Thundersnow. Just the sound of it is exciting—snow accompanied by thunder and lightning. Although it is fairly rare east of the Rocky Mountains it is a bit more common across the west.
And we had multiple rounds of thunderstorms producing snow yesterday (Saturday, 13 February 2021) in Flagstaff. It was pretty amazing to see heavy snow falling and then a sudden flash of lightning followed by the muffled sound of thunder a few seconds later.
There were several clusters of thunderstorms that moved across the area during the afternoon. None of these were recorded by the ASOS at KFLG—and it’s not obvious why they were missed. The ASOS certainly captured the start of snow and then the moderate (SN) and heavy snow (+SN). Perhaps the lightning was just far enough away to not register.
Here is a loop of the visible channel from the GOES-17 satellite. Superimposed on the clouds are color blobs showing Group Flash Count Density from the satellite lightning mapper. The next image shows lighting from surface-based lightning detectors and shows numerous cloud-to-ground strikes across northern Arizona.
Model-generated soundings from the HRRR showed that there was very slight convective instability with surface-based CAPE values of around 100 J/kg.
That is a shallow layer of instability and very weak instability—but was enough to generate thundersnow.
This is the second year in a row in which the North American Monsoon has failed to deliver its normal weather to Arizona. The monsoon had a late start in July with only a few isolated rain events early in the month and the main event starting around the third week of July. But even that faltered after a week and the final week of July was dry.
August was even worse with no measurable precipitation until after mid-month and even then the amounts were light. The National Weather Service in Flagstaff has posted some climate data for the area for August. It was the hottest August and the 2nd driest on record in Flagstaff and most of the west experienced similar conditions (Figure 1; Figure 2;Figure 3).
Photographing summer monsoon storms has been a challenge this year because there were so many dry periods. Even so, there are always interesting weather events and clouds that make it worthwhile. So here is a collection of the most interesting weather photographs from this summer.
A time-lapse movie shows that the ducks are more interesting than the convection.
Full rainbows eluded me this year butI did manage to photograph a rainbow segment.
As with rainbows, lightning was elusive this year. It was typically a case of being in the wrong place on the wrong day and at the wrong time. But I did get lucky with the following image.
And when there is no lightning and no rainbow, one can be content with the sunset.
It’s been a challenging season for storm photography. First was a late start to the North American Monsoon. And, then, just as it was finally ramping up it shut down quickly. Current model forecasts suggest at least another week until it ramps up again.
A bit of moisture managed to produce some thunderstorms right around sunset. And there was enough lightning to make it worthwhile to be there and get some photographs.
It has been a dry October and the last measurable precipitation at the Flagstaff airport was September 26 until rain and snow fell on Sunday, October 27.
Forecast models had been showing a slight chance of rain and/or snow with the passage of a cold front but precipitation amounts were light. The GEFS plumes showed generally less than 0.03 inches. The airport actually measured a bit more than that as 0.05″ of rain fell with a trace of snow.
Overall, not a bad forecast. So I was not surprised that rain and some snow arrived with the cold front. I was surprised that it was accompanied by thunder and lightning.
It’s always interesting to observe Thundersnow!
A look at the lightning map shows that the only place where there was cloud-to-ground lightning was in the vicinity of Flagstaff.
It’s been an unusual monsoon season across Arizona this year. After both a wet winter and wet spring—with above normal precipitation amounts all the way into the month of May—things went dry. The North American Monsoon started late this year with the first significant rainfall not arriving until the second half of July. This was unfortunate as the dryness partially contributed to a very damaging wildfire (Museum Fire) burning across portions of the San Francisco Peaks.
Just a few days later, the rains finally arrived. And, then, they stopped again. And it has been that way much of this monsoon season. A few days of rain, then a week or more of dry weather. A normal pattern would have rain falling perhaps four days out of seven for a two-month period. Folks around here have dubbed this monsoon the “nonsoon”.
And, of course, with the lack of moisture and thunderstorms opportunities for photographing storms, heavy rain, lightning, and sunsets has been a challenge. But it only takes one great photograph to make it a successful season. I’m still trying to get that photograph.
Here are some of the more interesting photographs from this “nonsoon monsoon” season.