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November-December 2016

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Hot Alaska: As the Climate Warms, Alaska Experiences Record High Temperatures

Starting in late May 2013, Alaska has experienced a long run of headline-grabbing warm weather. Most months, and even more seasons, have been well above normal, with multiple “warmest of record” months. In parts of southern and coastal Alaska, mild winters tend to push more of the cold season precipitation into the rain category, resulting in “snow droughts.” At shorter timescales, many daily record high temperatures have been set, while very few new low records have been established at long-established climate sites. The frequent drone of records and outstanding mild-weather related events can numb us into forgetting just how extreme weather and climate conditions have been across the Last Frontier over the past three years. So in this article, we present a recap.

2013

Following a very cold spring over mainland Alaska, much of Alaska was excessively warm during the summer. The third week of June brought one of the greatest heat waves of record to southcentral Alaska. Temperatures hit 90°F at usually maritime Cordova and Valdez, and Amber Lake, west of Talkeetna, recorded 97°F—one of the highest reliable temperatures ever recorded in Alaska. This heatwave was widespread, with all-time record high temperatures set or tied at the western Alaska communities of McGrath (94°F), Nome (86°F), and Kotzebue (85°F).

During late June, Fairbanks had the warmest week in more than a century of climate observations, with an average temperature of 75.2°F. Temperatures were not so extreme in July, but Anchorage still managed to tally 17 days in a row with high temperatures of 70°F or higher—the longest such streak of record.

The hot weather in June set the stage for a serious wildfire season. The Stuart Creek Fire threatened the community of Two Rivers early in July, forcing the evacuation of hundreds of people and even more sled dogs. The remainder of the summer and early autumn were generally not extreme, though in early August, Eagle, on the Yukon River, set a new record for the latest date in the summer for a temperature in excess of 90°F (92°F on August 12), and Petersburg, in southeast Alaska, set a new record high for the month of August (83°F on August 1).

The warmth returned with a vengeance in October. Many locations in mainland Alaska south of the Brooks Range had the warmest October of record, and freeze-up was greatly delayed. For the month as a whole, October 2013 was nearly 1°F warmer than any other October since 1925. The delay in freezing weather directly contributed to damage wrought by a series of severe coastal storms in early November, with minimal sea ice present south of the Bering Strait and little ice on the Yukon River. The same series of storms brought unusual warmth north into the Bering Sea, where Dutch Harbor recorded a high temperature of 66°F on November 14, just one degree shy of the state record for the month.

2014

The year started off with a return of unusually mild weather. The warmth was especially pronounced across southcentral and southwest Alaska, where many places, including Talkeetna, Bethel, Homer, and King Salmon, were at or close to the warmest January of record. The apex of the warmth occurred late in the month. NOAA's Climate Reference Network station near Port Alsworth recorded a high temperature of 62°F on January 27. This tied the all-time record high for Alaska for the month of January. Other communities also set January record highs, including Seward (61°F), Iliamna (57°F), and Nome (51°F).

The mild weather melted away much of low elevation snowpack that was in place over the Kenai Peninsula and the Anchorage area, which was only partially replenished later in the winter. February, while not as extreme, was mild enough to allow a few communities, including Barrow and Cold Bay, to have the mildest mid-winters (December through February) of record. March and April were mostly mild, but May brought both additional extreme warmth and the impacts of the mild winter.

The Funny River Fire, south of Soldotna, started on May 19. Very low snow pack, early snow melt, and persistently dry conditions after snow melt allowed the fire to spread until cooler and wetter weather returned the last days of May. The fire grew to more than 193,000 acres, making this the largest wildfire on the Kenai Peninsula since 1947. For May as whole, it was the warmest of record at several sites around the southern mainland, including Anchorage, Homer, and Kodiak. Summer was exceptionally warm around the Bering Sea and the western Gulf of Alaska. At Cold Bay, July, August, and September were each the warmest of record, while at both Saint Paul and Homer, the warmest August was promptly followed by the warmest September. The next widespread round of extreme warmth was in November. Cordova and McGrath both set all-time record high temperatures for November, while Homer and King Salmon reported the highest average temperatures for any November.

The warmth continued in December, with Kodiak, Homer, and Talkeetna all posting the warmest Decembers of record. 2014 finished up as the warmest calendar year of record at a number of coastal locations from the western Gulf of Alaska westward, including Anchorage, Kodiak, Saint Paul, Nome, and Kotzebue. The statewide annual temperature of 30.3°F set the record for the warmest year in the National Centers for Environmental Information (NCEI) database (1925–present).

