Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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894 FXUS65 KCYS 072356 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 556 PM MDT Fri Jun 7 2024 .KEY MESSAGES... - Warm weather will continue through late week, with widespread highs in the 80s and lower 90s Friday. - Threat for strong downburst winds this afternoon and evening from high based thunderstorm development. - 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. && .SHORT TERM /THROUGH SUNDAY/... Issued at 405 PM MDT Fri Jun 7 2024 Pretty nice weather this afternoon with temperatures in the mid 80s to mid 90s, hottest over western Nebraska. Current observations show the leading edge of the cold front across the northern Nebraska Panhandle and eastern Niobrara County at this hour, with winds shifting into the north and slightly cooler temperatures (95 at Scottsbluff compared to 84 at Chadron). This front will likely remain stationary through this afternoon as some afternoon convection continues to develop across the mountains and slide east-southeast over the area through this evening. Current KCYS radar loop shows a band of showers and thunderstorms near the leading edge of the cold front. This activity is expected to continue moving east while the line gradually propagates southward along the cold front this evening. High resolution models show additional development of thunderstorms along the I-80 corridor later this afternoon into this evening once the cold front moves into the central high plains. With high base thunderstorms and showers expected, gusty winds will be the primary concern...but can`t rule out some small hail as well. Environmental winds have already been pretty gusty this afternoon with some gusts between 40 to 50 MPH. Any additional thunderstorm outflow will likely result in gusts over 60+ MPH. May need to issue a Special Weather Statement later to cover these gusts, or handle them with individual SVR Tstorm warnings when necessary. For this weekend, models continue to show the upper level flow shifting into the northwest with east and southeast winds at this surface. The surface cold front will stall across the mountains Saturday afternoon and provide additional convergence/lift across the high plains. Increased POP Saturday with with numerous showers and scattered thunderstorms likely. Pretty good forcing with this event with event some moderate jet dynamics within the right entrance region of a departing weak jet streak aloft. Showers and thunderstorms are expected to develop over the mountains/near the frontal boundary and push southeast. Expect several rounds of convection to impact portions of I-80 and I-25 corridors with some decent (and much needed) rainfall amounts. Can`t rule out some strong thunderstorms but any signals for severe weather appear to be pretty marginal due to limited instability, poor lapse rates, and a cooler boundary layer. Moisture will definitely be in place with the NAEFS showing mean Precipitable Water in the 95th to 99th percentile for this time of the year over most of southeast Wyoming and western Nebraska Saturday afternoon. High temperatures on Saturday and Sunday will be tricky since any amount of limited sunshine this time of the year will rapidly warm the lower atmosphere. However, cloud cover, several chances for showers, and persistent upslope flow should keep max temperatures around 70 degrees for much of the day. However, any additional cloud cover, fog, or stronger upslope winds may result in highs struggling to warm up out of the low to mid 60s. The warmest location will likely be Carbon County and Rawlins with highs in the low 80s. Areas near the Carbon county/Albany county border, including Rawlins and Laramie, may have the best chance to see some strong to severe storms as they`ll be warmer with mostly sunny or partly sunny skies...resulting in more instability compared to areas further east. Sunday will be similar, but models are now showing a transitory shortwave ridge axis moving across the Front Range later in the day. Even lower confidence for Sunday`s temperature forecast with a wider spread in ensemble solutions. For now, kept temperatures close to Saturday as winds shift into the south. Also, added fog to the forecast late Saturday night/early Sunday due to persistent moist east to southeast winds. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Issued at 254 PM MDT Fri Jun 7 2024 Unsettled weather will continue into Monday for our area, but expect a warm and dry pattern to take hold for the middle part of next week. Shower and thunderstorm activity will continue well into the evening or overnight hours on Sunday, fueled by an approaching shortwave trough. This feature moving over top the flattened ridge will pass through the area Monday, and help kick off another round of showers and thunderstorms. Ensembles are in pretty good agreement that low level moisture will stay in place east of the Laramie range for Monday with southerly winds over the plains. The approaching shortwave trough will start to introduce a slight cooling aloft, around 500-mb, leading to slightly steeper lapse rates and instability. High altitude winds are not expected to be that strong, but veering winds should allow for sufficient shear to get a few strong to severe storms going across the area. It`s a little early to dig into specific hazards, but will need to continue monitor this possibility. As the upper level shortwave moves off to the east, the persistent ridge over the southwest will rebound across the area. This is not a very high amplitude ridge as an active jet stream will remain over the far northern US. Still, look for temperatures to return to above normal values over the High Plains as westerly flow pushes the dryline a little further east. Drier air will also work in from the west, reducing storm chances for Tuesday. A few showers and storms will still be possible, but expect this to be quite a bit less widespread than Friday through Monday. The ridge strengthens further for Wednesday and Thursday, pushing ensemble mean 700-mb temperatures to around +15 to +17C. There is some potential for a weak cold front to slide through Thursday and deliver slightly cooler temperatures, but other ensemble members actually peak the heat wave on Thursday. Regardless, expect above normal temperatures both Wednesday and Thursday. The probability of record heat is low, but certainly non zero, especially if the stronger ridge scenarios plays out. A few showers/storms will still be possible mainly over the higher terrain these days, but they should be very isolated. Shower and thunderstorm chances return to the area by the end of next week, as models are in pretty good agreement on a closed low that will be sitting off of southern California all week getting pulled back into the flow and across the Four Corners states around the Friday/Saturday time frame. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 555 PM MDT Fri Jun 7 2024 Showers and thunderstorms continue early this evening with gusty, erratic winds in the vicinity of storms for southeast WY terminals. Thunderstorm activity should calm down over the next few hours, but lingering showers will remain overnight. Moist northeasterly flow overnight into Saturday morning will give way to the potential for MVFR conditions with low ceilings. HREF guidance currently shows low, but non-zero probabilities of ceilings dropping below 3000 ft continuing through Saturday midday. && .HYDROLOGY... Issued at 254 PM MDT Fri Jun 7 2024 Above normal temperatures have resulted in accelerated mountain snowmelt across the Rocky Mountains this week. Temperatures in the Snowy and Sierra Madre Ranges are expected to remain elevated this weekend, even as a cold front stalls across the mountains. 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 today. 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 week due to some slightly cooler air. However, rainfall in and around the mountains may become an issue this weekend and could lead to rapid additional rises in creeks and rivers. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...TJT LONG TERM...MN AVIATION...MB HYDROLOGY...WFOCYS