Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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222 FXUS63 KFSD 222323 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 623 PM CDT Wed May 22 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 254 PM CDT Wed May 22 2024 TONIGHT: Surface ridge from eastern Nebraska to central South Dakota this afternoon will move across the forecast area tonight. Lingering gusty west-northwest winds and diurnal cumulus will diminish this evening, with winds turning southerly late tonight/early Thursday. Warm advection with the southerly flow should result in increasing mid-level clouds, and cannot rule out a few sprinkles across our northwest counties late tonight, though deep sub-cloud dry layer should limit potential for measurable precipitation. THURSDAY-THURSDAY NIGHT: Much of Thursday will be dry, with the day dominated by increasing southerly flow and mild temperatures ahead of an approaching cold front. Gusts 30-35 mph will be common by late morning and through the afternoon, as temperatures climb into the mid 70s to around 80. The southerly flow will draw increasing low level moisture northward, with a narrow ribbon of mid-upper 50s dew points into our western counties ahead of the front. This will help support a tongue of stronger instability west of the James River by late afternoon with MUCAPE values 1500-2500 J/kg. Forecast soundings show a pretty stout capping inversion above 850mb through 20Z, but this cap weakens through 22Z-23Z, allowing for rapid development of storms along the cold front by late afternoon/early evening across our far western counties. Moderate deep layer shear of 30-40kt along/ahead of the front should support some organized storms, with steep mid level lapse rates yielding a threat of large hail up to golf ball size, while initially dry mid levels and DCAPE values above 1000-1500 J/kg supporting a potential for damaging wind gusts to 70 mph with initial development. As the evening progresses, more favorable instability and DCAPE become focused along/south of the Missouri River Valley (SD/NE state line), which should likewise focus the greater threat for severe storms through the southern portions of our forecast area from mid- evening into the early overnight hours. Storms may be increasingly elevated the night progresses which may result in hail becoming the dominant threat. However, the dry mid-levels persist, and with an increasing low level jet at/above 2kft AGL, could still see some isolated strong to severe gusts punch through the stable boundary layer as well. Storms projected to push east of the forecast area by 08Z-09Z, though could see some lingering light showers into early Friday morning. FRIDAY-SATURDAY: A trailing wave rotating around the main mid-upper level low may produce some lingering light showers or an isolated storm into the day Friday, but otherwise looking at a brief stretch of dry but cooler weather as we head into the weekend. Coldest temps aloft swing through during the day Friday, which should keep highs in the 60s at best, combined with brisk west-northwest winds gusting as high as 30-35 mph. Slight warming builds in for Saturday, though temperatures look to remain on the cool side of normal with highs in the upper 60s-lower 70s for the start of the Memorial Day weekend. SUNDAY-MEMORIAL DAY: Cooler than normal temperatures persist across the area as we head through the latter half of the holiday weekend. A stronger trough looks to dig into the region Saturday night-Sunday with another wave diving across the region in the northwest flow. These systems could produce scattered showers and perhaps a few storms, but instability and shear are both on the weaker side, so not looking at a severe risk at this point. TUESDAY-WEDNESDAY: Mid-upper level ridging builds in behind the departing weekend system, bringing dry weather and warming temperatures through the middle of the week. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 623 PM CDT Wed May 22 2024 VFR conditions are expected for the TAF period. Light to marginally breezy southwesterly flow begins the TAF period along with a CU field across the area. The CU field will dissipate as mixing ceases this evening. Winds will also weaken and turn southerly for the overnight hours. The low level jet (LLJ) will strengthen tonight and create low level wind shear (LLWS) along and west of the James River tonight, including at KHON. There is also a chance of sprinkles tonight around KHON but have omitted from KHON`s TAF as confidence is too low in sprinkles reaching the surface. Southerly winds become breezy tomorrow with gusts up to 20-30 knots expected. These conditions will finish out the remainder of the TAF period. The other aspect to tomorrow is the chance for showers and thunderstorms towards the end of the TAF period. Storm development is likely across central and south central South Dakota but the exact time of initiation is a bit uncertain at the moment. As such, have left any mention of showers and storms out of all TAFs but will be monitoring this potential. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...Meyers