Cold Day in Utqiaġvik

The past couple of days were very warm across the interior, but yesterday was a very chilly day for the time of year in Alaska's northernmost town of Utqiaġvik.  With a daily maximum temperature of 31°F at the airport, it was the latest sub-freezing day in "spring" since 1996, and the daily mean of 27.5°F ties with 1979 for the latest on record for such cold.  Other than the same date in 1979, such a chilly day (mean temperature below 28°F) has not been observed before between June 22 and August 12.

Similar conditions were measured at the nearby high-quality CRN observing site, with a daily mean temperature of 27°F.  This site's period of record only goes back to 2003, but the latest date with such chill was previously June 12.

There was also a little snow, and the late morning report of snow falling with a temperature of 26°F is the second latest on record for such conditions: the record is June 29, 1976.

One day's weather in isolation is not significant from a broader climate perspective, but nevertheless the chart below shows a striking contrast with the trend of recent decades: it shows the lowest daily mean temperature in the window June 15 - August 15.

As for a cause, there have been episodes of strong mid-atmospheric low pressure over the Arctic Ocean this month, and one of these troughs brushed past Alaska's Arctic coast in the past couple of days, bringing a cold air mass over the nearby ocean.  A northerly breeze for most of the day yesterday, combined with heavy cloud cover and abundant sea ice nearby, was enough to keep temperatures below freezing.

More Lightning

Yesterday was the seventh day in a row of very substantial lightning activity in interior Alaska, and it was the second most active day on record (2012-present) for the Lower Yukon region, with nearly 3500 strikes in that part of the western interior.  Only July 11, 2019 had more lightning strikes in a single day in the Lower Yukon zone; but this year's activity is far ahead of 2019 year-to-date:

Here's a preliminary look at the spatial distribution of lightning this month, with data through the 25th.

The historical normal for June tends to be much reduced to the west of Galena and McGrath, and also across the northern interior, so the westward and northward extent of heavy lightning activity is the most unusual aspect of this persistent lightning outbreak.

On the other hand, the lightning "hole" around Fort Yukon this month is pretty typical.

Like Clockwork

[June 24, June 25: see updates below]

The calendar can be a remarkably good guide to seasonal weather changes at times, and especially in very continental climates where the pace of change is typically rapid.  The onset of widespread lightning across interior Alaska over the past several days is a case in point: check out the similarity between this year's accumulated lightning strike count and the climatological median (thick black versus dashed black lines): 

Based on historical data since 2012, the climatological median takes off right at June 15, and this year major lightning activity began on June 19.  Each of the past four days has seen more than 4000 lightning strikes statewide, and while the 4-day total of about 20,000 is not particularly noteworthy, the impeccable timing is interesting.

Last year saw a similar but more dramatic surge beginning on June 16: over 50,000 strikes in 5 days at that time.

In terms of spatial distribution, the most pronounced activity has been in the Kuskokwim and Lower Yukon regions, as well as the central interior (South and West Tanana zones).  Here's a map of the AICC Predictive Service Areas and other geographical divisions that I use to track totals (click to enlarge):

Compared to the historical median, the Lower Yukon region has seen the largest excess of lightning strikes, with the season's total already having reached the normal for a whole season:

In contrast, the northern interior has seen less lightning than normal, and the North Slope has seen only 10% of its typical 1200 lightning strikes to this date:

As for fire, statewide reported acreage remains minimal, despite the rather significant lightning outbreak.  There have been plenty of fire starts, of course, but "so far so good" in terms of containment and limited growth.  Significant rains were widespread today in the upper half of the Tanana Valley, and the southwestern interior has also seen good rains in the last few days - so that helps.  Perhaps lingering moisture from the very wet spring has been enough to hinder quick fire growth after all, despite concerningly dry conditions earlier this month.

The 2026 statewide fire acreage is still nearly indistinguishable from zero on the year-to-date chart below, with total acreage at only 17,000 acres compared to a median of 184,000 for the date.

Looking ahead, distinctly cool conditions appear likely to return next week, and there's also rain in the forecast, so the fire risk appears set to subside for a time.

