Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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073 FXUS63 KFSD 230809 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 309 AM CDT Thu May 23 2024 .KEY MESSAGES... - Breezy conditions prevail through the end of the work week, with increasing south winds Thursday, and west-northwest winds Friday, gusting to 30-35 mph. - Clusters of strong to severe thunderstorms are possible from late Thursday afternoon into early Friday morning. Level 2 of 5 risk for severe storms through the Missouri and James River Valleys, with a Level 1 of 5 risk to the northeast. Large hail and damaging wind gusts would be the primary threats. - Periods of unsettled conditions continue into early next week, though confidence in timing/location of favored precip chances is low. Higher confidence that temperatures will be on the cool side of normal for much of the Memorial Day holiday weekend, coldest on Friday. && .DISCUSSION... Issued at 308 AM CDT Thu May 23 2024 THURSDAY: Southerly winds will increase throughout the morning as a low pressure system approaches from the west, tightening the SPG. Look for sustained winds to peak around 15-20 mph with gusts 25-30 mph by mid-afternoon, highest through the James River Valley. Plentiful WAA will warm our highs into the upper 70s and 80s for today. Our southerly winds will also transport modest moisture northward, helping dewpoints to climb into the mid-upper 50s west of the James River Valley and low 50s east. These will support some moderate instability of around 1500-2000 J/kg MUCAPE over central South Dakota. Model soundings continue to indicate a capping inversion today, that will erode quickly once we reach peak afternoon heating. At the same time the cold front will be approaching from the west, forcing convection initiation. Strong vorticity from the top of the boundary layer through the mid-levels, coupled with 35-45 kts deep layer shear, is enough to support a few strong updrafts. This set of model runs also indicates similar steep mid-level lapse rates mentioned in the previous discussion which will support large hail up to 1.5-2 inches in diameter. Dry mid- levels at convection start and high DCAPE values around 1000 J/kg support strong down drafts, and so damaging wind gusts up to 70 mph are also possible. As the storms progress eastward, 700 mb steering winds are nearly parallel with the forcing, indicating quick upscale growth into a line. From here, the better instability is along and south of the Missouri River along the South Dakota and Nebraska border. This should focus the stronger storms along our southern counties for the evening/overnight hours. As the storms move into northwestern Iowa around 05-06Z, they look to become more elevated and hail will become the more dominant threat. However, at the same time the low level jet kicks into gear, which increases the chance that a few strong to severe gusts could make it to the ground. Storms should move east of the region by early Friday morning. FRIDAY AND BEYOND: Things dry out for Friday with breezy northwesterly winds gusting up to 30-35 mph. Strong CAA limits highs to the 60s. Saturday warms a little more into the upper 60s and low 70s. Meanwhile, another upper trough is digging south along the Pacific Northwest. Saturday night into Sunday there is another chance for showers and thunderstorms. Currently, we do not expect these storms to be strong, as the better dynamics are over southern Nebraska and Kansas. Light scattered showers continue for most of Memorial Day and highs remain on the cool side of normal, in the low 70s. An upper ridge begins to build in for Tuesday, finally allowing us to dry out and warm up a bit through the end of the week. Look for highs to warm from the mid 70s Tuesday into the upper 70s and mid 80s by Thursday. && .AVIATION /06Z TAFS THROUGH 06Z FRIDAY/... Issued at 1042 PM CDT Wed May 22 2024 VFR conditions begin the TAF period. Winds are currently beginning to turn southerly this evening and will remain southerly through the overnight hours with light speeds of only 5-10 knots. The low level jet (LLJ) remains on track to strengthen during the overnight hours, bringing low level wind shear (LLWS) to locations along and west of the James River. As such, have included LLWS in KHON`s TAF. Southerly winds strengthen tomorrow as mixing increases with gusts up to 20-30 knots expected. Latest hi-res guidance has convection developing across south central South Dakota tomorrow afternoon and moving into locations east river during the evening hours. Confidence has increased enough to to include mention of VCTS in KHKON`s TAF. Storms may reach KFSD and KSUX by the end of the TAF period but confidence is not high enough to include in their TAFs as of now. The storms will finish out the TAF period. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...AJP AVIATION...Meyers