textproduct: Cheyenne

KEY MESSAGES

- Numerous rain showers and widely scattered thunderstorms expected on Saturday. A few strong thunderstorms or an isolated severe storm possible.

- Mostly dry and warmer weather will prevail for Sunday through Wednesday, with thunderstorms possibly returning late in the week.

SHORT TERM /THROUGH MONDAY/

Issued at 255 AM MDT Sat May 9 2026

Current KCYS radar loop this morning shows scattered showers across the high plains stretching from the North Platte River Valley southward to the I-80 corridor. Brief rain showers have been reported at times, but most of the rainfall isn't reaching the ground. This activity is likely the result of some some midlevel WAA as a short wave ridge axis slides southeast across the region. This band of showers is forecast to continue moving southeast and out of the area by sunrise. Further north, models show the next potent upper level trough and associated cold front in western and central Montana. This will be our next concern as we head into Saturday afternoon.

Forecast for this weekend remains on track with only some minor tweaks to today's forecast. Models show the short-wave ridge axis quickly moving southeast of the area as the upper level trough across Montana digs south into Wyoming over the next 6 to 12 hours. This trough appears stronger compared to the previous system on Thursday with better forcing and a more defined cold front for early-mid May. All models, including short range high resolution guidance, show numerous rain showers and widely scattered thunderstorms developing first across east central Wyoming and the northern Nebraska Panhandle shortly after sunrise through noon today. This activity will gradually work its way south towards the North Platte River Valley and the I-80 corridor by mid to late afternoon, respectively. SPC has increased the areal coverage of the Marginal Risk of strong to severe thunderstorms to include all areas south and west of the North Platte River Valley this afternoon through this evening, including Laramie, Cheyenne, and clipping Scottsbluff and Sidney Nebraska. There is some good forcing with the mid level trough and associated cold front, with good low level convergence near the frontal boundary in addition to any outflow from storm formation further north. CAPE values and model soundings haven't changed much, showing 800 to 1200 j/kg of CAPE. Noting some pretty good low to midlevel lapse rates near the front, which should help hail potential if any cells get organized. The GFS and NAM do show between 35 to 40 knots of 0-6km bulk shear, so this scenario can't be ruled out. However, mediocre low level moisture and relatively cool temperatures should be the limiting factor in this event, especially with dry westerly flow at the onset of this event towards the I-80 corridor that most models are showing. For hazards, expect the main concern to be strong gusty winds, with straight hodographs initially. Hail will be a secondary concern mainly because freezing levels will be relatively low in addition to some storm organization near the cold front boundary due to backing winds aloft. The greatest potential should be south of a Douglas to Wheatland and Scottsbluff line, including most of the southern Nebraska Panhandle. Increased POP after 300 PM today with activity likely lingering after sunset across portions of western Nebraska.

For Sunday, all models show a drying trend as the fast moving upper level trough axis slides southeast into the southern plains. Early Sunday morning could be relatively cold with good radiational cooling behind the front. Will likely see some low temperatures below freezing in the upper 20s to near 30. Upper level ridge axis across the Great Basin region is forecast to nudge eastward into Wyoming and Colorado, resulting in a drier airmass and increasing temperatures at the surface and aloft. Sunday afternoon will be pleasant with highs in the middle 60s to low 70s for most of the area. As this ridge axis moves over and east of the region on Monday, expect high temperatures to be 15 to 20 degrees above average with highs in the upper 70s to upper 80s. Locations below 4500 feet may see highs around 90 degrees Monday afternoon.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Issued at 221 PM MDT Fri May 8 2026

Tuesday...Brisk northwest flow aloft continues, and dry conditions remain with scarce low and mid level moisture availability. Cooler temperatures in the post cold frontal sector as upslope north and northeast winds develop.

Wednesday...Another warming trend ensues as 700 mb temperatures reach 14 Celsius, yielding highs in the upper 70s to near 90 degrees. The dry northwest flow aloft prevails, and with warm mid level temperatures producing enough convective inhibition, also known as CIN, no showers or thunderstorms are anticipated.

Thursday...The ridge aloft moves further east over western Wyoming. Some pseudo like monsoonal moisture will affect Wyoming and Colorado, and there is a moderate likelihood that isolated to scattered afternoon and evening showers and thunderstorms will develop in a swath from Chadron to Cheyenne, across much of the forecast area. Model solutions have been changing, lowering confidence, so will keep it dry for now to blend in with our neighboring offices at Denver/Boulder, Grand Junction, Riverton, Rapid City and North Platte, though this day promises hope for some beneficial rainfall.

Friday...Negatively tilted and fast moving shortwave trough aloft progged to move across Wyoming, sending a Pacific origin cold front to a Lusk to Cheyenne line by late afternoon. This trough aloft will be moisture scant, thus only isolated showers and thunderstorms are anticipated.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 600 AM MDT Sat May 9 2026

Main Aviation concern today will be a potent upper level trough and associated cold front, which will dig south across the area late this morning through this afternoon. Showers and widely scattered thunderstorms are expected at most terminals this afternoon and possible lingering into late this evening for the high plains.

HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 12 to 18 hours. Showers and thunderstorms will develop after 17z with heavy rainfall, frequent lightning, hail, and strong gusty winds the primary concerns. Models have trended further south with the stronger thunderstorms with KCYS, KBFF, KSNY seeing the most favorable conditions. Timing for thunderstorms should be between 20z to 24z for the northern terminals (KBFF, KCDR), and between 22z and 02z (Sunday) further south near KSNY, KCYS, and KLAR. Another round of showers and thunderstorms possible after 05z due to outflow boundary interaction, but probabilities are lower than 30%. Otherwise, there is some indication that some low CIGS and stratus may form behind the front/outflow later this evening.

CYS WATCHES/WARNINGS/ADVISORIES

WY...None. NE...None.