Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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838 FXUS63 KFGF 220936 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 436 AM CDT Sat Jun 22 2024 .KEY MESSAGES... - Scattered thunderstorms are forecast in the Devils Lake Basin and northern Red River Valley regions this afternoon into early evening. A few these storms may become strong to briefly severe. - Severe storms may develop Monday afternoon and evening. && .DISCUSSION... Issued at 425 AM CDT Sat Jun 22 2024 ...Synopsis... Early this morning, water vapor imagery depicts broad upper troughing making its way into the Northern Plains, with at least a couple of mid level shortwave troughs working their way east within eastern MT/western Dakotas and within AB/SK. Objective analysis still suggests there is still some connection of a departing upper jet to keep divergence aloft over our area through the morning. As seen on microwave satellite imagery, overall low-mid level moisture content ahead of these shortwaves and underneath upper divergence will remain sufficient enough to allow continued areas of weak convection in the absence of better instability. Easterly flow in the lower levels will also continue drizzle/fog chances west of the Red River Valley in eastern ND. Getting into this afternoon, guidance suggests the influence from the entrance region of upper jet is replaced by incoming shortwave trough out of Canada. Cooling temperatures aloft and sufficient low level moisture coupled with daytime heating will support weak instability ahead of an incoming weak cold front attendant to its parent shortwave. This will set the stage for scattered thunderstorms forecast within the Devils Lake Basin into northern Red River Valley. And with at least weak shear associated with the approaching shortwave, there is a chance for organization of storms allowing them to be strong to briefly severe this afternoon into early evening. As Saturday`s shortwave trough exits east, Sunday will see a post-frontal air mass and shortwave ridging over our area keeping conditions dry. This is ahead of another approaching mid-upper level shortwave trough traveling east through the southern tier of Canada. Increasing warmth and instability builds ahead of this next shortwave trough as it approaches our area Monday, allowing Monday`s temperatures to reach into the 80s and 90s amid higher humidity. This coupled with sufficient shear will allow the opportunity for severe storms on Monday, of which may be significantly severe. However, there are uncertainties revolving around this potential, of which will be discussed in more detail below. Depending on Monday`s convective evolution and timing/speed of surface trough, Tuesday may hold a chance for strong to severe storms in portions of Minnesota. This is also very uncertain. Getting into mid next week, post frontal air mass and upper ridging aloft extending out of broad upper anticyclone over the majority of the central and western CONUS will favor mostly dry conditions and near average temperatures. Late next week, ensemble guidance is starting to hone in on the next shortwave trough that should influence our region`s weather, similar to Monday`s ridge riding fashion. This would favor at least one period of increased chance for showers and thunderstorms, along with average to potentially above average temperatures. ...A few strong to briefly severe storms later today.... Overall, today`s severe potential looks meager given the persistence from majority of guidance to keep instability and shear on the lower end, but still sufficient to allow opportunity for some thunderstorm organization. Unidirectional shear around 35 kt coupled with weak instability between 500-1200 J/kg will allow for transient mesocyclone development within strongest storms. Most shear is displaced within the mid-upper portions of the updraft, which would support hail production. Based on thermodynamic and kinematic spacing, hail up to the size of quarters seems reasonable. Cooler temperatures aloft will also allow for gusty winds between 40-60 mph through evaporative cooling of downdrafts. Coverage of thunderstorms may range from isolated to scattered, favored to be within northeast ND into northwest MN closer to better forcing somewhat displaced into Canada. Given dependency on daytime heating, lessening cloud cover will also be necessary to support building instability. Most guidance depicts this occuring closer to central ND into southwest MB this afternoon, and seems reasonable based on the expectation of exiting upper divergence. Best timing for potentially strong to severe storms exists between 5 PM - 10 PM. ...Severe storm potential Monday... As the shortwave trough skirts across the southern tier of Canada, it will drag a notable portion of an already established EML out of the Great Basin into the Northern Plains Monday. This is atop enriched boundary layer moisture comprised of dewpoints in the 60s to potentially low 70s. This will contribute to high confidence of high to very high instability within a warm sector overspreading ND into MN on Monday. The aforementioned stout EML will however also bring strong capping. This is important as it may subdue the chance for thunderstorms to develop altogether given better synoptic forcing expected to remain in Canada. This is where majority of uncertainty comes in: amount and location of forcing to overcome capping. While best forcing for ascent aloft will remain in Canada, there will still be some surface/low level features to perhaps focus forcing for ascent. This comes in the form of a warm front and surface trough/weak cold front bounding the warm sector as it moves through our area. Most guidance still times the surface cold front to pass through our area during the day Monday, with favored passed during peak heating (when capping will be at its weakest) within Minnesota. Additionally, there may be another opportunity to develop thunderstorms near and north of the warm front through low level isentropic lift/WAA. This supports the chance of robust thunderstorm development on Monday. Given the presence of sufficient shear associated with increasing wind field ahead of the approaching shortwave trough and likely very unstable air mass, any thunderstorms that can sustain themselves will likely be severe. This includes the potential for supercells, allowing for damaging winds, large hail, and possible tornadoes. Of course, mesoscale and finer details such as early day convection, orientation and timing of surface fronts, and influence of evapotranspiration this time of year introduces that much more uncertainty. Ultimately to say, should robust thunderstorms develop Monday in our area (still uncertain), they will hold a higher than normal chance of becoming severe, potentially significantly severe. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 1155 PM CDT Fri Jun 21 2024 Scattered light showers/sprinkles continue across parts of eastern ND and northwest MN, as several waves split around the region. MVFR (and a few pockets of IFR) stratus are beginning to develop in southern ND and guidance is starting to better reflect timing expanding north and northeast through the early TAF period. Eventually all sites should drop below VFR but confidence in widespread/prevailing IFR is still low (except at KBJI) based on trends. Eventually guidance supports all locations in ND improving to VFR by Saturday evening. Weak surface gradient is keeping light winds in place (less than 10 mph, with a tendency fro easterly or southeasterly directions (though prevailing calm or variable conditions are just as likely). && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ DISCUSSION...CJ AVIATION...DJR