Hail Reports

The Fairbanks area saw some hefty showers and thunderstorms yesterday and last Friday, and hail was reported around town on both days.  The storm on Friday afternoon was isolated but quite intense, with three-quarter inch hail reported.  Here's a radar image from 3pm, when the storm's intensity peaked as it moved from northwest to southeast over the north side of town (click to enlarge):

Another cell dropped pea-sized hail at the NWS office on the UAF campus a little while later.

Yesterday saw a larger and more organized storm track into town from the northeast, bringing both hail (up to half-inch reported) and damaging wind gusts.  The radar reflectivity reached an impressive 65 dbZ over quite a lengthy track.

Courtesy of the NWS on Twitter/X, this was the view to the northeast from the airport at the same time as the radar image above:

There was an impressive display of mammatus clouds after the storm passed.  These clouds form as pockets of cold air, loaded with ice crystals, sink out of the high-level cloud shield that forms in the wake of a mature thunderstorm.

Here's a simple animation of the storm evolution on radar:

As of yesterday, Fairbanks is up to 7 days so far this season with thunder reported at the airport.  That's the same as last year at this date, and it's a little ahead of the long-term normal of 4-5 days.  The normal for the whole season is 9-10 days.

Statewide lightning activity has resumed climbing since Friday, and the year-to-date strike count total has nearly reached the median for the seasonal total.

The Lower Yukon region is now well above the 2012-2025 record.

Meanwhile, there's a heat advisory in effect for the interior North Slope, and the NWS forecast for Umiat is currently calling for 87°F tomorrow.  The RAWS thermometer there will no doubt be a few degrees too high as usual, so it will be interesting to see if we can get a 90°F reading - it would be the first since 2013.

[Update: it reached 83°F, a typical value for the summer's highest temperature in Umiat.]

Southeast Interior Heatwave

I was about to post a quick summary of August climate anomalies, but a more urgent imperative is to comment briefly on the remarkable heatwave of last Thursday in the southeastern interior (I overlooked it at the time).  Here's the 500mb setup at 4pm Thursday, showing a tremendous ridge over northwestern Canada:

The deep southerly flow brought extremely warm air up from the south, and eastern Alaska was actually just on the western edge of the thermal anomaly:

Here are some of the observed high temperatures, with the highest readings found in the upper Tanana River valley and the Fortymile country (click to enlarge).

Some of the RAWS measurements are no doubt a few degrees too high, as is typical in warm, sunny weather, but reliable data from established sites confirms that this was a record-breaking event.  For example:

80°F in Northway is a record for September: the previous record was 79°F in 1982.

78°F in Eagle is close to a monthly record, but 80°F was observed on the 12th in 2021.

76°F in Gulkana is a tie for the warmest on record so late in the season; it seems there was a remarkably hot spell in early September 1917 (Eagle was also very warm at the same time).  If not for that event, this would be a new monthly record.

Perhaps most remarkable of all, Chicken reached 80°F - the same location that dropped to 14°F only 5 days earlier.  This is a remarkable feat, and it's worth a bit of research to see if such a temperature rebound to summer-like warmth has ever been observed anywhere in Alaska before.  It certainly hasn't in Chicken (with data only back to 1997) - the previous warmest subsequent to a 14°F freeze was 71°F in 2012.  In Northway it once reached 72°F after dropping to 12°F (in 1987), and it may have reached 74°F in Tok after a 14°F low (in 1989).  But I'm not seeing anything close to 80°F.  Needless to say, the 80°F is also a monthly record for Chicken (previously 72°F in 2019).

More Heat and Lightning

[Update July 10]

Rick Thoman pointed out that a SNOTEL site near Kobuk reached 93°F on Saturday, a remarkable temperature for this typically (slightly) more maritime area in the northwestern interior.  (Note that SNOTEL thermometers are more reliable than the warm-biased RAWS instruments.)

