Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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471 FXUS63 KGRB 130902 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 402 AM CDT Thu Jun 13 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - Showers and embedded storms will taper off over central and east central WI early this morning, and another round may occur south of Hwy 29 during the late morning and early afternoon. - Well above normal temperatures are forecast from Sunday into the middle of next week. Heat indices may surpass 90 degrees at times. - The next chance for widespread rainfall arrives Saturday night. It is uncertain if these storms would become severe, but locally heavy rainfall will be possible. - There are periodic chances of thunderstorms next week, although there is a lot of uncertainty in timing and location of the storms. With the building heat, stronger storms and locally heavy rainfall may be possible at times. && .DISCUSSION... Issued at 401 AM CDT Thu Jun 13 2024 Short Term...Today...Tonight...and Friday An area of showers and embedded storms was moving through C/EC WI early this morning. This activity was being sustained by moisture convergence and WAA associated with a 35-40 knot WSW low-level jet. This activity should continue to shift east and weaken shortly after daybreak as the LLJ veers west and convection shifts into a less unstable air mass. South winds gusting to 30 to 35 mph were occurring due to a wake low on the northern periphery of the eroding stratiform precipitation shield. Farther west, additional thunderstorms were developing in northern ND, in association with mid-level frontogenetic forcing. A weak cold front extended from western Lake Superior SWWD to SC MN. A moist and marginally unstable air mass was present in advance of the front, with MUCAPE of 400-800 j/kg and PWATs of 1-1.25 inches. Thunderstorm Potential and Gusty Winds Today: Ongoing storms over C/EC WI should shift south and east of the forecast area by 7 am, followed by a short break in the activity. The previously- mentioned mid-level frontogenetic forcing and the RRQ of an upper jet should bring another area of showers and embedded storms to areas south of Hwy 29 during the late morning/early afternoon. CAPE is expected to increase to 1000-1500 j/kg by the time this convection arrives, so a few strong storms with gusty winds and small hail may occur. Otherwise, do not expect extensive development as the weak cold front moves through, as westerly flow at 925/850 mb will result in shallow/weak convergence. Later in the day, short-wave energy will brush through northern WI, and bring isolated to scattered light showers to areas near the WI/MI border in the late afternoon and early evening. High temperatures will be in the middle 70s to lower 80s. Lower humidity should be noticed later in the day, in the wake of the cold frontal passage. Deep mixing through 6-8k feet should tap into strong winds aloft, resulting in west winds gusting to around 30 mph this afternoon. Gusts should not be as strong over Lake Michigan, due to more stable conditions over the relatively cool waters. Thus, expecting gusts to remain below the 25 knot threshold for a Small Craft Advisory. Tonight/Friday: Canadian high pressure will bring mainly dry conditions tonight into Friday, along with comfortable temperatures and lower humidity. Lows tonight should range from the upper 40s/lower 50s northwest to the 50s elsewhere. On Friday, developing northeast winds and Canadian air mass will result in highs in the lower to middle 70s, except mid to upper 60s lakeside. Long Term...Friday Night Through Wednesday The change in the 500mb pattern early next week will lead to the potential first heat wave of the summer. The 00z models tonight all indicate building 500mb ridge across the eastern United States with developing 500mb trough over the western United States. The ECMWF is most aggressive with the ridge building into the western Great Lakes. The placement of the 500mb features will put us in the ring of fire for much of next week. The differences in the model solutions with the upper air features and the placement of convective systems can be seen in the model guidance, especially the surface features and the Qualitative Precipitation Forecast (QPF). The ECMWF/Canadian model are considerably warmer than the GFS, and this shows up on the numerical guidance values for highs/lows based off the GFS/ECMWF models. For Friday night, it will be cool across the north with several locations falling into the middle to upper 40s. On Saturday, temperatures will rebound into the 70s as clouds will be on the increase during the day. There are still timing difference when the rain will arrive, but looking at mid to late afternoon across our western counties. On Saturday night, the low level jet cranks up to near 40 knots with plenty of moisture flowing northward. Elevated instability will lead to the increasing chances of thunderstorms during the evening across our western counties, then across the entire area overnight. Locally heavy rainfall is the main concern, although some stronger storms are possible with gusty winds and hail as 0-6km shear values increase to 30 to 35 knots. The greatest risk of stronger storms would be across central into east-central Wisconsin. Sunday continue to be problematic with respect to high temperatures. Ongoing convection and cloud cover linger through much of the morning with some partial clearing possible in the late morning and afternoon. Additional convection may redevelop during the afternoon. Have trended lower on high temperatures on this day due to the continued persistence of the convection and expected cloud cover. For Monday, the Canadian and ECMWF model push the front into northern Wisconsin which would allow temperatures to climb well into the 80s and lower 90s across central and east-central Wisconsin with the afternoon heat index values climbing into the lower to middle 90s. The GFS model solution has the front south of the area with convection along it. From Monday through Wednesday, will need to worry about the ring of fire as thunderstorm complexes are expected at times that would move across the Upper Midwest and western Great Lakes. These features can produce outflow boundaries and push the front southward that could mess up the high temperature forecast at times, with cooler readings than expected. The forecast high temperatures from Monday through Wednesday are a blend of the warmer ECMWF numerical guidance and the cooler GFS guidance. The Canadian model would support the warmer ECMWF guidance values. && .AVIATION...for 06Z TAF Issuance Issued at 1050 PM CDT Wed Jun 12 2024 A cluster of showers and thunderstorms will continue tracking through the TAF sites during the overnight hours from northwest to southeast. The strongest storms could produce small hail and gusty winds, but should remain below severe limits. This activity will wane through early Thursday morning. Conditions could briefly drop to MVFR with the showers and thunderstorms. In the wake of the storms, MVFR low clouds may stick around for a time over far northern WI, including RHI, but then clear for a time on Thursday morning. Convective clouds are then expected to build over east-central WI by late morning, which could lead to scattered showers developing. Gusty west winds to 25 kts are possible at the taf sites on Thursday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/Eckberg AVIATION.......Kurimski