slightly greater than last year, so I'm not sure if this idea holds water...

Seasonal Forecast

Here's a quick update to show the latest CFSv2 model forecast for next month.  The model ensemble is calibrated with the historical re-forecasts and converted into the probabilities that the climate anomalies will be significantly below-normal, near-normal, or significantly above-normal.  The temperature forecast for May shows continued high probabilities of unusual warmth for most of Alaska, exceeding 90% over the warm water in the Gulf of Alaska and Bristol Bay, and 60-70% in most of the interior except the east.

The forecast for the May through July average is similar, although the probability of warmth is not quite as high in the interior.  There is a surprising area of expected cooler than normal conditions in the Chukchi Sea; this is probably related to the CFSv2 sea ice forecast, which is not known to be particularly reliable.

Interestingly the 3-month forecast for sea-level pressure shows a low pressure anomaly across interior Alaska, and the precipitation forecast hints at above-normal rainfall in the southeastern interior.

The probability forecast for Fairbanks shows a modestly enhanced probability of a wet May-July period, and it seems the model expects this anomaly to show up in July; the probability of significantly above-normal rainfall in July is 48%, compared to 36% for the near-normal category and only 16% for below-normal.

The official CPC forecast will come out tomorrow:

http://www.cpc.ncep.noaa.gov/products/predictions/long_range/

Also, I added the March verification at the end of my post from 2 months ago:

http://ak-wx.blogspot.com.es/2016/02/seasonal-forecast.html

Update: here's the CPC forecast; the most interesting aspect may be the expectation for above-normal precipitation across northern Alaska in May-July.  It's also interesting that the CPC doesn't buy the CFSv2 forecast for an increased chance of wet conditions in southeast Alaska.

Breakup Update

This is just a quick update to note that Fairbanks thawing degree days exceeded 100 yesterday, which is not far off the record pace of 1940; but a cooler air mass has moved in and the next week appears likely to be cooler; so a record early breakup at Nenana (before April 20) no longer appears quite as likely.  The chart below shows the updated 2016 TDD trajectory (solid line) along with the latest GFS MOS forecast through the 20th (dotted line).

In Fairbanks it appears that the Chena River has gone out or is about to:

Regular readers should note that I'll be traveling in Europe for the rest of this month, so posting will probably be sporadic and brief.

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.

Nenana Ice Classic

The 100th Nenana Ice Classic closes to entries today, and I'm guessing those entries are heavily front-loaded towards an early breakup, given the warm weather of recent weeks and months in interior Alaska.  The ice is slightly thicker than it was last year at this time, but the visual appearance has been quite poor, judging from the webcam view in recent weeks.  It's actually looking a bit better today thanks to a little fresh snow on Saturday night.

I've mentioned before that April mean temperatures in Fairbanks are highly correlated with the breakup date at Nenana - see the chart below.  The warmest April in Fairbanks history was in 1940, and that year also produced the earliest breakup on record - narrowly ahead of 1998.  However, the early breakup of 1940 was quite an outlier for those early decades; 6 of the earliest 7 breakups have occurred since 1990.  In the past few decades, it's been more common to see breakup in April than in May, in contrast to earlier years.

Another way of looking at the relationship between breakup and temperature is to calculate the thawing degree days up until the date of breakup.  Thawing degree days (TDDs) are the accumulation of temperature excess above freezing; for example, a daily mean temperature of 42°F equates to 10 TDDs.  If we add up the daily TDD values for each year between March 1 and the date of breakup, we get the following chart:

The first thing to note is that there is quite wide variation in the amount of thermal energy needed to produce breakup, as measured by TDDs; since 1930, the Fairbanks TDDs have varied from 75 (in 2002) to 265 (in 1975).  It's slightly counter-intuitive to see that the latest breakups occur after a relatively small accumulation of TDDs; the reason for this (I believe) is that late breakups allow more time for the increasingly intense solar radiation of May to work on the ice, even though air temperatures are low.

In contrast, if breakup is to occur early, then melting has to be accomplished more by the warmth of the air than by direct solar heating, and so warmer temperatures are required.

We can see that recent decades have been characterized more by early breakups in association with large TDDs, in contrast to earlier years that tended to have smaller TDDs and later breakup.  The last two years, 2014 and 2015, were actually a little unusual in having early breakup AND relatively low TDDs - perhaps a consequence of the warm winters and poor ice conditions.

