725 FXUS63 KFGF 112026 AFDFGFArea Forecast Discussion National Weather Service Grand Forks ND 326 PM CDT Thu Sep 11 2025
.KEY MESSAGES...
- There is a level 1 out of 5 risk for severe storms in northeast ND into northwest MN today into early Friday morning. Most likely hazards include hazards include hail to the size of ping pong balls and wind gusts to 60 mph.
- An active pattern continues this weekend into next week with periodic chances for storms, some of which may be severe. There is also a risk for localized flash flooding impacts with this upcoming pattern.
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.DISCUSSION... Issued at 129 PM CDT Thu Sep 11 2025
...Synopsis...
Observational datasets and ensemble guidance illustrates high confidence in an omega block-type pattern setting up over the northern CONUS, with the Northern Plains into Upper Midwest region generally in the exit region of the upstream upper low. This would promote continued active pattern with periodic chances for showers and thunderstorms, as well as above average temperatures through at least early next week. Into mid to late next week, ensemble guidance suggests the omega block pattern starts to break down, but with generally weak flow aloft and/or quasi-zonal flow aloft, suggesting continuation of above average temperatures or trend back toward average. Compared to this weekend into early next week, this would trend toward slightly drier pattern mid to late next week; however, confidence in this is not high due to spread within ensemble guidance associated with synoptic pattern.
...Severe storm risk today into early Friday morning...
Marginally-strengthed low level jet lingers from this morning, continuing to feed scattered thunderstorms early this afternoon, amid around 35kt of effective shear and 1000 J/kg of instability. This will continue to support potential for a few strong to severe storms in portions of northeast North Dakota this afternoon capable of hail up to the size of ping pong balls. Thunderstorms remain elevated in altitude, with a clear stable layer near the surface mitigating the potential for severe wind gusts at the surface. This current low level jet is expected to wane mid afternoon, bringing a brief lull in strong to severe storm potential this afternoon.
On caveat to this expectation of "lull" is an uncertain window of opportunity of surface based thunderstorms in central North Dakota between Bismarck, Jamestown and Cooperstown area this afternoon. Currently, SPC mesoanalysis shows surface convergence near an effective warm front, with eroding inhibition among filtered sunshine and increasing low level moisture. Lending some credence to this scenario is towering altocumulus south of Bismarck hinting at forcing aloft from a subtle mid level impulse. However, main uncertainty stems from whether or not enough forcing for lift will be sufficient to initiate sustained thunderstorms in this area.
Should thunderstorms develop near central North Dakota this afternoon, supercells are the expected storm mode given wind shear in excess of 35kt, surface instability around 2000 J/kg. Large hail exceeding 2 inches and locally gusty winds to 70 mph would become likely hazards. Relatively strong storm relative flow in a cyclonic fashion in the lowest 1 km will also allow for the potential for tornadoes. While this scenario is more likely into central ND, this could eek into our area of the Sheyenne River Valley and/or southern Devils Lake basin. Referencing the 12Z REFS, there is around a 20% chance of this scenario to occur.
Into this evening, a low level jet reinvigorates after midnight tonight. This re-invigoration will reignite scattered storms in portions of northeast North Dakota again, with general movement toward the east into northwest Minnesota early Friday morning. Instability and shear parameter spacing look very similar, with slightly more shear to work with pushing effective shear around 40kt. Again, storms will be elevated in altitude atop a nighttime surface stable layer. This again would bring hail up to the size of ping pong balls at the forefront of potential hazards, but wouldn`t discount gusty winds to 60 mph should storms merge into more linear-type complex within an area of DCAPE of around 1000 J/kg and low level jet rooted around 925 mb.
...Active pattern continues into next week...
With our area stuck in the "stormier" portion of the omega block pattern just downstream of the western upper low, periodic chances almost daily today through at least Monday is forecast in portions of our forecast area. With the upper low to our west, locations closer to central North Dakota hold a relatively higher chance in seeing more intervals of thunderstorms compared to elsewhere into eastern North Dakota and Minnesota. Machine learning severe weather guidance highlight the Dakotas into Minnesota for low probabilities of severe storms Friday through at least Monday. Sunday into late Monday hold a relatively higher chance compared to other days, coinciding with a shortwave trough rounding the eastern flanks of the upper low, lending slightly higher confidence in severe storm potential in our area late Sunday into early Monday. It remains unclear to the expected hazards, although there are no signals for significant severe potential at this time, keeping strong to severe storm potential more on the lower end of severity spectrum.
With persistent intervals of thunderstorms, and ample overall moisture content as well as sufficient instability into our area for an extended period of time, localized flash flooding is also a potential hazard this weekend through early next week. Confidence is not high in coverage or location of this potential hazard, and will likely hinge upon mesoscale/storm-scale processes to drive this potential - something that wouldn`t likely be known until very near the event (less than 24 hours).
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.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/... Issued at 129 PM CDT Thu Sep 11 2025
Main impact to aviation through 18Z Friday will come from thunderstorms.
Scattered showers and thunderstorms are forecast across the region today through tonight into Friday morning. -TSRA has been included in TAFs within the near term where confidence is high enough in thunderstorm impacts to respective sites, with VCTS after 06Z at respective sites highlighting currently favored timeframe for thunderstorms tonight into Friday morning. In addition to lightning, storms may hold hail and erratic, gusty winds, as well as brief periods of lowered ceilings in the IFR and/or MVFR category.
Winds will be generally out of the south and southeast 10-15kt, gusting to 25kt outside of thunderstorms. Winds may hold on to gusts tonight at some locations like KFAR. There is also expectation of a low level jet to develop between 04Z-15Z, although it remains unclear if it will exceed 40kt to include in TAFs, and remain more in the 25-35kt range rooted around 5kft.
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.FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None.
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DISCUSSION...CJ AVIATION...CJ
NWS FGF Office Area Forecast Discussion