Area Forecast Discussion
Issued by NWS Cheyenne, WY
Issued by NWS Cheyenne, WY
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399 FXUS65 KCYS 292143 AFDCYS Area Forecast Discussion National Weather Service Cheyenne WY 343 PM MDT Wed May 29 2024 .KEY MESSAGES... - Strong to severe thunderstorms mainly along and east of I-25 into the Nebraska Panhandle Wednesday afternoon with large hail and strong winds. - Active weather pattern will continue through the weekend with daily chances for showers and thunderstorms. - Summertime temperatures will be on the horizon next week. && .SHORT TERM /THROUGH THURSDAY NIGHT/... Issued at 131 PM MDT Wed May 29 2024 Latest radar loop was showing the cluster of showers and thunderstorms continuing to develop along and east of the I-25 corridor. The storms so far have been producing small hail and some gusty winds over 50mph. This cluster of showers and storms should continue their trend with moving east-northeast at 20 to 30 mph through the remainder of the afternoon. The one interesting thing we have noticed this afternoon is that dewpoints have been dropping into the 40s across much of the Nebraska panhandle this afternoon which is quite a bit lower than what some of the hi resolution models have been projecting this afternoon. Meanwhile, the effective shear is closer to 30kts. These factors may limit the large hail potential this afternoon to sizes mainly to quarter to half dollar with the bigger threat becoming strong winds of 50 to 60 mph. The bulk of these storms should move out the forecast area by 8pm or so, but cannot rule out a few showers or an isolated storm or two developing behind this cluster during the evening and overnight in response to the shortwave moving through Wyoming. Thursday afternoon should be a much quieter day with regards to convection. We are looking at much drier air, but still cannot rule out a few isolated thunderstorms developing along the higher terrain. However, things may become more active over the Nebraska panhandle Thursday evening into Thursday night as the isentropic lift and low level jet kicks in and surges good moisture advection into that region. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Issued at 131 PM MDT Wed May 29 2024 The pattern of mild to warm temperatures and near daily chances for thunderstorms will continue through the weekend, but a warming and drying trend is expected for the first part of next week. On Friday, a broad trough will be located to our north, and another piece of 500-mb vorticity will rotate through the area. As a result, Friday looks like the coolest day of the forecast period across the area with a sharp north to south gradient in 700-mb temperatures across the area from about 2 to 3C near US20 to 6 to 8C along I-80. Meanwhile, a surface high sliding down the east side of the Rockies Thursday night will push the dryline back west against the Laramie range and return low-level southerly to southeasterly flow over much of the High Plains. With some subtle added lift from the passing vorticity maximum, look for another round of thunderstorms to develop. While storms may just be isolated to widely scattered, they may have a slightly greater potential to become strong to severe on the Wyoming side. Veering wind profiles and more low-level moisture will be present. Forecast soundings show higher instability and sufficient wind shear over southeast Wyoming. However, a potent inversion around 700-mb will be stronger further north and east, which will limit the severe potential in the northern/eastern portions of the forecast area. The upper level trough quickly skirts to the east into the weekend, with a more quasi-zonal flow pattern setting up after this. The axis of a subtle ridge moves through the area on Saturday with another weak vort-max on its leading edge. Expect temperatures to climb back above normal as 700-mb temperatures return to around +10C. The dryline position is expected to be a little further east on Saturday compared to Friday, but its too early to say exactly where this will set up. While the vort-max aloft should help kick off scattered showers and thunderstorms, this will mainly be a virga and wind threat west of the dryline. However, once these storms reach a more moisture rich environment with southerly low-level flow, strong to severe convection could be on the table once again. There is still uncertainty regarding whether this will occur in our forecast area or to the east. Sunday looks similar, just a touch warmer and a touch drier as the ensemble mean dryline position edges further to the east. Thunderstorm activity should be a little bit more limited with drier air working into the area, but we`ll have to watch the exact dryline position as areas to the east of this will once again have a greater strong to severe storm potential. Right now, it looks like this area will be to our north/east, but it`s very close. Low level westerly downslope winds should support enhanced warming over the high plains, with highs expected in the mid 80s. Some of our hotter spots (Torrington/Scottsbluff, etc.) will also have a chance at the first 90F day of the year. Probabilities for a high over 90F are around 60% for Scottsbluff, 50% for Chadron, and 40% for Sidney at this time. While 700-mb temperatures may drop briefly behind a weak shortwave Sunday night into early Monday, they should rebound quickly. Ensemble mean values over KCYS climb tack to +15C by 00z Monday. Look at another warm to hot day. Temperatures aloft, around 500-mb, will warm faster than the low levels as the more potent upper-level ridge tries to work in across the area. The warmth aloft will limit instability and thunderstorm potential on Monday, and possibly into Tuesday as well. Almost all ensemble members keep most of the area dry on Monday, and most continue this through Tuesday and Wednesday. There is good consensus around another upper level shortwave pushing across the northern Rockies in the Tuesday/Wednesday timeframe, but the chance for precipitation with this is fairly low. However, this introduces some uncertainty in temperatures, with a more southerly track leading to a stronger shot of cool air, and a more northerly track leading to the hot temperatures continuing. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1147 AM MDT Wed May 29 2024 Latest satellite loop was showing some cumulus developing over the I-80 corridor between Cheyenne and Rawlins. This looks to be the breeding ground for our showers and thunderstorms early this afternoon. This cluster of showers and thunderstorms should push east through the course of the afternoon and become more linear and stronger as they approach the Nebraska panhandle. The bulk of these storms are expected to move east-northeast around 15 to 20kts, but any stronger storms may deviate to the east-southeast and slow down a bit. The majority of the storms should affect the Nebraska panhandle between 22z-01z with some of these storms possibly becoming severe especially in the southern panhandle. A frontal boundary is expected to push through the Wyoming TAF sites after midnight and the Nebraska panhandle Thursday morning and possibly bring some lower MVFR ceilings. Later shifts will need to keep an eye on that potential. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...None. NE...None. && $$ SHORT TERM...REC LONG TERM...GCC AVIATION...REC