But it was back down to 30°F yesterday morning - that's quite a change.  Click to enlarge:

[end of update]

The second big heat wave of the summer for central and northern Alaska came to an end with a tremendous amount of lightning in the past couple of days.  The ALDN recorded over 12,000 cloud-to-ground lightning strikes in the 24 hour period ending at 6am today, with several regions of strong activity:

Yesterday was the 5th day this summer with over 10,000 ground strikes recorded, and this is the most of any summer in the modern ALDN history since 2012 (note that this calculation includes northwestern Canada to the west of 129°W).  Previously the record was 4 such days in both 2016 and 2017; but some summers don't see a single day this active - for example, the peak lightning day last summer was 6500 strikes on June 23.

In terms of total year-to-date strikes, 2025 remains in second place behind 2015.

Many new fires will have been started by this latest round of lightning, but the weather is now much cooler and more humid, which will greatly aid fire control efforts.  There are two substantial fires between Fairbanks and Nenana, collectively called the Nenana Ridge Complex, with expansive evacuation orders in place.  These fires have been burning since around June 20.

Looking back at the heat wave, it peaked over the holiday weekend, and was focused over the northern and northwestern interior, as well as the Brooks Range.  After seeing its latest measurable snow on record (again) only 4 weeks earlier, Bettles reached 90°F on Saturday, and that's only the second 90°F this century at Bettles - the other was in 2019.  Bettles is now running in second place for number of 80°F and 85°F days this summer (15 and 8 respectively).  What a turn-around from the cold start to summer:

Up at Anaktuvuk Pass, the temperature reached or exceeded 80°F for 4 days in a row, which is quite extraordinary for the location (2100' elevation at 68°N).  Even a single 80°F day is very unusual up there, but the count has now reached 6 days this summer; the previous record from recent decades (since the mid-1980s) is just 2 such days in 2016.

Heat and Floods

There's an autumn chill in the air for much of Alaska this morning, but summer had a record-breaking last gasp in the eastern interior at the weekend.  Chinook flow from the south produced extraordinary downslope warming for southeastern locations, including 89°F at both Northway and Eagle on Sunday (the 90°F in the map below is a rounding error):

It's hard to overstate how anomalous this kind of heat is at this point on the calendar.  Northway, at 1700 feet above sea level, has only ever reached 89°F or higher in June, with data back to 1943.  The record highs for both July and August are 88°F, and of course the August record was set early in the month.  The previous highest temperature in the second half of August was only 84°F.

As for Eagle, with data (some gaps) back to 1902, the latest in the year for 89°F was August 15, 1982.   It also reached 90°F on August 12, 2013.

This is the second time this month with record-breaking heat for these communities: just two weeks ago, Northway saw its latest measurement of 87°F, on the 6th of the month.  Eagle was 90°F then too.

Here's the 500mb flow (as of 4pm AKDT on Sunday) that produced the downslope warming: notice the strong southwesterly winds between the major North Pacific ridge and the strong trough near the Bering Strait.

The Bering Sea trough and associated storminess has been causing havoc for the Kuskokwim Delta coast, with major flooding reported:

https://alaskapublic.org/2024/08/18/bering-sea-storm-brings-erosion-and-flooding-to-western-alaska-communities/

Two strong and very similar storms moved up the Bering Sea into the Seward Peninsula in the past several days: here are MSLP analyses from Friday morning (top) and Sunday afternoon (bottom):

Next up is the remnant circulation of Typhoon Ampil, which affected northern Japan last week.  The now-extratropical storm moved through the western Aleutians yesterday, and will near the Bering Strait late tomorrow.  Wind and flood warnings are in place for most of Alaska's west coast.

Arctic Coast Heat Record

I'm traveling this week, but yesterday's significant new heat record at Deadhorse deserves a mention.  Remarkably, the temperature reached 89°F at the airport there, with a southeasterly breeze adding downslope warming to an already extremely warm air mass.  The previous all-time record for the Deadhorse/Prudhoe Bay area was 85°F, with data going back to 1999 at Deadhorse itself, and back to late 1968 at Prudhoe Bay.

