Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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290 FXUS63 KFGF 191808 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 108 PM CDT Sun May 19 2024 .KEY MESSAGES... - Isolated severe thunderstorms are possible between 8 pm and Midnight in far southeast North Dakota. Hail to 1.5 inches is the primary threat. - The probability for greater than 1 inch of rainfall is 50% Tuesday into Wednesday across parts of northwest and west central Minnesota. && .UPDATE... Issued at 105 PM CDT Sun May 19 2024 Dry air is sill preventing much of the precipitation aloft from reaching the ground, save some sprinkles under returns in the 20-30 dbz range. Adjusted potential hail size for this evening`s possible isolated severe storms to ping pong balls. This adjustment to slightly higher hail size was based on the expectation of storms to be elevated, with a larger portion of updrafts to be within the hail growth zone amid sufficient shear. Issued at 1005 AM CDT Sun May 19 2024 Dry air in the lower levels is preventing much of this morning`s precipitation as seen on radar from reaching the ground. This dry layer underneath mid to low level ridging will linger in place over our area through mid afternoon before pushing northeast away from the area. As such, reduced PoPs in the forecast this update to match expectation of virga much of the day. There may be some sprinkles that do make it to the ground, with better chance (40%) of seeing intermittent light rain in the southern Valley into west-central MN. Still expecting the chance for deeper convection from the central Dakotas to move east into our area, first in southeast ND, late afternoon and evening. Issued at 700 AM CDT Sun May 19 2024 Light returns associated with high based showers are spreading into the southern Red River Valley matching up with earlier trends in CAMs/guidance. There is some lightning activity in SD, but confidence is low this more unstable air mass will make it up this far north during the early morning hours with this current wave. Otherwise, forecast for the rest of the day is still on track per earlier discussion. && .DISCUSSION... Issued at 351 AM CDT Sun May 19 2024 Southwest flow is beginning to build into the central/Northern Plains in response to building mid/upper level troughing over the Pacific Northwest. This trough is expected to continue to amplify and deepen southwest flow over the plains and a series of waves ejecting through this flow (along with increase moisture advection) will keep periodic rain/thunderstorm chances in our forecast area, with confidence reasonably high through mid week despite some variations with timing/evolution of some of these waves. By late next week this trough breaks down and a more zonal/progressive flow featuring lowered heights aloft as the northern storm track shifts south. There is lower confidence in evolution of any waves and low confidence in any potential impacts). Temperature trends will be seasonably mild in the mid 60s to lower 70s the next several days, but below average temperatures (50s/lower 60s) become favored during the later periods. Severe risk today: Several impulses bring scattered showers/isolated thunderstorms during the day, with a more organized mid level shortwave passing south of our region late this afternoon and evening. THe norther extent of this will feature a near by baroclinic zone where southerly flow will help increase BL Tds. Mid level lapse rates are shown to steepen enough to support an axis of elevated instability near our forecast area by late afternoon/evening. Consensus is favoring better instability farther west and southwest based on the surface pattern and with increasing low/mid clouds resolved by all current guidance there isn`t currently a risk for surface based parcels (elevated parcels will support hail/wind as primary threats if there is any threat). As current guidance shows lowered instability towards our area (around 1000 J/KG max MUCAPE) confidence is lowered in any strong/severe storms. There is still high shear (40-60kt effective shear) and some CAMs try to hold some organized/embedded cells together as they approach far southeast ND during the 6pm-10pm period. 0-3km shear is in the 30-35 kt range, so while profiles are not that supportive of a wind risk (DCAPE less than 800 J/KG) there is still a low threat for downburst winds if a cell takes on brief/orthogonal linear structures (as some CAMs show). Midweek rainfall (Tuesday-Wednesday): There is increased consensus on a stronger negatively tilted mid level trough passage through SW flow over our eastern forecast area, with the potential for organized/deformation and widespread moderate to localized heavy rainfall. Excessive rainfall isn`t expected as any higher totals (1-3") would fall over a longer duration. Impacts to possibly delay any planting operations are possible though across northwest MN/west central MN as 24hr probs for at least 0.5" is near 80% and 1"+ is 50%. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 1255 PM CDT Sun May 19 2024 VFR conditions are forecast through 00Z, followed by lowering ceilings in the MVFR to IFR categories between 00Z to 12Z. Most likely to be impacted with IFR ceilings is KBJI between 08-18Z, with a 20% chance of LIFR ceilings in the 08-15Z timeframe. Virga can be anticipated this afternoon across the area before 00Z. The chance for scattered showers and thunderstorms increases between 00Z-06Z. The chance for thunderstorms remains low enough to omit from TAFs for now, although sites like KFAR hold highest chance (40%) of seeing -TSRA between 03Z-05Z. Some storms may be strong bringing lightning and hail within southeast North Dakota within this timeframe. Winds will be light under 12kt, shifting from the southwest to southeast, then turning variable after 06Z. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...CJ/DJR DISCUSSION...DJR AVIATION...CJ