Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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889 FXUS63 KFSD 210928 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD Issued by National Weather Service Lincoln IL 428 AM CDT Fri Jun 21 2024 .KEY MESSAGES... - Another round of heavy rain is likely tonight with the development of another MCS. Probabilities of over 2 inches of rain are around 60-80%, focused generally south of a Sioux Falls to Jackson MN line and north of US-18. - The Flood Watch has been expanded southward a bit in Iowa to include Plymouth, Cherokee and Buena Vista Counties. - Extensive river flooding will develop over the next day or two, with best chances of reaching major flood stage on parts of the James, Vermillion and Big Sioux Rivers. && .DISCUSSION... Issued at 425 AM CDT Fri Jun 21 2024 Through Saturday: Expansive MCS that produced widespread 3 to 6 inch rains across the heart of the forecast area has shifted eastward early this morning, with the heaviest rain in northwest Iowa as of 4 am. However, numerous flash flood warnings continue along the I-90 corridor and in the row of counties south of there. Latest surface map shows the stationary front draped across northern Nebraska to about the US-18 corridor in northwest Iowa. High-res models continue to show convection redeveloping near it through the afternoon, then another MCS firing later this afternoon and moving through the forecast area this evening. Precipitable water values remain highly anomalous into tonight for the area (around 1.9 inches, near record territory for this time of year per Aberdeen/Huron sounding climatology). As one might imagine, flash flood guidance is extremely low in the areas that have been pounded overnight, but is around 1.5 inches a little further south toward Sioux City. The Flood Watch has been expanded a bit further to include Plymouth, Cherokee and Buena Vista Counties in Iowa. Probabilities of seeing another 2 inches of rain are high (60-80%), though the exact alignment is a bit uncertain given the ongoing activity. NBM guidance would favor more of an area near and north of I-90, while the HREF begins to shift it more near and south of the MN/IA border. Much of the rain should be out of the forecast area by midday Saturday, though lingering into the afternoon east of I-29. Sunday through Thursday: A couple welcome days to dry out are expected to start the new week, as upper level ridging slides across the Plains. Once we get to Monday night and Tuesday, global models are in agreement with a strong upper low moving across the Lake Winnipeg region, drawing more of a northwest flow into the Dakotas. The associated surface cold front moves through Monday night and Tuesday morning, though the general trend suggests the heaviest rain amounts more to the north and northeast of the forecast area. Temperatures are expected to peak on Monday in the lower 90s, but drop off by mid week to the upper 70s near the Buffalo Ridge and mid 80s along the Missouri River. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1117 PM CDT Thu Jun 20 2024 Showers and thunderstorms - some with heavy rain - will expand eastward overnight, with the focus from south central SD and along and north of the Interstate 90 corridor. The activity may diminish on Friday morning, before showers and thunderstorms develop once again along and north of Interstate 90 in the afternoon and evening. Some of these storms could be severe, with heavy rain likely. Visibility and ceilings will be in the MVFR/IFR range with any shower and thunderstorm activity. Other than in thunderstorms, east to southeast winds will be relatively light through the TAF period. && .HYDROLOGY... Issued at 425 AM CDT Fri Jun 21 2024 MRMS rainfall estimates since about mid afternoon Thursday show a substantial area of 3 to 4 inches of rain across the heart of the forecast area, with upwards of 6 inches across Turner and Lincoln Counties in SD and and Lyon County IA. With this amount of water and another slug of hefty rain amounts expected tonight, moderate to major flooding is likely to develop over the next couple days along parts of the James, Vermillion, and Big Sioux Rivers. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...Flood Watch through Saturday morning for SDZ038>040-050- 052>071. MN...Flood Watch through Saturday morning for MNZ071-072-080-081- 089-090-097-098. IA...Flood Watch through Saturday morning for IAZ001>003-012>014- 020>022. NE...None. && $$ DISCUSSION...Geelhart AVIATION...JM HYDROLOGY...Geelhart