Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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014 FXUS63 KUNR 020018 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 618 PM MDT Mon Jul 1 2024 .KEY MESSAGES... -Severe storms this afternoon and evening -Daily chances for showers and thunderstorms -Temperatures near average Wednesday, and slightly below average the rest of the week -Warmer and drier this weekend && .DISCUSSION...(This Evening Through Monday) Issued at 129 PM MDT Mon Jul 1 2024 Upper level analysis has a trough over the Intermountain West with a ridge over the Central Great Plains, resulting in southwest flow over the forecast area. Water vapor imagery has a shortwave over southern Wyoming that is moving into the area. At the surface, there is a surface low over Lake Oahe and a secondary low near Casper. A cold front connects to two surface lows, with the front oriented along the Cheyenne River. Temperatures are currently in the 80s ahead of the front, with 70s behind the front. Dewpoints are in the 60s. For this afternoon, shortwave energy will interact with the boundary and daytime heating to initiate storms. Strong forcing should allow storms to grow upscale into isolated supercells and convective line segments, supporting large hail and damaging winds given bulk shear of 35-45 kts. CAPE will be somewhat limited in western SD, but dynamic forcing should make up for the lack of CAPE. Deeper moisture and better CAPE will reside over central SD where storms will likely intensify as they shift east in the late afternoon. Further west across Wyoming, plenty of shear will be in place for very isolated supercells, but given conditional nature of convection and limited CAPE, any severe threat will be isolated. Storms move through pretty quick this evening and expect they would be out of the area by 02Z. The surface front will move south of the forecast area tonight, but another impulse could support shower development along and north of the front, across the southwest third of the area. Daytime heating on Tuesday combined with the unstable environment, could lead to some showers or storms during the afternoon. Temperatures will be cooler though, with highs slightly below average in the low 70s to low 80s. On Wednesday, the upper flow starts our more more zonal, but the main upper trough starts to dig over Montana and Wyoming ejecting an impulse across the forecast area in the afternoon. Return flow at the surface with moisture pooling ahead of the wave will increase chances for strong to severe storms given sufficient shear profiles. The upper trough will linger over the area on Thursday the 4th, with cool conditions and chances for showers with a cold pool aloft. CAPE will be limited, hence not expecting any severe weather. Things will then dry out into the weekend with warmer temperatures. && .AVIATION...(For the 00Z TAFS Through 00Z Tuesday Evening) Issued At 616 PM MDT Mon Jul 1 2024 Isolated thunderstorms are possible tonight through Tuesday. Outside of thunderstorms, VFR conditions will prevail through the forecast period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...MLS AVIATION...13