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Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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044 FXUS63 KFGF 142359 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 659 PM CDT Wed Aug 14 2024 .KEY MESSAGES... - Showers and thunderstorms will increase in coverage through this evening and last into Thursday. Heavy rain and lightning are the main impacts. - Wildfire smoke from Canada may return to the region Friday, with a chance for air quality impacts. && .UPDATE... Issued at 659 PM CDT Wed Aug 14 2024 Rain has pushed northeastward into the Devils Lake Basin, northern Red River Valley, and western MN. A bit of elevated instability in the 500-1000 J/kg range has entered southeastern ND, so we are getting some thunderstorm activity in that area. With the better CAPE remaining to the south and effective shear around 25 kts, think that we won`t see any severe impacts, but will monitor for heavy rain and anything popping up to produce some small hail. Adjusted for timing and placement of POPs but otherwise no major changes to overall messaging. && .DISCUSSION... Issued at 334 PM CDT Wed Aug 14 2024 ...Synopsis... A mid/upper level trough is slowly deepening over the Northern Plains, with a 700MB/500MB low eventually closing off over our region tonight into Thursday before moving east. A plume of deep moisture highlighted by PWATs in the 1.5-1.8" range extends over our CWA and several areas of showers and embedded thunderstorms will track through or develop over our area through tonight before coverage becomes more scattered Thursday. We remain on the northern fringe of centered over the southwest US, and progressive flow will returns in several shortwave ridge and trough passages. The amplitude of the ridging does vary in time between ensemble clusters with stronger ridging supporting drier and warmer conditions, while more clusters keep flow flatter/more progressive. This keeps near seasonal highs in place next week and allows for progressive waves and shower/thunderstorm chances. Regarding thunderstorm impacts today-Thursday: This afternoon/evening features an axis of steep to marginal mid level lapse rates and marginal instability (1000 J/KG) near our west and south through sunset. Deep layer shear is weak. There may be enough forcing for a few marginal cores/smaller hail, and eventually a linear MCS may pass to our south (as shown by some CAMs), but with the main axis of instability south and 0-3km shear is less than 20kt/DCAPE less than 1000 J/KG wind organized severe this evening. PWATs are very high but broader areas of moderate showers and embedded thunderstorms/locally heavy rain. As thunderstorm activity will tend to be more progressive/embedded within larger areas of moderate rain the signal has continued to decrease within CAMs for higher totals above 3" and 24hr PMM show a very "spotty" signal for 1.5"+, which lowers confidence in even localized excessive runoff. Signal is still there for many locations to see above 0.25"+ rainfall over the next 24hr, with swaths over 1". It is a low probability, but it is worth monitoring the track/depth of the mid level low Thursday. Stratus may persist and any dry slot may fill in, however if there is clearing the high vorticity environment in place may support funnels or conditionally landspout/weak tornado potential (particularly near surface low/boundaries. As this is highly dependent on clearing an mesoscale/smaller scale evolution the probabilities are low and ultimately funnels would be favored over landspouts in the most likely scenario. Smoke potential Friday: As the mid/upper low transitions east RAP/Canadian smoke models are showing a dense plume of wildfire smoke that is currently bottled up over northern Canada advecting south into our region. This is far enough out in time, however dense the smoke will be an any potential air quality impacts are uncertain, however the signal in near surface smoke fields is there and it is worth monitoring, especially if part of a sensitive group health-wise. && .AVIATION /00Z TAFS THROUGH 00Z FRIDAY/... Issued at 659 PM CDT Wed Aug 14 2024 Conditions a mix of VFR to IFR with rain pushing north and east across the forecast area. Some convection getting going south of KFAR which will bring some VCTS to at least the Red River airports later this evening. There will be -RA or VCSH for most of the night, with those locations seeing VFR ceilings currently gradually decreasing to MVFR then IFR towards morning. Winds will shift around to the northwest at least on the ND side of the Red River by tomorrow. Some slight improvements possible by the end of the period, but overall clouds and scattered showers are expected to stick around through much of the day on Thursday. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...JR DISCUSSION...DJR AVIATION...JR