Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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971 FXUS63 KFSD 212008 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 308 PM CDT Tue May 21 2024 .KEY MESSAGES... - The severe risk is quickly waning across the area, though there will be a narrow window through 4 pm that could result in the potential for large hail and gusty thunderstorm winds over portions of northwestern IA and southwestern MN. - Strong north to northwest winds will continue to develop through the afternoon and evening. Some potential for gusts to 40 to 50 mph through the I-29 corridor and then across Southwest Minnesota. - After a brief break from rain, additional thunderstorms are expected Thursday night through Friday. Isolated strong to severe thunderstorms are possible. && .DISCUSSION... Issued at 305 PM CDT Tue May 21 2024 Current SPC mesoanalysis indicates a surface low centered over far eastern NE and western IA as of late this afternoon. An area of showers and thunderstorms align with this low through northwest IA, with a stronger line of storms oriented from north to south along the extreme southeastern portions of our CWA in association with convergence along the surface low axis. Mesoanalysis indicates MUCAPE of 1000-2000 J/KG residing from parcels lifting from around 2- 3 kft AGL, with effective shear of 35 to 50 kts over that area. Although we have had no severe reports with this activity as of yet, these parameters would suggest a continued possibility of hail to the size of ping pong balls and thunderstorm wind gusts of up to 65 mph. In addition, with low LCLs and surface vorticity maximized along this line, cannot rule out a isolated tornado - though other better tornado parameters reside well east of our CWA. All that being said, this line of convection is expected to exit the area over the next hour or so as the surface low pushes off to the east - so the severe threat is expected to be short lived. On the back side of the low - where the tighter surface pressure gradient (SPG)resides - winds have been gusting around 40 mph through the mid afternoon. May see these winds pick up a notch more through the late afternoon/early evening as the low moves east and the tighter SPG slides over the area. In light of that, will keep the existing Wind Advisory going over portions of our area into late this evening. With the surface moving into eastern IA/eastern MN between 00Z-01Z, showers and thunderstorms will completely move out of our area by then. With cold air advection on the backside of the system, it will be a cooler night with lows in the mid to upper 40s. On Wednesday the surface low tracks from the Upper Mississippi Valley into south central Canada, leading to a dry day over our area. There will be enough of surface pressure gradient remaining that breezy easterly winds will persist through the northeastern portions of the CWA. Temperatures will be near normal - in the upper 60s to lower 70s. After the one quiet day on Wednesday, active weather returns to the area on Thursday as another surface low develops through the Central and Northern Plains while an upper level low tracks out of the Northern Rockies. This will bring our next chance of showers and thunderstorms, focused on Thursday night into early on Friday. Still some uncertainty regarding any severe potential for that period, though convective parameters would suggest at least some possibility - as evidenced by SPC Day 3 Marginal outlook for our area. Latest ensembles suggest around a 70% probability of receiving at least a quarter of an inch of rainfall with this system. The active pattern looks to continue into the beginning of next week, with shower/thunderstorms chances focused on Saturday night and Sunday night. Temperatures remain at or just above normal through the period. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1150 AM CDT Tue May 21 2024 Showers and thunderstorms, with MVFR/IFR ceilings, are expected to redevelop in coverage through the afternoon. Some of these storms may become severe, with large hail, strong erratic winds, and even an isolated tornado over northwestern IA. Storms are then expected to push off to the east between 22Z and 00Z. On the backside of the system, synoptic winds will gust at 40-50 mph through the evening, tapering downward through the early nighttime hours. Ceilings will lift tonight, with VFR conditions expected through the remainder of the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Wind Advisory until 10 PM CDT this evening for SDZ039-040-055- 056-062-067. MN...Wind Advisory until 10 PM CDT this evening for MNZ071-072-080- 081-089-090-097-098. Flood Watch until 7 PM CDT this evening for MNZ081-090. IA...Wind Advisory until 10 PM CDT this evening for IAZ001>003- 012>014. Flood Watch until 7 PM CDT this evening for IAZ003-013-014-021- 022-031-032. NE...Flood Watch until 7 PM CDT this evening for NEZ014. && $$ DISCUSSION...JM AVIATION...JM