FXUS65 KCYS 030923 AAD AFDCYS Area Forecast Discussion...UPDATED National Weather Service Cheyenne WY 323 AM MDT Sat May 3 2025 .KEY MESSAGES... - A pleasant Saturday expected across the region ahead of a cooler, more unsettled pattern for Sunday onwards. - Increasing chances for showers and thunderstorms Monday through Wednesday with some snow for our mountainous regions. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 208 AM MDT Sat May 3 2025 Clear skies and calm winds overnight tonight with only a few high clouds drifting just southeast of Cheyenne County. Temperatures are remaining fairly mild, despite the clear skies overhead. Most locations are in the 40s, with only a few sites in the low- to mid- 30s. Clear skies continue through the day. Temperatures on Saturday will warm nicely into the upper-60s to mid- 70s across the region under and upper-level ridge building over the Intermountain West. Subsidence from this ridge will lead to clear skies, light winds, and no precipitation chances across the region. During the day, the Omega Block will continue to built and strengthen across the central CONUS, propagating just far enough east to put the CWA under a favorable regime for precipitation starting Sunday onwards. Precipitation chances do not start ramping up until Sunday afternoon onwards, due to the influence of the upper- level ridge across the region. On Sunday, the upper-level Omega Block will move just far enough east to put the CWA downstream of the western upper-level low. As a result, southerly to southeasterly winds throughout the atmosphere will continuously advect in additional moisture from moisture-rich regions of the southern CONUS. Several 500mb vorticity maxima will eject out ahead of the western low, leading to the development of showers and potentially even some thunderstorms Sunday afternoon as daytime temperatures warm into the 60s and 70s once more. The eastern low of the Omega Block at 700mb will wobble westward throughout the day Sunday, leading to increased height gradients between the two lows and the ridge sandwiched between. As a result, a 700mb jet, around 40 to 45kts, develops across eastern portions of the CWA. Surface winds will ramp up due to the tightening height gradient at 700mb leading to a very windy day on Sunday for locations that usually remain out of high wind during the winter. Primary concern for these strong, southerly winds will be locations just downstream of the Pine Ridge across the northern Panhandle. Some decent downward omega values exist across the Pine Ridge in the northern Panhandle Sunday evening into early Monday morning. Forecast soundings from the NAM, RAP, and GFS also suggest inverted- V soundings with steep mid- and low-level lapse rates. This suggests that strong winds aloft are favored to mix down to the surface with the steep lapse rates present. Chadron could see some fairly strong gusts potentially approaching high wind criteria gusts due to both environmental winds and subtle downsloping from the Pine Ridge. Decided not to issue high wind headlines for this region as forecast gusts remain below criteria and the confidence is not there for high winds at Chadron, but it is definitely a possibility. Will let day crew take another look at the winds to determine if any headlines are necessary. && .LONG TERM /MONDAY THROUGH FRIDAY/... Issued at 208 AM MDT Sat May 3 2025 An active pattern is expected for the long term as a weak omega block pattern sets up over CONUS Monday through Wednesday. Upper- level lows located roughly over the Four Corners region and Midwest will stagnate over these areas for a few days with a ridge stuck between them. Placement of the further west low will allow sufficient moisture transport from the Gulf. In fact, NAEFS climatology shows IVT values in the 90th percentile and above for portions of the CWA on Monday. Because the low over the Four Corners is expected to sit over the same spot for a few days, continued moisture from the Gulf will lead to a prolonged period of wet weather for the beginning of the work week. Precipitation chances are expected Monday through Wednesday with widespread scattered showers likely during this time. Severe weather seems unlikely at this time as cooler, below average temperatures are expected with this low, leading to only a few hundred J/kg of CAPE each day and rather unimpressive lapse rates. Still cannot rule out gusty winds and hail in these storms, however, it seems like potential rainfall amounts will be the more impressive factor over these few days. Ensemble means from both the GFS and ECMWF are rather consistent, showing anywhere from 0.4 to 0.75 inches of rainfall over the three day period. These ensembles are actually higher around the Cheyenne area, showing about an inch of QPF, which would help with the below average precipitation amounts this year. Conditions look to dry out and warm up for the end of next week as the omega block breaks down and an upper-level ridge builds over the Rockies. Temperatures make a return to above average with highs in the 60s and 70s on both Thursday and Friday. Most locations will also see mostly sunny skies as subsidence under the ridge keeps clouds and precipitation at bay. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1004 PM MDT Fri May 2 2025 A ridge aloft will prevail through the period. Clear skies will continue. Winds will gust to 20 knots at Rawlins from 16Z to 00Z. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...AM LONG TERM...SF AVIATION...RUBIN