Area Forecast Discussion
Issued by NWS Rapid City, SD

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000 FXUS63 KUNR 202256 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 456 PM MDT Tue Apr 20 2021 .DISCUSSION...(This Evening Through Tuesday) Issued at 151 PM MDT Tue Apr 20 2021 Long-wave trough currently dominates much of the CONUS weather as small short-wave troughs move south across the northern high plains. Diurnally driven heating at the surface combined with a cold pool aloft was fostering scattered/numerous convective snow showers across much of the CWA. As heating wanes and the large- scale trough axis shifts southeast this evening, snow showers should come to an end, and northwest winds also should diminish. Models/ensembles agree very well on the large-scale evolution through much of the forecast period. Tomorrow and tomorrow night will feature rising heights with return southerly surface flow developing. Temperatures also will be moderating. A low over the Southwest U.S. will move to east-central WY by 12z Thursday, spreading some snow/rain showers toward south-central SD on Thursday where a low-level jet and WAA will focus ascent. On Thursday night and Friday, an elongated upper trough will approach the CWA, ushering in a frontal passage Thursday night. This will be followed by CAA and gusty northwest winds on Friday, along with scattered showers (mostly snow). Moisture, instability, and lift do not appear to be as substantial with this Friday system as with the current system, so expect less coverage and amounts overall. On Friday night and Saturday, the upper trough axis shifts east and a subtle upper ridge builds over the area. This should lead to temperatures getting back to near- (or even above) average for Saturday-Monday. Return southerly flow and a low-level jet with WAA may support some showers over south- central SD late Saturday night, but confidence is rather low at this point. Otherwise, better chances of more widespread precipitation (mostly rain, at this time) appear in order by late Monday and Tuesday as a large upper trough moves across the Southwest U.S. and deep southwest upper flow affects the CWA. Again, models/ensembles agree rather well on this evolution. && .AVIATION...(For the 00Z TAFS Through 00Z Wednesday Evening) Issued At 455 PM MDT Tue Apr 20 2021 Isolated/scattered SHSN will continue through early this evening with local MVFR/IFR CIGS/VSBYS at times. SHSN will taper off as skies clear overnight allowing VFR conditions to prevail by Wednesday morning. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION...Bunkers AVIATION...10 is the U.S. government's official web portal to all federal, state and local government web resources and services.