Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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371 FXUS65 KCYS 181736 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1136 AM MDT Sat May 18 2024 .KEY MESSAGES... - Warm & breezy conditions are expected again for today. Overall chances for showers are low, but an isolated storm cluster may develop during the late afternoon and/or early evening along and southeast of a line from Cheyenne to Alliance. - The risk for showers and thunderstorms is expected to increase from Sunday afternoon through Monday as significant upper- level troughing deepens and digs into the 4 corners region. - Widespread rain and high-elevation snow may be possible as early as Monday afternoon, courtesy of lee cyclogenesis over southeast Colorado with a sub-1000-mb surface low tracking to the northeast across Kansas and Nebraska. && .SHORT TERM /THROUGH MONDAY/... Issued at 427 AM MDT Sat May 18 2024 A warm & breezy start to the weekend across southeast WY and the western NE Panhandle as fast, quasi-zonal flow aloft persists in association with an active northern stream jet. Despite the cold frontal passage last evening, 700-mb temperatures should rebound nicely this AM with the majority of models suggesting +6 to +8 C over much of the area by 18-21z today. Most areas should see day time highs in the 70s F. Greater precipitation chances should be confined to the S and E across Colorado and central Nebraska for today as weak short wave energy traverses the southern stream in the next 12-18 hours, but there will be a chance for a couple of showers or weak thunderstorms during the late afternoon into the early evening, particularly to the southeast of a line from KCYS to KAIA. A transition to a more unsettled weather pattern should commence for Sunday and Monday as a stronger mid and upper-level trough deepens over the Pacific NW, ending the persistent split- flow pattern. As the trough deepens and digs into the 4 Corners, lee cyclogenesis should occur by mid-day Monday w/ potential for a more widespread wrap-around precipitation episode taking shape by late in the period with the sfc low lifting into the southern and central plains. As such, expect increasing daily chances for showers and thunderstorms across much of the area for Sunday and Monday. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... Issued at 427 AM MDT Sat May 18 2024 No major changes for the long term forecast. An progressive pattern will continue with daily chances for precipitation across the region. On Tuesday, the upper-level trough associated with the cold front on Monday will push through the region. A reinforcing shot of cold air will funnel in behind the front, leading to much cooler temperatures for Tuesday. Highs will be in the upper-40s to mid-50s area wide. With the cooler temperatures and 700mb temperatures below 0C, snow showers cannot be ruled out across southeast Wyoming. As the trough rotates out of the region throughout the day Tuesday, brief zonal flow followed by a low amplitude ridge will move overhead for Wednesday, leading to a quick warm up in temperatures with highs in the upper-50s to upper-60s. Some energy will remain overhead at 500mb cyclonic vorticity advection remains across the region. Therefore, isolated to scattered showers are expected once more. Long range model agreement falls apart on Thursday, as the GFS suggests a potent trough digging across the region while the ECMWF favors a low amplitude trough that remains well north of the region. Given the disagreement between models, kept PoPs in the 15-30% range for much of the CWA, as some isolated precipitation may be likely with the energy aloft. The trough in the GFS is progged to move out of the region for Friday and Saturday, but disagreement still remains between the models. Long range models suggest a longwave trough developing over the western CONUS, but timing, strength, and evolution are very different between models at this time. Kept low- end PoPs in the forecast as some precipitation may be possible with the energy aloft. Temperatures Friday and Saturday will be in the mid-60s to mid-70s across the region. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1134 AM MDT Sat May 18 2024 VFR conditions expected through the forecast period. Mainly quiet this afternoon with some breezy conditions in Wyoming. A few isolated thunderstorms may develop between about 23z and 03z, mainly in the southern NE panhandle. A low level jet is expected to bring gusty southerly winds at times to NE panhandle terminals overnight and into Sunday morning. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...CLH LONG TERM...AM AVIATION...MN