Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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452 FXUS63 KABR 181740 AAC AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 1240 PM CDT Sat May 18 2024 .KEY MESSAGES... - Strong west to northwest wind gusts between 30-45 mph will be possible this morning through the early afternoon. Highest probabilities for the strongest gusts are across our northern tier of counties along the ND border. - Another system will bring the return of shower and thunderstorm chances (30-55%) across the area Sunday. There is a marginal risk (1/5) for strong to severe storms Sunday afternoon and evening. Main threats include up to quarter size hail and wind gusts around 60mph. - Active pattern with additional rounds of showers/thunderstorms for Tuesday-Friday. Below normal temperatures Tuesday-Friday as well. && .UPDATE... Issued at 1233 PM CDT Sat May 18 2024 See below for an aviation forecast discussion for the 18Z TAFs. UPDATE Issued at 1020 AM CDT Sat May 18 2024 The only adjustment made to the forecast was to adjust temperatures up a couple of degrees. Still maintaining the warmest high temperatures across the southern/eastern forecast zones where the warmest 925hpa thermal progs should reside at the end of peak heating/mixing late this afternoon. Will continue to see wind gusts ranging from 30 to 45 mph through early afternoon before winds begin to diminish some. Looks like the highest gusts will still be situated across the northern/eastern half of forecast zones. && .SHORT TERM /TODAY THROUGH SUNDAY AFTERNOON/... Issued at 301 AM CDT Sat May 18 2024 As of 3am, showers and thunderstorms have exited the CWA with the cold front extending from northeastern SD into the southern part of the state. The front continues to push east and will exit the eastern CWA here in the next few hours (by 12Z). Behind this front, a high pressure system sits over the northern Rockies and will push east/southeast over the area bringing dry weather and cooler temps for the rest of the day with highs in the upper 60s to the lower 70s. Behind the system, cooler air is being filtered in with northwest flow at 850mb as RAP indicates 850mb temp advection of -10 to -17C/12 hrs at 12Z over the CWA. RAP also indicates pressure rises of 4 to 13mb/6hr through mid morning. With this, HRRR/RAP indicates winds increasing behind the front through the morning. Grids show this well ranging from 15-25kts with gusts 30-40kts, mainly across north central to parts of northeastern SD though this afternoon. I did not have high enough confidence on doing a wind advisory as gusts are just below criteria, so went with an SPS. If gusts do become higher than forecasted, an advisory may be needed. Winds will diminish from south to north late this afternoon into the evening as the high moves in, lessening the pressure gradient with 850mb winds turning more zonal as the trough tracks northeast. Zonal flow aloft continues this evening as another shortwave deepens over the Pacific Northwest overnight into early Sunday (and track east), turning winds out of the southwest. At the surface, the high moves northeast with a inverted surface trough, and developing low, setting up over the CWA along with a strengthening LLJ. This will bring our next round of moisture as NBM indicates pops (20-40%) between 6-12Z from north to south central SD into parts of northeastern SD. As the warm front lifts north through the day, pops become more widespread ranging from 10-60%, highest east of the Mo River. HREF indicates SBCAPE/MUCAPE increasing to 1000-1700j/kg, mainly from north central to south central SD and wind shear around 30-40kts by ~22Z through the evening. However, we will be dealing with a cap and some cloud cover forecasted through the day, but the MUCAPE would support elevated convection. HREF Z>40dbz paintballs indicates storms firing up around this time over and around the Mo River (and possibly becoming a liner if enough instability ahead of the cold front) as it tracks east. Latest SPC puts much of the CWA in a marginal risk (1/5) for wind and hail threat. && .LONG TERM /SUNDAY EVENING THROUGH FRIDAY/... Issued at 301 AM CDT Sat May 18 2024 Will start out with elevated convection associated with a southwest flow regime as a surface low moves from southwest to northeast across the state. Still looking at a narrow ribbon of surface instability potentially but rapidly diminishing after 00Z though with still around 500-2k j/kg MUCAPE though the Sunday night period in a 40-50kt 0-6km shear environment. SPC upgrade to a marginal risk for that timeframe aligns with the low, non-negligible risk for isolated to scattered convection suggested by the twilight hours of the CAMS. Monday will see weak high pressure build into the region from the northwest initially, however a Colorado low develops in response to the next shortwave rounding the base of the deepening western CONUS trough. Being on the western approaches of the system, this will feature less convection and more deformation zone/TROWAL type rainfall. NBM QPF still shows a rather wide spread (over an inch between the 25th/75th percentiles for Watertown) however mean QPF between a quarter inch for Mobridge to 3/4 inches for Watertown seams a reasonable mean at current. And the active weather doesn`t stop there, with another wave for late in the week though at these timescales confidence on timing/trajectory and associated weather is low. With the active pattern, moisture and changes in airmasses, will continue to advertise slightly below normal temperatures through the extended. Temperatures are fairly close to NBM mean with a 25th/75th percentile range around 5-10 degrees for highs and a slightly narrower range for lows. No major cold surges outside of the random model run or two and so no threat of frost for now (plus everyone has had adequate moisture this spring so everything is nice and green). && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 1233 PM CDT Sat May 18 2024 Terminals KABR,KATY,KPIR,KMBG VFR conditions are forecast for all terminals. Gusty northwest winds at +30kts will gradually draw down from late this afternoon through late this evening. Late tonight (after 06Z), when mid- level warm air advection and a low level jet develop, isolated to scattered elevated showers, perhaps even a thunderstorm or two, could develop across portions of central and eastern South Dakota, persisting through late Sunday morning. When this low level jet develops, low level wind shear potential could happen, particularly for KPIR, KMBG and KABR. By late Sunday afternoon, thunderstorms, capable of large hail and damaging winds, could begin developing throughout and/or west of the Missouri River valley. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...Dorn SHORT TERM...MMM LONG TERM...Connelly AVIATION...Dorn