239 FXUS63 KGRB 091722 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1222 PM CDT Wed Jul 9 2025 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - Next chance for widespread active weather will be Friday into Saturday. Heavy rainfall and a few strong storms will be possible with this system. - Another round of active weather may be possible around the middle of next week. && .DISCUSSION... Issued at 452 AM CDT Wed Jul 9 2025 Patchy fog... Low level moisture has pushed in a low stratus deck early this morning, accompanied by some patchy fog at the surface, mainly across portions of north-central Wisconsin. This low stratus deck will likely curb our morning temperature rise, but cloud cover is expected to dissipate again by the early afternoon, with clear sunny skies by the evening. End of the Week Precip... Attention then turns to the next approaching weather maker Friday and Saturday. An initial surge of warmer air aloft and accompanying moisture plume could push showers into portions of central Wisconsin as early as the morning hours on Friday, but better organization likely won`t arrive until a mid-level shortwave crosses into the region during the afternoon. This 700mb shortwave should support at least some convection through the afternoon and evening, but the overall strength of convection remains uncertain. The potential early arrival of rain may inhibit some of the better instability, but model soundings do show potential for some elevated instability by the afternoon as the surface warm front gets into southern Wisconsin. Probabilistic guidance continues to keep severe potential relatively low, suggesting around 5 to 15% probabilities for the region. If any stronger storms were to form, the most likely timing would in the late afternoon to evening hours, before weakening again overnight with the departure of the shortwave. How long rain sticks around into Saturday remains uncertain as of this forecast as well, with models like the ECMWF and GFS suggesting a prolonged rainy period as an upper jetstreak crosses the area early Saturday, possibly sustaining any showers a bit longer. All things considered, the main concern with this system will be heavy rainfall. PWATs push to around 2-2.3 inches through the evening to early overnight period as convection moves through. Deterministic guidance does suggest corridors of 1+ inches of rain are possible through the overnight period, mainly for areas in central to north-central Wisconsin. Probabilistic guidance keeps the probability of exceeding an inch at any one location to around 20-40%. Taken together this suggests potential for localized heavy rainfall is high, but the exact locations of where the highest amounts fall is less certain although central Wisconsin will be the best bet. A final consideration will be how long rain lasts into Saturday, which will add on to any rain totals from Friday through Friday night. On the worst case side, rainfall totals could push over two inches by end of day Saturday if rain sticks around for a longer duration. Next week... Quieter conditions are then expected for the rest of the weekend and early next week. Long range guidance doesn`t bring another round of active weather through the area until around the middle of the week, when the next cold front will cross the area. && .AVIATION...for 18Z TAF Issuance Issued at 1221 PM CDT Wed Jul 9 2025 A lingering low stratus deck and the development of afternoon cu has left MVFR cigs at all TAF sites except MTW at the start of the 18z TAF issuance. Anticipate the cigs to gradually rise to VFR and/or clouds dissipating over the next couple of hours. However, clouds will linger the longest across the far north due to lake enhanced clouds dropping south from Upper MI. Clearing skies and calm winds should occur by this evening and continue overnight. If enough clearing occurs, could see some patchy fog development across some of the TAF sites by early Thursday morning. Decided to include TEMPO groups with MVFR vsbys at all TAF sites except GRB and MTW. VFR clouds will begin to increase from the west by the end of this TAF period. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Uhlmann AVIATION.......Kruk