Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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095 FXUS63 KFSD 160358 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 1058 PM CDT Sat Jun 15 2024 .KEY MESSAGES... - Heat advisory criteria with heat index readings nearing 100 degrees will be approached over Nebraska and Iowa Sunday afternoon and possibly Monday afternoon. - Potential for a higher end severe weather risk Sunday night into Monday across the region. Very large hail will be the primary risk, but damaging wind gusts may develop. Confidence remains low to moderate on location and timing. - Concern for heavy rain and flash flooding develops late Sunday night into Monday north of the I-90 corridor. By early Monday in this area, there`s a high chance of 1+ inches of rain with a few locations potentially receiving 2+ inches. - An active weather pattern continues through most of next week. Ensemble guidance through the week suggests a high (>70%) chance for 2+ inches of rain with potential for some locations to see 4+ inches by next weekend. && .DISCUSSION... Issued at 301 PM CDT Sat Jun 15 2024 Instability slow to recover after a morning MCS in eastern NE has carved out a large relatively stable air mass. The outflow can be seen on satellite extending from eastern KS into central NE early this afternoon. With the wave in place across central NE into eastern SD a combination of diurnal heating and increased southerly flow should gradually work through this stable air mass. A decent pool of instability at 1500-2000 J/kg CAPE exists across south central NE which should spread northeast. The big question mark is just when storms may fire. With the delayed response from the morning MCS the deeper instability may not approach far northeast NE and northwest IA until closer to 0z, bringing the best chance for isolated severe storms into northwest IA from about 7 pm to 11 pm. While the overall shear profile is not very impressive the lowest km or so does have some decent speed and directional shear along with a fairly low LFC/LCL which means an isolated tornado cannot be ruled out. If development is much later than 0z isolated hailers will be the main threat. Once this wave passes this evening, weak mid and upper level ridging will build into the area as a strong low level cap develops. This cap will server a couple of purposes. The first will be to suppress any convective potential on Sunday afternoon and possibly into the early evening, even with an incoming weak boundary. The other purpose this boundary will serve is to limit mixing and allow moisture to pool near and ahead of this incoming front, resulting in surface dew points in the upper 60s to lower 70s. Combined with highs of 90 to 95, heat indices in mostly northwest IA could climb to around 100 in the afternoon. This brings us to Sunday night into Monday. The big battle will be between capping and forcing/moisture. A significant cap will continue into Sunday night, and current trends suggest that just about any parcel that tries to lift below about 850-800mb will not make it. This suggests we may need to wait for the main wave to eject northeast late Sunday night which would put the main threat for any severe weather and heavy rain from about midnight to noon Sunday night into Monday. Just how much instability will exist if lifting above 800 mb will be a big question. Overall there will be a late evening threat for some isolated elevated supercells with damaging hail the biggest threat, but the main threat will be later in the night with a likely lesser severe threat but a higher heavy rain threat. This potential continues to remain highest near and especially north of I-90. The models become less agreeable Tuesday into Wednesday with the strength of the wave to the northwest and the resultant position of the surface front. For now not enough confidence to worry about a whole lot during this time, but there will be a continue threat for showers and thunderstorms. Once the convective potential lifts north on Monday morning the precipitation chances should wane, but another system is expected to move into the area on Monday night into Tuesday which will bring a renewed threat into the area. The better chances appear to be near and west of I-29. The pattern remains active Thursday into Saturday with seasonally warm and humid conditions. The flow aloft is expected to become a bit more westerly but still indications that multiple weak waves will traverse this flow and bring continued chances for showers and thunderstorms. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1055 PM CDT Sat Jun 15 2024 Mainly VFR conditions with southerly winds will prevail overnight. Showers and isolated storms continue to exit eastward out of northwest IA. Further west, showers and isolated storms continue to spread east from central SD into eastern SD overnight. Severe weather is unlikely with this activity, but there may be occasional MVFR stratus sliding in underneath the cirrus near and east of the I-29 corridor overnight. VFR conditions will prevail across the region through the day and early evening Sunday. A passing cold front will turn winds southwesterly and eventually northwesterly at KHON and KFSD on Sunday, becoming stationary between KFSD and KSUX by the end of the day. Another round of showers and strong to severe storms is expected to spread into the region late Sunday night. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...08 AVIATION...BP