Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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398 FXUS65 KCYS 090001 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 601 PM MDT Sat Jun 8 2024 .KEY MESSAGES... - Scattered to numerous showers and thunderstorms are expected over the next 24 to 36 hours. - Monday and Tuesday will see the greatest coverage of late day showers and thunderstorms, while Wednesday and Thursday will be warmer with a general decrease in shower and thunderstorm coverage. Showers and thunderstorms look to return again for Friday. && .SHORT TERM /THROUGH SUNDAY NIGHT/... Issued at 340 PM MDT Sat Jun 8 2024 Will keep short term discussion brief due to ongoing severe weather threat this afternoon. High resolution models performed pretty well today with severe weather reported in Laramie County, with even some flooding reported east of Cheyenne along with 2 inch diameter hail earlier this afternoon. Current KCYS radar loop shows most of this activity is further south into Colorado with another area of weaker thunderstorms around the southern Nebraska Panhandle. Another line of thunderstorms has developed across northern Carbon County and is currently moving southeast across region slowly. We`re not totally confident that the severe weather is over, so will keep the Severe Thunderstorm Watch going for Laramie, Kimball, and Cheyenne counties for now. However, believe the most organized convection is coming to a close over the next hour or two as these lines of storms move into less favorable thermodynamic environments. As we head into tonight, expect these thunderstorms to slowly become more isolated...but activity could linger through midnight along and east of Interstate 25 due to moist upslope flow and some elevated CAPE still present in the upper part of the boundary layer. Otherwise, expect showers and thunderstorms to come to an end tonight with low stratus and some patchy fog becoming the main concern overnight towards early Sunday morning. Added fog to the forecast for portions of far eastern Wyoming and western Nebraska. Considerable uncertainty exists for the thunderstorm forecast for Sunday as shortwave upper level ridge axis develops and translates eastward over the region by Sunday afternoon. High resolution guidance and the NAM showing hardly any thunderstorm activity for most of southeast Wyoming and western Nebraska. Believe this is partly due to lingering low clouds across the eastern plains and enhanced subsidence aloft associated with the ridge axis...even though CAPE values will likely range from 800 to 1500 j/kg. Synoptic models are a little more bullish with thunderstorm activity compared to high res modeling. Lowered POP a bit, but kept them between 20 to 40 percent for now. If current model trends continue, may need to lower POP/prob of thunder even more for Sunday. High temperatures today were a few degrees higher compared to previous forecasts, so increase high temperatures a few degrees on Sunday with a little more sunshine expected. Overnight lows should be near average for this time of the year and generally in the upper 40s to upper 50s. Thunderstorm forecast looks a little more promising on Monday as another weak upper level disturbance moves east across the area. && .LONG TERM /MONDAY THROUGH SATURDAY/... Issued at 356 PM MDT Sat Jun 8 2024 The unsettled weather pattern will come to an end on Tuesday as the ridge re-strengthens across the southwest CONUS. Drier air and modest subsidence will also work its way into the area as another warming trend begins. For Tuesday, look for temperatures just about 5F warmer than average with more sunshine than the preceding days. The ridge strengthens further on Wednesday, drawing 700-mb temperatures up to around +17C on the ensemble median over KCYS. Wednesday`s highs look to be about 10+F warmer than Tuesday`s, climbing into the upper 80s to 90s for much of the area along and east of I-25. Records don`t look very likely, but several locations will be within 5 degrees or so of daily record highs. Significantly drier air in the mid-levels will lead to limited convective chances, mainly to isolated showers/storms focused on the higher terrain. There is a little more uncertainty on Thursday. A weak shortwave riding over the top of the ridge may be able to get a cold front into our High Plains counties and knock down temperatures a touch. Other ensemble members keep this further north, which would result in a continuation or possible intensification of the hot temperatures. If the front manages to get further south, this would also allow for a little bit more afternoon convection with an increase in low-level moisture. The ridge axis shifts just east of our area by Friday. However, guidance is in pretty good agreement on the closed low that will be stuck off of the California coast all week finally getting picked up by the flow aloft. A fairly vigorous closed low will then move across the Four Corners states and into our area on Friday into Saturday. This will result in increased chances for precipitation and slightly cooler temperatures by Friday and Saturday. Details on rainfall and severe weather potential, if any, remain uncertain. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 542 PM MDT Sat Jun 8 2024 The main concern with this TAF issuance is the thunderstorm potential this evening followed by the dense fog potential overnight especially in KCYS and perhaps Sidney. Latest radar loop was showing scattered showers and thunderstorms continuing to develop west of the I-25 corridor. This cluster of showers and thunderstorms may impact KLAR and KCYS during the next couple of hours. For now, we have kept VCTS in both TAF sites and monitor before amending these TAF sites. The next concern is the low ceiling/fog potential later tonight. Rich dewpoints (50s) have stayed in place through much of the afternoon across KCYS, KBFF, KAIA and KSNY this afternoon. This combined with moist advection of south-southeast flow this evening and overnight will aid in low IFR/MVFR ceiling development tonight across many of these TAF sites. The best fog potential appears to be near KCYS where upslope flow will be in place late tonight. The HREF even keeps these low ceiling over the Cheyenne ridge most of the day tomorrow. The remainder of the TAF sites should see clearing skies by midday. && .HYDROLOGY... Issued at 254 PM MDT Sat Jun 7 2024 Above normal temperatures have resulted in accelerated mountain snowmelt across the Rocky Mountains. Temperatures in the Snowy and Sierra Madre Ranges are expected to remain elevated this weekend. Flood warnings for snowmelt continue for the Little Laramie River west of Laramie, and the Encampment River south of Saratoga, mainly due to minor flooding concerns. Emergency Managers have reported some flooding in these areas over the last 48 hours. Flood Watches continue for the upper North Platte River valley and Medicine Bow River near Elk Mountain for potential impacts this weekend. Current forecasts suggests river levels will peak later this weekend and remain elevated into early next wee. Will continue to monitor the potential for locally heavy rainfall due to thunderstorms in and around the mountains this weekend. However, the last round of thunderstorms generally produced less than a quarter inch of rain Saturday afternoon. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...TJT LONG TERM...RUBIN AVIATION...REC HYDROLOGY...WFOCYS