Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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664 FXUS63 KABR 180153 AAB AFDABR Area Forecast Discussion...UPDATED National Weather Service Aberdeen SD 853 PM 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. The threat then moves east of the James Valley for Wednesday evening. - Above normal temperatures will continue through Thursday before more seasonable temperatures move in through early next week. - Showers and storms through the weekend (20-40% chance for moisture). && .UPDATE... Issued at 846 PM CDT Tue Sep 17 2024 Delayed onset of PoPs and eastward expansion across the western/southwestern CWA by a couple hours. Currently watching a line of convection across southwest SD moving off to the north- northeast, which has produced wind gusts in excess of 60 mph. Outflow has surged out well ahead of the line, and still expect an overall weakening trend over the next couple hours as it approaches the CWA. That said, will continue to watch obs closely as it nears the southwest counties. Otherwise, breezy southerly winds will remain in place overnight with lows staying rather mild for this time of year as we drop into the 60s. && .SHORT TERM /THIS EVENING THROUGH WEDNESDAY NIGHT/... Issued at 258 PM CDT Tue Sep 17 2024 Low pressure will move north through the western Dakotas tonight. Southerly winds remain breezy into Wednesday on the warm side of the low. As the upper low shifts east across Montana and Wyoming tonight, shortwave energy will eject out ahead of it into the Dakotas. Coupled with a 30 to 50 kt llj, showers and thunderstorms are expected tonight (central SD) into early Wednesday morning (east of the James). Not the best set up for severe weather, though there is a marginal risk for central SD this evening and one for east of the James valley Wednesday evening. Storms later Wednesday will be dry line-induced, and hi-res models keep the bulk of the activity in MN. There are a couple of models, though, including the HRRR, that develop storms along the Coteau in the evening. The other thing of note will be elevated fire weather concerns for Wednesday afternoon across central SD. Well-above normal highs and a mid level dry air intrusion will see min RH fall to 15 to 25 percent. If, as expected, any wetting rains from tonight`s rain are only localized with stronger thunderstorms, fuels will still be burnable. Combined with the 30 to 40 mph southwesterly wind gusts, a red flag warning may be necessary especially for Hughes county south. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 258 PM CDT Tue Sep 17 2024 The deterministic models are fairly consistent in showing an upper-level low moving east across North Dakota. This causes the flow to transition into southwest flow Thursday evening into Friday, as well as moving a jet streak over SD. While the models have mid- level moisture and CAA over SD, they keep from developing precipitation because of the lack of lift at the surface. Instead, the forcings help to provide higher lapse rates Thursday, leading to stronger winds and wind gusts over central SD. Models show winds reaching around 30kts with stronger gusts Thursday morning into the afternoon. The clusters and NBM show a similar picture, with gusts reaching over 35kts in counties west of the James River Valley. The ECMWF ECI table shows values in the 0.6-0.7 range over areas west of the Missouri river, signifying stronger winds. Friday morning, mid- level WAA and dry air is pushed in over SD as the low continues to move east. The WAA, along with the southwesterly flow, help to keep temperatures about 10 degrees above average into the weekend. By Saturday, the clusters and deterministic models start to push another upper-level low from the north. The models do differ on the location and strength of the low, as the Canadian model has the low to the west of SD over WY. On the other hand, the GFS and the ECMWF move the low northeast of SD into Ontario. This causes the models to have a difference in the location of forcings and moisture on Saturday. The ECMWF and GFS models have fairly zonal flow aloft Saturday morning, causing only a few pockets of positive vorticity to move over SD. Additionally, these models move mid-level dry air and WAA over SD during Saturday afternoon. There looks to be enough moisture and forcing Saturday morning to allow precipitation to develop along a front attached the low, however, the best precipitation chances in these models are to the north in ND. Once the dry air moves in, the precipitation chances dissipate. The Canadian model, on the other hand, shows a different solution to the precipitation and keeps it going for most of the morning and afternoon. The Canadian model has more linear vorticity attached to the low as well as mid-level moisture and CAA over SD. With the abundance of forcings and moisture, the Canadian model develops precipitation at the surface a bit before a front moves into central SD, then the model develops larger values of precipitation along the front during the afternoon as it moves through SD. This lines up with one of the clusters, which has stronger shear values and some CAPE values of around 500 J/kg. While it likely won`t lead to severe weather, these values could lead to areas of stronger precipitation development along the front. Through the rest of the long term, the models continue to vary the location and strength of the upper-level low. This affects the mid- levels, as the Canadian model keeps moisture over SD with occasional pockets of dry air moving through, while the GFS and ECMWF models keep it dry aloft. Even with these differences, the models are consistent on at least two things. One, there will be no precipitation occurring through the beginning of the next work week, because there are not enough forcings and/or moisture to develop precipitation. And secondly, maximum temperatures will be dropping to be around average for this time of the year after the cold front and some CAA moves through Saturday. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 641 PM CDT Tue Sep 17 2024 Terminals KABR,KATY,KPIR,KMBG VFR conditions are forecast through the TAF period. Chances for showers and thunderstorms will increase into the evening/overnight hours, although areal coverage is expected to remain scattered at best. Low-level wind shear will be a concern overnight and have inserted mention of this into the TAFs for all terminals. Breezy/gusty southerly surface winds will continue through the period. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...TMT SHORT TERM...Wise LONG TERM...Vernon AVIATION...TMT