Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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310 FXUS65 KCYS 281750 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 1140 AM MDT Fri Jun 28 2024 .KEY MESSAGES... - Strong to severe thunderstorms are expected this afternoon as a cold front sweeps across the CWA. At this time, the best chance for convection appears to be in the southern Nebraska panhandle. - Active week ahead, with a cooling trend possible throughout the week due to several passing upper-level troughs. && .SHORT TERM /THROUGH SUNDAY/... Issued at 247 AM MDT Fri Jun 28 2024 Cold front analyzed across the northern CWA from Alliance to Wheatland to Casper to a low near Riverton this morning. South of the front...seeing dewpoints in the 50s across the southern Panhandle with 40s north. Looks like a couple of cold fronts impacting the weather today. The first moves through this morning...turning winds northerly for a time. A secondary cold front associated with the colder air moves through around 00Z. Given what happened yesterday...thunderstorms are in question today. HRRR and RAP simulated radar only showing isolated to widely scattered convection this afternoon mainly from Sidney to Cheyenne. Best instability looks to be south in Colorado today and this is where the HRRR/RAP simulated radar is showing most of the convection. MUCAPE in the southern Panhandle up near 1000 J/KG. SPC has a SLight Risk area highlighted for the southern Panhandle. Not too sure of that happening. Did decrease PoPs for this afternoon from the previous forecast. With that secondary front moving through early evening...700mb temperatures fall from +13 to +14C currently down to +5 to +6C by Saturday morning. Expecting to see 40s for lows Saturday morning with afternoon highs in the 70s and low 80s. Mainly dry Saturday except for our western mountains. Maybe better chances for storms Sunday as we get low level moisture advected north into the Panhandle with a low level south to southeasterly jet of 30-35kts. Much warmer as well Sunday as the upper ridge builds back over the area. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Issued at 247 AM MDT Fri Jun 28 2024 An active week is expected for southeast Wyoming and western Nebraska with daily chances for afternoon showers and thunderstorms. Sunday night into Monday, an upper-level ridge will slowly push to the east as an upper-level trough digs into the western CONUS. Southwest flow aloft develops early Monday morning with several vorticity maxima ejecting out ahead of the incoming trough. 700mb temperatures will remain in the 14-16C range, leading to high temperatures on Monday in the mid-80s to mid-90s area wide, with slightly warmer temperatures across Converse and Niobrara counties. As the upper-level trough pushes closer to the region, 700mb heights will begin to tighten, leading to gusty winds across much of the region west of the Laramie Range. High winds are not likely, but breezy conditions will be present throughout the day. Precipitation chances will ingress in the afternoon as surface heating along with passing vorticity maxima promote convective development. A fairly typical summertime pattern for the region. On Tuesday, the upper-level trough pushes through the region as a secondary trough develops off to the west. This trough will foster improved chances for convection across the region and dropping 700mb temperatures back into the upper-single digits. This departing trough and cooler 700mb temperatures will lead to a slightly cooler day on Tuesday, with highs int he upper-70s to mid-80s area wide, rather than widespread 80s and 90s once more. Precipitation chances will increase for the afternoon, before dropping back off later in the evening. Similarly for Wednesday, the upper-level trough will keep 700mb temperatures in the 8-10C range with surface temperatures slightly warmer across the region in the low-80s to low-90s once more. Precipitation chances are expected again in the afternoon, with isolated showers and thunderstorms possible. Significant model differences are noted for the late-week. Previous model cycles suggested a strong ridge overhead, leading to a very warm 4th of July holiday. However, long range models are now suggesting troughing over the central CONUS, leading to cooler temperatures and increased precipitation chances. The GFS is much cooler than the ECMWF at this time, with the GFS dropping 700mb temperatures into the 3-5C range by Friday morning, while the ECMWF has 700mb temperatures in the 6-8C range. With the disagreement between the models, but the general consensus on cooler temperatures, decreased high temperatures on Thursday a few degrees to highlight the cooling trend. The GFS suggests a cold front moving through the region, whereas the ECMWF keeps it further to the northeast over South Dakota. Therefore, the GFS is wetter for the 4th of July holiday than the ECMWF. Overall, it will still be a warm day out there, but likely a few degrees cooler than previous days with colder overnight lows expected at this time. Does not look to be like the 4th of July last year when it rained all day and temperatures struggled to reach the 60F mark! && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1140 AM MDT Fri Jun 28 2024 A stationary front near the Laramie Range/I-25 corridor this morning will lift northeast as a warm front this afternoon, while a strong cold front, for this time of the year, will move southeast across the area tonight. This frontal system may aid in shower and thunderstorm develop late this afternoon through early this evening, but coverage appears limited to western Nebraska at this time. HAZARDS/WEATHER TRENDS: VFR conditions will prevail over the next 24 hours. Kept VCTS in the western Nebraska TAFs due to the relatively low coverage of thunderstorms and limited confidence this afternoon. Surface winds are forecast to shift into the north late this afternoon and tonight as the cold front moves through, with breezy conditions possible after 03z. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...GCC LONG TERM...AM AVIATION...TJT