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Area Forecast Discussion
Issued by NWS Aberdeen, SD
Issued by NWS Aberdeen, SD
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926 FXUS63 KABR 130509 AFDABR Area Forecast Discussion National Weather Service Aberdeen SD 1209 AM CDT Tue Aug 13 2024 .KEY MESSAGES... - Near normal temperatures on Tuesday, as well as increasing chances (20 to 50+ percent) for showers and thunderstorms Tuesday night. - Additional chances for moisture in the form of thunderstorms run from Wednesday through early Thursday. Severe storm potential looks limited to Wednesday with a marginal risk (1 out of 5). With the slow movement of the thunderstorms, periods of heavy rain are possible. && .UPDATE... Issued at 915 PM CDT Mon Aug 12 2024 Will be monitoring potential for stratus expansion northward into the CWA as the nighttime progresses, which various models suggest to some degree. Cannot rule out areas of fog/light fog for some locations, and may need to insert mention of this as well. Otherwise, not much in the way of changes for the overnight other than adjusting sky conditions to better fit satellite trends. && .SHORT TERM /THIS EVENING THROUGH TUESDAY NIGHT/... Issued at 140 PM CDT Mon Aug 12 2024 At 1 PM CDT, skies are partly to mostly sunny and winds are generally about 5 to 15 mph ranging from being out of the south to being out of the east. Temperatures are warming through the upper 60s to mid 70s, heading for the low 80s for some. So, this area of surface high pressure that has been around since last Thursday looks to finally be chased off to the east later tonight into the daytime hours on Tuesday, as mid/upper level heights rise due to an approaching mid/upper level ridge axis. The ridge axis aloft will be inducing some lee-of-the-Rockies surface troffing out into the central and northern high plains over the next 24 hours, which will create a return flow pressure gradient as the surface high shifts east into the Great Lakes region. Suspecting it will get, at least, breezy (per BUFKIT momentum transfer tool) on Tuesday, with 15 to 25 mph sustained southeasterly winds (higher over the James River valley westward and lower east of the James River valley). Low level WAA is subtle, but it does appear that there will be a few degrees of low level airmass warming tonight into Tuesday. So, looking at/expecting a bit wider coverage of high temperatures getting up into the 80s on Tuesday. Then, there is also the question of what will all this low level moisture steadily advecting up from the south do overnight and on Tuesday in regards to cloud-cover. A pesky low level stratus deck could affect the realization of Tuesday high temperatures. Finally, as the upper level ridge axis translates east of the CWA Tuesday night, shortwave energy pulling monsoonal moisture up into the region will have a chance to interact with low level jet winds and mid-level WAA to introduce some 30 to 70 percent PoPs for showers and thunderstorms across the CWA. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Issued at 140 PM CDT Mon Aug 12 2024 The long term forecast will start unsettled on Wednesday, with an upper trough and associated surface low approaching from eastern MT/WY. This will bring the potential for some heavy rain and thunderstorms as it moves east through the area, but uncertainty remains on where the storms will be. That upper trough will depart by Thursday night, with ensemble clusters consistent in a building ridge over the central CONUS starting this weekend and continuing into next week. This will lead to generally drier conditions, with temperatures running near or slightly above normal. Going into the details for Wednesday, the track of the upper trough and the associated forcing does lead to some concern in how much rain we`ll get in our CWA. Latest trends in the deterministic/ensembles is for two areas of increased precipitation amounts. The first over central/eastern ND (associated with the stronger/northern shortwave) and a second area to the southeast of our CWA (southeast SD into NE/IA border region) associated with the warm front and increased mid level warm air advection. Between those two areas, we`re still expecting precipitation, potentially heavy at times, but with weaker forcing, confidence is reduced on the where/when of the rain. With the setup, severe threat is on the lower end, with instability in the 1000-1500 J/kg range and shear around 20kts. Both of those values are at or below the 25th percentile of our local 2013-2022 severe weather parameter climatology based on storm reports, thus feel that the severe threat is limited with the tall/skinny CAPE profile. SPC has a marginal risk at this time, which seems reasonable based on the current forecast. Heavy rain looks to be the main threat, with slow storm motions (15-20mph) and ample moisture (PWATs of 1.75 inches or higher across the area on Wed). That matches up with the EC-ENS EFI data, which is highlighting central SD with QPF values in the 0.6- 0.7 range. In addition, latest NBM probabilities of 0.5" of rain in central SD are around 50% and 25% for an inch of rain. The rain will shift east with time Wed night into Thursday, as the upper trough continues to move eastward. There are some differences in the amplitude of the upper trough and how quickly it departs, which impacts the intensity of the low and precipitation amounts, but the overall trend from the ensembles is for the surface low and associated precipitation to shift to the east and out of the area during the day on Thursday. As the ridge builds over the central CONUS, the primary thing to watch for is waves riding the ridge and dropping southeast across the region. Ensembles point to both shear and instability increasing heading into next week, which would led support to storms, if/when disturbances move through. Being able to predict the timing/location at this time range is nearly impossible, thus leading to a lot of 10- 20% probabilities of precipitation across the area this weekend into next week. Overall, expect largely dry conditions outside any disturbances that move through. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1209 AM CDT Tue Aug 13 2024 Terminals KABR,KATY,KPIR,KMBG Signs still point to stratus developing/moving northward into the area by early morning, bringing with it MVFR/IFR CIG potential. Have expanded mention of this in the TAFs to include KABR/KATY/KPIR, and cannot rule out some FG/BR as well. As Tuesday progresses, expect conditions to trend VFR once again. && .ABR WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. && $$ UPDATE...TMT SHORT TERM...Dorn LONG TERM...SRF AVIATION...Connelly