Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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077 FXUS63 KABR 171538 AAB AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 1038 AM CDT Tue Sep 17 2024 .KEY MESSAGES... - A Marginal Risk of severe weather (level 1 of 5) has been highlighted along and west of the Missouri River this evening. The main threats will be strong wind gusts and isolated large hail. - Warm temperatures will continue through Thursday before cooler air returns late in the week. - More seasonal temperatures for mid-week though the weekend. - Showers and storms through the weekend (20-40% chance for moisture). && .UPDATE... Issued at 1037 AM CDT Tue Sep 17 2024 The forecast remains on track this morning. No major changes are planned. && .SHORT TERM /TODAY THROUGH WEDNESDAY AFTERNOON/... Issued at 452 AM CDT Tue Sep 17 2024 Main forecast challenges will be precipitation chances and associated severe weather potential tonight into Wednesday as a storm system organizes and shifts into the Northern High Plains and portions of the western Dakotas. Early this morning, the forecast area remains mainly quiet weather- wise, although there`s been a few showers and sub-severe storms working through far eastern zones in northeast SD and west central MN. This activity will clear our forecast area by the 5AM hour. We`ll be left with mainly dry conditions during the daytime hours as temperature readings warm well above normal again. Highs this afternoon will top out in the 80s with a few low 90s along and west of the Missouri Valley. Pressure falls ahead of an upper level low across the Great Basin will lead to strengthening sfc low pressure across eastern WY/MT and western ND/SD. A tightening gradient will lend to an increase in southerly winds with gusts reaching 25-35 mph during the day. These winds look to persist into tonight as the aforementioned upper low shifts into the Rockies and Northern High Plains and a strengthening low level jet on the order of about 50+ kts develops. Scattered thunderstorm development is expected across the High Plains this afternoon. Guidance progs this activity to shift northeastward tonight into central South Dakota. Instability locally looks to be modest but limited with moderate deep layer shear. Hi- res guidance and CAM solutions do paint a picture of somewhat rather robust convection working into our West River zones this evening into the early overnight hours. SPC currently highlights our Missouri Valley zones with a Marginal Risk for severe weather. The main threats with any storms will be damaging winds and isolated large hail. Some of this activity will wane in intensity as it shifts eastward into the remainder of the forecast area overnight through Wednesday morning. Although, wouldn`t be surprised if some is longer lived as it shifts eastward into the James Valley and points east as that low level jet persists. PoPs will continue in our eastern zones during the day Wednesday, as a sfc warm front shifts across the eastern Dakotas and western MN followed quickly by a cold front. SPC currently highlights northeast SD and west central MN for a Marginal Risk for severe weather on Wednesday. Not surprising given the more favorable instability and deep layer shear that`s progged to be in place Wednesday afternoon. Much drier air will move into central SD Wednesday afternoon with dew points dropping into the 40s. This in combination with gusty southwesterly winds will lead to elevated fire weather concerns as relative humidity values fall to around 20- 25 percent West River. && .LONG TERM /WEDNESDAY EVENING THROUGH MONDAY/... Issued at 452 AM CDT Tue Sep 17 2024 The upper pattern through the long term evolves from a longwave trough over the western CONUS, and departing upper low/wave in eastern Montana/western ND to a more zonal/progressive flow late Wednesday/Thursday. There will be a cutoff low across the 4-corners region that will eventually re-integrate into the flow over the region for the weekend resulting in the development of a weak longwave trough across the central CONUS. There is recent better consistency between the long range deterministic members, particularly the GFS/EC... with the Canadian is a little stronger with the longwave trough that develops late in the period, with the 12Z cluster analysis suggesting a much greater spread in ensemble solutions than what would be inferred from the current 500mb analysis...raising confidence in the overall forecast. At the surface, the departing wave and wrapped up low over eastern MT/western ND will support a cold front looping down into western South Dakota. There will also be the remnants of a trough washed out in eastern South Dakota which by this point is mainly just convergence in the low level winds. This will support continued convection from earlier in the day, under a high shear low CAPE environment. The other issue of concern is the strong southwest flow behind this boundary, particularly across the Missouri valley, which will enhance mixing leading to warm, dry and windy conditions. Thankfully much of the area has seen recent rainfall and much of this is happening during the evening/overnight...so fire weather is less of a concern. Cold frontal passage and zonal flow aloft means much milder/more seasonal temperatures through the extended. NBM 25th/75th percentile temperatures trend towards increased range as a weak system Friday/Saturday supports a surge of warm advection followed by a cold front. It remains around +/- 8F for the weekend into next week. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 645 AM CDT Tue Sep 17 2024 Terminals KABR,KATY,KPIR,KMBG All 4 terminals will continue to experience VFR conditions through the next 24 hour forecast period. Southerly winds will gust up to 30 kts from late morning through tonight. Strong winds just off the surface will allow for the potential for low level wind shear to develop at KABR/KATY/KPIR terminals late tonight into early Wednesday. Showers and thunderstorms are expected to develop west of the area this afternoon and make their way toward KPIR/KMBG area by mid to late evening. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Wise SHORT TERM...Vipond LONG TERM...Connelly AVIATION...Vipond