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Forecast Discussion for Aberdeen, SD
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392 FXUS63 KABR 131137 AAA AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 637 AM CDT Sun Sep 13 2026 .KEY MESSAGES... - Cooler than normal temperatures expected through Wednesday (highs in the 60s to low 70s) with the exception of a brief warmup on Monday (highs in the mid to upper 70s over much of the forecast area). A gradual warming trend will begin mid- week and continue through the weekend. - Confidence is high on widespread rain and perhaps weak thunderstorms overnight tonight through Monday afternoon. Highest rainfall totals are expected along the US-212 corridor, where totals may exceed one inch (40-60% chance). - Strong northwesterly winds take hold behind a cold front Monday afternoon into evening. Along and west of the Missouri River, wind gusts will reach as high as 35 to 45 miles per hour. && .UPDATE... Issued at 626 AM CDT Sun Sep 13 2026 See below for an aviation forecast discussion for the 12Z TAFs. && .DISCUSSION... Issued at 154 AM CDT Sun Sep 13 2026 Monitoring the potential for some early morning rain showers this morning. Area of focus is mainly over central South Dakota, although there is some signal in model guidance for some rain over parts of northeastern South Dakota and western Minnesota as well. There is a fair degree of model consensus for these showers to develop and move overhead beginning around 08-09Z and continuing through sunrise and into the morning hours. Expecting only light rain out of these showers, with little accumulation. More robust chances for rain arrive Sunday night into Monday morning. Ensemble medians for precipitation continue to increase, and models have trended the heaviest precipitation further south as well. The heaviest rainfall is now expected over parts of eastern South Dakota, with medians up over an inch in that area. NBM probability to see an inch or more for the 24 hours ending Monday evening ranges from around 40 to 60 percent along the US-212 corridor. While no severe weather is expected with this rain, there is some hint to some flooding potential due to heavy rain. The main driver of this signal is a plume of strong moisture into the area, and PWATs sit at around 1.5"-1.75" Monday morning. This would be well over 90th percentile values for this time of year by about 0.25"-0.5". Given the warmth above the surface, the warm cloud layer is expected to be somewhere between 11000-12000 feet, another ingredient in the flooding formula. With forcing coming from a 50+ knot low-level jet, storm motion will likely be fairly quick, meaning that a training storm setup will be necessary for flooding to develop. Perhaps the greatest limitation is a lack of instability in the area. MUCAPE values struggle to hit even 500 J/kg, so there is much to be desired. All this to say that while flooding can`t quite be ruled out, it does appear to be somewhat of an edge case with otherwise benign rainfall. Latest Flash Flood Guidance values still exceed NBM 90th percentile values, so in all likelihood whatever rain falls, the ground will be able to handle. It should also be noted that while there is currently a focus on the US-212 corridor, the recent shift southward should be a reminder that further shifts of the axis of heaviest rainfall will still be possible despite a limited time frame before the precipitation arrives. Behind the rain Monday morning, a cold front will pass through the forecast area Monday afternoon. As the front passes, winds will turn from southerly out ahead to northwesterly behind. These northwesterly winds will increase to 20 to 30 miles per hour, particularly along and west of the Missouri River. Gusts may exceed Wind Advisory criteria at times, although the latest NBM guidance keeps those chances (~20-50%, increasing moving northwest) over Corson and Dewey Counties. While no product will be issued on this shift, a headline may be needed with future forecast packages, especially with the NBM`s tendency to under-forecast wind speeds under a cold air advection regime. Temperatures Tuesday will return to slightly below normal (highs in the mid to upper 60s) after a brief warmup to near-normal on Monday. Mid-week, a weak upper-level ridge begins to build overhead. This will lead to a gradual warming trend through the end of the week. Expect multiple shortwaves to make their way into the region and bring additional chances for rain to the forecast area. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 626 AM CDT Sun Sep 13 2026 Terminals KABR,KATY,KPIR,KMBG VFR conditions are forecast with mid/upper level CIGS during the first 18 hours of the TAF valid period. After 06Z Monday, the return flow set up of strong south-southeast 15 to 25 knot winds will be drawing low level moisture up into the region. This sets the stage for some potential sub-VFR cigs, and perhaps even some pockets of IFR fog, particularly over the KPIR/KMBG terminals. A couple bands of light rain have developed over the region. Have transitioned the PROB30 groups to TEMPO groups. By 15Z, the majority of this light precipitation should be out of the area, leaving conditions dry until later tonight when the next round of showers with embedded thunder begin to develop and move up into central and north central South Dakota. Light east winds at or less than 10 knots this morning will eventually settle into a southeasterly direction today and increase tonight to 15 to 25 knots with higher gusts. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...10 DISCUSSION...BC AVIATION...10 |
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