textproduct: Cheyenne

KEY MESSAGES

- Temperatures warm on today and Monday with increasing precipitation chances.

- Severe weather chances return on today, with Monday seeing a potential critical fire weather environment alongside high winds.

- Much cooler on Tuesday with temperatures a few degrees warmer through the end of next week and daily chances of showers and thunderstorms.

SHORT TERM /THROUGH TUESDAY/

Issued at 240 PM MDT Sun Sep 13 2026

Scattered thunderstorms are in store this afternoon through the overnight hours as another shortwave passes through our neck of the woods. Some strong to possibly severe thunderstorms could develop in the late afternoon as a surface low moves northeast through our forecast area. CAPE values look to be between 500 to 1,000 joules with couple potential pockets of 2,000 joules as depicted by the RAP between 3 to 7pm. The synoptic forcing of the surface low should sustain the showers and thunderstorms through the evening. However, in the morning we have a substantial cap to erode away in the morning and afternoon before any strong to severe thunderstorms could develop. It will be a little tough too since the forecasted convective temperature is in the mid 80's and the forecasted high temperature are either at or below the convective temperatures. Most of the area is still capped with the exception of Niobrara county according to the latest RAP mesoanalysis. Most of the hi-res models continue to show initiation around 20/21z with true scattered thunderstorm coverage by 00z. Synoptic winds will start to pick up this evening as the Upper level low moves into eastern Montana and Western North Dakota. A high wind watch and a Red flag Warning go into effect Monday afternoon as the pressure gradient tightens and the upper level low drags drier air across Southeast Wyoming. RH values are expected to drop into the teens as the 700mb flow starts to reach 50-55 knots by mid morning. Most likely winds will be westerly 20 knots gusting 45 knots but 53 knots or 60 mph wind gusts will be possible in our wind prone areas however, not quite sure how much of that jet will mix down hence why it was kept as a high wind watch. In-house random forest model guidance has kept its 30 to 40% chance for elevated to high winds at Arlington, Rawlins, Bordeaux, Coleman, and northern Carbon County. With these increased westerly downsloping winds on Monday, high temperatures were raised higher that what was being depicted by the global ensembles and the NBM. Elevated downsloping winds are going to warm us up rather quickly and may negate the effects of the colder airmass being pulled into the Intermountain West behind the cold front.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

Issued at 240 PM MDT Sun Sep 13 2026

Tuesday and into the weekend, the upper level low keeps migrating east into the Great Lakes and Hudson Bay region. The counter clockwise circulation will begin filtering cold air from the Arctic into the region undergoing some warming/modification as it pushes south over us. 700mb temperatures will drop between 8 and 12C translating daily surface temperatures into the cooler 60's and 70's and overnight temperatures into the 40's and 50's. Daily rainfall chances start to occur Wednesday as a train of Low pressure system system are expected to travel through the Pacific Northwest over the next 7 days. This precession of low pressure systems will push the ridge eastward into the central and southern plains leaving the intermountain west susceptible to multiple accompanied shortwaves but ahead and following each progged low pressure system.

AVIATION /18Z TAFS THROUGH 18Z MONDAY/

Issued at 240 PM MDT Sun Sep 13 2026

Scattered showers to possibly severe thunderstorms are expected to start really evolving after 21z and looks to start affecting terminals around 21z. These thunderstorms will start to decrease in intensity around 03z with only a couple waves of scattered showers around 06z. Some model guidance has the showers persisting overnight and continuing into tomorrow morning. The only terminals not really favored to be affected by the thunderstorms looks to be KRWL and KSNY. However, if the showers persist through the night then KSNY may see some rainfall tomorrow morning. Model guidance has also hinted at low stratus setting up across the Nebraska Panhandle tomorrow morning much like Alliance airport today. MVFR ceilings were currently kept into the TAF but IFR ceilings between 500 and 1,000 ft could be possible.

CYS WATCHES/WARNINGS/ADVISORIES

WY...Red Flag Warning from noon to 8 PM MDT Monday for WYZ417>423- 427-432-433. High Wind Watch from Monday morning through Monday afternoon for WYZ106-109-110. NE...None.