Severe Weather Expected in Eastern Wyoming This Afternoon/Evening

May 20th, 2021
The SPC has expanded the Slight Risk zone for this afternoon, and it now includes Cheyenne and...
The SPC has expanded the Slight Risk zone for this afternoon, and it now includes Cheyenne and Wheatland along with Douglas. Casper is now included in the Marginal Risk zone along with Buffalo, Sheridan, Worland, and Thermopolis.(KGWN)
Updated: May. 20, 2021 at 12:11 PM CDT
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The warmest day of the week has arrived in Wyoming, and once again it is on a Thursday. Things are feeling rather pleasant outside as the afternoon hours draw upon us, but unfortunately given the setup in the upper levels of the atmosphere, the abundance of sunshine and warmth is not necessarily a good thing, especially in the eastern half of the state. The Storm Prediction Center has issued a Slight (Level 2) risk for severe weather in Eastern Wyoming and the Nebraska Panhandle for this afternoon, and the heating from the sun is only going to provide more instability and fuel for storms.

There are many ingredients in place for today’s severe weather potential, and it actually starts close to the east coast of the US. There is a powerful high pressure system at the surface currently hanging over the Carolinas, pushing the air around it in a clockwise motion. This air is being blown northwest from the Gulf of Mexico, and it is bringing some warmth and moisture into the middle of the country with it. Some of that moisture is indeed making its way into Wyoming, where we typically have a drier climate. Surface winds this afternoon in the eastern part of Wyoming and the Nebraska Panhandle are from the south-southeast and southeast respectively, so there is some influence from that high pressure even as far west as Wyoming.

Aloft the jet stream is taking a dip over the Pacific Northwest, similar to the end of last week, only this time it is dipping further south. This means the wind direction coming into the northwestern corner of the country is coming out of the northwest, meaning it is cold and dry. These two different air masses are meeting over the northwestern portion of Wyoming early, however as the dip in the jet stream slowly moves eastward, that collision of air masses is also making its way eastward with the cold front. Additionally, with the eastern side of the trough over Wyoming, wind direction aloft will be coming from the southwest and the south-southwest, bringing warm and dry air from Arizona with it. Luckily the south-southwest flow is more likely to be over the risk zone later this afternoon, which will limit the amount of direction change in the wind from the surface to the upper levels. This should limit the tornadic potential, however that potential is most certainly not zero.

The red arrows on the map represent the warm moist air being driven into the high plains by a...
The red arrows on the map represent the warm moist air being driven into the high plains by a high pressure system over the East Coast of the US. The black arrows represent warm, dry air being driven into Wyoming at the mid levels thanks to the trough coming in from the west. The blue arrows represent the cold, dry air being brought into Wyoming with the cold front ahead of the weekend, starting with the upper levels.(KGWN)

The primary threats for today are naturally strong wind gusts and hail, and these will likely be seen with storms in the northeastern corner of the state and Western Nebraska as they intensify. The window for storms looks to be between 1 and 8 PM, with the highest intensity likely between 4-7 PM. The cold front will drop temperatures a good bit for much of the state tomorrow, though for Southeastern Wyoming and the Panhandle that will not be felt until Saturday as temperatures remain warm for Friday afternoon in the region. Luckily, an abundance of cloud cover on Friday will limit the severe weather potential for that day. As of now it is only a Marginal (Level 1) risk for far East Wyoming and much of Nebraska and South Dakota. Places like Casper however will see drops from the low 80s into the upper 60s between today and tomorrow thanks to the cold front.

Storm activity is expected to be more widespread Friday and Saturday as the cold front finishes its march through the state, however as stated above cooler conditions will keep severe weather activity at bay. Powerful winds look to move in on Sunday as the trough sweeps through the state, initially coming from the south-southwest on Sunday and shifting to the southwest on Monday. Next week looks to have a good amount of sunshine to accompany the recent warmth, finally allowing for weather that will encourage us to get outside.

CHEYENNE, Wyo. (Wyoming News Now) -

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