A margin of 4°F is impressive for breaking an all-time heat record, although the period of record isn't that long, and Prudhoe Bay is a bit cooler in summer than Deadhorse, being slightly closer to the ocean.  The highest temperature recorded in Prudhoe Bay (1969-1999) was only 83°F.  Prudhoe Bay exceeded 80°F only 6 times in those 30 years, then Deadhorse did it once from 1999-2014; but it has happened more often recently: in 2015, 2016, 2017, and last year (also in early August).

Here's a map of high temperatures around the region (the blog software won't let me upload an image at this time):

https://s2s.worldclimateservice.com/wcs/tmax_20240806.jpg

Note that 90°F is indicated for Deadhorse, but that's a product of unit conversion-related rounding errors on the sub-hourly data feed; the actual high was 89°F.  Note too that the top-quality Deadhorse CRN site reached 87°F, which is also 4°F higher than anything measured in the previous 10 years of data at that site.

Extreme Weather in McGrath

The heatwave is on the way out, and Fairbanks didn't reach 90°F after all, but McGrath did - and it's a much more unusual event down there.  McGrath tends to have a more maritime influence, being closer to the sea and to the west of the Alaska Range.

With data back to 1941, McGrath has only reached 90°F on 5 days: once in 1969, on 3 consecutive days in 2013 (reaching an amazing 94°F), and once in 2019.  All were in June.  However, July and August have both seen 89°F, most recently on July 8, 2019.

To dispel doubts about the accuracy of yesterday's measurement, the AWOS instruments measured 88°F upstream (on the Kuskokwim River) at Nikolai and 86/87°F downstream at Sleetmute and Aniak.  As usual, RAWS thermometers in the area were higher, but they should be disregarded.

However, the heat is only half the story.  Shortly after the temperature peaked at 6pm, a very intense rain shower developed, dropping over an inch of rain in a very short time.  Brian Brettschneider notes that the rain rates exceeded the estimated threshold for a 1000-year recurrence interval!  Here are the precipitation frequency intervals from NOAA's Atlas 14 (click to enlarge):

Between 7:23 and 7:53pm, the ASOS reported 0.78" of rain (compare to 0.73" for a 30-minute event with a 1000-year recurrence interval), and 1.22" fell in 1 hour 24 minutes.

The notion of return interval is based on historical statistics and the assumption of a stable climate, which is of course never quite true, and we do expect more frequent heavy precipitation events in a warming climate with more atmospheric water content.  Nevertheless, this was clearly an extremely rare event for McGrath.

Putting the two aspects together, the combination of rare heat and rare heavy rainfall was obviously way outside the historical climate record for McGrath.  For instance, the warmest day in the past 84 years with a daily precipitation total of 1" or higher was only 72°F.  There have only been 3 days with a high temperature above 80°F and a daily rainfall above 0.5" (most recently - again - in 2019).

Summer Heat

The heat is on for the eastern half of the interior today, with widespread 80s, including 83°F so far in Fairbanks and 84°F in Eagle.  Many RAWS site are hotter, but that's typical under strong summer sunshine.  More notable is the heat across the eastern North Slope: 72°F at Barter Island, and 80°F at Deadhorse on a southwest wind before the sea breeze kicked in.  Click to enlarge:

The 80°F at Deadhorse is the first time in nearly 3 years that the temperature has exceeded 73°F.  The calendar years of 2019 and 2020 had maximum temperatures of 73°F and 71°F respectively, which is actually the coolest pair of summers (by this metric) since 1987 and 1988.  But all four years from 2015-2018 saw at least one 80°F day in Deadhorse.  Here's a visual representation of all 75+ and 80+ days since 1970 in the combined history from Deadhorse and (prior to 1999) Prudhoe Bay.

It's interesting to note the occurrence of warm days in August - remarkably late in the summer for the Arctic coast - between 1989 and 2007.  Also, the trend towards earlier hot days seems notable: prior to 1990, the earliest 75°F was July 3, and today was the earliest 80°F on record.

