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Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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182 FXUS63 KGRB 281129 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 629 AM CDT Fri Jun 28 2024 Updated aviation portion for 12Z TAF issuance .KEY MESSAGES... - Thunderstorms are possible from late this afternoon through tonight which will bring an isolated chance for rainfall amounts greater than 1 inch, gusty winds, and hail. The overall severe thunderstorm potential is low. - Increasing winds and waves will create hazards for mariners and beach-goes on Friday. A Small Craft Advisory and Beach Hazard Statement have been issued. - Some rivers and streams will remain above bankfull or near minor flood stage into the middle of the week. - The next period to watch for heavy rain or stronger storms will be late Monday through Tuesday. && .DISCUSSION... Issued at 335 AM CDT Fri Jun 28 2024 Short Term...Today...Tonight...and Saturday Precipitation will likely occur in two waves today and tonight. The first wave, currently shown on doppler radar making its way into central and north-central Wisconsin, will track through today as a string of weak shortwaves tracks through the western Great Lakes region. The surface low, currently analyzed over eastern North Dakota, will slowly track east towards northeastern Minnesota by this afternoon. This initial round of rain will be fairly light, with rainfall amounts well below an inch. Probabilistic rainfall amounts for today bear this out as the probability for an inch is only around 10 percent and mainly focused on western portions of central and north-central Wisconsin. Some thunderstorms are possible this afternoon as MUCAPEs rise to 300 to 600 J/kg. These initial storms are not expected to be severe given the limited instability, forcing, and effective shear of only 20 knots. Highs today are expected to range from around 70 across the north, to the lower 70s across central and east-central Wisconsin. The second wave of rainfall will occur tonight as the main low continues tracking east through the northern Great Lakes as the attendant cold front makes its way into Wisconsin. The heavy rainfall threat still isn`t high, but higher than the precipitation today as the probability for an inch or more of rain rises to 20 to 40 percent across the region. Therefore, while rainfall amounts of 0.50 to 0.75 are generally expected tonight, amounts up to 1 inch are possible. Thunderstorms will likely be more likely tonight, especially this evening, with better forcing, instability and shear. MUCAPEs rise to around 1000 J/kg along with effective shear of 40 knots and a potent mid level shortwave tracking through the western Great Lakes coincident with the cold front. Some storms could be strong to severe with gusty winds and hail the main threats. Lows tonight are expected to mainly be in the lower to middle 60s. Although the initial cold front will be through the area late tonight into early Saturday morning, a secondary cold front will track through on Saturday. This will bring additional chances for showers on Saturday (20-30 percent) mainly across central and northern Wisconsin. Some modest SBCAPE values of 300-600 J/kg will mean thunderstorms will be possible with the shower activity but should remain below severe levels. Highs on Saturday are expected to range from around 70 across far north-central Wisconsin given the earlier fropa from the second cold front, with highs in the lower 80s across east-central Wisconsin with the later arrival of the front. Long Term...Saturday Night Through Thursday Focus of this forecast revolves around the thunderstorm and heavy rainfall potential from Monday night through Tuesday night. Saturday night...A potent shortwave trough will be passing across northeast Wisconsin in the evening. With such strong forcing, could see scattered showers lingering along the Lake Michigan shoreline early in the evening. Instability is negligible by this point, so the risk of strong thunderstorms is low. Then clearing will occur overnight. Monday night through Tuesday night...On the backside of a large high pressure system, strong warm advection will occur on Monday night thanks to a 30-40 kt low level jet, pushing precipitable water values (pwats) over 1.50 inches. Models generate widespread precipitation in the elevated moisture gradient/convergent zone from late evening into the overnight hours. Despite the strong ascent, instability is very weak at 100-200 j/kg, so severe weather chances look low. But some showers could generate a moderate rainfall with probability of 1/2 inch of rain from 25 to 50%. After a relative lull in the precip on Tuesday morning, a second round of precip is expected on Tuesday afternoon and Tuesday evening along the cold front. Most unstable cape values remain modest and up to around 1000 j/kg, likely because of cloud cover and intermittent light precip through the day keeping the boundary layer cool. With pwats climbing above 2.00 inches, heavy rainfall and strong storms appear possible, so will need to monitor trends in subsequent forecasts. Scattered showers look to continue on Wednesday beneath flattened troughing. && .AVIATION...for 12Z TAF Issuance Issued at 621 AM CDT Fri Jun 28 2024 VFR conditions this morning will give way to deteriorating conditions into the MVFR/IFR categories as rain spreads across the area. Thunder threat is very low with this first area of showers. A secondary area of showers is forecast to spread in this evening, with better (mainly elevated) instability. But there is still some uncertainty on if/how widespread the storms will be, so will hold off on a mention of thunder. Some LIFR conditions will be possible in central and north-central WI this evening and across the rest of the area late tonight. Some low- end LLWS will be possible today as a LLJ of ~50 kts pushes over the area. && .GRB WATCHES/WARNINGS/ADVISORIES... Beach Hazards Statement from 10 AM CDT this morning through Saturday morning for WIZ022-040-050. && $$ DISCUSSION.....Kurimski/MPC AVIATION.......Kurimski