Area Forecast Discussion
Issued by NWS Grand Forks, ND
Issued by NWS Grand Forks, ND
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806 FXUS63 KFGF 120434 AFDFGF Area Forecast Discussion National Weather Service Grand Forks ND 1134 PM CDT Tue Jun 11 2024 .KEY MESSAGES... - Scattered severe thunderstorms are possible tomorrow afternoon in northwest Minnesota. Significant hail (2") and damaging wind gusts (up to 70 mph) are possible. && .UPDATE... Issued at 1133 PM CDT Tue Jun 11 2024 Increased POPS near the International Border for ND as we continue to see isolated showers move across Towner, Cavalier, and Pembina counties this evening. No lightning has been detected as CAPE is low. UPDATE Issued at 1000 PM CDT Tue Jun 11 2024 We are watching shower activity in the Turtle Mountains region this evening and its prorogation eastward. HiRes guidance has picked up on this trend and having it potentially continue through the rest of the overnight period along and north of the Highway 2 corridor. We will continue to monitor these showers as MUCAPE ranges between 500-1000 J/kg. Otherwise, we bumped up temperatures slightly in the southern Red River Valley for tomorrow afternoon into the lower 90s as cloud coverage will be limited. UPDATE Issued at 632 PM CDT Tue Jun 11 2024 We are seeing mid level clouds moving into the Devils Lake Basin this evening, with clear skies in the Red River Valley. Winds are starting to slowly weaken this evening and should diminish in intensity post sunset. Still looking for the thunderstorm chances tomorrow afternoon and evening. && .DISCUSSION... Issued at 130 PM CDT Tue Jun 11 2024 ...Synopsis... Surface analysis at 18z indicates the center of the low that brought us rain over southern Manitoba and Ontario. A relatively enhanced region of a stronger pressure gradient has developed on the backside of this low as a result, and is giving us sustained winds between 20-30 mph. Winds will diminish as this low continues to exit the region through the day today, so headlines are not likely (5% chance of Wind Advisory). A progressive shortwave trough will sweep through zonal flow aloft tomorrow afternoon, bringing the potential for severe thunderstorm development. There are a myriad of uncertainties outlined below, but at this point in time expect the potential for severe thunderstorms in northwest Minnesota. Upper air flow towards late week shifts to northwesterly as an intensifying ridge sets in. This should keep us quiet at least through Friday until southwesterly flow replaces it and gives us increased chances for widespread rainfall. How much rain falls is dependent on intensity and track of the system, of which ensembles are significantly struggling to get a handle on. At this point in time, NAEFS percentiles do have an enhanced corridor of IVT in the 99th percentile across the northern plains from South Dakota to SW Minnesota with diminishing probabilities radially away. This gives us solid confidence in a more widespread rain event but also the potential for more focused moisture advection across the northern plains. After this system, ensemble guidance falls apart and predictability for impacts next week is low. There is a strong signal for another wave to move through early next week, although the potential range of outcomes is very wide and predictability needs to increase to ascertain potential impacts. ...SEVERE THUNDERSTORMS TOMORROW... A rather complex convective scenario is expected to develop across the region tomorrow. In advance of a progressive shortwave trough (centered over the Pacific Northwest per WV satellite), a modest 850mb low level jet is expected to provide meaningful moisture advection to the area overnight tonight into tomorrow morning. Elevated convection is likely to develop with this low level jet, but at this point in time the most likely zone of this occurring is south of the area. As we progress through the morning and early afternoon, strong theta-e advection in advance of the surface low propagating through the southern Canadian Prairie will create a surface theta-e boundary. This will serve as the initiating boundary for convection tomorrow afternoon. Hodographs along the initiating boundary are effectively straight but have ample deep layer shear (exceeding 50 knots thanks to a strong 250mb jet) to facilitate supercell development. Both mean wind and Bunkers right vectors are effectively parallel to the initiating boundary so initial discrete mode should be anticipated. Within supercells that remain discrete, strong CAPE within the hail growth zone coupled with modest storm-relative flow will allow for significant hail to develop. With strong vertical mixing anticipated tomorrow as well, it is very likely we will see very cold RFDs from any supercells so the potential for wind to 70 mph is also there. With the cooler RFD potential and straight hodographs facilitating splitting, there is the potential for upscale growth/clustering to develop. If this does occur in our area, expect the potential for significant hail to increase as updraft width increases. An attendant stronger wind threat may develop although confidence is low due to the potential for fast developing surface inversions from outflow/RFD. Lastly, the tornado threat tomorrow should remain fairly limited. Very deep vertical mixing and drier profiles (LCLs approaching 1500m) should make it difficult for a tornado threat to arise. Additionally, streamwise vorticity in the lowest 1 km is very limited except where guidance has a more zonal component of the theta-e gradient in southern Manitoba. Here winds become more backed at the surface, allowing for slightly better streamwise vorticity. The potential for significant tornadoes should be kept to a minimum thanks to very poor thermodynamics. A tornado threat may arise in more north-central Minnesota but this will be highly dependent upon storm-scale modification of the environment. so there is a very low predictability horizon for this. && .AVIATION /06Z TAFS THROUGH 06Z THURSDAY/... Issued at 1133 PM CDT Tue Jun 11 2024 VFR conditions prevail this evening and overnight, with a few isolated showers north of DVL and remaining near the International Border overnight. Winds have subsided and shifted toward VRB or the south. This continues through the overnight with LLWS appearing near sunrise and lasting through the early morning as a frontal boundary shifts through. -RA chances increase for FAR and GFK in the afternoon, with -TSRA chances for TVF and BJI around 19-21z. Chances for showers and storms through 02-04z. Winds will be breezy for GFK, DVL, FAR, and TVF 19z-02z, with gusts up to 25kts possible. Drier conditions expected near the end of the TAF period. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...None. MN...None. && $$ UPDATE...Spender DISCUSSION...Perroux AVIATION...Spender