Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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562 FXUS63 KUNR 252033 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 233 PM MDT Tue Jun 25 2024 .KEY MESSAGES... - Above average temperatures through midweek with isolated to scattered showers and thunderstorms through Wednesday, mostly during the afternoon into nighttime hours, a few storms likely strong to severe each day. - Better potential for severe storms later on Thursday as a cold front approaches the area. - Becoming cooler and drier for Friday into the weekend. && .DISCUSSION...(This Evening Through Tuesday) Issued at 233 PM MDT Tue Jun 25 2024 Current surface analysis shows cool front across the central plains into the Rockies, with low pressure along it across central WY. A surface trough extends east-northeast from the low into western SD. Upper level analysis shows near zonal flow across the Rockies and Plains, with developing high pressure over NM and west TX. Skies are clear to partly cloudy with temps mostly in the 80s and light northeast to east winds. Isolated to scattered showers and thunderstorms have developed early this afternoon along the surface boundary over northwest into north central SD. This activity is moving to the east-southeast toward the northern Black Hills and west central SD. Warm air will remain in place across the region, with above average temperatures expected to continue through the midweek period. Highs will reach the upper 70s to around 90 in most areas through Thursday. Many of the CAMS continue to show isolated to scattered storms moving/developing from mostly west central to south central SD for the rest of the afternoon into the evening hours. Steep low to mid level lapse rates are in place across these areas, helping to produce MLCAPE values of 500 to over 1500 j/kg. Shear is sufficient for isolated supercell development, especially east of the Black Hills to south central SD. Large hail would likely be the primary threat from any supercell storms, with stronger wind gusts more likely accompanying linear convection. A tornado cannot totally be ruled out either with any supercells toward south central SD later today. Activity should taper off and exit southeastern portions of the area by late evening. Frontal boundary remains southwest of the area on Wednesday, with winds turning to the southeast during the day. Increasing low level moisture will pool to the northeast of the frontal boundary across much of eastern WY into southwest SD and western NE. Upper high will strengthen over the Four Corners area, with ridge building north across the Rockies. Enough embedded energy within the trough will bring chances for showers and thunderstorms later Wed afternoon and evening from at least southern parts of northeast WY through southwest and south central SD. Threat for stronger storms looks to stay mostly south of the forecast area, but MUCAPE values up to 750 j/kg across far southern SD could lead to a few stronger storms late in the day, especially across far southwest SD. Strengthening low level jet over eastern portions of the CWA into central SD/NE Wed night will likely keep showers and storms going across areas northeast and east of the Black Hills into early Thursday, with some beneficial rains a good possibility. Upper ridge moves over and east of the area on Thursday as an upper trough moves from the Pacific NW into the northern Rockies. Low pressure will move across MT, with frontal boundary lifting northeast across the forecast area as a warm front. Chances for storms will increase mid to late afternoon as upper energy moves into the area ahead of the trough and MLCAPE values increase to 1000 to 2000 j/kg across much of the forecast area near and east of the warm front. Further west, a surface trough/dryline looks like it will move across northeast WY during the afternoon and into western SD by the evening, helping to aid in storm development as well. The better chances for severe storm development right now, a slight risk at near or above 15 percent, looks to be from far northeast WY to northwest SD, where better forcing aloft is expected. Chances drop off some to the south and southeast of these areas, but there is still some potential with uncertainty still existing on the track and timing of upper level and surface features. Trailing cold front should push through the area Thursday night and early Friday, with much cooler conditions and brisk winds for Friday. Highs look to mostly be in the upper 60s and 70s on Friday and Saturday. Upper low will pass north of the area on Friday, with some lingering chances for showers and isolated thunderstorms. Drier air in place should keep most or all of the area dry on Saturday. Passing shortwave ridge on Sunday will bring very warm conditions back for Sunday and early next week. Another upper trough likely passing north of the area Monday into Tuesday would bring chances for storms during that time, especially across northern portions of the forecast area. && .AVIATION...(For the 18Z TAFS Through 18Z Wednesday) Issued At 1028 AM MDT Tue Jun 25 2024 Isolated thunderstorms are expected to develop this afternoon, mainly over western SD. Severe storms are possible. Besides any brief MVFR conditions near storms, VFR conditions will continue through the TAF period. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...26 AVIATION...Pojorlie