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Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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112 FXUS63 KFGF 210302 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 1002 PM CDT Sat Jul 20 2024 .KEY MESSAGES... - There are daily chances for showers and thunderstorms today through Monday. While the chance for severe weather is less than 10%, a few strong storms capable of small hail and gusty winds to 50 mph may occur. - Smoke from Canadian wildfires will linger across the region through at least Monday, potentially longer. This may impact air quality. && .UPDATE... Issued at 1002 PM CDT Sat Jul 20 2024 There are still a few thunderstorms moving into the northern Devils Lake Basin, along with other showers and exiting thunderstorms in the southern part of the basin (exiting our area). Trend has been for activity to weaken in our area as better instability has shifted southwest and lower levels have started to decouple. This activity could still linger through the evening in our northwest before finally dissipating, though in the absent of organized forcing most of it will struggle to hold together. There have been reported in the northern Red River Valley of 3-6sm vis reductions, which may be a combination of light ground fog and near surface smoke that mixed to the surface. During this update I made adjustments to linger mention of showers/storms in our northwest later, but held off on adding fog/smoke for now (will monitor those trends). Impacts from thunderstorm activity at this point will mainly be small hail and lightning activity. UPDATE Issued at 700 PM CDT Sat Jul 20 2024 Pulse type convection continues, but has shown a general weakening trend as inspected, with the decrease in solar angle. Shear is less than 20kt lowering confidence in any sustained/organized cores. So far most thunderstorms have had narrower cores (even the tallest) and have been short lived. There has been enough storm scale vorticity that under the right conditions, it could support a brief funnel along the escarpment where surface convergence is a little higher. Low level lapse rates in those areas are questionable and most convection is now outflow dominant, resulting in very low chances for brief/weak tornadoes (near zero as we approach sunset). There was one funnel report earlier 6-7 miles east of Finley, ND. This specific report seemed to coincide with an updraft along the intersections of outflow with some of the pulse convection, but it was short lived as the parent updraft weakened and outflow moved on. && .DISCUSSION... Issued at 318 PM CDT Sat Jul 20 2024 ...Synopsis... Water vapor satellite imagery reveals an expansive, well defined upper low over western QB into ON, with high amplitude upper ridging through the western CONUS into western CAN. This is placing the Northern Plains and portions of the Upper Midwest under weak northerly flow aloft, with weak flow is greatly limiting wind shear. At the surface, a backdoor cold front is pushing through western ON into northern MN pushed by the aforementioned QB/ON upper low. Sufficient instability and moisture is present for convection. Thick and widespread smoke is also noted on visible satellite imagery over the majority of central and western CAN into the northern tier of the CONUS. Ensemble guidance indicates the upper synoptic pattern will be rather stagnant over the next several days. Because of this, the backdoor cold front stalls and washes out/retreats back east tonight into tomorrow. Because of this stagnant pattern, the buoyant air mass lingers around the area. Additionally, weak northerly flow aloft will help funnel smoke from Canada into our area through at least Tuesday. ...Daily chances for showers and storms... The resident air mass over the region is composed of rich boundary layer moisture, seen by sfc dew points in the upper 60s to low 70s. There is likely some enhancement from evapotransportation that typically peaks around this time of year as most CAMs this morning did not show 70 dew points. This is aiding moderate instability. While wind shear is weak, there is enough instability to generate tall enough storms to deposit small hail, as well as downdrafts resulting in gusty winds up to 50 mph. With a lack of changing air masses, and stagnant synoptic pattern, the potential for small hail and gusty winds to 50 mph will be present in relatively stronger storms today through Monday. Due to wind shear less than 25kt and lack of better forcing for lift, the chance for organized thunderstorms leading to severe hazards is very low, less than 10%. ...Wildfire smoke... Most smoke is from wildfire activity in northern BC, AB, and into the Yukon and Northwest Territories of Canada. Persistent flow from this source region into our area is forecast by ensemble guidance through mid week, keeping smoke confidently over the area through Monday, potentially lasting as long as Thursday/Friday even. There will also be opportunity for smoke to reside at the surface during this timeframe, which would reduce air quality. Low confidence in how when and how thick smoke will be at the surface, thus lowering confidence in impacts from reduced in air quality. But ultimately there will be potential for impacts from reduced air quality through much of the week. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 700 PM CDT Sat Jul 20 2024 Isolated to widely scattered thunderstorms are still lingering over parts of the region, mainly in northeast ND and parts of northwest MN with vcts mainly at KDVL and KBJI. This activity should quickly dissipate with sunset this evening. High level smoke should linger through the TAF period, with a low chance for visibility reductions during the overnight/early morning periods if pockets of smoke were to get trapped near the surface (confidence too low at this time to go lower than 6sm). Otherwise, light/variable winds continue with weak surface gradient and weak winds aloft. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...DJR DISCUSSION...CJ AVIATION...DJR