Thundersnow!

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.

Radar depiction of precipitation across northern Arizona at 1:51 P.M. on 13 February 2021. Note the small lightning symbols near Flagstaff showing locations of cloud-to-ground lightning.
Radar depiction of precipitation across northern Arizona at 1:51 P.M. on 13 February 2021. Note the small lightning symbols near Flagstaff showing locations of cloud-to-ground lightning.

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.

KFLG 132307Z VRB06G25KT M1/4SM +SN FZFG VV004 M01/M02 A2960 RMK AO2 P0006 T10111017
KFLG 132257Z 29009G27KT 260V340 1/4SM SN FZFG VV005 M01/M01 A2961 RMK AO2 PK WND 24031/2239 SLP027 P0007 T10061011
KFLG 132243Z 27012G31KT 1/4SM SN FG BKN008 OVC029 00/M01 A2959 RMK AO2 PK WND 24031/2239 P0004 T00001006

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.

 

Locations of cloud-to-ground lightning across northern Arizona on the afternoon of 13 February 2021.
Locations of cloud-to-ground lightning across northern Arizona on the afternoon of 13 February 2021.

Model-generated soundings from the HRRR showed that there was very slight convective instability with surface-based CAPE values of around 100 J/kg.

Model-derived sounding for Flagstaff at 20 UTC 13 February 2021 (1300 MST)
Model-derived sounding for Flagstaff at 20 UTC 13 February 2021 (1300 MST)

That is a shallow layer of instability and very weak instability—but was enough to generate thundersnow.

The 2020 nonsoon-Monsoon

A thin band of clouds partially blocks the sun and creates an array of crepuscular rays of light.

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.

Convection

Early stages of convection over the San Francisco Peaks as viewed from Marshall Lake.
Early stages of convection over the San Francisco Peaks as viewed from Marshall Lake.

A time-lapse movie shows that the ducks are more interesting than the convection.

Developing Cb's over the San Francisco Peaks.
Developing Cb’s over the San Francisco Peaks.
Small cumulus clouds over the Painted Desert.
Small cumulus clouds over the Painted Desert.
A weak thunderstorm near Two Guns, Arizona.
A weak thunderstorm near Two Guns, Arizona.
A well-developed thunderstorm over the Mogollon Rim viewed from Sedona.
A well-developed thunderstorm over the Mogollon Rim viewed from Sedona.

Rainbows

Full rainbows eluded me this year butI did manage to photograph a rainbow segment.

Rainbow segment over the North Rim of Grand Canyon.
Rainbow segment over the North Rim of Grand Canyon.

Lightning

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.

Lightning illuminates the interior of Grand Canyon.
Lightning illuminates the interior of Grand Canyon.
In-cloud lightning illuminates a small Cb near the Grand Canyon. I was trying to photograph the comet so I got lucky with this storm.
In-cloud lightning illuminates a small Cb near the Grand Canyon. I was trying to photograph the comet so I got lucky with this storm.
Lightning at sunset over the Mogollon Rim viewed from Sedona.
Lightning at sunset over the Mogollon Rim viewed from Sedona.
Weak storms over the San Francisco Peaks produced these two bolts of lightning.
Weak storms over the San Francisco Peaks produced these two bolts of lightning.
In-cloud lightning partially illuminates Grand Canyon while the nearly-full Moon provides additional illumination.
In-cloud lightning partially illuminates Grand Canyon while the nearly-full Moon provides additional illumination.

Sunsets

And when there is no lightning and no rainbow, one can be content with the sunset.

A small rain shaft is illuminated by the setting sun.
A small rain shaft is illuminated by the setting sun.
Distant rain catches the last light of the sun and provides backlighting for the Cockscomb.
Distant rain catches the last light of the sun and provides backlighting for the Cockscomb.
A thin band of clouds partially blocks the sun and creates an array of crepuscular rays of light.
A thin band of clouds partially blocks the sun and creates an array of crepuscular rays of light.
The sun sets over ruins in Wupatki National Monument.
The sun sets over ruins in Wupatki National Monument.
The setting sun illuminates both Cathedral Rock and the clouds above.
The setting sun illuminates both Cathedral Rock and the clouds above.

Miscellaneous

Crepuscalar Rays—Wupatki National Monument.
Crepuscalar Rays—Wupatki National Monument.
Crepuscalar Rays—San Francisco Peaks.
Crepuscalar Rays—San Francisco Peaks.
Even thought it is supposed to be the wet and rainy season, we still managed to get cap clouds on the high peaks with stars above.
Even thought it is supposed to be the wet and rainy season, we still managed to get cap clouds on the high peaks with stars above.

Perhaps 2021 will be a normal monsoon year.

Lightning at 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.

This storm eventually produced lightning after sunset.
This storm eventually produced lightning after sunset.
Sunset and lightning north of Sedona.
Sunset and lightning north of Sedona.
Evening twilight colors and lightning.
Evening twilight colors and lightning.

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.

Thundersnow in Flagstaff

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.

Radar depiction of rain and snow moving across northern Arizona (2019_1028_2235).
24-hour lightning map.
GEFS plume forecast for Flagstaff.

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.

And now we return to our dry weather pattern.

The non-Monsoon of 2019

Beams of light from the setting sun illuminate the landscape near Sedona.

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.

The Museum Fire burns in the San Francisco Peaks near Flagstaff.
The Museum Fire burns in the San Francisco Peaks near Flagstaff.
A thunderstorm develops above the San Francisco Peaks as seen from the South Rim of Grand Canyon.
A thunderstorm develops above the San Francisco Peaks as seen from the South Rim of Grand Canyon.
Convection develops over the North Rim of Grand Canyon.
Convection develops over the North Rim of Grand Canyon.
Convection is reflected in the waters of Marshall Lake.
Convection is reflected in the waters of Marshall Lake.
A growing thunderstorm is reflected in Marshall Lake.
A growing thunderstorm is reflected in Marshall Lake.
The sun sets over Wupatki National Monument.
The sun sets over Wupatki National Monument.
Beams of light from the setting sun illuminate the landscape near Sedona.
Beams of light from the setting sun illuminate the landscape near Sedona.
Lightning strikes in the distance behind Upper Lake Mary.
Lightning strikes in the distance behind Upper Lake Mary.
Lightning on the North Rim of Grand Canyon.
Lightning on the North Rim of Grand Canyon.
Twilight lightning in Wupatki National Monument.
Twilight lightning in Wupatki National Monument.
Lightning strikes near the confluence of Grand Canyon and Little Colorado River.
Lightning strikes near the confluence of Grand Canyon and Little Colorado River.