2015

The slow, warm grind continued during the first two months of the year. Some daily temperature records were broken, and Homer chalked up a new February record high temperature with 53°F on the 21st. The snow drought intensified in the Anchorage area, with little precipitation early in the winter, resulting in a late establishment of the winter snow pack that was not able to build up.

Anchorage saw a return to normal precipitation in February, but nearly all of that fell as rain, with the snow pack diminished to just patches by the end of the month. Kodiak recorded the warmest mid-winter (December through February) of record, with an average temperature of 36.7°F. As March began, the lack of snowpack south of the Alaska Range, and especially in the difficult Dalzell Gorge on the north side of Rainy Pass, forced Iditarod Sled Dog Race officials to move the race start from Willow to Fairbanks and reroute the race. This was only the second time the start of the iconic race has been moved to Fairbanks; the other time was in the warm winter of 2002–2003.

March brought a spell of cold weather, but that quickly turned around, with several daily record high temperatures set late in the month. Annette Island, in southern southeast Alaska, had its second warmest March of record. Late March and April brought a very early snowpack melt-out to much of southcentral Alaska. Both Anchorage Airport and Homer came in with the warmest Aprils of record. During May, the warmth spread north and eastward. Delta Junction, Northway, and Gulkana all reported the warmest Mays of record, as did Juneau in southeast Alaska. The warmth was punctuated by a heat wave during the fourth week of the month, when Eagle reported a high temperature of 91°F on May 23. This is the earliest date in the year the temperature has reached 90°F or higher in Alaska. During the lead-up to this warmth, Northway set or tied daily record highs on seven consecutive days. The North Slope also experienced record heat. Just after mid-May, temperatures soared into the 50s and 60s over inland areas (temperatures more typical in June), spreading to the coast a few days later. This produced very rapid snowmelt and resulted in road-closing flooding on the Dalton Highway south of Prudhoe Bay.

Early snowmelt and the unusual warmth primed the boreal environment for wildfires. Human-started wildfires during mid-June in the Susitna valley and on the Kenai Peninsula resulted in the loss of nearly five dozen homes. Even as firefighters were working to control these blazes, a week of widespread and frequent lightning ignited hundreds of wildfires in the Interior. An amazing 4.79 million acres burned between June 15 and July 15. The fires coincided with extreme warmth across much of the state. Anchorage experienced its warmest day of record on June 16, with a high of 83°F and low of 61°F. The same day, the temperature topped out at 80°F at the Kodiak Airport station—the earliest in the summer the temperature has been that warm at Kodiak. June as a whole was the warmest of record at Barrow and Anchorage.

The heat continued right into July. Most notable was the heat in southern southeast Alaska between July 5 and 7, when temperatures rose into the upper 80s at many locations. Hyder, northeast of Ketchikan, topped out at 94°F—one of the highest reliable temperatures of record in southeast Alaska. During August, there were a few days with record heat early in the month, including three days setting new records at Anchorage. Kodiak set no daily records, but the month finished up as the warmest of record. September was a cool month, but the warmth returned in October. Daily record high temperatures were set on several days around mid-month in southeast Alaska, while more records were set or tied over the western Gulf of Alaska coast and at King Salmon. Yet another record warm month was set, this time at Annette in southern southeast Alaska.

November brought some chilly weather, but a dramatic warm-up in Anchorage the week of Thanksgiving melted away a foot of snow, leaving only patches. It was the first time that much snow has melted out in Anchorage at that time of year. December also finished up with daily record warmth at a number of locations, including Anchorage and Fairbanks. Alaska ended 2015 in a tie for the second warmest year on record, falling short of the 2014 temperature by just 0.2°F.

2016

The first two months of the year were mild over the entire state. At Barrow, January was the second warmest of record. Juneau had the second warmest February of record. For the December through February mid-winter season, this was the warmest of record of at Barrow and at Sitka. Anchorage had the second warmest mid-winter of record. Another outstanding feature of the 2015–2016 winter was the nearly complete absence of deep cold. The lowest temperature reported from any community in Alaska during the winter was –47°F at Arctic Village on December 24 and 25. The previous “warmest” lowest temperature in the state was –53°F at Umiat during the winter of 1987–1988.

The outstanding feature of March was the unprecedented warmth during the last days of the month over much of the southeastern and the southern mainland. The temperature rose to 71°F at Klawock, on Prince of Wales Island, on March 31—the highest reliable temperature of record in the month of March. The previous record of 69°F at Ketchikan had stood since 1915. Possibly even more amazing was the high of 68°F at Cordova Airport; this exceeded the previous March record by 10 degrees and is the warmest temperature so early in the season by four weeks. Anchorage, Homer, and Tok also set all-time record highs for March. This set the stage for a remarkably warm April. Anchorage, Bethel, Juneau Airport, Kotzebue, and Nome all recorded the warmest Aprils of record.