In other (but related) news, Fairbanks airport has been reporting distant wildfire smoke this afternoon: presumably the result of the Haystack fire 20 miles north of town.  This is the first smoke report at the airport since June 1st of last summer, and that was the only day last year that reported smoke.

Heat and Smoke

As I'm sure all readers are fully aware, an extraordinarily intense heat wave has been occurring across much of southern Alaska in the past week, and longstanding temperature records have been falling left and right.   Here's a quick summary that Rick Thoman posted yesterday:


 

There's far too much to comment on, but the remarkable July 4 heat in Anchorage may be the most astonishing statistic: the previous all-time record for the city's official climate site was only 85°F.

Dense smoke from wildfires has held temperatures down in some parts of the interior, including Fairbanks, but many locations in western and southern Alaska are well up into the 80s today.  Particularly striking to me is the 87°F currently being reported from Noatak in the northwest - above the Arctic Circle - and 92°F earlier today at the high-quality CRN station to the southeast of Ruby.

Here's an annotated true-color satellite image, courtesy of Rick Thoman and UAF:

Nasty wildfire smoke blankets a fair chunk of Alaska. Smoke from the big fires west of McGrath inundated the lower Kuskokwim and Bristol Bay regions Sunday, and today the smoke has turned northward across western Norton Sound. #akwx @Climatologist49 @KYUKNews @kdlgradio @KNOMnews pic.twitter.com/GcxurQP7yW

— Rick Thoman (@AlaskaWx) July 8, 2019

Click on the image below for a higher resolution version:

 As bad as the smoke is at the moment in Fairbanks, this summer has a long way to go to equal the awful summer of 2004 in terms of duration and choking density of smoke - see the chart below, showing data from the Fairbanks airport ASOS instrument.  Here's hoping that 2004 remains an outlier.

Heat Update

Here's a list of the highest reliable temperatures observed in the recent heat wave: all are found in the Tanana River valley, from Fairbanks up to the Tok 70SE CRN site (at 2000' elevation, close to the Alaska Highway, and only 10 miles from the border with Canada).

94°F   Tok 70SE
92°F   Whitestone Farms COOP
91°F   Tok #2 COOP (June 9 and June 10)
90°F   North Pole COOP
90°F   Ester 5NE COOP
90°F   Fairbanks Intl AP

The Tok 70SE site experiences a remarkably continental climate with large diurnal temperature ranges in summer; the low temperature on Friday was 43°F, and just 3 days earlier it was 29°F.

Here are the temperatures recorded by the various thermometers at the CRN site, at 5-minute intervals from 5-6pm AKDT on Friday.  The maximum of 34.3°C is 93.7°F; pretty impressive for the 9th of June.

Interior Heat Wave

The heat is on across the interior today, with temperatures pushing up to 90°F in some spots.  The map below shows the high temperatures through about 5pm; note that RAWS thermometers tend to run several degrees too warm on days like this, so most of the low 90s are probably erroneous.  Nevertheless, at 5pm it was a very consistent 89°F at Fairbanks airport, Fort Wainwright, and Eielson AFB.

Assuming the high temperature reaches 90°F in Fairbanks today [update: confirmed by NWS], this is quite a rare event; it happened in 2013 (two days), once in each of 2009 and 2010, but prior to that 90°F was not reached at all from 1995 through 2008.  Today is almost but not quite the earliest in the year that 90°F has been reached; the only earlier occasion was May (!) 28 in 1947.

It's hard to imagine, but temperatures on the eastern North Slope this afternoon are actually below freezing; Barter Island has been hovering around 28°F all day.  It was 23°F in Barrow this morning with clear skies and a strong breeze; it was a beautiful scene, but amazingly cool considering the heat on the other side of the Brooks Range.

The temperature difference we're seeing here between the North Slope and the interior is right at the limit of what has been observed historically at this time of year; for example, the largest difference in daily high temperatures between Fairbanks and Barrow is 58°F in June, and it looks like today's difference will be about 55°F (90°F vs 35°F).

