Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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303 FXUS65 KCYS 282133 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 333 PM MDT Fri Jun 28 2024 .KEY MESSAGES... - Active weather pattern ahead, with a cooling trend possible next week due to several passing cold fronts. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 159 PM MDT Fri Jun 28 2024 Radar continues to be quiet, only showing a few lonely blobs across the southern Nebraska panhandle. Hi-Res guidance continues to trend precipitation downwards, however, severe weather still cannot be ruled out with the RAP showing a bubble of 2000 J/kg of CAPE later this afternoon in Kimball and Cheyenne Counties. Being in the right entrance region of a 250 mb jet streak and and forcing from an incoming secondary cold front should provide the necessary lift, however, the better environment looks south of the Nebraska/Colorado border. If storms do develop, they should dissipate by this evening. Quiet weather is expected on Saturday as brief ridging passes over the Rockies. For the most part, this should keep storms at bay, however, a weak disturbance aloft could spark some convection along the high terrain. Temperatures behind the cold front will be about 10 degrees cooler compared to Friday, so mainly looking at highs in the mid 70s to low 80s. More severe weather is possible on Sunday as the ridge slides eastwards and a trough begins to enter western CONUS. Southwest flow aloft will usher in a plume of moisture east of the Laramie Range. Combined with more southerly surface flow into the panhandle, PWs will be over an inch, which is roughly the 90th percentile for this time of year. This will likely lead to heavy rain in storms Sunday afternoon. As mentioned, severe weather could be possible with a weak shortwave passing overhead. Currently, it appears more like a wind threat on Sunday with DCAPE values exceeding 1200 J/kg. Can`t rule out some large hail with MUCAPE values approaching 1500 J/kg. Hi-Res guidance shows wide scattered storms throughout the day, so we`ll have to monitor most of the CWA. && .LONG TERM /MONDAY THROUGH THURSDAY/... Issued at 315 PM MDT Fri Jun 28 2024 Medium range models in good agreement with the overall weather pattern through Wednesday, but then models diverge significantly late this week...including Independence Day. Starting on Monday, models indicate another Pacific upper level trough and associated cold front pushing southeast across Wyoming and western Nebraska late in the day after the brief warm up on Sunday. Another round of windy conditions are possible, especially west of I-25, as the cold front slides east across the area. Not expecting High Wind criteria (40+ mph sustained/58+ mph gusts) at this time, but a few recent events have overperformed, so will have to keep an eye on this one for mainly Monday morning through mid Monday afternoon. Thunderstorm probabilities actually look lower on Monday due to dry westerly winds and substantial mid to high cloud cover shown by most deterministic models and also the majority of ensembles as the cold front moves into the area. Kept POP between 15 to 25 percent for most areas with higher coverage/chances in the mountains and east central Wyoming/northern Nebraska Panhandle. Slightly cooler weather is expected for Tuesday and Wednesday as most models show northwest flow aloft and east to southeast winds at the surface. However, afternoon temperatures should still be seasonable for this time of the year with highs in upper 70s to middle 80s. Models and ensemble are hinting at a lower coverage of showers and thunderstorms across the area, even with the natural convergence zone along the Laramie Range. Further analysis indicates relatively low PWAT for this time of the year across southeast Wyoming with values around 0.40 to 0.60 inches. Granted, this is enough for thunderstorm initiation but strong to severe storms look unlikely at this time and limited to gusty outflow winds. Lower PWATs are likely due to the progressive west to northwest flow across the Pac NW and northern/central plains, with poor moisture transport from the Gulf of Mexico. Will continue to keep an eye on this since northwest flow in July can lead to some pretty big severe weather events, but without the moisture, kept POP below 25 percent for now. For later in the week, large ensemble spreads exist for both precipitation and especially temperatures. Deterministic models show a pretty strong upper level shortwave trough digging south into the northern high plains on Independence Day/Thursday. Models all show 700mb temperatures as low as 0c to 4c as the cold front pushes south into northern Wyoming Thursday morning. Will need to monitor this front due to the possibility of late night/early morning convection possible across the plains, and much cooler temperatures for July 4th celebrations. With significant timing differences and ensemble spreads, not very confident in either of these scenarios, so kept highs in the 80s with a mention of thunderstorms north of Interstate 80 for now. Further out, all long range models seem to come into better agreement after day 7...showing a strong 600dm upper level high forming over the western Great Basin Region. Hot temperatures are possible across the whole forecast area next weekend. && .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...SF LONG TERM...TJT AVIATION...TJT