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Area Forecast Discussion
Issued by NWS Sioux Falls, SD
Issued by NWS Sioux Falls, SD
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319 FXUS63 KFSD 050844 AFDFSD Area Forecast Discussion National Weather Service Sioux Falls SD 344 AM CDT Fri Jul 5 2024 .KEY MESSAGES... - Diurnal showers/weak storms will rotate southward across the area this afternoon, dissipating by sunset. Rainfall will be spotty and light, but isolated lightning may impact outdoor activities. - Unsettled weather continues Saturday-Monday, with periods of scattered showers/storms, mainly focused during the afternoon to early evening by Sunday-Monday. A few strong to severe storms are possible Saturday afternoon, with large hail/damaging winds the primary threats. - Cooler than normal temperatures for early July through the early part of next week, but trending closer to normal by the end of the week. && .DISCUSSION... Issued at 343 AM CDT Fri Jul 5 2024 TODAY-TONIGHT: Well-defined upper low spinning over central Minnesota early this morning is expected to make slow eastward progress toward the western Great Lakes by this evening. We remain in northwest flow on the back side of this low, with cool and moist mid-levels contributing to weak instability as we modestly warm into the 70s this afternoon. Expect to see scattered showers or weak thunderstorms develop and rotate southward across the area through the afternoon, diminishing rather quickly as we approach sunset and lose surface heating. Most locations should remain less than 0.10" rainfall, though HREF does show streaks of low-moderate (20-40%) probability of exceeding 0.25". However, these higher values appear to be overly influenced by more robust development in the FV3 which is not seen in other HREF members, so confidence in higher rainfall amounts is low. SATURDAY-MONDAY: This period will be dominated by a broad trough sagging into the northern Plains, with various shortwaves sliding through the base of the trough. First, and perhaps the strongest wave will swing through the area Saturday afternoon, providing some upper level support during diurnal peak of instability. Models show broad area of MLCAPE 1000-1500 J/kg, with a modest deep layer shear of 30-40kt as the wave slides through, the latter mainly focused through the southwest half of our forecast area. This could support a few stronger storms capable of large hail, though mid-level lapse rates are on the weak side, so thinking quarter to perhaps half dollar size in a more organized storm. Forecast soundings indicate a dry sub-cloud layer which could support isolated damaging wind gusts, but tornadoes appear unlikely given high LCLs seen in the soundings. Stronger storms could also produce locally heavy rain, but given progressive storm movement, widespread heavy rainfall is not expected. Timing of stronger storms should be focused from mid afternoon until about sunset, with the wave sliding east and instability quickly waning thereafter. Sunday-Monday we remain within the broad trough. Modest afternoon instability could support scattered showers/storms driven by the diurnal heating. However, shear is severely lacking so would not expect severe storms during this period. TUESDAY ONWARD: The early week trough makes a push east by midweek, allowing a dominant upper ridge over the western CONUS to at least attempt to build into the Dakotas for the latter half of the week. Still some differences among models in how far east the ridge and associated warmer air will build beneath this ridge, influenced by the remnants of tropical system Beryl sliding northeast through the southern Plains toward the mid-Mississippi Valley late next week. Ensembles do show increasing probabilities of temperatures topping 80F during this period, though, so there is hope of temperatures trending closer to normal. This tropical remnants should keep any meaningful moisture blocked from reaching our area, so rainfall chances look to be on the low side. && .AVIATION /06Z TAFS THROUGH 06Z SATURDAY/... Issued at 1043 PM CDT Thu Jul 4 2024 An area of stratiform rain has developed and is slowly moving south down the I-29 corridor, but is expected to shift eastwards before reaching the I-90 corridor as it dissipates during the overnight hours. Observations show very light accumulations on the orders of a trace to a few hundredths, with some very isolated MVFR/IFR cigs/visbys occurring across SW MN. Formerly breezy northwest winds will remain light tonight, becoming gusty again tomorrow morning with gusts into the teens and 20s. Our next round of scattered showers and thunderstorms is likely tomorrow afternoon for areas generally east of the James River Valley, with no severe weather expected. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && $$ DISCUSSION...JH AVIATION...APT