So far this spring Fairbanks is accumulating TDDs more rapidly than in the past 3 years, although it's not a record; in 1965, 45 TDDs were observed already by April 4 (but breakup didn't occur until May 7).  According to today's 7-day NWS forecast, Fairbanks will accumulate another 29 TDDs through April 11, putting the total at 59.  There doesn't seem to be any sign that the warm weather will abate in subsequent weeks, so the melting rate will probably accelerate in the middle of April, especially as snow cover will be gone by then.

Subjectively, then, it seems we are on pace for something pretty close to a record early breakup, but much will depend on just how warm it is after April 15.  I'd say the most likely window for breakup at Nenana is April 21-24; and that's probably close to what everyone else is thinking without any of the temperature analysis.  In other words: your guess is as good as mine.

Statewide Extremes

Extreme weather contrasts are continuing across Alaska today, as some places experience high summer conditions while others are locked in winter.  The warmth in the south and east is the really big story, as a new all-time state record high temperature for the month of March has been observed at Klawock in the far southeast: 71°F.  Never before has 70°F or higher been recorded in March in Alaska.  Several other locations have set all-time March high temperature records by large margins, including (data through 00 UTC):

Homer: at least 59°F (previous record 54°F set last year)
Cordova: at least 68°F (previous record 62°F in 1913; 59°F in 1965 was the record in the NWS/Weather Bureau era)
Eagle airport: at least 59°F (previous record 53°F in 2010)  [UPDATE: Rick Thoman sends word that Eagle's COOP site reports in the morning, so technically this will go down as the high temperature for April 1st]

Each of these stations has long periods of record.  In Cordova and Klawock these temperatures would be unusual for the height of summer.  Here's this morning's 500mb analysis, showing the intense ridge over the southeast.

Here's a webcam image from Klawock at the time of a 70°F reading from the airport ASOS:

Meanwhile a bona fide winter storm is affecting parts of the west coast; Shaktoolik has seen increasingly heavy snowfall today with sustained winds over 40mph and temperatures in the single digits.  Here's a simple animation of the deteriorating conditions during the middle part of the day.

Record Rainfall

In what could hardly be more unusual weather for the time of year, valley-level Fairbanks residents have endured rainy conditions in the past couple of days.  The 2-day total of 0.35" is the most rain ever observed in the month of March without a measurable accumulation of snow; the previous record was 0.34" on March 7, 1921 (but that event occurred at the end of a major storm with 16" of snow in previous days).

Remarkably, prior to this week there were only 9 calendar days in March since 1930 with 0.05" or more of rain and a trace or less of snowfall in Fairbanks; 6 of these days were in the 1930's.  We added two more such days on Monday and yesterday.  In and of itself some light rain or rain/snow mix is not too uncommon in Fairbanks in March, but to have significant rainfall with no snow is rare.

The 500mb charts below show the mid-tropospheric conditions at 4am AKDT on Tuesday (top) and 4am today (bottom).  The pattern looks just about perfect for bringing very unusual warmth along with precipitation to central interior Alaska: the air mass source is far to the south, but there is west-southwesterly flow across the interior in association with a strong frontal zone.

Reflecting the strength of the frontal zone, the temperature gradient across northern Alaska has been nothing short of amazing in the past few days.  While Fairbanks has experienced near-record warmth, the North Slope has been colder than would be normal for the dead of winter; Deadhorse airport dropped to -38°F this morning, and the temperature has struggled to get above -20°F in brilliant sunshine this afternoon.

Here are some splendid images from the Chandalar Shelf FAA webcam yesterday afternoon.  This is what March is supposed to look like in interior Alaska.