June 24 update:

Yesterday - the fifth day of widespread lightning - was the most active day so far, with over 7000 strikes statewide.  There were 3000 in the southern Tanana zone by itself, pushing the year-to-date total well above normal in the heart of the interior:

The statewide year-to-date total is slightly above normal now, but the current lightning outbreak is still much less intense than last year's mid-late June onslaught.

June 25 update:

And another big day: yesterday produced the largest statewide strike count so far, over 7400 strikes.  The northern interior had major lightning activity for the first time, with the northern Tanana zone seeing nearly 2800 strikes, suddenly taking the year-to-date total into second place locally.  Last year was far and away the most active year in the 2012-present history for the north-central interior.

The southern Tanana zone is now almost at a record high for year-to-date activity:

Last Wednesday's comment that the "pattern looks conducive to the onset of more widespread lightning in the near future" turned out to be more correct than I expected.

Minimal Fire So Far

Interior Alaska finally saw some genuinely warm weather last weekend, with temperatures pushing up toward the 80°F mark in many areas; and Fairbanks saw its first 80°F of the season - a few days later than normal.

The mini-heatwave didn't last long, but renewed warmth is on the way in the coming days, and the predicted mid-atmosphere pressure pattern looks conducive to the onset of more widespread lightning in the near future.  The map below shows the expected 500mb height anomaly (departure from normal) for the next 7 days, indicating a broad axis of above-normal heights (i.e. a ridge) from eastern Russia to northwestern Canada:

Contrast the pattern in the first two weeks of this month, when a strong trough over the Arctic Ocean brought cool northwesterly air flows to interior and northern Alaska:

Atmospheric moisture has been well below normal for the time of year, and that means a lack of atmospheric fuel for thunderstorms.

No surprise, then, that statewide lightning activity is below normal and is now moving into "significantly below normal" territory; the climatological median ramps up quickly from June 15 on.  Click to enlarge:

Thanks to the lack of lightning, year-to-date fire activity is close to zero: only 5600 acres have burned statewide so far, compared to a historical median of 85,000 acres for this date.  In view of the weather forecast, this seems likely to change soon.

It's also worth noting that the past two weeks have been quite dry for most of the interior, a marked change from the wet spring; fire fuels have no doubt dried out quite a bit.

June Chill, May Climate

Yesterday NOAA/NCEI came out with their climate statistics for May, and it was the sixth consecutive month with a statewide mean temperature below the 1991-2020 normal in Alaska (although April was only marginally below).  It was also the third consecutive May with a cool anomaly relative to recent decades:

Significantly above-normal temperatures have been rather scarce in most areas in recent months, and Rick Thoman noted that many interior locations had their lowest May maximum temperature since 2000.  The statewide temperature index barely rose above normal at any time in the month, although the first few days of June turned much warmer.

As if to re-emphasize the cool theme, a very notable cold front swept across the interior and north yesterday, ushering in a very chilly air mass for the time of year.  Here's an enhanced satellite image showing the frontal cloud band at 3:20pm AKDT.  Blue colors across the North Slope and high terrain indicate snow cover, and sea ice is visible in Kotzebue Sound and along the northern Arctic coastline.

The 500mb analysis from about the same time yesterday shows the connection to a very strong mid-atmosphere cyclone over the Arctic Ocean.  Judging from ERA5 data, it appears to be one of the strongest - if not actually the strongest - on record for the month of June in this region.

Temperatures this morning were near or below freezing widely across the interior, with hard freezes across the northwest and Brooks Range.  The NWS (courtesy of Rick Thoman) noted that the wind chill of 13°F in Kotzebue at 5am was the lowest on record for this late in the spring.  Here are a couple of zoomed-in maps of minimum temperatures across the Arctic northeast and interior/Arctic northwest.

Looking back in more detail at the month of May, NOAA's data indicates that the Bristol Bay climate division saw its coldest May since 2001.  However, the coarse climate division perspective completely obscures the fact that it was notably warmer than normal in Alaska's northwest; Kotzebue had its warmest May since 2020.

