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Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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320 FXUS63 KABR 140802 AFDABR Area Forecast Discussion National Weather Service Aberdeen SD 302 AM CDT Wed Aug 14 2024 .KEY MESSAGES... - There is a Marginal Risk (level 1 of 5) for the entire area late Wednesday afternoon through the early overnight hours. Large hail and strong wind gusts are the main threats. Probability for moisture is between 30 and 70 percent. - Showers and weak thunderstorms will wrap back into northeast South Dakota and western Minnesota during the day Thursday (30-60%) and tapper off Thursday afternoon. - Temperatures will remain seasonal through early next week. && .SHORT TERM /TODAY THROUGH THURSDAY AFTERNOON/... Issued at 301 AM CDT Wed Aug 14 2024 The ridge axis continues east with a southwest flow shortwave headed from western Nebraska into southeast South Dakota while another wave is located in western North Dakota, while the main shortwave/trough sits in eastern Wyoming. Thus, we really remain in a gap with only weak convective elements scattered across the CWA. As the day progresses, the shortwave to the south could generate some convection along the CWA border between Chamberlain/Huron/Brookings but there is low confidence much will actually make it up to even Watertown, while the convection in North Dakota develops through the course of the day. The southwards extension of that shortwave, and wave progressing towards the western portions of the state will phase enough that there is some potential for storms to develop in northwest/north central South Dakota during the afternoon. There should be a very subtle inverted trough across the area, helping to provide a focus for convection. The rest of the CWA, between systems, will continue to only see a low chance for moisture through the afternoon without much forcing and a weakly unstable atmosphere overhead. The environment during the afternoon in north central/central South Dakota will have favorable MUCAPE at around 2k j/kg, but shear is still relatively weak at 30kts or less. This might just enough for some storm organization as CAMS generate a cluster/line type system. High PWATS and a slow storm motion (hodographs suggesting about 10-20mph) present a heavy rain risk, though overall storm motion would be enhanced by the organization into an MCS if CAMS are correct. The subtle shortwave/trough pivots into south central North Dakota this evening and then loops down into western Minnesota allowing convection to migrate eastwards across the northeast of the state and on into western Minnesota. Severe weather threat should diminish with only about 1k j/kg MUCAPE and weakening shear. Those who need moisture will probably benefit from the system lingering across northeast SD/western MN with showers/wrap around moisture persisting into the day Thursday. && .LONG TERM /THURSDAY EVENING THROUGH TUESDAY/... Issued at 301 AM CDT Wed Aug 14 2024 Clusters have a good handle on the synoptic pattern Friday into the weekend with a ridge building over the central CONUS (and mid level high underneath) as the shortwave/sfc low continues to push east and over the Ohio River Valley/Northeast by Sunday. To our west, the low off the Pacific coast will continue to strengthen. This setup creates an omega block pattern with not much movement through early next week. Models indicate this closed low over the Pacific weakens a bit into an open wave by Tuesday, but there are differences between the Clusters on exact timing of this. By midweek, ensembles really diverge on exact location and amplitude of the ridge. Thursday evening into Friday morning, the occluded low is forecasted to be positioned over ~MN/WI border, which could bring ongoing lingering wrap around elevated rain showers/storms over northeastern SD/western MN. However, the western extent of this precip remains in question and exacting timing of departure as EC/GEPS is a little quicker with the exit compared to GEFS. Latest NBM has a 15-20% pops over far northeastern SD/western MN between 00-06Z Friday with precip exiting this area before 12Z. Otherwise, a high moves in and remains dominant over the Northern Plains Friday through the weekend. A low pressure system looks to move eastward over Canada, north of this high, during this time. Models indicate several potential shortwave vorts/pulses moving up the ridge and along the axis (from the trough out west) along with pockets of mid level moisture. This could lead to isolated chances of thunderstorms as the ensembles show spotty chances of precip here and there over the CWA occasionally through the period, especially with diurnal heating. There is the possibility of a couple surface boundaries passing through early to middle parts of next week too. Low confidence on exactly where precip is possible, due to the isolated nature at this point. NBM keeps a generalized 15-25% through the long term period. Cape looks to creep up to 1000-1500 J/kg over central SD with shear 30-40kts over this area on Saturday. CSU highlights a 5% chance of severe weather possible. With the backside of the low, northwest winds continue over the eastern CWA with southeasterly winds over the western CWA at 850mb for Friday. Forecasted highs will range in the mid to upper 70s to the upper 80s, warmest around and west river. As the ridge builds and southeasterly winds expand eastward, highs through the weekend will mainly be in the 80s with possible lower 90 readings over south central SD on Sunday/Monday where the warmer 850mb temps are (~20- 22C), under the ridge. NBM prob of 90 ranges from 30-50% in this area. Climate Prediction Center indicates prob of above average temps next week only between 35-45% from the James River Valley and westward so expect closer to near normal to slightly above temps. && .AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/... Issued at 1220 AM CDT Wed Aug 14 2024 Terminals KABR,KATY,KPIR,KMBG MVFR/IFR CIGs are forecast to overspread the region by morning, with areas of SHRA/TSRA as well. Areal coverage and placement of shower/storm clusters are a bit uncertain, but signs point to better coverage during the afternoon/evening hours. Any heavier downpours may produce MVFR/IFR VSBY at times if they manage to move over a TAF site. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ SHORT TERM...Connelly LONG TERM...MMM AVIATION...Connelly