Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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533 FXUS63 KGRB 030815 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 315 AM CDT Mon Jun 3 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - Showers and thunderstorms this morning mainly north-central. Chance of showers and storms all areas this afternoon. Heavy downpours possible, but the greatest risk of isolated severe storms will be south of Highway 10. - Scattered showers and storms tonight with heavy downpours the main hazard. - More strong storms are possible late Tuesday into Tuesday night. Gusty winds, small hail, and heavy rain will be the primary hazards. - Conditions hazardous to small craft will be possible at times from Wednesday through Saturday. && .DISCUSSION... Issued at 311 AM CDT Mon Jun 3 2024 Short Term...Today...Tonight...and Tuesday Regional radar shows subtle MCV with convection producing heavy rain from central MN into northwest WI. This initial MCV will shift into northwest WI this morning pushing showers and embedded thunder into areas northwest of AUW to IMT. As the morning progresses, primary H5 shortwave over the Dakotas shifts northeast and main H85 jet shifts north versus east. Result is this initial round of showers and storms will slide more north than east and tend to diminish as they work toward northeast WI and east-central WI. Even so, isolated to scattered showers will be moving across the area. By late morning into early afternoon, area of more concentrated showers and storms will begin to arrive from the southwest. This convection will be from a stronger embedded H7 shortwave within broad mid-level trough that is helping to generate storms over southwest MN to northwest IA this morning with additional activity emerging out of this after daybreak this morning. These rounds of showers and storms with enhanced effective shear peaking over 30 kts eventually shifts east and will have increasing instability to work with into southern CWA mid to late afternoon. Appears at least MLCAPES will reach 500J/kg, if not more toward 1000J/kg. This is when greatest risk of severe storms will occur, though think better chances for more organized storms will be farther south. SPC has nudged the Slight risk (level 2 of 5) into Waushara County with a marginal risk farther north generally south of a line from Wausau to Sturgeon Bay. Generally limited instability and effective shear on the northern edge of this zone will keep severe risk to minimum that far north with greatest risk in our area south of highway 10. Gusty winds and heavy rain could occur though, especially on the northern fringe of the expected stronger storms that will be clipping southern CWA. Temps are tricky today. Most confident that lowest temps upper 60s/near 70 will be over north-central with morning rain and upslope SE winds. Elsewhere, H85 temps up to 15c would yield highs well into the 70s, but readings that high will only be realized with substantial clearing mid morning onward, a dicey proposition today with incoming decaying showers and developing showers and storms from the southwest. Went mid 70s for top end, which is below MOS guidance. If it ends up staying partly to mostly sunny into early afternoon east-central, then temps in the upper 70s, if not near 80, would occur just inland from cooling influence of Lake Michigan. Tonight, cannot rule out some showers or storms at times though generally coverage will be lower than what occurs this afternoon. Main drivers for convection tonight will be warm front in the area and right entrance jet forcing along with an increasing low- level jet. Best chances for rain over northeast and east-central WI. PWATs stay well above 1.5 inches, so heavy rain could occur. Small MBE vectors for a time tonight and warm cloud heights over 11kft support the slow moving, heavy rain idea as well. Mild and muggy night with lows mainly 60-65F. Tuesday will start off generally quiet as the low-level jet from tonight shifts north as does sfc warm front and stronger forcing doesn`t arrive over the far west until late in the day ahead of sharp mid-level trough from scntrl Canada to the northern Plains. Cold front tied to the trough will remain well to the west of Wisconsin through late afternoon. The day will have a summery feel with highs reaching around 80 most areas and dewpoints in the mid to upper 60s. Broad lift ahead of the trough spreads into Wisconsin during the afternoon and will combine with building instability (MLCAPES 1000-1500J/kg) and convective temps that will be achieved fairly early (early to mid aftn) to result in blossoming showers and thunderstorms with greatest coverage over central WI. As it has looked like for last couple days, severe potential is lower and pulse type given weak effective shear less than 25 kts and marginal mid-level lapse rates near 6.5 to 7.0C/km. Heavy rain potential continues with PWATs pushing 1.75 inches which is near the top range for early June and well above the 90th percentile. Long Term...Tuesday Night Through Sunday The extended weather pattern will see a large upper low slow down and "park" over the Great Lakes, keeping periods of active weather in the region in the area through the early weekend. That said, after Wednesday the cooler and drier airmass brought in by this same low will mainly only support light rain and rumbles of thunder but no stronger systems. Tuesday night through Wednesday... Active weather will be on its way across the region during this period of the forecast as a cold front crosses the area in the late evening to overnight hours. While thunder does seem likely at times, especially earlier on in the night, severe weather for our area does not seem likely as the front will passage after instability has already dropped off across the area. That said, lingering weak upper instability plus low level forcing could provide the impetus for some heavy rainfall in the overnight period through Wednesday morning. Precipitable water values up to 1.5-1.7 inches would support another inch or so of rainfall in this overnight period alone, which combined with the rain from Monday and during the day Tuesday could bring some river rises or local ponding on roads. Wednesday afternoon could be bit drier behind the frontal passage, but the next fast moving shortwave could quickly bring in the next round of rainfall Wednesday evening. Rest of the forecast... The upper low is expected to establish itself around the border between northern CONUS and southern Canada by Wednesday night while slowly drifting eastwards over the next 3-4 days. This pattern will make for a gradual shift to more northwesterly flow, which will bring some cooler and drier air along with periods of light rain each day in the forecast. The exact exit speed is not certain, but if you`re looking for a drier forecast there is some hope towards the end of the upcoming weekend and early next week. && .AVIATION...for 06Z TAF Issuance Issued at 1029 PM CDT Sun Jun 2 2024 Conditions will start to deteriorate late tonight into Monday morning as a system approaches from the west. A line of showers is expected to arrive early Monday morning, affecting RHI, CWA, and AUW by around 10Z to 13Z. MVFR to IFR conditions are expected to build in from west to east throughout the morning, becoming more widespread by early afternoon. As storms move through the area Monday morning, western TAF sites are likely to exceed the LLWS threshold as a nocturnal low-level jet propagates to the east. Onshore flow may also result in some early morning lake fog making it inland to MTW. As a result, vsbys may briefly drop to MVFR. Some strong to severe storms may be possible across east-central Wisconsin early Monday afternoon through the evening. Best potential for stronger storms would be from the southern Fox Valley to the lakeshore. Opted not to include thunder in the TAFs due to low confidence given timing and the effect of a stable lake breeze shunting most instability north and west of the Fox Valley. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....JLA/Uhlmann AVIATION.......Goodin