Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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297 FXUS63 KFSD 152323 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 623 PM CDT Sun Sep 15 2024 .KEY MESSAGES... - Temperatures remain above normal through at least the middle of this week. Nighttime lows show greater departures above normal (10- 15F) than daytime highs (5-10F) due to anomalously high low level moisture/dew points. - Greater chance for rain (40-70+%) returns mid-week, mainly focused west of I-29 Tuesday night to early Wednesday. Moderate (40- 50%) probability of rainfall exceeding 0.25", but low (10-30%) probability of exceeding 0.50". - Moderate chances (40-60%) for showers/storms late week, currently focused Thursday night-Saturday night, though exact timing and location details are still uncertain. && .DISCUSSION... Issued at 156 PM CDT Sun Sep 15 2024 Isolated showers and storms remain possible this afternoon with weak elevated instability and a shearing weak wave aloft. Latest trends are seeing the ACCAS dissipate, so the chances seem to be dwindling. South to southwest flow aloft remains in place through tonight, with the faster flow to the west. Will once again see a small chance for showers and thunderstorms in central SD tonight but severe weather looks unlikely. With a bit better mid level wave coming in later tonight into Monday the chances will linger mainly west of I-29 through the day Monday. Much above normal temperatures continue with lows in the mid and upper 60s and highs in the mid 80s. Monday late afternoon and evening a weak wave will drift north into central SD and should allow a few thunderstorms to develop. There is marginal instability and weak shear so if something can develop an isolated severe storm will be possible. More of the same on Tuesday and Tuesday night as the main faster upper level flow remains west of the area and just a few weak waves drift northeast which could interact with any weak elevated instability to produce isolated showers and storms, with a very low chance for severe weather. Highs on Tuesday will be in the 80s with lows Tuesday night into Wednesday in the 60s. Wednesday into Saturday the models are in fairly good agreement in deepening an upper level low over the central and northern Rockies and swinging it north northeast. This continues to leave the area in southwest flow aloft with periodic waves ejecting ahead of the main low. Still some questions marks with the main upper level support so far northwest. Still looks like periodic chances for showers and thunderstorms during this time, just a continuation of relatively low confidence on coverage and timing. Some larger differences begin to appear Sunday into Monday, with the GFS much more aggressive in swinging this stronger low to the north eastward, which will advect colder air into the region. The Canadian and ECMWF weaken this low and develop a new low across the Plains which would keep warmer air in place and better chances for rain and thunderstorms. No real confidence one direction or the other. && .AVIATION /00Z TAFS THROUGH 00Z TUESDAY/... Issued at 623 PM CDT Sun Sep 15 2024 VFR conditions are expected for the TAF period. Elevated southeasterly winds this evening will persist through the overnight hours with speeds up to 5-10 knots. Showers and thunderstorms have developed across the front range of the Rocky Mountains this evening. The storms will track northeastwards into the overnight hours. They could push into areas along and east of the Missouri River Valley but confidence is low (<30% chance) in this scenario occurring. Will continue to monitor trends. Otherwise, breezy southerly winds will return tomorrow with gusts up to 15-30 knots expected. The strongest gusts will occur west of I-29. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...Meyers