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.]

Wildfire Update

Alaska's fire season has been fairly subdued up to this point, although residents of the Tanana Valley near Salcha might be forgiven for thinking otherwise, as a large fire is burning on the west side of the Tanana River.  The McDonald fire, as it's named, has burned about 40,000 acres, or nearly two-thirds of the state's total of 63,000 acres so far this season.  It's by far the largest fire in the state and has produced dense smoke in the local area.  Here's the latest update from the Alaska Fire Service:

https://akfireinfo.com/2024/06/20/mcdonald-fire-remains-west-of-the-tanana-river/

Elsewhere there are a number of fires in southwestern Alaska, sparked by widespread lightning activity on Monday:

https://akfireinfo.com/2024/06/18/recent-lightning-sparks-multiple-new-fires-in-southwest-alaska/

Also, a few large tundra fires are active in the northwest.

The 1995-2023 median statewide acreage for this date is about 100,000 acres, so the season is slightly less active than normal so far, but it's still early.  The median acreage jumps four-fold in the next 30 days, so things can change fast.

Here's a photo of pyrocumulus cloud over the McDonald fire on Monday, courtesy of the NWS via X/Twitter.  The fire was stirred up on Monday afternoon by winds related to nearby thunderstorm activity.

Speaking of thunderstorms, Bettles reported a heavy thunderstorm with quarter-inch hail yesterday.  This is unusual but certainly not rare: I found the following hail reports in the last 30 years at Bettles.

May 15, 1997   1/4" hail

May 11, 1998   1/2" hail

June 19, 2000   hail reported but no size specified

June 11, 2002   1/2" hail

July 1, 2005   1/4" hail

June 28, 2008   1/2" hail

May 26, 2017   1/4" hail

July 12, 2017   hail reported but no size specified

June 5, 2019   less than 1/4"

Fairbanks has had fewer hail reports in the same time, but the official data is from the airport, and other parts of town are more prone to thunderstorms.

June 8, 1997   no size specified

August 9, 2002   1/4" hail

May 14, 2012   3/16" (reported as graupel or small hail)

June 2, 2019   3/8" hail  (blog post here)

June 16, 2021   less than 1/4"

Severe Thunderstorms

The east-central interior saw a remarkable and rare outbreak of strong to severe thunderstorms yesterday evening, and the NWS meteorologists in Fairbanks had their hands full issuing warnings for the numerous storms.  The first severe thunderstorm warning was issued at 5:47pm AKDT for a storm about 30 miles west of Fairbanks, and 12 more warnings were issued over the next two and a half hours.

Here's the Fairbanks radar image at the time the first warning was issued (click to enlarge).  The storm cell in question is the one just to the north of the Parks Highway (the red line) to the west of Fairbanks.  The storm just to the southwest of that, closer to Nenana, dropped half an inch of rain at the airport there in 22 minutes.

Two particularly severe storms developed a bit later well to the northeast of Fairbanks, near Central, and eventually crossing the Yukon River.  Here are the radar snapshots from 7:08 and 7:24pm: note the very high radar reflectivity values, which are strongly indicative of large hail.  The Weather Service issued warnings for "half dollar size" hail, i.e. 1.2 inches in diameter.

The ingredients for the storms involved very high humidity at low levels and a powerful impulse (widespread lifting/ascent) in association with a strong cold front approaching from the west.  The dewpoint reached 61°F in Fairbanks in the early evening, which is about as high as humidity typically gets in summer there, and Fort Yukon's dewpoint made it up to 63°F.  Low-level humidity greatly adds to convective instability, which is the fuel for deep, vigorous overturning in thunderstorms.

Here's the 500mb analysis at 4pm yesterday.  Note the very sharp trough over southwestern Alaska and the strong pressure gradient to its east, with strong southerly flow between the trough and a ridge downstream over northwestern Canada.

 

That southerly flow and the strong Canadian ridge produced excessive heat over Alaska's far eastern interior, western Canada, and southeastern Alaska: here are maximum temperatures yesterday (click to enlarge).

I imagine Rick Thoman will provide more expansive historical context for the heat wave on his Substack channel, but the 91°F reported by the co-op observer at Eagle is pretty unusual: before 2012 it was about a once or twice a decade occurrence.  Father east, the 95°F at Carmacks is within a degree of the all-time high in 2004.  Canada has been breaking all sorts of heat records this summer.

Finally, here are simple radar animations from yesterday evening: split into two halves for the sake of file size (i.e. the second animation picks up where the first one ends).  What a remarkable event!  I'd be very glad to hear of any reports from those on the ground - feel free to share in the comments.

