Area Forecast Discussion
Issued by NWS Aberdeen, SD

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916 FXUS63 KABR 181732 AFDABR Area Forecast Discussion National Weather Service Aberdeen SD 1232 PM CDT Tue Jun 18 2024 .KEY MESSAGES...
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- A break from the active pattern is anticipated tonight through Wednesday. However, it quickly turns more active again by the end of the week into the first half of the weekend with a 40-90% chance of precipitation with the highest chances Thursday night through Saturday.
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&& .UPDATE...
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Issued at 1225 PM CDT Tue Jun 18 2024 Front continues it progression east, with low clouds, falling/stalling temperatures and a little drizzle/sprinkles in its wake. Out ahead of the front we also continue to see light showers and a few lightning strikes. CAMS still support convective development just east of the CWA later this afternoon in that 80 over 70 degree airmass (which still persists near Ortonville/Milbank/Watertown areas at this time). No major changes of note to the forecast but will continue to watch the far east for convective potential until they end up in the post frontal airmass.
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&& .DISCUSSION... Issued at 318 AM CDT Tue Jun 18 2024 As of 3am a strong line of storms ahead of the cold front, within an MCS, extends from northwestern MN and southwestward through south central SD. Radar rain estimates have been between 2-4 inches in central SD as the line has trained over the same areas around and west of the Mo River. A Flash Flood Warning has been issued for parts of Stanley County as Crest Unit Streamflow`s values have risen up to values of 600cfs/smi! HREF/CAMs indicates the line will continue eastward through the morning. With the LLJ and northerly moisture surge, ahead of the front, these storms could still stay strong for the next couple hours, but looks to become more outflow dominant after this. By 18Z, lingering stratiform rain will be over our extreme eastern CWA as the line continues into MN. Little bit of a difference between CAMs on the exact exit time here. A few of the models do show some light straggling precip behind the main line, associated with the 850mb front. I left pops under 10% for now. HREF and LREF ensembles indicate southwest flow continuing over the CWA with a longwave trough over the western CONUS as the associated shortwave tracks over the Northern Plains today and continues northeast into Ontario by early Wednesday. Winds aloft continue to be strong downwind of this shortwave, ranging from 50-65kts, increasing to 60-70kts this evening from central SD through ND by 00Z Wednesday. By 12Z, the 850mb low will centered over the Northern Plains with the ongoing LLJ in place over eastern to southeastern SD into the Central Plains. Speeds are between 50-60kts, decreasing mid morning or so as it moves east with the low. The surface low is forecasted to be over northeastern SD with the cold front draped southward through NE. Winds will switch to northwesterly from west to east across the CWA with northwest flow into tonight. GFS indicates 6 hour pressure rises of +9 to +13mb will move in from west to east over the CWA with the incoming high today. This will bring in CAA (-3 to -15C/12hr. With pressure rises and CAA this will help steepen low level lapse rates a bit. We do lose that LLJ so 850mb winds won`t be anything impressive this afternoon but we do reach between 20-25kts, at peak heating, at the top of the mixed layer, mainly over central SD per RAP soundings. I did blend NBM/NBM75 to show for this with gusts up to 35kts in our usual Corson and Dewey Counties. High pressure keeps the area dry this evening into Wednesday. With the cooler air from the high, lows will dip down into the 40s to the lower 50s. MaxT temps for Wednesday will range only in the upper 60s to the lower 70s. Unsettled weather returns to the area Wednesday evening through the end of the week. The longwave trough remains unchanged through Friday with a northern shortwave pushing west to east over the northern CONUS and over the Northern Plains/southern Canada by the weekend. Models agree on this setup, but still some differences between the ensembles on intensity and timing of wave. GEFS shows this wave deeper and GEPS keeps it more broad. A surface stationary front is forecasted to be centered over the Central Plains Wednesday into Thursday and lift northward, as a warm front, into Friday morning as a lee side low develops. So pretty similar setup to what we have been dealing with. CSU does peg our CWA with a 5% chance of severe during this time but still to early to nail down details. This low will sweep across the CWA Friday into the Saturday time frame. Our highest pops (70-90%) will be Thursday night into Friday morning. A high will move in behind the low Saturday into Sunday. Well into the extended LREF ensembles indicate another shortwave/mid low in Canada that will bring a surface front in, from the northwest, early next week. High temps do not look to be anything extreme through the weekend Temps will range in the 70s and 80s with warmer air moves back in early next week as a ridge moves overhead aloft, with forecasted highs in the 80s into the lower 90s. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
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Issued at 1225 PM CDT Tue Jun 18 2024 Terminals KABR,KATY,KPIR,KMBG A mix of MVFR/IFR CIGS follows a cold front that should pass through KATY shortly and has already impacted the other CWA terminals. CIGS will gradually improve through the evening/overnight as drier air moves in on a northwest wind.
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&& .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Connelly DISCUSSION...MMM AVIATION...Connelly