Spring river ice break-up was at or near the earliest of record over much of the length of the Yukon and Kuskokwim Rivers. The Kuskokwim River at Bethel broke up four days earlier than any previous year, and the Yukon River in Dawson City, Canada, eclipsed its earliest break-up on record by five days. During May, the warmth continued across Alaska. Barrow had the warmest May of record, breaking the record set in 2015. Bethel also set a new monthly average temperature record for May. Many locations finished up with their warmest springs (March through May) of record, including Anchorage, Fairbanks, Juneau, and Ketchikan. In June, there was little in the way of record heat, though that in part was due to the warmth of the previous three years. At Anchorage, the average temperature of 59.0°F was high enough to rank as the third warmest June, with the only warmer June months occurring in 2013 and 2015. The warmth continued through July across the state, when Anchorage and Kenai both recorded their warmest months on record, and Homer and Sitka each saw the warmest July.

This litany of notable warmth, while important as a record of what has happened, is difficult to digest due in part to the long duration. One way to characterize the past three years at the scale of individual locations is to compare counts of new daily record temperatures. Figure 1 shows the counts of new daily records at 15 long-term climate observation locations around Alaska. The records are based on the periods of observation typically used by the NWS for determining records (all of these locations have at least 64 years of observations).

Even accounting for differences in the period of record, several features stand out. First, while at most locations there have been a very small number of record low temperatures set in the past three years, these counts are dwarfed by the number of record high temperatures. Second, even accounting for differences in the lengths of the period of record, the focus of the warmth, by this measure, has been in coastal areas of southwest Alaska and the western Gulf of Alaska. Third, at many sites, the number of daily “high minimum” records (roughly, record mild nights) exceeds the daily maximum temperatures.

While the individual location viewpoint is in some ways the most natural, since people generally experience day-to-day weather where they live and work, there is much to be gained by stepping back and taking a look at larger areas and larger chunks of time. The NWS Alaska Region maintains a daily temperature index using temperature observations from 25 statewide locations. Using this index, Figure 2 shows the counts of three categories (below, near, and significantly above normal) of the index value over the past five and one-half years. The lack of significantly below normal days is remarkable, and illustrates the long persistence of the warmth.

Figure 1.  Daily temperature records since June 2013 (maximum, minimum, low maximum, high minimum) for selected long term climate sites around Alaska. Records based on individual station period of record, and ties are proportionally prorated based on number of occurrences.

Figure 1. Daily temperature records since June 2013 (maximum, minimum, low maximum, high minimum) for selected long term climate sites around Alaska. Records based on individual station period of record, and ties are proportionally prorated based on number of occurrences.

Figure 2.  Three-category distribution of the Alaska Statewide Temperature Index since 2011. The index, maintained by NWS Alaska Region Climate Services, tracks the mean standardized anomaly from 25 geographically representative locations around the state.

Figure 2. Three-category distribution of the Alaska Statewide Temperature Index since 2011. The index, maintained by NWS Alaska Region Climate Services, tracks the mean standardized anomaly from 25 geographically representative locations around the state.

Figure 3.  Three-category Alaska climate division mean monthly temperature anomalies since June 2013. Divisional mean temperature downloaded from National Centers for Environmental Information.

 

Figure 3. Three-category Alaska climate division mean monthly temperature anomalies since June 2013. Divisional mean temperature downloaded from National Centers for Environmental Information.

Recent advances in climate science made at the University of Alaska Fairbanks and the NCEI have facilitated the construction of monthly temperatures since 1925 at the regional and Alaska-wide scale that systematically account for changes in station data availability. Figure 3 shows the percentage of months that the monthly average temperatures have been significantly above normal, near normal, or significantly below normal (1981–2010 reference period) for each of the 13 climate divisions. Over the course of several decades, each category occurs about one-third of the time. While all parts of the state have been significantly warmer than normal much of the time, this clearly shows differences across the regions, with coastal divisions showing fewer months with well below normal monthly average temperatures; in fact, the Aleutians Island division has not observed a single month in the past three years in the below normal category, and the Northwest Gulf Coast division has had only two.

Taking a look at Alaska as a whole, we can use the well-known NCEI ranking system to characterize the past three years of Alaska temperatures. Here, each month is ranked against all the previous months (since 1925) and put into one of five categories. Remarkably, temperatures for the state as a whole have been in the much above normal category (technically, in the warmest 10% of all years) more than 45% of time (by construction, we expect this occur 10% of the time over courses of decades), and not a single month has been in the much below category.

