Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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770 FXUS63 KGRB 071147 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 647 AM CDT Sun Jul 7 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Isolated strong thunderstorms are possible this afternoon/evening. Main threats with any stronger storms will be gusty winds and heavy rain. Severe weather is not currently expected. - On and off chances for showers and thunderstorms will continue Monday through Wednesday. 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 summer pattern may be in store toward the end of next week. && .DISCUSSION... Issued at 406 AM CDT Sun Jul 7 2024 Short Term...Today...Tonight...and Monday Thunderstorm coverage and strength through tonight main focus of the short term. WV loop shows broad mid to upper level trough is present from south central Canada to the northern Plains. Within the trough sharper shortwave is lifting into northern MN with additional shortwaves crossing IA with some weak convection. At the surface, weak low is over eastern ND while broad ridge is centered over the Ohio Valley. As high departs and low approaches, elevated warm front works across the region this morning. Isentropic ascent along the boundary coupled with moisture advection is spurring will continue to support broken band of showers and some rumbles of thunder slowly pushing into western WI. Today...Some of the remnants of these showers as well as the other area of showers moving into far southwest WI will slowly move into far west and southwest CWA by mid morning. Appears they will weaken as they outrun higher MUCAPEs well to the southwest since there is minimal low-level jet to carry the instability farther east. Eventually by early afternoon, expect additional showers and some thunderstorms to develop likely over north- central WI and over southern WI ahead of another shortwave coming out of IA. MLCAPEs forecast to reach 1000-1500J/kg (as temps reach mid 70s to lower 80s) which will verify so long as the initial mid-level clouds and any showers don`t dampen the instability too much. That instability will be acted upon by modestly stronger mid-level winds ahead of the trough which yields 30-35 kts of effective shear. Greatest risk of an isolated stronger storm will be over far north-central WI closer to the mid-level low and sfc lows over northern MN. PWATS climb above 1.25 inches but warm cloud depths well under 10kft are lower than recently. Corfidi vectors do suggest storm motions could become slow, so could have some heavy downpours. Gusty winds also possible, especially if we realize the insolation and increasing CAPEs, steeper low-level lapse rates. Mid-level lapse rates lacking at only 6c/km or less, so don`t expect much chance for anything more than small hail. Tonight...After this potential for thunder impacts the area into early evening, could be another round of showers and some thunder overnight especially east-central WI where better low-level jet is forecast to develop ahead of sfc low and approaching front. This is also where corridor of highest PWATs (perhaps up to 1.80 inches) will be located. Some models and CAMS point to this idea, but others keep showers and storms mostly to our east. HREF and NBM probabilities for 6hr QPF are rather muted with <10 percent chance of seeing over 0.50 inch during the overnight period. Thus, will not play this potential up too much. If it did occur though, main hazard would be heavy rain over east-central WI where soils remain saturated and rivers remain high after recent heavy rainfall. So, something to watch in a nowcasting sense. Monday...Probably a general lull in wake of what occurs tonight and as low-level jet gradually veers more WSW-W. Better chances for showers and some thunder in the afternoon as primary front arrives over central to north-central WI. Depending on extent of instability building up in the afternoon (current indications are at least pockets of MLCAPEs over 1000J/kg) could see some stronger storms as mid-level jet is stronger and effective shear ramps up to 40 kts. Stronger low-level jet will be aimed into MI but the shear, instability balance and approaching front supports another mention of gusty winds and heavy rain with stronger storms. Most likely best chances for strongest storms would be ahead of the front during peak heating from northeast to east-central WI. Long Term...Monday Night Through Saturday Not many changes to the extended. Focus continues to revolve around on and off rain/storm chances through Wednesday as the central CONUS remains under persistent troughing. Main forecast concern will involve monitoring the track of Beryl and what impacts it may have on the eastward progression of upper-level ridging toward the middle of the week. Monday evening through Tuesday... A combination of decent moisture, daytime instability, and weak shortwave energy will be enough to keep some pulse showers/storms in the forecast through Tuesday. Coverage will likely be spotty given high convective temperatures and lack of any real surface features. Some stronger storms may be possible during peak heating, although overall convective elements aren`t supportive of anything severe. For this reason, locally heavy rainfall looks to be the main threat with any stronger cells. Rest of the extended... As has been previously advertised, a warmer/drier pattern may be in the works for much of the Midwest toward the end of the week. However, there are still some questions as to how long this dry spell will last, especially as the remnants of Beryl make their way up into the Great Lakes on Wednesday. Most models currently suggest a northeast track through Michigan`s lower peninsula as Beryl weakens and enters an environment of prevailing westerly flow. However, any westward shift would likely spell out additional rain chances for eastern Wisconsin through the end of the week. Will continue to monitor over the next few days. && .AVIATION...for 12Z TAF Issuance Issued at 646 AM CDT Sun Jul 7 2024 A weak warm front will lift across the region today. Showers this morning should gradually fade away as they move across central WI. Scattered showers and a few thunderstorms are possible this afternoon during the heating of day with greatest coverage north- central. Another round of showers and some thunderstorms will lift across the region overnight tonight. The greatest risk for thunderstorms will be across east-central WI. Other than local IFR fog through 14z at MTW, expect VFR conditions to prevail through most of tonight. Heavier showers or storms could drop conditions to MVFR briefly though. Late tonight, IFR/MVFR conditions may become more widespread over north-central WI, including at RHI. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA/Goodin AVIATION.......JLA