Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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020 FXUS63 KFSD 291733 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1233 PM CDT Wed May 29 2024 .KEY MESSAGES... - Dry, breezy, and mostly sunny today. Multiple chances for showers and thunderstorms starting late tonight and continuing into next week. - An isolated strong to severe storm is possible on Thursday into Thursday night. A few storms this weekend may become strong to severe. Locally heavy rainfall is possible. - Near normal temperatures prevail with periodic breezy conditions into early next week. && .DISCUSSION... Issued at 350 AM CDT Wed May 29 2024 TODAY: High pressure overhead is leading to a pleasant morning with calm to light winds, temperatures in the upper 40s to lower 50s, and clear skies. Can`t rule out some patchy fog toward daybreak, but should be short lived. Surface high pressure slides to the east through today, with mid level ridging following suit. WAA increases as the next wave/trough begins to approach from the west. South to southeasterly winds also increase as the high pressure slides off to the east and the surface pressure gradient tightens. West of the James River, sustained winds could reach 20 mph with gusts 30 to 35 mph. Elsewhere, expect winds to be around 10-15 mph and gusts around 20-25 mph. Highs climb into the 70s. Mostly sunny skies prevail. TONIGHT THROUGH FRIDAY NIGHT: Trough slides east this evening and tonight. Ahead of this, WAA continues across our area which with the leading forcing from the initial short wave, should provide enough forcing for showers and thunderstorms to develop in western SD and move east through the overnight hours. Most of the 29.00z guidance shows the wave and precipitation splitting our forecast area - with one area of precipitation tracking along/north of Hwy 14 and the other skirting well south of the MO River. Another round of showers and storms looks to develop near the cold front during the later morning and early afternoon. Some of the deterministic models (namely the NAM and the RAP) show instability increasing to near 2000 J/kg of CAPE; however, confidence is fairly low that we`ll be able to recover that much instability given the potential for morning showers and storms with the main push of WAA. This is also true given that ensembles show a < 40% chance of 1000 J/kg of CAPE by tomorrow evening. If the atmosphere can recover that much, can`t rule out an isolated strong to severe storm during the early afternoon through the evening hours, but think that with mid level lapse rates around 5.5 deg C/km, 0-6km bulk shear around 20 kts, and freezing levels around 12kft, severe risk looks very low. Slightly more concerned with the potential for locally heavy rainfall than this time yesterday, as guidance is increasing with PWATs and QPF over the area, now showing widespread values near 1.5". Ensembles show a very low chance (< 15%) of seeing this much rain in 24 hours. Flash flood risk is still low, with 1 hour guidance for most areas west of I-29 over 1.5" but can`t rule out some ponding and localized rises on smaller tributaries. Lows tonight in the 50s. Highs in the lower to mid 70s. Showers and storms slowly push off to the east - slowly - through the day on Friday, with continued redevelopment ahead of the surface cold/stationary front, with another short wave passing off to the south and the trough axis off to the north. Showers and isolated storms will linger for most of the day, especially along and east of I-29. Total rainfall amounts through the end of the week of widespread 0.5" (> 60% chance), and about a 30% chance of exceeding an inch or more, mainly south of I-90. Current QPF is near the 50th percentile of guidance. Again, think that flash flood risk is low through Friday, but will have to keep an eye on trends especially if heavier rain falls Thursday/Thursday night. SATURDAY THROUGH TUESDAY: Upper level trough slides across the International Border through the first part of the weekend, with quasi-zonal flow Saturday. Models diverge in handling the next wave Saturday night into Sunday, with a more defined/agreed upon wave tracking through a portion of the northern Plains late Sunday into early Monday. This will keep shower and storm chances in place through the early part of the week. Again, locally heavy rain is possible with ensemble probs of at least an inch of PWAT over 80% (and low chances of over 1.5"). Any flash flooding potential would be dependent on where the heavier precip sets up earlier in the week. Strong to severe storms are possible over the weekend as instability and moisture increases. Ensemble guidance shows a high likelihood (> 80%) of more than 1000 J/kg of CAPE, and moderate to high chances (> 60%) of over 2000 J/kg. Shear also is on the increase, along with steepening mid level lapse rate. Other ensemble and machine learning continues to support at least a 5-15% chance of severe weather over the area. There remains some uncertainty though given the variance in models, but those with outdoor plans this weekend should keep an eye on the forecast. Temperatures will be near to above normal into early next week. Expect breezy conditions to prevail as well. && .AVIATION /18Z TAFS THROUGH 18Z THURSDAY/... Issued at 1233 PM CDT Wed May 29 2024 VFR conditions are expected to prevail through the evening and much of the overnight period. S/SE winds will also remain fairly breezy during this time, with gusts between 20 to 35 MPH - the strongest along and west of the James River. Cloud cover increases this evening ahead of our next system, with showers and storms possible near/shortly after midnight. Expect coverage to become more widespread after daybreak. MVFR cigs will be likely, with brief reductions in vsbys also possible under any strong storm. Have opted to exclude mention of thunder for the time being though, as confidence in exact location still remains low. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...SG AVIATION...SST