Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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219 FXUS63 KFSD 231126 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 626 AM CDT Thu May 23 2024 .KEY MESSAGES... - Breezy conditions as south winds increase for Thursday. Look for mid-afternoon gusts around 25-30 mph. Gusty winds continue for Friday as winds become northwesterly gusting to 30-35 mph. - Strong to severe storms are possible Thursday afternoon through the overnight. Risk level for severe storms is 2 of 5 from the James River Valley and west. Risk level 1 of 5 for areas to the east. The greatest threat with these storms is large hail and damaging wind gusts. - Periodic showers and thunderstorms for Memorial Day weekend. While we are not currently expecting strong storms, lightning is still possible. When thunder roars, go indoors! && .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 /12Z TAFS THROUGH 12Z FRIDAY/... Issued at 626 AM CDT Thu May 23 2024 VFR conditions expected for the first half of the period. Clouds will build in after noon as a low pressure system approaches from the west. Winds are southerly around 20 kts sustained, with gusts 25- 29 kts. Expect thunderstorms to develop from west to east beginning around 23.22Z. Some of these storms could be strong to severe with the greatest threats being hail up to 2 inches in diameter and damaging wind gusts up to 70 mph. These storms will impact KHON around 24.00Z and progress eastward impacting KFSD around 24.04Z and KSUX around 24.05Z. Storms will then move east into central Iowa. Behind this system, winds will become northwesterly and increase to around 20 kts by the end of the period. Gusts will be stronger at 27- 32 kts. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...AJP AVIATION...AJP