Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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550 FXUS63 KGRB 041207 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 707 AM CDT Tue Jun 4 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - A few strong storms are possible this afternoon into tonight. Gusty winds and small hail will be the primary hazards. Locally heavy rainfall is also possible with isolated amounts of 1 to 2 inches. This may lead to localized flooding, especially in urban and low-lying areas. - Gusty southwest to west winds up to 35 mph are expected on Wednesday. Locally higher wind gusts are possible in the afternoon and early evening associated with any shower or storm. - Conditions hazardous to small craft will be possible at times from Wednesday through Friday. && .DISCUSSION... Issued at 427 AM CDT Tue Jun 4 2024 Short Term...Today...Tonight...and Wednesday Active weather continues this afternoon into Wednesday with rounds of showers/storms expected. Main forecast focus is on the potential for heavy rain, localized flooding, strong storms and fog trends. Lingering showers and possibly a rumble of thunder will remain possible across eastern WI early this morning, then the rest of the morning is looking dry. A weak shortwave/boundary and increase in theta-E will work north/east across the area this afternoon and evening, bringing isolated to scattered showers and storms. Then a cold front will sweep across the state later this evening into the overnight, bringing a round of more widespread showers and storms. A secondary shortwave will rotate across the state Wednesday morning, likely producing an uptick in activity, before everything exits to our east by noon. Additional showers and storms are expected later on Wednesday as the parent upper low/shortwave drops south into Lake Superior, swinging another cold front across the state. Threat for widespread severe weather is low today due to the lack of much shear (under 15 kts), but a pulse-type stronger storm will be possible as CAPE increases to over 2000 J/kg this afternoon. Gusty winds and small hail (high wet- bulb heights and skinny CAPE will limit hail production) will be the main threat. CAPE will wane in the evening as we lose daytime heating, so as the front arrives, severe chances remain very low. But if the line of storms has enough momentum, it could sneak into parts of central and north- central WI with some stronger winds. Instability will be down Wednesday afternoon, under 500 J/kg, but shear will be better, closer to 35 kts. So a stronger storm will be possible late in the afternoon, especially across northern WI, with strong winds (inverted-V signature) and hail the main threats. PWATs between 1.3-1.7" will provide for a heavy rain threat in any storm. But due to the 1+ inches totals yesterday being fairly spotty, the heaviest rain overnight staying south of Fond du Lac and the progressive nature of the front, will hold off on a flood watch. Most rivers are well below bankfull as well. However, localized flooding will be possible where/if any storms can move across the same location ahead of the front, especially in urban areas. And rises in some area rivers is expected through at least mid-week. Fog and Trends: Patchy/areas of fog and low stratus will continue north and west of the Fox Valley. The fog may be locally dense at times, especially just south of the low stratus deck and north of the mid/higher clouds to the south/east. The fog and low clouds will mix out and lift through morning. If clouds can clear by sunrise Wednesday morning, some fog could develop across central and north-central WI, but current forecast has clouds hanging on just long enough to avoid fog development. As dewpoints climb on Lake Michigan, and lake temps in the low to mid 50s, some lake fog will be possible as well. Temps / Dewpoints: It will be a warm and humid day with highs climbing into the upper 70s to mid 80s, except cooler readings near the Lake Michigan shore line. Dewpoints will be in the mid to upper 60s for most spots, with a 70 possible (currently 70 degree dewpoints in far southern WI). This will push heat index readings a couple/three degrees warmer. Behind the front, slightly cooler and less humid air will arrive, but will remain on the mild/muggy side in the Fox Valley. Highs mainly in the 70s are expected on Wednesday, with less humid conditions expected as dewpoints drop mainly in the 50s. Long Term...Wednesday Night Through Monday The long term forecast will be dominated by an upper-level closed low progged to sit over the central Great Lakes region. This will result in multiple chances for light showers and isolated thunderstorms through this weekend and into early next week. Wednesday evening through Thursday...Before the closed low reaches the central Great Lakes region on Friday, it will gradually be diving southeast across the Upper Mississippi Valley Wednesday evening through Thursday. Meanwhile, a cold front will sweep across the forecast area Wednesday evening. Anticipate showers and some thunderstorms to accompany the front. While severe weather is not expected, cannot rule out a few strong storms capable of strong winds as forecast soundings indicate an inverted-V signature, aiding to transport stronger winds to the surface. These showers and storms will quickly exit by late Wednesday night, but additional showers are anticipated for Thursday as the upper-level low will be moving overhead. Rest of the extended...With the upper-level closed low in position over the central Great Lakes Friday through early next week, additional precip chances will be determined by shortwaves circulating around the low. However, at this time it is too difficult to determine when the precip will occur due to weak forcing and the light nature of the precip. Overall, anticipate on and off chances for showers and isolated thunderstorms from Friday through early next week. && .AVIATION...for 12Z TAF Issuance Issued at 707 AM CDT Tue Jun 4 2024 Low clouds and stratus will lift this morning, leaving VFR conditions. Then spotty MVFR conditions are expected as isolated showers and storms develop this afternoon. Best chances (40-50%) will be in central and north-central WI (AUW/CWA/RHI), with lower chances (under 30%) at GRB/ATW. Did not include any thunder with this activity as chances are too low to include in any one spot. Better chance for thunder, along with IFR/MVFR conditions, arrives tonight ahead of a cold front. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Bersch/Kruk AVIATION.......Bersch