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Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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466 FXUS63 KFGF 130758 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 258 AM CDT Sat Jul 13 2024 .KEY MESSAGES... - Heat related impacts are expected this weekend, especially Saturday afternoon. Impacts will be highest for heat sensitive or vulnerable groups and anyone without effective cooling or hydration. - There is a level 2 out of 5 risk for severe thunderstorms across northwest Minnesota and southeast North Dakota. A level 1 out of 5 risk exists in northeastern North Dakota. - There is a level 2 out of 5 risk for severe thunderstorms Sunday night into Monday morning. && .DISCUSSION... Issued at 147 AM CDT Sat Jul 13 2024 ...Synopsis... The overall synoptic pattern should continue through the remainder of the weekend into early next week, with a large anticyclone over the desert southwest and frequent shortwaves generating convection. These shortwaves are fairly weak until Sunday night, which is why we have such high uncertainty in the voltuion of convection through the weekend. Towards Sunday night into Monday, a cold front should remove instability from our area through next week, giving way to much quieter weather after Monday. Large scale ridging with almost no flow aloft will replace the current pattern, ending our chances for more organized severe convection. ...Heat Risk This Weekend... Forecast highs will rise into the 80s and 90s this afternoon with dew points ranging from the 60s to 70s. This will increase the risk for heat stress and allow heat index values to approach the triple digits in the southern Red River Valley. Lack of wind and ample sunshine behind the convection this morning should push Wet Bulb Globe Temperatures into the Extreme category this afternoon in the south. For this reason, the Heat Advisory will continue through the day today. Heat issues will persist into Sunday, albeit with cooler temperatures with less impact, but heat stress could continue for vulnerable populations due to repeated days of higher temperatures. Excessive heat is unlikely to develop due to recovery overnight. As humidity exits Monday, conditions for heat should improve. ...SEVERE STORMS TODAY... A very complicated environment exists for us today with very low confidence in how convection will evolve through the day. As of 07z, surface analysis indicates a developing MCV over Griggs/Steele Counties, which is also confirmed via Nightime Microphysics RGB indicating cyclonic rotation over the area. This has developed in the wake of elevated convection that is along a line from Fargo to the tri-state borders. To keep things simple, we will start with the ongoing convection. This is expected to translate eastward through the day today, aided primarily by persistent elevated instability from southwesterly winds aloft. There is a pocket of enhanced effective bulk shear along western Minnesota with this convection, so it is feasible we may see some intensification. Given the linear structure of ongoing convection, if we do see intensification as this line translates east, the primary hazard will be damaging wind gusts. Some cores have gone up along the outflow boundary, so there may be a brief chance of severe hail, but the main hazard will be wind. As the sun rises today, an eroding surface inversion should allow for convection to become more surface-based, however the question is will this occur before it exits our area. Again, primary hazards are likely to be damaging wind gusts. This afternoon is where things become really complicated. There is low confidence right now in how much instability return we see today thanks to the ongoing convection across the south and the development of an MCV over eastern North Dakota. Dew points right now range in the upper 50s to low 60s, which are heavily under what most CAMs have around this time. However, there is a reservoir of 70+ dewpoints remaining across South Dakota and Nebraska. The main question right now is how much this ongoing convection scours that 70s reservoir away from our area. In any case, it is very likely we will see strong to potentially extreme instability develop across the region this afternoon. Forcing, however, is very nebulous and this is where the dewpoint question becomes much more precarious. There are a wide array of potential forcing mechanisms ranging from the ongoing MCV to outflow boundaries to potential inverted troughs. As a result of this low predictability, it is not possible at this time to really say exactly where storms will develop. What we can say is where they will most likely develop, which is in west-central Minnesota later this afternoon. Confidence decreases as you head further north as forcing becomes much more nebulous. However, with how much we could potentially destabilize today, the lightest tap will likely send parcels going. In any case, if storms do develop this afternoon and evening, supercells initially are possible, but should congeal more into multicellular to linear mode. Bulk shear around 40 knots should be enough to generate solid wind production to 70 mph and hail to 2". Tornado issues should be limited thanks to very limited surface flow (and 0-1km shear primarily in the single digits). Severe convection should exit the area just before midnight. Attention will then turn upstream where severe convection is likely to be pushing from Montana into western North Dakota. HREF members primarily keep this activity away from our area, but we could see this scraping our southern counties overnight. If this occurs, the primary hazards by then should be damaging winds with a very low chance for a QLCS tornado. ...SEVERE THREAT SUNDAY NIGHT INTO MONDAY... There is much better confidence thanks to stronger synoptic forcing on Sunday. A much stronger wave with a cold front will progress through the region Sunday night. With stronger shear pushing 50 knots, supercells are possible in advance of the frontal boundary, likely capable of severe hail to 1.75" and damaging wind gusts. Eventually, we expect upscale growth to occur, allowing for the threat to transition to wind to 70 mph. A lot of what happens today may impact this, so stay tuned for further updates as we get closer. Right now, this looks to be the highest confidence risk for our area. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1155 PM CDT Fri Jul 12 2024 VFR ceilings continue through the overnight period and into Saturday morning. Look for isolated thunderstorms overnight, with the possibility of a strong to severe thunderstorm or two. The primary concern with these stronger storms will be gusty winds and hail. Heading into Saturday, there is another chance for scattered showers and thunderstorms, with isolated severe storms possible once more. Confidence is very low regarding exact location, thus left out VCTS until we get a bit closer and have more updated data. Impacts are possible during the afternoon and evening hours at all sites, with KGFK, KTVF, and KBJI seeing the greatest chances at this time. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...Heat Advisory from noon today to 8 PM CDT this evening for NDZ030-038-039-049-052-053. MN...Heat Advisory from noon today to 8 PM CDT this evening for MNZ002-003-029-030-040. && $$ DISCUSSION...Perroux AVIATION...Lynch