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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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617 FXUS63 KFSD 290804 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 304 AM CDT Sat Jun 29 2024 .KEY MESSAGES... - Rivers across the area have crested or are presently at crest. Should see levels continue to slowly trend downward this weekend, with largely dry conditions expected to prevail. - Below normal temperatures continue today into Monday, with the coolest temperatures Saturday through Monday. - Stronger westerly flow aloft develops Monday through the end of the week which should bring a bit busier pattern next week. - Monday and especially Monday night will be the next better chance for severe weather and heavy rain. Higher confidence in showers and storms (60-80%) with decent chances for more than an inch of rain in northwest IA (20-40%). Definitely a time frame to keep an eye on. && .DISCUSSION... Issued at 302 AM CDT Sat Jun 29 2024 Drier and cooler air surges into the region this morning bringing marginally breezy conditions and temperatures well below normal, about 10-15 degrees below normal. Highs will generally be in the upper 60s to lower 70s. While any meaningful rainfall is not expected, some very weak instability at the top of the mixed layer could produce an isolated sprinkle or very light shower late this morning into the afternoon. With high pressure settling in at the surface this afternoon and evening, winds will drop off quickly and bring a pleasant, but cool evening. This will lead to some chilly temperatures on Sunday morning. Lows should be in the mid 40s to lower 50s. High pressure slowly shifts east of the area on Sunday, allowing for a bit warmer temperatures to return. This should lead to highs more in the lower to mid 70s as well as a breezy southerly wind west of I- 29. Moisture below about 700 mb is pretty scarce so at least on Sunday and Sunday night will need to look at the EML and with fairly steep lapse rates some ACCAS showers and thunderstorms will be possible. The challenge appears to be whether or not we can get some moisture into the 800-700 mb layer to help bust through the mid level capping. With an increasing upper level jet and a weak mid level wave some mid level moisture should aid in producing some convective activity. More than likely this activity will be sub- severe as instability and shear are not quite there. The better chance for ACCAS showers and thunderstorms will be Sunday night as the moisture begins to increase a bit. Monday will be the next chance for severe storms, with the better chance coming Monday night. The challenge may be a decent mid level wave moving through the area during the day on Monday which will likely suppress any deeper instability into Nebraska. As is the case in most events the Nam appears to be overdoing the instability, but both the Nam and GFS agree that any activity should be elevated, likely about 850mb. It looks like the 925 mb to surface instability will remain to the south. So, with decent shear and instability an isolated stronger updraft or elevated supercell could produce golf ball sized hail and wind gusts to 60 mph. Right now confidence is fairly low on this activity. One thing to watch out for will be heavy rain, especially across parts of northwest IA where both the GEFS and EC ensemble point towards the higher chances. This matches up to closely to some fairly strong forcing within the LLJ, so this will need to be monitored closely because of the recent flooding. Lingering showers and thunderstorms will be possible on Tuesday but for now the severe threat looks low. Tuesday night into Wednesday looks dry and seasonally warm with lows 55 to 65 and highs in the upper 70s to mid 80s. Thursday into Friday has a fairly well agreed upon system that moves through and will likely keep temperatures below normal. With Thursday being the 4th of July will need to keep an eye on trends as any shower and Thunderstorm activity may alter some plans. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1055 PM CDT Fri Jun 28 2024 VFR conditions with relatively light northwest to north winds are expected through the overnight hours. After daybreak, most likely after 12Z-13Z, a secondary cool front drops south, followed by areas of stratus which could bring a period of MVFR ceilings to areas near/north of I-90 Saturday morning. This most likely to impact KHON, but could also brush KFSD before the stratus lifts above 3kft AGL. Gusty north-northwest winds will also accompany this stratus, with frequent gusts 20-25kt expected through sunset Saturday evening. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...JH