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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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787 FXUS63 KFSD 151942 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 242 PM CDT Mon Jul 15 2024 .KEY MESSAGES... - Small threat for isolated severe storms late this afternoon in mainly northwest IA. - Another small threat for isolated severe storms on Tuesday, the better chances in south central SD. - Temperatures will be about 5-10 degrees below normal through the weekend. - Next better chance for showers and thunderstorms after Tuesday will be Friday and Friday night. && .DISCUSSION... Issued at 241 PM CDT Mon Jul 15 2024 Currently looking like a very small window for any severe convection. Areas near and south of a Sioux City to Storm Lake line could see a quick updraft develop from about 5-7 pm. Model soundings are suggesting that capping may be tough to overcome, but if it can be about 2500 J/kg CAPE and deep shear of 30-40 knots would support the potential for large hail and damaging winds, with the wind threat potentially more concerning. A few hi res models are hinting that an isolated updraft could develop in southwest MN during this time along the cold front but model soundings suggest that capping will hold. The freezing level is at about 13000 feet AGL which can limit the hail potential but there is a decent dry sub cloud layer at and below about 700 mb which may support some stronger straight line winds and microburst potential. The right entrance region and a weak wave will swing through on Tuesday which will bring another chance for showers and thunderstorms. Current expectations are for upwards of 1000 J/kg CAPE and about 30 knots of deep shear, with the better chances for this environment in south central SD. So the overall threat for severe storms is low, but an isolated severe storm around Gregory county will be possible. Otherwise temperatures and humidity will be much lower with highs from the upper 70s to lower 80s and dew points more into the upper 50s to mid 60s. Tuesday night into Thursday cooler air spills into the area as weak northerly flow aloft develops. This is in response to a slow moving trough of low pressure across the Great Lakes and upper level ridging developing in the southwest United States. This should bring mostly dry conditions with lows in the 50s and highs in the 70s. The next piece of energy of potential interest will come on Friday. With the potential strength of the warm advection and with weak to moderate instability suspect at least isolated severe storms will be possible. Once this system moves through models diverge a bit, but the overall trend is to take this energy and slowly drift it southward. This should take the better chances for showers and thunderstorms with it, but will also reinforce the cooler air leaving temperatures 5- 120 degrees below normal. Saturday and Sunday will see isolated chances but confidence is low right now. && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1218 PM CDT Mon Jul 15 2024 Isolated very light showers will spread from west to east through the afternoon. An isolated stronger thunderstorm will be possible in parts of northeast NE and northwest IA from about 22z through 0z, but confidence is low. Scattered showers and isolated thunderstorms will be possible mainly west of I-29 from about 12z-18z Tuesday. Away from any showers or thunderstorms VFR conditions are expected. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...08