


Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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847 FXUS63 KFSD 140339 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1039 PM CDT Sun Jul 13 2025 .KEY MESSAGES... - Heat and humidity continue for Monday and Tuesday, with increasing storm chances on Tuesday and Tuesday night. With that comes a chance for severe storms along with heavy rainfall. - Cooler temperatures expected for mid to late week, with periodic low precipitation chances continuing through next weekend. && .DISCUSSION... Issued at 238 PM CDT Sun Jul 13 2025 Surface trough and its associated boundary have pushed into the area this afternoon, currently sitting west of the James River. A weak shortwave trough at 700 mb is just west of the boundary and looks to develop convection along it during the later half of the afternoon. CAPE values on the order of about 1,500 J/kg is present along with deep layer shear values up to 30-40 knots. With only minimum forcing in place from the previously mentioned wave, this will support isolated severe storms along the front with large hail up to the size of a quarter (1 inch) and damaging winds to 60 mph being the main threats. The coverage of storms is expected to be mainly isolated as the main forcing from the wave looks to stay mainly across and northeast of southwest Minnesota. Storms could still develop on the boundary towards the southwest across south central and southeast South Dakota but think that showers are more likely then actual storms due to the lack of forcing. Should see any chance for showers and storms persist into the evening hours before coming to an end before midnight. Lows will fall to the 60s overnight. Another shortwave trough will begin to push out of the Rockies and into the Northern Plains on Monday. This wave will spawn a surface low via lee cyclogenesis and set the stage for rain chances. However, the best lift will be situated well west of the forecast area. Thus, Monday will be dry but hot and humid as high temperatures warm to the upper 80s to 90s along and west of I-29. Locations towards central South Dakota could see highs top out at 100F. With a tighter surface pressure gradient in place, breezy southeasterly winds will return to the area. Overnight low temperatures will remain on the mild side thanks to the southerly winds with lows only falling to the upper 60s and 70s. Rain chances return on Tuesday as a cold front pushes into the area from the northwest. Moisture will pool ahead of the front, pushing dew points to the 60s and 70s. Highs again will warm to the 8-s and 90s, making for another hot and humid day. With steeper mid level lapse rates on the order of about 7 C/km, sufficient instability will be in place. The GFS, Euro, and Canadian ensembles show a 40- 80% chance for CAPE values to exceed 2,000 J/kg. Vertical shear will be marginal however as the upper level jet will be displaced well north of the area, towards the international border. In fact, any marginal shear will be behind the surface front. This makes severe storm potential a bit tricky as there is not much overlap between the instability and shear. However, think that the instability may be able to overcome the weaker shear keeping a lower risk for severe storms in place. The other aspect to these storms is their heavy rain risk. Precipitable water (PWAT) values look to rise to the 90th percentile of climatology per the NAEFS ensemble. The Euro Extreme Forecast Index (EFI) also shows about a 50% chance for anomalous rainfall Tuesday evening as well. Mean flow is also parallel to the front, further increasing confidence in this potential heavy rain threat. At this time, the ensembles show a broad 40-80% chance for rainfall amounts to exceed a quarter of an inch. While not a high amount of rain, this event is looking to be convectively driven which could make for localized heavier amounts possible. While the front will push through the entire forecast area during the overnight hours on Tuesday, the elevated front looks to remain over the area on Wednesday. This will continue rain chances across the area though it looks to be dependent on the evolution of a new surface low developing on the boundary. Outside of rain chances, Wednesday will be a cooler day, relatively speaking, with highs only warming to the 70s to mid 80s. Thursday through the rest of next weekend look to see continued chances for rain as weak shortwaves pass through the upper level flow. However, medium range guidance shows large variance in the upper level pattern and especially mesoscale details. Tough to say which day has the best potential to see rain at this point in time. Will continue to monitor this potential over the coming days. Aside from rain chances, high temperatures will remain near to below average, coolest in the 70s and 80s on Thursday and Friday before warming to the 80s for the weekend. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1032 PM CDT Sun Jul 13 2025 Expect VFR conditions for most of the area through the period. However, seeing some MVFR conditions (likely lingering smoke) for some locations in northwestern IA. This should improve through the early overnight hours. Guidance this evening is showing some potential of fog and stratus developing (about a 35% chance or less from the HREF). Think that some of this is due to where guidance thought there would be precip this evening/earlier tonight, and we did not see any precip. This keeps confidence in development very low, but will continue to watch trends. Winds become light and variable tonight, turning southerly and gusting 15-20 knots Monday. NAM guidance shows some potential for marginal LLWS at KHON toward the end of the period, but confidence remains low enough to preclude inclusion. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...Meyers AVIATION...SG