Another question we can ask is: how does the current prolonged warm spell compare to the past? Figures 4 and 5 show the 36-month average temperature for each month from December 1928 through June 2016. Because this is composed of three complete years, the annual temperature cycle is removed, and individual months or even a couple of seasons account for only a small fraction of any given three years. Several features stand out, most obviously that the most recent three years are unprecedented in the past 89 years, and the current jump in temperatures is similar in magnitude to the spike that occurred in the late-1970s. The cool mid-twentieth century, from the late-1940s through the mid-1970s, is also evident. Last, the recent cool period, from 2007 through 2012, which was significantly cooler than the first years of the 21st century, was nonetheless warmer than most of the mid-20th century.

Figure 4.  Five-category Alaska statewide mean monthly temperature anomalies since June 2013. Statewide mean temperature downloaded from National Centers for Environmental Information.

Figure 4. Five-category Alaska statewide mean monthly temperature anomalies since June 2013. Statewide mean temperature downloaded from National Centers for Environmental Information.

Figure 5.  Alaska-wide 36-month running mean temperature 1925–July 2016. Statewide mean temperature downloaded from National Centers for Environmental Information.

Figure 5. Alaska-wide 36-month running mean temperature 1925–July 2016. Statewide mean temperature downloaded from National Centers for Environmental Information.

Figure 6.  Ordinal rank of 925mb temperatures for three consecutive 12-month periods. The maps show the ordinal ranking, from warmest to coolest, of 925 mb temperatures compared to all other years in the Reanalysis database. Red colors represent the warmest (Rank No. 1) of all years. Data downloaded from NOAA/ESRL Reanalysis. Analysis by Brian Brettschneider, Kalnay, E. and Coauthors, 1996: The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, 437–471.

Figure 6. Ordinal rank of 925mb temperatures for three consecutive 12-month periods. The maps show the ordinal ranking, from warmest to coolest, of 925 mb temperatures compared to all other years in the Reanalysis database. Red colors represent the warmest (Rank No. 1) of all years. Data downloaded from NOAA/ESRL Reanalysis. Analysis by Brian Brettschneider, Kalnay, E. and Coauthors, 1996: The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, 437–471.

Finally, we can take the really large-scale view and put the Alaska warmth in a hemispheric content. Using a technique developed by one of the authors (Brian Brettschneider), is the ranking (since 1949) of low-level temperatures based on the NCEP/NCAR reanalysis. This is a weather model, updated daily, that is run on past data back to 1948. This has the advantage of providing a coarse but reasonably consistent snapshot of global surface and atmospheric conditions every day (in fact every six hours). Figure 6 shows the rank from 1949 through 2016 at each grid point for the three years (July through June) 2013 through 2016 of 925 millibar temperatures. This illustrates that the persistent warmth over Alaska is not just a regional feature, but is part of the general northern hemisphere, and especially high latitude warmth over the past three years.

Why Has It Been So Warm?

Unsurprising, for a three-year period there is no single cause. This is particularly the case seasonally. During the winter, southerly flow in the mid-levels of the atmosphere that transports warmer air from lower latitudes is a primary producer of mild weather over Alaska. The strong El Niño of 2015–2016 certainly was a contributor to the Alaska cold season warmth, while in 2013–2014 and 2014–2015, most of Alaska was on the warm side of the same upper level high pressure that resulted in widespread drought along the United States West Coast. In contrast, during the summer, warm weather is frequently “homegrown,” and is more dependent on sunshine and dry conditions. For those parts of Alaska close to the coast, variations in sea surface temperatures contribute significantly to temperature anomalies. Starting in late 2013 (remember “the Blob”?), sea surface temperatures near Alaska have been persistently above normal, with both the eastern Bering Sea and the Gulf of Alaska recording among their warmest surface temperatures of record. The influence of the sea surface temperature anomalies is seen in the daily record counts of coastal stations and in the lack of cold months in the coastal climate divisions of western Alaska. Farther north, the long-term decline in late summer and autumn sea ice coverage near Alaska has a dramatic impact on temperatures during the times of year when ice used to be present (most of the time) but is no longer the case. On shorter time scales, early loss of the winter snowpack (and to a lesser extent the late establishment of the seasonal snow cover) can dramatically increase temperatures relative to the long-term normal (which have snow cover “built in”). And of course, on top of all this is the very long term environmental warming driven by increasing greenhouse gas concentrations.

RICHARD THOMAN has worked for the National Weather Service in Alaska since 1988 and currently serves as the Regional Climate Science and Services Manager.

BRIAN BRETTSCHNEIDER is an Alaska-based research climatologist affiliated with the International Arctic Research Center (IARC) at the University of Alaska Fairbanks.       

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