Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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629 FXUS63 KUNR 220349 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 949 PM MDT Fri Jun 21 2024 .KEY MESSAGES... - Storms this afternoon and evening. - The risk of flooding continues across south central SD, with more rain on the way - Becoming hot and mostly dry this weekend into next week && .DISCUSSION...(This Evening Through Friday) Issued at 103 PM MDT Fri Jun 21 2024 At the upper levels, there is high pressure across the southeastern CONUS and a trough over the west coast, the positioning of these two features are allowing moisture to advect into the northern plains. Shortwave energy moving through southwest flow is contributing to thunderstorms across the Dakotas. At the surface, a boundary extends through eastern Wyoming into Colorado, with a warm front extending from the Nebraska Panhandle into southeastern SD. Southern and western portions of the area are beginning to break-out of the low clouds/stratus, as temperatures are rising into these areas. This is already leading to thunderstorm development. For the rest of today and tonight, expect scattered showers and storms to develop as a more potent shortwave moves east northeast into the area. As the energy combines with the persistent easterly low-level winds and moisture, will see storm development. MUCAPE of 1000-2000 J/kg combined with 35-50kt shear, should be sufficient to promote supercell storm structures capable of hail and damaging winds. The strong cap should limit the severe potential across much the SD Plains. Nonetheless, another round of rain will move across the CWA tonight. PWs remain 150-200% of normal, and so heavy rain will again be possible. If additional precipitation falls over south central SD, mainly Tripp County, additional flooding is expected. HREF chance of >1" of precip falling over south central over the next 24 hours is 50-70%. Thus, will keep the Flood Watch going there. Considered expanding to Todd and Mellette, but latest CAMs are backing off on storm coverage later this evening and overnight. (Models are pushing the convective activity further east and south). Therefore, will leave Todd and Mellette out of the Flood Watch. Summertime weather is expected 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. Conditions will be mostly dry, although cannot rule out an isolated thunderstorm each day. && .AVIATION...(For the 06Z TAFS Through 06Z Saturday Night) Issued At 946 PM MDT Fri Jun 21 2024 Widespread MVFR/IFR ceilings along with local IFR visibilities will persist overnight on the SD plains, clearing from west to east around 15Z Saturday, with widespread VFR conditions after 18Z. Scattered showers/thunderstorms will also push east across western SD overnight, diminishing by sunrise. VFR conditions expected across northeast WY through the period. && .HYDROLOGY... Issued at 103 PM MDT Fri Jun 21 2024 Keeping flood watch going over Tripp County through tonight. PWs remain 150-200% of normal, and so heavy rain will again be possible. If additional precipitation falls over south central SD, mainly Tripp County, additional flooding is expected. HREF chance of >1" of precip falling over south central SD over the next 24 hours is 50-70%. Thus, will keep the Flood Watch going there. Considered expanding to Todd and Mellette, but latest CAMs are backing off on storm coverage later this evening and overnight as models are now pushing the convective activity further east and south). Therefore, will leave Todd and Mellette out of the Flood Watch. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Flood Watch until 7 AM CDT Saturday for SDZ049. WY...None. && $$ DISCUSSION/KEY MESSAGES...MLS AVIATION...Johnson HYDROLOGY...MLS