Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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991 FXUS63 KFSD 221728 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1228 PM CDT Wed May 22 2024 .KEY MESSAGES... - Breezy west-northwest winds today with gusts up 20-30 mph, strongest over southwest MN. - Winds become southerly and strong for Thursday afternoon with gusts around 30 mph. Strongest winds expected along the James River Valley. - There is increasing potential for strong to severe thunderstorms late Thursday afternoon into early Friday. Greatest threat with these storms will be large hail and damaging wind gusts. - An active pattern continues through the weekend and into next week with multiple chances for showers and thunderstorms. && .DISCUSSION... Issued at 311 AM CDT Wed May 22 2024 WEDNESDAY: Westerly flow aloft today as the low pressure system that brought thunderstorms yesterday continues to move off to the north into Canada. Clouds will also flow out as the morning continues. At the surface, west-northwesterly winds remain on the breezy side around 10-15 mph. Gusts will be around 15-20 mph, with the highest gusts remaining east of I-29. Winds will become light as they turn southerly overnight. A push of strong CAA early in the day will limit our highs in the upper 60s to low 70s with lows in the 50s. THURSDAY-FRIDAY: Mostly sunny skies and southerly winds bring a push of WAA that will help Thursday warm into the upper 70s and 80s, which is about 5 or so degrees warmer than normal for this time of year. Winds will increase after sunrise due to an approaching low pressure out of Wyoming tightening the SPG. Winds should peak around 20-25 mph with gusts up to around 30 mph. Strongest winds look to be along the James River Valley in the mid-afternoon. Thursday night into Friday morning brings the next chance for thunderstorms. 1500- 2500 J/kg of MUCAPE collocated with an elevated mixed layer indicates the potential for convection. 0-6km bulk shear in the 40 kt range, with SRH in the 150 m2/s2 in the 0-1 km layer, and around 200 m2/s2 in the 0-3 km layer indicate the potential for initial updraft rotation. Steep lapse rates around 8 C/km in both the low levels and in the mid-levels indicate air parcels will accelerate quickly once triggered. If convection initiates over central South Dakota, where the forcing is mostly perpendicular, cells will be initially surface based and discrete. Gradually growing upscale into a line and becoming elevated as they move east. If they initiate over eastern South Dakota, forcing is a little more muddled and instability is more elevated, indicating elevated convection in more of a line/MCS. Current CAMS favor the more central South Dakota initiation scenario, and hold the strongest convection along and south of I-90. With all of this in mind, I feel that the current SPC day two outlook with a Slight risk (level 2 of 5) over central South Dakota to be in good shape. The greatest threats with these storms will be large hail (1.25-1.75 inches) and damaging wind gusts. There remains some uncertainty in track, with the GFS and ECMWF taking the low northeast faster than the Canadian which brings it directly through southeastern South Dakota. Storms should be clear of the area by Friday afternoon. Highs will be cooler thanks to the CAA behind the storm system, reaching the low to mid 60s. Lows will be in the 40s. SATURDAY AND BEYOND: An active pattern continues through the weekend and into next week. Saturday night into Sunday there is another low pressure system ejecting out of Colorado that brings chances for thunderstorms. Monday a low tracks out of Montana and Wyoming. Highs will be around normal in the upper 60s to low 70s. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1221 PM CDT Wed May 22 2024 VFR conditions are expected through the period, with isolated 4-6kft AGL cumulus through sunset. West-northwest winds gusting 20-25kt across mainly southwest MN this afternoon will become light/variable, and eventually south overnight. The southerly winds increase Thursday morning as a low level jet begins to mix to the surface. Gusts 25-30kt are likely along/west of I-29 by the end of this period, with further increases after 18Z. Aforementioned low level jet may result in non-convective low level wind shear late tonight-early Thursday, mainly west of the I-29 corridor, though low confidence in timing/extent precludes mentioning in the TAF at this time. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...AJP AVIATION...JH