FXUS63 KFGF 271518 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 1018 AM CDT Sun Apr 27 2025 .KEY MESSAGES... - Severe thunderstorms are possible after midnight tonight through Monday morning. The primary hazards will be large hail and damaging winds. - Additional severe thunderstorms may develop Monday afternoon. All hazards are possible if they do develop including large hail, damaging winds, and tornadoes. - North winds increase behind a cold front Monday, with a 60 percent chance for wind gusts greater than 45 mph along and west of the Red River Valley in the afternoon and evening. && .UPDATE... Issued at 1018 AM CDT Sun Apr 27 2025 It is a pretty cloudy and wet start to the day today. There is some very light rain or drizzle and fog across portions of the FA this morning. There are a few spots with visibilities below 3 miles, like Langdon, Devils Lake, Cavalier, and Grafton. Did go ahead and add the mention of fog for a couple more hours yet this morning to these areas. Some drizzle and fog may linger through or past the noon hour, but will see how the mid to late morning plays out before extending it any longer. Only other change at this point was to remove the spotty mention of thunder this afternoon. That will become more likely very late tonight into Monday. UPDATE Issued at 646 AM CDT Sun Apr 27 2025 Increasing low level moisture and WAA have contributed to areas of light rain/drizzle which are barely showing up on radar due to how low in the atmosphere the activity is occuring. The pattern that supports it is better handled by guidance with only some CAMs reflecting the light precipitation signal as widespread and west as it is currently occurring. The trend should be for a gradual reduction in coverage through the morning hours as this initial period of isentropic ascent and weak PVA transitions east-northeast. I made adjustments to better reflect the current trends this morning. && .DISCUSSION... Issued at 358 AM CDT Sun Apr 27 2025 ...Synopsis... A mid/upper low is building over the southwest US, with southwest flow already building into the central Rockies ahead of this feature. This will continue to advect deep moisture into the region, with diffluent flow eventually spreading northeast this evening. Large scale forcing overspreads our region as the mid/upper low passes over our CWA through Monday night. This will support multiple periods of showers and thunderstorms, including locally heavy rain and several periods of severe. Probabilities for at least 0.5" remain very high (60-90%) across our CWA, with the probabilities for rainfall greater than 1.0" 40-70% associated with narrower bands/areas of convection. On the back side of precipitation late Monday evening into the overnight strong cold air advection may help change rain over to a brief wintry mix before it finally ends. Due to warmer ground temperatures and the brief nature of change over impacts would not be anticipated. After a weaker shortwave passes Wednesday out of northwest flow (light rain chances), the pattern transitions to dominant large scale ridging late next week into the weekend, supporting dry and warm conditions. ...Severe Thunderstorms Late Tonight-Monday Morning... A strengthening LLJ combined with steepening mid level lapse rates will set the stage for increasing thunderstorm chances within areas of rain later tonight, with highest instability (MUCAPE greater than 1000 J/KG) arriving along/behind a warm front along and south of I-94 after 3am to 6am (still some spread). Parcel traces remain elevated favoring large hail, however there are indications in some CAMs that linear clusters moving northeast may become line normal with stronger 0-3km shear values (greater than 30kt) which may support a damaging wind threat due to localized surges. Due to the elevated nature of the morning activity (based on current guidance), a more organized damaging wind threat or any tornado threat will tend to be minimized. ...Severe Thunderstorms Monday Afternoon... As surface low pressure deepens near eastern/northeast SD the warm front is favored to linger near our southeast CWA before the cold front finally sweeps into the region in the afternoon rapidly stabilizing the mixed layer and decreasing the severe threat. There is still variance on these surface features with a recent trend in clusters now favoring a slightly slower solution, though there are still faster members. This will be important as the slower solution allows for discrete supercell development and possibly QLCS type linear features forming farther west (as some CAMs hint in out far south-southeast). We continue to monitor two generalized scenarios, though impacts/timing could fall somewhere in-between based on all factors: 1.) Lower impact/coverage of elevated embedded severe thunderstorms with large hail the primary threat ending quickly by 2pm based on the HREF members that support this scenario. This is associated with the faster frontal timing and the warm sector remaining south. 2.) Higher impact/coverage of severe thunderstorms, including discrete supercells capable of significant hazards. All severe modes would be possible including large hail to the size of golf balls, damaging wind, and tornadoes. The severe threat would also linger longer into the afternoon in this scenario, potentially through 6pm based on the HREF members that support it. This is dependent on slower frontal timing and enough breaks in cloud cover across our south and east. Regardless, prepare ahead for potential severe thunderstorms and stay up to date on latest forecasts as many details will likely not have a high predictability horizon. ...High Wind Potential Monday Afternoon/Evening... Regardless of thunderstorm impacts, there is increasing confidence in advisory wind impacts (gusts 45 mph or higher) behind the cold front Monday due to the synoptic pattern, with strong CAA and increasing pressure gradient. Probabilities are greater than 60% for advisory winds along and west of the Red River Valley and there is even a signal in NBM probabilities for warning (58 mph or higher gusts). Best pressure rises/gradient tend to remain to our west-southwest, and sounding profiles show shallow mixing behind the front limited by widespread stratiform rainfall/deep saturation. However, even within that layer peak winds are near 40kt due to the strength of winds aloft/gradient. Ultimately we may need to consider a Wind Advisory if the pattern continues to trend as it has, with less confidence in warning impacts. && .AVIATION /12Z TAFS THROUGH 12Z MONDAY/... Issued at 646 AM CDT Sun Apr 27 2025 IFR conditions this morning are associated a low level saturated layer that is also contributing to areas of light rain/drizzle across eastern ND and northwest MN. As this exists through 15Z expect a trends towards MVFR ceilings that should prevail into the evening. Later tonight as the main system begins to approach, deeper moisture arrives and IFR (potentially LIFR) ceilings overspread the region once again. Better chances for rain showers arrive after 08Z with the best chance for thunderstorm activity before 12Z at KFAR. Isolated severe thunderstorms to develop into southeast ND with large hail and damaging winds in the 03-12Z time period, though confidence is low at this range on occurrence near the terminal at KFAR (will need to monitor). SOutheast winds remain 12-18kt through this afternoon, with periodic gusts to 25kt. As this winds decrease they begin to shift to the east later this evening/overnight due to low pressure building just south of the region in SD. A cold front also arrives near KDVL near the end of the TAF period where northeast winds would begin to increase above 15kt once again. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...Godon DISCUSSION...DJR AVIATION...DJR