Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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019 FXUS63 KABR 080807 AFDABR Area Forecast Discussion National Weather Service Aberdeen SD 307 AM CDT Mon Jul 8 2024 .KEY MESSAGES... - Isolated afternoon and early evening showers and thunderstorms (15- 25% chances of precipitation) remain over eastern SD today and Tuesday. - Heat and humidity will be on the increase through the week into the weekend. Friday through Sunday, temperatures will be about 5 to 10 degrees above average, with highs for the weekend in the upper 80s to mid 90s and lows in the upper 60s to low 70s. Dewpoints are expected in the mid 60 to low 70 degree range, with heat index values in the mid/upper 90s to near 100F. && .SHORT TERM /TODAY THROUGH TUESDAY AFTERNOON/... Issued at 307 AM CDT Mon Jul 8 2024 The area of high pressure stretching from WY to eastern CO and portions western portions of NE/KS will keep a ridge extended across our forecast area today (which will linger across the area through Tuesday). The 500mb map shows a high amplitude ridge over the west coast into western Canada, and a trough centered over the eastern Dakotas and MN with a trough trough dominated much of the rest of the central to northeastern states. As we move into the late morning hours the 500mb trough will shift across MN, with northwest flow returning to all of eastern SD/west central MN. While the intensity and coverage will continue to diminish over this afternoon and Tuesday afternoon, afternoon to early evening pop up showers and thunderstorms. The chance of precipitation will be in the 15-25% range mainly east of the Missouri River today and a little more east Tuesday (mainly east of a line from Leola to Miller) in our warming airmass with dewpoints in the mid 50s to mid 60s. The NST (Nonsupercell Tornado)Threat parameter showed values up to 2-3 over northeastern SD yesterday, but is less today and generally less than 1 from the eastern slopes of the Sisseton Hills to MN both today and Tuesday afternoon. While still possible, conditions are less favorable for cold air funnels/landspouts, especially with the main 500mb wave to our east. && .LONG TERM /TUESDAY EVENING THROUGH SUNDAY/... Issued at 307 AM CDT Mon Jul 8 2024 Will continue with high confidence for a slow building heatwave that develops late in the week, peaks over the weekend, and then degrades slightly next week, though by that point the uncertainty is increasing as to what degree temperatures/humidity subside. We do open Wednesday with an upper ridge folding over southern Canada and the Dakotas as remnants of Beryl merge with the departing upper trough over the Midwest/Great Lakes region. There is still a reflection of the upper trough over the eastern CWA however, which limits those higher 850/700mb temperatures to our west. Over the eastern CWA, we`ll also continue to have some weak instability that could result in a few daytime driven showers/weak thunderstorms with limited shear and skinny CAPE. Added a 20 percent chance for storms for the Sisseton Hills/Coteau region. Thursday is when we see the ridge expand to more properly cover the CWA, with the higher 850/700mb temperatures also expanding across most of the CWA...though deterministic guidance shows a tight west to east gradient with about a 10C range from central to eastern South Dakota. That expansion continues into Friday which is when the 850/700mb temperatures reach a standard deviation above climo, with that degree of an anomaly continuing through the weekend. So at peak intensity, current heat index values fall below criteria, with a HeatRisk still running in the Moderate category with a few counties showing up as Major on Saturday. NBM dewpoints continue to run in the mid/upper 60s but again suspect as the corn sweats we may see higher values...but even still, NBM 90th percentiles are only 68- 72 degrees across the CWA. The grand ensemble probability of a heat index of 100 degrees currently stands at 20 and 22% for Saturday and Sunday in Aberdeen respectively, and 30% for both days in Pierre. As is somewhat standard for this time of year with this type of pattern, we can expect systems crossing over the ridge could generate some convection as well as relief in the form of fast moving fronts that briefly make inroads into the Dakotas. We can see that in deterministic guidance for the start of next week, and besides deterministic guidance, there is also evidence in the NBM thermal/dewpoint trends and GEFS plumes. && .AVIATION /06Z TAFS THROUGH 06Z MONDAY/... Issued at 1204 AM CDT Mon Jul 8 2024 Terminals KABR,KATY,KPIR,KMBG For the most part, VFR conditions will prevail across the area overnight and through the day Monday. The exceptions will be across the far eastern part of the area, where there is potential for some patchy fog early Monday morning, then in that same area late Monday afternoon/early evening where some scattered thunderstorm activity may result in brief periods of MVFR vsbys. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ SHORT TERM...KF LONG TERM...Connelly AVIATION...Parkin