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Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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258 FXUS65 KCYS 262342 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 542 PM MDT Fri Jul 26 2024 .KEY MESSAGES... - Scattered to numerous showers and thunderstorms are developing this afternoon and again Saturday afternoon/evening. Some storms may produce gusty winds and locally heavy rainfall. - Drier air aloft will move overhead for Sunday into midweek, limiting shower and thunderstorm chances and producing a warming and drying trend through Tuesday, then slightly cooler temperatures for Wednesday and Thursday. && .SHORT TERM /THROUGH SATURDAY NIGHT/... Issued at 300 PM MDT Fri Jul 26 2024 A plume of monsoon moisture moving through the area is giving parts of the area a temporary break in the hot and dry pattern for the next 36 hours or so. Satellite water vapor imagery shows the moisture plume centered over our area stretched out ahead of a longwave trough in western Canada. A weak shortwave is moving across the area this afternoon, providing a little extra lift to shower and thunderstorm activity. This shortwave trough axis is located more or less from Rawlins to Denver. Ahead of this, a weak stalled frontal boundary is positioned roughly from Cheyenne to Chadron, which is providing the focus for precipitation activity. This axis along the front is where we have the least CIN also at this time, whereas storms are struggling both to the northwest and southeast of this corridor. Convective parameters are fairly modest with MLCAPE around 250 J/kg and weak shear, though this is a little more appreciable across the northern portions of the forecast area. Expect additional rounds of showers and thunderstorms over the next several hours. While an isolated strong wind gust or small hail report is possible, this looks like mostly moderate to briefly heavy rainfall and occasional lightning today. Storm coverage should decrease with skies trending clearer behind the shortwave trough axis which should clear the area late this evening. A few HiRes models show some thunderstorms lingering behind this, so do have some low end PoPs continuing through the evening to account for this possibility. Heading into Saturday, we will see some mid to upper level drying behind today`s shortwave but PW values will remain above average for this time of year. However, instability and flow aloft will be on the increase tomorrow as a more vigorous shortwave approaches from the southwest. While parameters will be marginal for severe weather, it does look like a better chance than today for a few organized strong to severe storms. Strong winds will be the main challenge for storms tomorrow, as well as the continuing chance for locally heavy rainfall and lightning. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Issued at 300 PM MDT Fri Jul 26 2024 On Sunday, the last-gasp of a weak longwave trough over the northern Rockies will pivot through the northern high plains. This system and attendant vort max may be just close enough to our CWA to help initiate a few afternoon showers and thunderstorms, primarily in far east-central Wyoming and into the NE panhandle. A potent dry push of air behind this system will be rapidly transitioning eastward through the day. Model guidance is still mixed as to whether there will be enough surface moisture in place to generate any notable showers and thunderstorms on Sunday, as the fast and dry westerly flow just off the surface layer may be enough to eradicate any useful boundary layer moisture/instability by peak heating. Regardless, have increased PoPs just slightly on Sunday afternoon to account for the low but non-zero thunderstorm threat anywhere east of I-25 if enough surface moisture can remain in place. Beyond Sunday, zonal flow and weak ridging will develop over the central Rockies into the central high plains. This pattern will result in a long period of hot weather with highs 10-15 degrees above average likely for each day from Monday through next Friday. Light westerly flow will help enhance a slight downslope component, giving a boost to afternoon high temps east of the Rockies in what would normally be not as ideal a height-based setup for extreme heat. Ensemble guidance becomes a bit less confident by the middle and end of next week as several different iterations of a fresh plume of monsoonal moisture from the southwest approach southeast Wyoming. If this monsoonal moisture can make it this far north, temps may relax somewhat by late week. However, there are still quite a bit of ensemble solutions (over 40%) that favor a generally dry and hot pattern for most of next week and beyond. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 534 PM MDT Fri Jul 26 2024 Numerous showers and embedded thunderstorms are expected to move slowly out of the area this evening. The bulk of the showers and embedded thunderstorms will affect the BFF, AIA and CDR TAF sites, but this activity should come to an end by 06z. The remainder of the night, we cannot rule out a pop up shower due to a moisture laden air mass in place. Otherwise, some high clouds will be in place. Could even see a shower around RWL near daybreak. Meanwhile, another round of scattered showers and thunderstorms are expected to develop over the higher terrain of southeast Wyoming by 18Z Saturday, and push into the Nebraska panhandle by late in the afternoon or early evening. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...MN LONG TERM...MAC AVIATION...REC