The largest summer-time same-day high temperature difference between Fairbanks and Deadhorse/Prudhoe Bay is 55°F, which occurred in the late June heat wave of 2013 (92°F in Fairbanks, 37°F in Deadhorse).  With the temperature reaching only 32°F so far today in Deadhorse, the record may be broken.

Heat Wave Review

As we look back at last week's hot spell, it's clear that it was historically significant for northern Alaska, as Thursday's 86°F in Kuparuk set a new all-time heat record for any Alaska location near the Arctic coast.  As we noted earlier, the 85°F in Deadhorse also broke the all-time record for the Deadhorse/Prudhoe Bay combined climate history (1969-present).  However, the heat wave may not long be remembered by residents of interior Alaska, as it was not particularly unusual there.  Fairbanks reached 88°F on 2 consecutive days, which is something that has happened 21 times before in the 86 years of NWS/Weather Bureau observations.  If the 88°F is the hottest temperature of the year, as seems very likely, it will be only 1 degree above what's typical for the annual maximum temperature.

Looking at 850mb temperatures, the Fairbanks soundings recorded a peak of 16.0°C, which is equal to the average maximum for the year.  This is a little lower than the GFS model forecast was indicating, so the air mass didn't quite heat up as much as expected.  Additionally, the surface temperature came a degree or two short of what might be expected based on the observed 850mb temperature, and this could be the effect of moist soil as I speculated earlier.  Humidity was high, with the heat index reaching 87°F at the airport after the rain on Thursday afternoon; the heat index only gets this high about once every 5 years, on average.

Here's a map of the maximum temperatures observed during the hot spell, courtesy of the xmACIS2 interface at http://xmacis.rcc-acis.org.  With one exception, all of the reports above 90°F are from RAWS stations, which are known to have a high bias in warm, sunny weather, because of inadequate ventilation of the thermometer.  The highest plausible non-RAWS temperature is the 92°F reported on July 14 by the Two Rivers COOP observer, about 25 miles east of Fairbanks.

It's interesting to look at the evolution of the temperature profile as measured by the Fairbanks soundings during the hot spell; the animation below shows the twice-daily soundings from Tuesday morning through yesterday morning.  The steady warming and then cooling of the lower troposphere is seen very clearly between 800 and 900mb, which is above the near-surface layer that undergoes rapid diurnal changes.  Notice the light winds throughout the column near the peak of the warmth and the strengthening westerly flow that brought an end to the event.

Courtesy of Environment Canada, here's the 500mb analysis from Wednesday afternoon, when the upper-level ridge was nearing its peak intensity.  Notice the proximity of the ridge to the Arctic coast and the low pressure far to the north over the Arctic Ocean; this is reflected in the sea-level pressure map (also below), which shows a pressure gradient from south to north across the North Slope.  The pressure gradient allowed south winds to prevail over eastern North Slope locations on both Wednesday and Thursday, thereby preventing the sea breeze from coming inland and bringing cooler air to places like Deadhorse and Kuparuk.

The 850mb temperature analysis from Wednesday afternoon (first map below) shows that the warmest air in an absolute sense was located over the interior, but compared to normal (second map below) the warmth was most anomalous well to the north of Alaska over the Beaufort Sea.  Again it was the unusual pressure gradient over northern Alaska and the southern Arctic Ocean that allowed warm air to flow north unhindered, and this is the key reason why the Arctic coast temperature record was broken.

Finally, to answer a question from reader Mike, here's a chart that shows the frequency of reaching specific thresholds of warmth in Fairbanks on or after dates in July and August.  We're already down to a chance of only 30% that 85°F will be observed again this year, and with a cool and very wet forecast the odds are even lower than that.  There's even a modest chance that Fairbanks won't get out of the 70s again; both last year and 2014 failed to see a temperature higher than 80°F for the rest of the year after this date.

As far as chilly nights are concerned, the median date for first 40°F at Fairbanks airport is August 18, but of course it could happen any time at colder outlying locations.

