Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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006 FXUS63 KUNR 280344 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 944 PM MDT Thu Jun 27 2024 .KEY MESSAGES... - Enhanced risk (level 3 of 5) for severe storms across much of western and south central SD this afternoon and evening as a cold front and upper level system approach the region. Slight risk (level 2 of 5) for severe storms across northeast WY. - Cooler, drier, and breezy Friday and Saturday. - Warming up for Sunday and early next week, with daily chances for showers and thunderstorms in many areas. && .UPDATE... Issued at 755 PM MDT Thu Jun 27 2024 Line of intense thunderstorms continues to track east across northwest SD and southwest ND, with a history of wind gusts at 60 to over 80 mph, with a 91 mph wind gust at K2WX. Some hail has also accompanied the more intense embedded cells. Elsewhere, gusty outflow winds from earlier convection in northeast WY are pushing southeast through portions of the Black Hills and southwest SD. Isolated strong to severe storms developed earlier across the Black Hills and areas to the east, but appears that the potential for additional stronger activity over southwest and south central SD is diminishing now as the sun goes down. Have just cancelled western portions of the watch and should be able to allow the rest of the watch to expire at 03z as the main line of storms over northwest SD moves into north central SD. && .DISCUSSION...(This Evening Through Thursday) Issued at 212 PM MDT Thu Jun 27 2024 Current surface analysis shows low pressure over southeastern MT, with warm front extending southeast across western SD into NE, a surface trough/dryline across far eastern WY, and a cold front trailing southwest from the low into north central and northwest WY. Upper level analysis shows trough moving over the northern Rockies, with low across southern AB. Very warm conditions are in place across much of the area this afternoon, mostly 80s and lower 90s. Southerly winds across the SD plains are bringing 60s dewpoints into the area, with 70s over south central SD. West to southwest winds are developing across northeast WY behind the dryline, bringing drier low level air into that area. KUDX radar showing showers and storms slowly developing across the Black Hills area and far northeast WY, near and a bit ahead of the dryline. Regional radars show more robust activity further northwest across central MT now with stronger energy tracking across the region. There remains good potential for an active late afternoon and early evening across at least portions of the forecast area as low pressure moves east-southeast into the area, along with the dryline and cold front. MLCAPE values are highest to the east of the Black Hills, especially from northwest to south central SD, where values of 1000 to around 2000 j/kg are noted. CIN is decreasing soonest across the Black Hills and northeast WY where storms have been developing. Better forcing aloft will be across eastern MT into ND and northern SD later this afternoon and evening, along with more favorable shear. This is where the best potential for robust storm development is expected, but good potential for at least isolated supercells and some organized development is still there to the south across far northeast WY and southwest/south central SD. Some of the latest CAMS suggest two areas/complexes of storm development. One moving across northwest SD with activity coming across eastern MT/western ND and another further south from the Black Hills to south central SD. Large hail and damaging wind gusts will be the biggest threats from severe storms, with wind likely becoming a bigger threat with time late today into the evening. A tornado or two is a possibility as well, especially across northwest SD and possibly further south/southeast toward south central SD with any discrete supercells. Activity should move quickly eastward, especially late today and this evening, helping to increase the wind threat. Severe threat should shift east of the area and diminish some by late evening as trailing cold front pushes through the area tonight. Cooler and breezy conditions will be in place Friday with temps back to near average levels, mostly mid 70s to lower 80s. Upper trough will pass across the northern Plains/south central Canada Friday and Friday night, with some chances for mostly afternoon and evening showers and thunderstorms. Buoyancy is expected to be minimal across most of the area, but MUCAPE values to near 500 j/kg are progged across portions of far southwest into south central SD, so a strong storm or two would be possible with any development in those areas. A secondary cold front will push through at least northern/eastern portions of the forecast area Friday night, with gusty winds possible north and east of the Black Hills. Saturday looks to be a dry and cool day behind the exiting system, with highs mostly in the mid 60s to mid 70s and decreasing winds. A few showers and storms could develop late Saturday night into Sunday morning across eastern areas as southerly low level jet develops to the east of the Black Hills. Ridge building in from the west should bring a quick warm up for northeast WY and most of western SD on Sunday. Highs will range from the upper 70s over south central SD to the 90s over northeast WY. As ridge shifts east late Sunday and Sunday night, developing southwesterly flow aloft will bring increases in shower and thunderstorm chances for later Sunday and at least the first part of next week. Northern stream trough will move across the Rockies and into the northern Plains Monday into Tuesday. At this time, there looks to be potential for strong to severe storms across at least portions of the area later on Sunday and again on Monday. Looking ahead to the Independence Day holiday period, near zonal flow aloft would bring near to slightly above average temperatures, with the potential for at least isolated thunderstorms at times with any disturbances that pass through the region. && .AVIATION...(For the 06Z TAFS Through 06Z Friday Night) Issued At 942 PM MDT Thu Jun 27 2024 Mainly VFR conditions are expected through at least 18Z Friday. However, strong northwest winds on the SD plains overnight will gradually diminish. Isolated thunderstorms are possible Friday afternoon and evening with brief MVFR conditions possible. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ UPDATE...26 DISCUSSION/KEY MESSAGES...26 AVIATION...Johnson