Intense Thunderstorm in Fairbanks

Yesterday evening the Fairbanks area experienced a very strong thunderstorm system that prompted a rare severe thunderstorm warning from the National Weather Service.  Here's the NWS public information statement from shortly after the event:

"Public Information Statement National Weather Service Fairbanks AK 802 PM AKDT Sun Jun 2 2019 ...Strong Thunderstorm Hits Fairbanks... Fairbanks had a thunderstorm move west across the city between 6pm and 7pm this evening. An NWS Weather Spotter in Hamilton Acres reported half inch size hail, and radar indicated hail of up to one inch diameter. There were numerous reports of pea size hail and frequent lightning in the Fairbanks area. The Fairbanks International Airport had 65 hundredths (0.65) of an inch of rain in a period of 21 minutes, which is one of the highest rainfall rates in recent memory in Fairbanks. There have been about 200 lightning strikes in the Fairbanks North Star Borough since the thunderstorms began around 3pm. As of 745 pm this evening, thunderstorms had moved south and west of Fairbanks and North Pole."

As luck would have it, a very intense part of the storm complex occurred over the international airport, and the ASOS instruments reported extremely heavy rain as well as hail of 3/8" diameter.  I have only been able to find a few instances of hail being reported from the Fairbanks ASOS (May 15, 2012, August 9, 2002, and June 9, 1997), and only the 2002 report included a hailstone size observation (1/4").

The ASOS precipitation data also show that 0.65" of rain fell in 21 minutes, and of that 0.55" fell in 8 minutes, which equates to a rate of 4.1" per hour.  This is a truly remarkable rainfall rate for such a high latitude, and I suspect it may contend for an all-time record for Fairbanks; more investigation would be justified.

According to the NOAA precipitation atlas, the estimated recurrence interval for a 0.55" rain amount is near 200 years for a 10-minute interval and over 500 years for a 5-minute interval, so this event lay somewhere in between.  In the graphics below, the black lines represent the recurrence interval estimates, and the green and red lines show the limits of the 90% confidence interval.

Here's a sequence of radar images showing the evolution of the storm system; its development was really explosive.  It's remarkable to see radar reflectivities of well over 60 dBZ, which is strongly indicative of hail.  This would be more typical of, say, the western Plains in Kansas or Nebraska at this time of year.

Looking at the balloon sounding from Fairbanks just a couple of hours earlier, the standard metrics don't show a particularly notable amount of instability (see below).   However, the northerly winds aloft produced a modest amount of wind shear (favorable for organized thunderstorms), and it was a moist environment.  Moreover, yesterday afternoon the NWS forecasters noted an upper-level wave that was expected to kick off some storm activity:

"Central and Eastern Interior: A shortwave moving to the south over the area will bring some scattered showers this afternoon and evening. The shortwave will be moving over an area with decent instability thanks to relatively moist antecedent conditions. The current GFS is showing surface based CAPE values of 300-500 J/kg across much of the Interior south of Livengood with weakly negative LI values. This swill be sufficient for some isolated thunderstorms across the area. Some thunderstorms may produce small hail or gusty winds."

Finally, here's a simple animation of the radar imagery.  An impressive event, indeed!

Hail in Eagle

Eagle was hit with quite a hail storm yesterday afternoon - here's photographic evidence via the NWS Twitter feed.

Hail at Eagle AK, between 3-4pm today. Courtesy John Borg. pic.twitter.com/Uk1U634iKk

— NWS Fairbanks (@NWSFairbanks) June 24, 2017

Here's how the storm was described in a NWS statement:

"The town of Eagle had a thunderstorm from 3 to 4 pm today with hail lasting for over one half hour. By the time the storm was over, an inch or more of hail was covering the ground. Some of the hail was one half inch in diameter. Eagle also had winds gusting to 25 mph, and had over sixty-six hundredths of an inch (0.66) of rain from that storm. A long time weather observer in Eagle reports that they have not had a storm like this since the 1970s."

And here's an animation of webcam images from the airport, showing the dramatic approach of the storm and what appear to be hailstones falling in one of the shots.  Note that the airport only reported 0.25" of precipitation and appears to have had much less hail; but the airport is more than a mile away from the village.

By way of explanation, the main culprit appears to be high humidity.  Surface dewpoints were in the upper 40s yesterday in Eagle as the temperature rose to 78°F, leading to convective instability.  Furthermore, the Fairbanks sounding from yesterday afternoon showed a rather notable moist layer in the mid-troposphere (750-500mb), and this is a favorable environment for storm updrafts to be maintained without dilution by surrounding dry air.

The upper-air map shows a ridge in place over northwest Canada, but high pressure certainly does not always translate into clear and dry weather - notice the correspondence of yesterday's lightning strikes with the upper ridge location.  Note also the lightning on the North Slope; Deadhorse reported a thunderstorm - a rare occurrence up there.