Thawing Commences

Continued unusual warmth is bringing an early start to the spring thaw in Fairbanks.  Today is the 4th day in a row with a daily mean temperature above freezing, and the airport snow depth reading has already dropped from 14" on Thursday to 11" yesterday.  Other than the great February 1943 chinook event, 4 such consecutive days have only occurred earlier in March 1965 and March 1998.  The 1997-98 winter was of course the last very strong El Niño winter; it was also the year of the second earliest breakup on record in Nenana.  The Tanana River ice isn't looking too healthy today, as a matter of fact:

Looking at snow conditions in the hills east and northeast of Fairbanks, the snowpack water content is not far from normal at mid-elevations and is slightly above normal at higher elevations.  Here are the latest snow water equivalent measurements from the SNOTEL sites, compared to the 1981-2010 median:

Teuchet Creek (1640'): 3.7" vs 3.8"
Monument Creek (1850'): 4.7" vs 4.6"
Little Chena Ridge (2000'): 3.9" vs 4.7"
Mt Ryan (2800'): 5.6" vs 5.0"
Munson Ridge (3100'): 7.4" vs 6.7"

The relatively healthy state of the snowpack is a reflection of the snowy start to the season in September (the early snow never melted in the hills) and November.  Nevertheless, the snowpack is actually the lowest for the date since 2010; this is also true of the in-town Fairbanks SNOTEL site.

Looking farther afield, here's the March 1 snow analysis (presumably snow water equivalent) from NRCS, for this year and last year.  The south-central part of the state is not as badly off as last year (except at very low elevation), but snowpack deficits are pretty pervasive in the southeastern interior this year.

More on Howard Pass

In last week's discussion of Brooks Range wind chill, I mentioned the fact that temperature tends to decrease as wind speed increases at Howard Pass.  An inverse relationship between wind speed and temperature is very different from what most Alaska residents experience - in most locations it's coldest when the wind is calm - so I thought it would be worth taking a closer look at the Howard Pass data.  I obtained the hourly observations (2012-present) and looked at the data from several angles.

First, the distribution of wind speed in December through February (see below) does not show anything too unusual, although it's obviously a windy place; the wind speed exceeds 40 mph about 15% of the time in winter.  And as we know, very high wind speeds sometimes occur.  Last Saturday's sustained wind speed of 98 mph (during the 7-8 pm hour) was the highest on record for the station; this measurement probably wouldn't have been possible without the new robust anemometer that was installed last summer.

The distribution of hourly temperature measurements is more unusual, showing a double peak, with the temperature most often falling between -10 and -20°F.

If we look at the joint distribution of temperature and wind speed, we see very clearly that the highest wind speeds are invariably associated with below-normal temperatures, and in fact significantly below-normal temperatures hardly ever occur without strong winds.  For temperatures of -30°F or below, the wind speed is typically above 40 mph.  We also see that calm winds are uncommon when temperatures are well above normal, so there is a minimum in median wind speed for temperatures near the climatological normal.

Looking at hourly wind chill values, the distribution shows a pronounced double peak, and the most common wind chill is between -40 and -50°F.  This is quite remarkable for a location at only 2062' elevation (although it is above the Arctic Circle).  Bear in mind that wind chill is undefined for wind speeds less than 3mph, so quite a number of calm-wind observations are excluded from the distribution.

Another way to look at the joint distribution of temperature and wind is to plot a kind of wind rose diagram - see below.  The red line shows the median wind speed for each point on the compass, and the blue line shows the median temperature.  Interestingly there are two peaks in wind speed; the primary one occurs when the winds are from the north-northeast, through the pass, and these winds import cold air from the North Slope, leading to extreme wind chill - the median temperature for this wind direction is -16°F.  The secondary peak in wind speed occurs for east-northeasterly winds, and in this scenario warm air reaches Howard Pass; the median temperature is about +20°F.

Here are two images showing the location of the Howard Pass RAWS relative to the surrounding topography (click to enlarge); in the first image, the Howard Pass site is the one with the red "20" next to it, at the northeast edge of the Noatak River basin.

It would be very interesting to look at the other RAWS sites scattered around the western Brooks Range, to see if any others show the same kind of behavior.  I plan on doing this when I have time to obtain and parse all the hourly data.  For now, I just looked at the data from Anaktuvuk Pass - see below.  Surprisingly, Anaktuvuk Pass appears to be remarkably non-windy in winter; the absence of strong winds in this data almost looks unrealistic, although a topographic map reveals that the site is actually very sheltered from most directions.  There is a slight increase of wind speed with warmer temperatures and there's no evidence of the cold northerly gales that are observed at Howard Pass.

For comparison, the Umiat RAWS on the North Slope shows behavior that is more typical of low-elevation Alaska in winter; wind speeds are typically light, and higher wind speeds are associated with relatively warm temperatures.