Area Forecast Discussion
Issued by NWS Rapid City, SD
Issued by NWS Rapid City, SD
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156 FXUS63 KUNR 260436 AFDUNR Area Forecast Discussion For Western SD and Northeastern WY National Weather Service Rapid City SD 1036 PM MDT Thu Apr 25 2024 .KEY MESSAGES... - Fairly widespread rainfall at times from Friday through much of the weekend, especially the Black Hills and eastward. - Warmer and drier conditions move in for much of next week. && .DISCUSSION...(This Evening Through Thursday) Issued at 228 PM MDT Thu Apr 25 2024 Current surface analysis shows low pressure over far east central WY, with Pacific cold front stretching from far western ND to far eastern WY. Upper level analysis shows trough over the Great Basin to Four Corners region, with developing low pressure over northeast AZ. Skies are variably cloudy, with the most clouds over northeast WY and far western SD. KUDX radar shows scattered to numerous showers and thunderstorms from northeast WY to the Black Hills area and northwest SD as stronger energy aloft pushes through western portions of the CWA. Temps are mostly in the 60s and lower 70s, with some 50s over the Black Hills and rain cooled areas. Brisk southeasterly winds are gusting to over 35 mph across central SD, with lighter and more variable winds to the west. Active weather pattern taking shape for the next several days as a couple of upper level systems cross the region. Any severe weather potential will be confined to the next several hours, with the heaviest rain potential expected through Friday as the first upper low approaches and passes over the region. Most favorable CAPE this afternoon has been over and east of the Black Hills, ahead of the front, with values around 1000 j/kg. Shear is rather weak in many areas, so individual storms have been pulsy in nature and not very long-lived, producing smaller hail for the most part. Various CAMS show numerous storms continuing to develop through the afternoon along and ahead of the front, trying to consolidate into at least a broken line of storms along the front by late afternoon/early evening. Marginally severe hail and strong winds would be the main threats with stronger storms through at least late afternoon, with gusty winds perhaps a threat into the early evening over portions of the western SD plains if a more organized line of storms did develop. With precipitable water values up to 150 percent of average, heavy rain will accompany the stronger storms as well. Initial activity with the cold front should shift east of the forecast area toward midnight. Upper low moves into the central Plains later tonight and somewhere across central NE/eastern SD on Friday. Showers and some embedded thunderstorms will wrap north-northwestward into the forecast area late tonight and Friday, especially for the Black Hills area and eastward. There appears to be at least a slightly further south and east trend to the low track for Friday in the EC and now the latest GFS, which would shift the heavier rainfall potential a bit further east onto the western SD plains Friday. Right now, probabilities are 40 to 70 percent for an inch or more of rainfall Friday into Friday night for the northern Black Hills and much of the west central to south central SD plains. It will be breezy and cooler Friday, with highs in the 50s and lower 60s. Lingering areas of lighter rainfall can be expected Friday night into Saturday, especially for the Black Hills area. Even cooler air pushes in for the weekend, with highs only in the mid 40s to mid 50s, 40s over the Black Hills. As the first upper low weakens and departs the region, a second one develops over the central Rockies Saturday and moves northeast across nearly the same areas as the first one Saturday night and Sunday. This one looks to be somewhat quicker moving and its pcpn shield not quite as big. Best chances for more significant rainfall later Saturday night into Sunday will be across south central SD, with mostly light rainfall elsewhere. Not much, if any, thunder expected with the second system. There could be a little bit of snow across the higher Black Hills Saturday night into Sunday, but any accumulations look to be very minor. Breezy north to northeast winds will persist through the weekend. After this system exits the region Sunday night, near zonal flow is expected to develop early next week. Above average temps will quickly return to the area Monday and likely persist through the week. Another low pressure system is progged to develop over the northern Rockies and track north of the region Monday night and Tuesday. There will be chances for showers and a few thunderstorms late Monday into Tuesday, mainly across the Black Hills and northern portions of the CWA. A building ridge behind this system should bring mild and mainly dry conditions midweek, with the possibility of a cold front passage in the Friday timeframe. && .AVIATION...(For the 06Z TAFS Through 06Z Friday Night) Issued At 1033 PM MDT Thu Apr 25 2024 Widespread MVFR/local IFR conditions expected tonight with an expanding area of stratus on the SD plains. Showers and isolated thunderstorms will linger over south central SD through the night. Northerly winds will increase to 15-25 kts with gusts around 35 kts Friday morning with showers continuing on the SD plains, shifting to more isolated activity to the west. Mainly VFR conds expected over northeast WY. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...None. WY...None. && $$ DISCUSSION/KEY MESSAGES...26 AVIATION...JC