Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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326 FXUS63 KGRB 081741 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1241 PM CDT Mon Jul 8 2024 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - Thunderstorms are possible through early this evening with heavy rain and localized urban flooding being the primary hazard. Severe weather is not currently expected. - On and off chances for showers and thunderstorms will continue through Thursday. Although the severe weather threat remains low, locally heavy rainfall will be possible. - Some rivers, creeks, and streams across east-central Wisconsin will continue to run above bankfull due to recent rainfall. - A warmer/drier period may be in store toward the end of the week and into the weekend. && .DISCUSSION... Issued at 403 AM CDT Mon Jul 8 2024 Short Term...Today...Tonight...and Tuesday Thunderstorm timing and coverage through tonight are the main concerns. Heavy rain will remain a potential given PWATs 1.25 to 1.5 inches and slower moving storm motions. Isolated stronger storm with gusty winds and small hail could occur this afternoon, but severe weather is not expected. Slow moving positive tilted mid-level trough trudges across the upper Great Lakes today. Weak front with wind shift but little temp change shifts through late this afternoon into this evening. Ahead of these features though, modest low-level jet and warm front is helping to generate clusters of thunderstorms south of highway 10 early this morning. Elevated MUCAPE up to 500J/kg feeding this activity and higher PWATs and warm cloud depths with minimal individual cell motion results in a concern for heavy rain through 11-12z before low- level jet weakens and veers WSW. Storms are showing some movement but training cells could offset this. Will continue to monitor the heavy rain potential through daybreak. After this activity diminishes, majority of showers and storms this afternoon will develop closer to weak front over north- central also where MLCAPEs build fastest into far northeast WI. Likely pops only used over north-central with closer proximity to front and approaching mid-level trough. Eventually chance of showers and storms will make it to the Fox Valley and Lakeshore but this may not be until very late afternoon or even early evening hours. Similar H85 temps to yesterday and mix of sun and clouds supports highs back into the lower 80s, with upper 70s far north. Weak front moves through this evening with sfc winds eventually shifting to the W-NW. Small chances for a shower or storm through late evening, then dry overnight. Temps will cool into the low to mid 50s north-central which is where best chance of fog resides, especially since those areas see rain today. Bit of a different pattern on Tuesday. Mid-level trough axis will be flattening and shifting to our east. General sfc high pressure will be building into the region in its wake. Meanwhile, the remnants of TC Beryl will be lifting to the mid Mississippi River valley and we`ll start to see some cirrus well to its north here in WI. The day will begin with W-NW flow behind the weak front, but by midday winds weaken to allow lake and bay breeze circulations to develop as temperatures just inland reach back into the lower 80s. Some showers and storms will develop during peak heating though MLCAPEs remaining under 750J/kg and weak large scale forcing should limit coverage. Severe weather potential low yet again, but with the weak wind fields aloft, any storms will be slow moving. Storms will drift from north to south though. Long Term...Tuesday Night Through Sunday Some spotty shower/storm activity is still possible Tuesday evening through Thursday as shortwave energy dives down from Manitoba and skims northwest Wisconsin. However, with models agreeing to a more southerly track for Beryl through the Ohio River Valley mid-week, expect the axis of highest QPF to remain well off to our south and east. Otherwise, quasi-zonal flow/weak ridging should keep any meaningful rainfall out of the forecast through the end of the work week. Tuesday evening through Thursday... A combination of partial clearing and decent low-level moisture will result in slightly elevated instability (~1,000 J/kg) Tuesday through Thursday. This may be enough to generate some pulse storms during peak heating, although meager forcing and weak dynamics indicate that any storm activity would be short-lived and sparse in coverage. Any westward shift in Beryl`s track would likely paint a different picture, although there is currently a strong signal that it will miss us to the southeast. Rest of the extended... As the current troughing regime breaks down and the western heat ridge edges into the central CONUS, anticipate that Friday into the first half of Saturday will be mostly warm and dry. Potential for rain/storms then returns Saturday afternoon into Sunday as ridge riders track through the western Great Lakes and interact with a warm, moist airmass. Speaking of warm airmasses: this weekend has the potential to be rather unpleasant as temperatures climb into the upper 80s to low 90s and a surge of low-level moisture brings dewpoints up into the low 70s. If temperatures in the low 90s are realized, the combination of heat and humidity would result in heat indices flirting with advisory criteria on Sunday. It is too soon to say anything for certain this far out, but definitely worth keeping an eye on. && .AVIATION...for 18Z TAF Issuance Issued at 1228 PM CDT Mon Jul 8 2024 A line of strong thunderstorms associated with an MCV was pulling out of far NE WI at issuance time. Additional scattered showers and isolated storms were ongoing across the forecast area. Showers and storms should be most numerous in north central WI this afternoon, as a weak boundary and upper trough impact the region during peak heating. Expect convection to weaken after sunset, with the loss of daytime heating/instability. Light winds, low-level moisture, recent rain and partly cloudy skies should set the stage for fog development overnight, especially in the Wisconsin River valley of NC/C WI. The fog should mix out rapidly by around 13z/Tuesday. Scattered cumulus development is expected to occur later in the morning, but any daytime convection should hold off until afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA/Goodin AVIATION.......Kieckbusch