Area Forecast Discussion
Issued by NWS Rapid City, SD

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493 FXUS63 KUNR 201714 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1114 AM MDT Thu Jun 20 2024 .KEY MESSAGES... - Despite cool/cloudy/showery conditions today and Friday, there will be chances for thunderstorms, mainly across southern parts of the CWA - Significant precipitation will be possible over south central SD through Friday - Becoming hot and mostly dry this weekend into next week && .DISCUSSION...(Today Through Wednesday) Issued at 206 AM MDT Thu Jun 20 2024 The northern plains is beneath southwest flow, between an upper trough to the west and a ridge to the east. High pressure across the southeast is advecting plentiful moisture in from the Gulf of Mexico. Combined with some weak shortwave energy, this moisture advection is resulting in some showers and weak thunderstorms across central SD early this morning. A surface high sits to our northeast, and a surface low to our southwest, producing southeasterly winds of 10-20 kts across the CWA. Temps are falling into the 50s. Low and mid-level moisture will continue advecting into the region today. Upslope southeasterly winds will aid in the development of low clouds, drizzle, and patchy fog today, especially across the SD plains. Highs will be only in the 60s where the low clouds persist; however, far southern SD and especially northeastern WY will warm into the 70s. MUCAPE will increase across southern SD to 1500-2000 J/kg, with CIN weakening, as a series of weak shortwaves approaches this afternoon and evening. With 0-6 km shear around 40 kts, strong to severe storms will be possible. Another threat will be heavy rain across south central SD, the same area receiving rain this morning. PWATs are still predicted to be 150-200% of normal, and 1-2 inches of precipitation will be possible there with this evening`s storms alone. The 6-hr FFG is 2.5-3.5 inches, so not expecting any flooding issues, but it is worth watching. Tonight, expecting fog to expand across much of the CWA. Cool, moist airmass lingers over the region Friday, and temperatures will be only slightly warmer than today`s. Buoyancy will increase across the warmer areas of northeastern WY and southern SD again, and as a more potent wave approaches Friday afternoon, storms may initiate across northeastern WY. Shear will be sufficient for supercells; however, uncertain how far these storms will be able to progress across much of our CWA with a staunch cap in place - perhaps again they will stay mainly across southern SD. PWATs will be high again, and so heavy rain is expected...potentially over south central SD again. By 12Z Saturday, ensembles` total QPF 50th percentile have 2-2.5" for south central SD. Still thinking the soil/sand will be able to hold this moisture; however, if more precipitation than expected falls tonight, additional precipitation Friday night will be of more concern. The weather will begin to feel more like summer this weekend, as a ridge begins to build over the Rockies. Highs will warm back into the 80s Saturday, near 90 Sunday, and well into the 90s Monday. Hot weather will continue through the week, and conditions will be mostly dry, although cannot rule out an isolated thunderstorm each day. && .AVIATION...
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(For the 18Z TAFS Through 18Z Friday) Issued At 1113 AM MDT Thu Jun 20 2024 Widespread MVFR/local IFR ceilings across much of western South Dakota into portions of NE Wyoming will continue through this afternoon and evening. Local MVFR/IFR visibility in fog will persist around the Black Hills. Scattered showers and thunderstorms are expected today and tonight with local IFR visibility near any storms. Low ceilings will persist through the overnight hours, with some gradual improvement after 14-16z Friday.
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&& .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...Pojorlie AVIATION...SE