Arctic Coast Heat Record

While Fairbanks reached a very unusual 88°F yesterday, tying a daily record, the really unusual heat was up on the North Slope.  A remarkable 85°F was reported at the Deadhorse airport (ASOS) and also by the COOP observer in Kuparuk, about 30 miles to the west of the Deadhorse/Prudhoe Bay area.  This is a new all-time high temperature record for both sites and is higher than any temperature in the historical record for any location near the Arctic coast in Alaska.  Umiat has exceeded 90°F in the past, but they are much farther inland.

The chart below shows the annual maximum temperature for the combined period of record from Deadhorse and - prior to 1999 - from Prudhoe Bay.  The two sites are about 5 miles apart, with Prudhoe Bay being closer to the water, so the question arises as to whether the Prudhoe Bay location is cooler in summer.  If so, then it's not quite fair to compare yesterday's Deadhorse record to the old Prudhoe Bay data.  Unfortunately there is almost no overlap in the data from the two sites, so a direct comparison is not possible; however, I was able to compare both sites to the Kuparuk historical data - read on below.

Looking only at temperature data from July, there is complete historical data at Kuparuk from 1984 to the present, except for 1990 and 2011; so we have a nice overlap with both Prudhoe Bay and Deadhorse, allowing us to see if the temperature differences changed systematically in 1999.  See the chart below.  While there is considerable year-to-year variation in the July temperature difference between Kuparuk and the other two sites, there's almost no systematic difference between Deadhorse and Prudhoe Bay; both sites are slightly cooler than Kuparuk, and Deadhorse is just 0.3°F warmer than Prudhoe Bay on average.

But what about very warm days?  It's possible that even though the mean July temperatures are similar, Deadhorse might get warmer than Prudhoe Bay on hot days.  To look at this, I pulled out the 86 days on which Kuparuk has observed 70°F or higher (in any month); of these days, Prudhoe Bay averaged 2.4°F cooler (44 days) and Deadhorse averaged 2.6°F cooler (42 days), so again there is no significant difference.  For all days on which Kuparuk reached 75°F, Prudhoe Bay averaged 3.8°F cooler (12 days) and Deadhorse averaged 4.1°F cooler (14 days).  I conclude that there is no reason to believe that Deadhorse is more likely to reach high temperature extremes than the old Prudhoe Bay site.  This in turn means that it's fair to compare yesterday's record to the entire historical period at Prudhoe Bay/Deadhorse; and that makes yesterday's record quite significant.

[Update July 18: Kuparuk managed to reach 86°F on Thursday - thanks to Rick Thoman for pointing this out - so they now hold the record for highest temperature near the Arctic coast.]

Heat Wave Imminent

This week is likely to bring the hottest temperatures of the year to the Fairbanks area, as an upper-level ridge intensifies over the state and heats up an already warm air mass.  Here's this morning's sounding from Fairbanks; in the next 48 hours, subsidence under the ridge will warm and dry the lower levels dramatically, and clear skies will allow the sun to do its work.

The current NWS forecast calls for 87°F tomorrow and 86°F on Thursday at Fairbanks airport, and I think that's a conservative prediction.  This morning's GFS MOS forecast has 89°F tomorrow and 90°F on Thursday, which seems about right.

The chart below shows a time-height cross-section of temperature according to the GFS model, showing that 850mb temperatures are expected to reach about 17°C.  If we trace that warm air down to the surface along a dry-adiabatic lapse rate, we get a surface temperature of 88°F at Fairbanks airport, and typically solar heating will boost temperatures a bit beyond that estimate.  For reference, the last time 90°F was reached in Fairbanks was in June 2013; the high was 92°F on the 25th and 26th, but the lapse-rate method gave a temperature of 88°F.  So lower 90s are certainly a possibility this week.

The one factor that might help keep temperatures down a bit is the high level of soil moisture remaining from recent wet weather; the moist ground will not heat up quite as much, and increased evaporation will soak up some energy compared to, say, 2013.  It will certainly be interesting to see if 90°F can be reached - for only the 5th time in the past 20 years.

Update: here's a radar image from Tuesday evening (see comments below):