Here in Southeast Alaska we get all kinds of interesting weather including, very occasionally, thunderstorms. Yesterday (Monday 6/16/2025) was one of those days. Here’s a lucky catch by the Gustavus FAA weather cam showing a classic roll cloud ushering in the heavy rain and outflow winds on the leading side of the convection.

We’ve had a low positioned offshore from the panhandle off and on for days, and in a configuration that tends to draw pockets or lines of convection ie, showers and thunderstorms, off the interior and over the panhandle. This is a common way we get hit with such storms, especially in the northern part. If the convective cells themselves don’t cross the mountains from the interior, then often it is the unstable airmass that does, setting the stage for the storms to blossom.

In this case, an upper-level short wave trough rotating around the low triggered the convection: you can see it easily on this 500 mb (mid-atmosphere vertically) map: a low off the coast with a reddish band (indicating vorticity, the business part of a trough) jutting through Sitka. (Map is from a computer model; this 12 hr forecast is about as good as an analysis, and I like the graphics – thanks to Tropicaltidbits).

At the surface level here’s another model graphic showing the model’s educated guess as to what a radar image might look like at 8 am ADT yesterday:

Not a bad general idea, but not detailed enough to be the best tool, and the timing was off — it had the forecast convection moving ahead of the actual by a few hours. But this is a large scale global model I mainly added to show the overall surface setup. Actual radar gave more details to the forecasters at the time, but since the radar antenna is on the outer coast near Sitka, the mountains block the signal from many parts of the panhandle, leaving an incomplete picture. So for the rest of this post I’ll rely mostly on web cams plus airport and remote automated weather stations.

Reporting the Alaskan part of the event from the south starts us at Ketchikan, where light steady rain overnight turned heavier and up-and-down in intensity in the morning, indicative of convection (showery precipitation). The gateway city picked up around two thirds of an inch of rain between 4 and 10 am, with 0.25 inches of that in the last hour. The rain stopped soon after that, as what was now an organized narrow band of convection moved north.

Interestingly, north of Ketchikan, precipitation amounts were not too high, about 0.15 inches or less at most places. This is due to how fast the storms came in the south door and went out the north door. Also, though there was plenty of lightning reported in the Juneau area, there seemed to be less so to the north.

The narrow band went through Sitka a bout 12:15 pm ADT, Petersburg and Wrangell between about 12:45 and 1:45 pm, then hit the southern parts of Juneau at about 3pm with increased vigor. Here’s a nice shot from the Mount Roberts tram.

If you look closely you can see the gust front kicking up waves on Gastineau Channel in the left part of the picture (click to enlarge). The surge of wind, rain and colder air (the gust front) is moving left to right in the picture, ie north up the narrow passage toward downtown Juneau. In the lower right of the cam shot is Juneau’s AML dock. Check out the graphs showing what happened with the weather there when the gust front arrived 4 minutes after the webcam shot. (Thanks to Marine Exchange of Alaska for the following graphs, and more importantly for installing and maintaining the many marine weather stations they have in recent years):

The peak gust shown was 58 kts (67 mph/107 km/hr). This was the highest anemometer reading I could find in the area from the storm. Look below at the  temperature drop when the gust front went through. Note that the temperature drop was a bit in advance of the strongest winds.

Other reports from Juneau included hail, downed trees, power outages, and a cruise ship broken free of its moorings by the wind.

The band of convective cells then moved generally northwest, but with our highly channeled topography, the winds follow the fjords. From the Marine Exchange and other stations we can track the gust front(s) as arriving at (w/ ~10 minute precision) Gustavus at 3:40 pm ADT, Eldred Rock at 4:20, Haines at 4:50 and Skagway at 5:10. This figures to a fairly consistent speed for the group of around 30 mph (50 km/hr) on the trip north.

At the 5:10 pm Skagway arrival, winds peaked at an impressive 51 kts (59 mph/94 km/hr) and the temperature dropped about 6 Fahrenheit degrees (3 Celsius degrees). But the small town with the big boats actually had an earlier “cold surge” moment around noon when light north winds and balmy 70F (21C) bliss were shattered by a sudden south wind gusting as high as 40 kts (46 mph/74 km/hr) and bringing the temperature down by 13F (7C ) in 15 minutes (the graph below shows both wind spikes). This is not a new thing for Skagway, but was probably new to many tourists who, if I might speculate, had probably just started to remove their parkas and extra sweaters when it hit.

Here’s the ominous-looking webcam shot looking south from Skagway:

Oh, it bears mention that since there were winds (gusts) in excess of 58 mph, the thunderstorm that hit Juneau qualified as severe by NWS criteria, and indeed, the NWS issued a severe thunderstorm warning, perhaps its first, or one of a very few?

I’d love to hear your side of the story, if you experienced the storms or just have a question or comment.