The mid-atmosphere pressure pattern responsible for this odd outcome is illustrated below.  A robust trough over Alaska brought chilly and wet conditions to most of the state, but the setup was conducive to above-normal sunshine over the northern Bering Sea and southern Chukchi Sea, and it seems that helped boost temperatures in the northwest.  I think there was also an element of chinook/downslope warming over the Seward Peninsula and near Kotzebue Sound, as winds from the northeast passed over the Brooks Range and then warmed on their way back down to sea level.

Winds were stronger than normal across the North Slope and much of the interior and south of Alaska:

Courtesy of the wonderful toolset at the Iowa Environmental Mesonet, here's a comparison of the May 2026 wind rose (top) compared to the long-term normal wind rose for May (bottom) in Utqiaġvik:

While easterly or east-northeasterly winds are always heavily favored in Utqiaġvik at this time of year, the regime was even more persistent, and with stronger winds, than normal this year (compare the frequency of winds in the 15-20 mph category).

For the climatological spring season as a whole (March through May), statewide average temperatures were the lowest since 2013, mostly because of March.  In the south it was the coldest spring since 1972 in the NCEI data from Bristol Bay to the mid-Panhandle, including Anchorage (and since 1974 in Juneau).

Wet and cloudy were also major themes from South-Central to the northern interior; but the bright side, of course, is that an early start to fire season was avoided.

Surprise Frosts in Fairbanks

A few days ago, reader Carl commented that the National Weather Service forecasts for overnight low temperatures in Fairbanks seem to have been biased high recently, with many occasions of low temperatures near or below freezing when much higher temperatures were predicted.

To look at this objectively, I was able to pull a history of NWS forecasts all the way back to 2009, and it turns out that the mean absolute error on the low temperature forecasts in the month of May was the highest in the data set.

The errors, as Carl observed, were largely due to a warm bias; the low temperature forecasts were generally warmer than the corresponding outcome.

(A small caveat is in order here: I'm comparing the NWS forecasts for "Fairbanks Metro Area" to the outcome at the airport, and there are microclimate differences that vary depending on the weather pattern.)

Here's a look at the daily errors so far in 2026: the warm bias for minimum temperatures has been quite persistent.

For extra credit, I also did a comparison of the recent NWS forecasts with pure model forecasts (NBM - National Blend of Models) for Fairbanks airport - see below, with the black line in the lower panel revealing the frost and freeze events that Carl mentioned.  As we might expect, the NWS forecasts closely follow the model predictions, so we can basically blame the recent warm bias on the models.  Ideally the forecasters might have adjusted the model numbers to improve the results, and actually it looks like they did start making a downward adjustment to the low temperatures starting on May 25.

None of this should be seen as criticism of the NWS folks in the Fairbanks office, who cover the weather over a staggering 359,000 square miles, over 4 times more area than any NWS office in the lower 48.

30 Years on Keystone Ridge

It was 30 years ago today that Rick Thoman began climate observations at his then-residence on Keystone Ridge, about 15 miles northwest of Fairbanks on the other side of Ester Dome.  At 1600 feet above sea level, the data from this site provides a unique record of interior Alaska climate well above valley level.  I for one am very grateful to Rick for his 19 years of service, and to his successors who continue to this day.

Here's a chart showing the monthly difference in mean temperature between Keystone Ridge and the international airport in Fairbanks.  The elevation provides major relief from valley-level cold in winter owing to the near-permanent temperature inversion, but in the warm season the ridge is slightly cooler.

Daily high temperatures are relatively cooler in the warm season, as there is less diurnal cycle on the hill, i.e. temperatures at elevation are more closely tied to air mass temperatures and don't typically vary as much over the course of a day:

The relative lack of variability also means that daily minimum temperatures are much higher on the ridge in the cold season; but from May through September there isn't much systematic difference in overnight minima.

As for precipitation, Keystone Ridge is of course consistently wetter than the airport, and the difference is substantial in summer.

Interestingly, July is marginally the wettest month at the airport (based on the overlapping period of record here), but August is wetter than July on the ridge.  In July Keystone Ridge is occasionally drier than the airport (4 of 29 years), but only one August was drier on the hill (1999).  (I excluded a few months with more than 2 missing days at either site.)

Here are a few photos of the Keystone Ridge observing site at the end of the extremely cold spring of 2013:

https://ak-wx.blogspot.com/2013/05/more-snow-to-go.html