Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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964 FXUS63 KFGF 220844 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 344 AM CDT Wed May 22 2024 .KEY MESSAGES... - Isolated severe thunderstorms are possible Thursday late afternoon and evening, mainly south of Highway 2. Hail up to the size of golf balls and 60 mph winds are the main threats. - Another period of heavy rain late Thursday into Friday may contribute to additional rises on rivers within the Red River basin. - Patchy frost is possible Saturday morning, with the best chances across the Devils Lake basin. && .DISCUSSION... Issued at 344 AM CDT Wed May 22 2024 The main low pressure system responsible for rain and wind impacts in the previous 24hr has transitioned east of the region, with lingering light rain within the cyclonic flow aloft on the back side of this system. Shortwave ridging eventually amplifies over our region ahead of the next approaching mid/upper level low that arrives later Thursday night shifting east Friday. This upper low has a stronger period of CAA and well below average temperatures are forecast Friday into Saturday morning. A complicated quasi-zonal pattern persists beyond this, allowing for additional mid level waves to pass through the Northern Plains before ensembles indicate a trend towards ridging next week (putting an end to our more active/cooler pattern). Severe threat Thursday: As southwest flow builds on the back side of the shortwave ridge ahead of the next developing mid/upper low, a theta-e gradient tightens and a warm front possibly lifts into southern ND/west central MN. South of this frontal zone increasing BL Tds will support potential for MLCAPE 1000-2000 J/KG (HREF shows probabilities for 1500 J/KG MLCAPE 30-60% along and south of I-94). CAPE becomes increasing elevated with stronger capping north of this front as BL will be much cooler (and possibly cloudier). Veering profiles with effective shear 30-40kt would support organized cells if they develop near that frontal zone, and about 30% of HREF members show brief UH tracks greater than 75 m2/s2 aligned with that region (a few outliers with longer stronger tracks). Timing of cap erosion, uncertainty regarding synoptic forcing due to mid level shortwave riding, and frontal position (which has varied over the last few days) will be complicating factors on coverage. Still, there is a window for severe storm development with all hazards being possible along/south of I-94 based on the current favored frontal position. Heavy rain impacts Thursday-Friday: The most organized period of rain will be with the mid/upper low passage Thursday night into Friday, with a broad area of rain expected to move over the region. Highest rates as usually will be with convection earlier in the event when coverage will be less certain, before a transition to more light/moderate stratiform rain. Ensemble probs for 1"+ 2hr rain are in the 50-60% (both raw ensemble probs and NBM), with the probability for 2"+ less than 20% and likely tied to convective components earlier on. As this wave will be relatively quick and there isn`t a signal for slower/back building convection flash flood threat isn`t highlighted. Where higher rain totals do occur though, they could contribute to eventual rises on rivers, though this will be directly related to where and how widespread the heavier rain is. Frost potential Saturday morning: There is a strong signal for below average 850MB temps on the back side of the departing mid/upper low (as low as -2C) and NBM shows high probability (60% or greater) for lows below 36F. For actual frost impacts though, it may be less certain as recent rains may hold surface Tds above freezing. Still, within ensembles there is a 20-30% chance for 32F temps, with better probs towards the traditional cold spots near the Devils Lake Basin. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1123 PM CDT Tue May 21 2024 Look for IFR CIGs at KBJI through the early morning before improving to MVFR conditions by mid to late morning Wednesday. A brief period of MVFR conditions is possible at KTVF just prior to sunrise. Look for VFR conditions elsewhere as rain continues to work to the east and northeast through the period. Skies will become mostly clear after midday. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ DISCUSSION...DJR AVIATION...Lynch