Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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845 FXUS63 KFGF 240926 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 426 AM CDT Mon Jun 24 2024 .KEY MESSAGES... - Thunderstorms will move into eastern North Dakota this morning, some of which may be strong to severe bringing hail and gusty winds. - Additional severe thunderstorms may develop late afternoon into early evening within portions of Minnesota. Should thunderstorms develop, damaging wind gusts, large hail, and tornadoes will be possible. && .DISCUSSION... Issued at 252 AM CDT Mon Jun 24 2024 ...Synopsis... Current satellite early this morning reveals broad upper trough in SK/AB into MT, with embedded shortwave impulses within the base of upper troughing over eastern MT/western ND as well as along northern ND. Areas of convection exist within these shortwave impulses, helped forced by low level jet feeding weak to moderate instability. Near the international border, high shear is interacting with convection, allowing organization of robust convection of which has been severe at times. Both impulses/areas of convection will continue east within enhanced westerly flow aloft within the base of the upper troughing. This will drive this morning`s potential for strong to severe storms. All guidance indicate these impulses and accompanying chance for perhaps continued convection to push into northern/central MN by mid afternoon (~21Z). At the surface, a surface low pressure will tend to develop near the tri-state area of ND/SD/MN by late afternoon, with a weak surface trough/cold front extending north-northeastward into northwest MN. These two surface features may provide foci for potentially additional thunderstorm development late afternoon into evening within northwest and west-central MN. By this time, confident amounts of high to very high instability will exist, within sufficient shear to organize storms. This instability and available shear will drive severe potential late afternoon into evening within Minnesota, including the chance for supercells. By Tuesday, post frontal air mass and increasing surface pressure behind the now departing upper troughing will make for a breezy and mostly dry day. Upper ridging then builds in the Northern Plains Wed/Thu favoring mostly dry conditions save some smaller areas of showers and weak thunderstorms. Getting closer to Friday, a seasonably stout upper wave moves east along the northern tier of the CONUS providing our next chance at more widespread and robust convection. CSU severe and excessive rainfall probabilities increase with this wave over our area, signaling a chance for potentially hazardous thunderstorms. ...Potentially strong to severe storm this morning... Mid level impulses moving out of central ND will confidently continue showers and thunderstorms into eastern ND this morning. There will still be a chance for a few storms to become severe, with main hazard being hail, and a somewhat muted signal for severe winds in excess of 60 mph. There is some indication that initial thunderstorms are outrunning better instability which is limiting chance for severe hazards as they enter Devils Lake basin early this morning. Still, gusty winds to 50 mph and small hail will remain possible. Getting toward mid-late morning, convection will likely be ongoing in portions of eastern ND into the Red River Valley. While instability will be on the rise, wind shear will be tampered as early morning low level jet subdues, along with winds aloft likely lessening in the heart of these mid level waves. So while overall chance for severe hazards this morning is generally low, there could still be some strong to briefly severe storms, with severe storms bringing hail not larger than golf balls and winds under 60 mph. ...Potentially severe storms late this afternoon into evening... SPC`s severe weather outlook issued at 1AM this morning illustrates this afternoon/evening`s severe potential and possible outcomes nicely. As such, I`m opting to not attempt re-write a similar discussion here, but can be found at spc.noaa.gov/products/outlook/day1otlk.html. However, I will comment on some features locally that may influence our severe weather potential. First, uncertainty in how convection this morning (and potentially still ongoing this afternoon) is lowering confidence in important mesoscale details that would influence areas where severe storm potential will exist, as well as hazards associated with it. This is particularly true for portions of west-central MN where guidance confidently suggests a highly unstable atmosphere will exist. Should convection continue into the afternoon, and perhaps be slower to move into this area by 00Z (7PM CDT), there is a chance for thunderstorms to reinvigorate, become surface based, and achieve severe status as low level jet kicks in. Given its proximity to progged surface low pressure, locally higher low level shear would favor potential for tornadoes and very large hail larger than 2 inches, especially if storms can stay more discrete. Should storms be more linear, damaging wind gusts in excess of 70 mph would be the more dominate hazard, with chance for line-embedded tornadoes. Closer to northwest MN, the surface trough will provide focus for potentially additional severe storms. However, there is question regarding sufficient amount of forcing to sustain robust convection with the likelihood of better synoptic forcing aloft to remain displaced in Canada, and in turn lowering chance for low level convergence to aid in forcing for ascent. Additionally, a lack of temperature difference between air masses on either side of this front will lower chance for sustained forcing for ascent. Should there be sufficient forcing for ascent to sustain robust convection, initially discrete supercells will develop within northwest MN capable of all hazards (winds to 70 mph, large hail to 2 inches, a few tornadoes). However, with wind shear generally unidirectional wind shear, splitting supercells in close proximity of each other may keep the window of discrete storm mode rather short, and become clustering of thunderstorms may lower the chance for a tornado some. Additional uncertainties exist in how this morning/early afternoon convection may influence this area`s environment as well. Ultimately to say, should robust thunderstorms develop this afternoon/evening in Minnesota, they hold a higher than normal chance of producing severe hazards. However, confidence still remains degraded in whether or not this unfolds. We may not know which scenario will unfold until this afternoon. && .AVIATION /06Z TAFS THROUGH 06Z TUESDAY/... Issued at 1145 PM CDT Sun Jun 23 2024 VFR conditions prevail at all sites through most of the period. Currently watching the progression of scattered showers and thunderstorms in northwest North Dakota tonight. These showers and thunderstorms are expected to move into eastern North Dakota during the late overnight period, impacting KDVL as early as 09Z, then moving off to the east through the remainder of the morning. Winds are expected to become southerly gradually through the overnight hours, with wind speeds in the 10 to 15 knot range by mid morning. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ DISCUSSION...CJ AVIATION...Lynch