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Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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641 FXUS63 KGRB 161952 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 252 PM CDT Fri Aug 16 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Isolated severe storms possible into this evening over central, east-central, and far northeast Wisconsin. Strong wind gusts, small hail and torrential rainfall are the main hazards. - Locally heavy rainfall in excess of an inch possible will accompany any slow moving thunderstorms. The heavy rain could produce localized flooding in urban, low-lying, and poor drainage areas. - Additional showers and storms on Saturday, especially eastern WI, then quiet weather conditions and near-normal temperatures in the mid 70s to low 80s are expected Sunday into much of next week. && .DISCUSSION... Issued at 251 PM CDT Fri Aug 16 2024 Short Term...Tonight and Saturday Forecast concerns include precipitation trends, and potential for severe weather and heavy rainfall. Numerous showers and scattered thunderstorms were ongoing over much of the forecast area this afternoon, as forcing associated with a western WI short-wave encountered a moist (PWATs around 1.5 inches) and unstable (SBCAPE of 1500-2500 j/kg) air mass. So far, thunderstorms have remained below severe limits, as deep layer shear was only 10-25 knots (strongest southeast) and wet-bulb zero heights were high (10.5-11.5k ft AGL). Pockets of heavy rainfall have been reported, and the threat of continued heavy rainfall and localized urban flooding will remain the primary concern through this evening. An isolated severe storm with damaging winds is still possible through about sunset. There will be a decrease in convection as the short-wave shifts east this evening, but showers and isolated storms will likely persist over far NE WI; especially Door County, through the night. Low clouds and patchy fog are expected overnight, though surface and boundary layer winds should increase enough to prevent dense fog formation. Lows will be in the lower to middle 60s. On Saturday, the upper low will shift east of the region, but short-wave energy will continue to wrap around its western periphery. This will combine with cyclonic north flow and modest daytime instability of 500-1000 j/kg to support showers and a few thunderstorms, especially during the afternoon. Shower coverage will be less over the far west; farther removed from the upper low. Highs will in the 70s. Long Term...Saturday Night Through Friday Low pressure crossing northern WI this evening will only shift across lower Michigan by Saturday evening. Some showers and thunderstorms over eastern WI will diminish by late evening. Fog on Saturday night probably ends up limited due to steady north winds developing in wake of the low. Still looks like Small Craft Advisories may be needed late Saturday night into Sunday Night. However, the north wind direction will result in an offshore flow and minimal wave action so will not need any Beach Hazards Statements. Thereafter, northwest flow will be present over the western Great Lakes through the middle of next week before the upstream ridge moves overhead late in the week. Still some hints a cold front may try to drop across late in the week. Overall though precip chances look low (staying less than 20 percent for any time frame). Temps will not be too far from normal with highs upper 70s to lower 80s. Lows will start out 40s north to mid 50s south, then gradually increase into the 50s to lower 60s by late in the week. && .AVIATION...for 18Z TAF Issuance Issued at 1237 PM CDT Fri Aug 16 2024 Showers and thunderstorms were developing over the region due to increasing daytime instability (CAPE of 1500-2500 j/kg) and the approach of a well-defined short-wave trough over western WI. The first line of storms is poised to impact AUW/CWA at TAF issuance, with potential for torrential rainfall and gusts to 35-40 knots. The storms will continue to shift east through early evening, so have framed out TEMPO groups for the most likely period of storms at each TAF site. Flight conditions will vary between VFR and MVFR this afternoon and early evening, except for local IFR/LIFR vsbys in heavy rainfall during storms. Expect shower activity to wind down early this evening, though showers and isolated storms may continue to impact eastern WI, and especially Door county, through the rest of the TAF period. Look for MVFR ceilings to gradually lower to IFR/LIFR later tonight, and vsbys to drop to MVFR/IFR in fog. Not really expecting dense fog at this time, as N-NW winds will be picking up a bit later tonight into Saturday morning. The very low ceilings should start to rise during by late morning, with most locations improving to MVFR toward the end of the TAF period. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/JLA AVIATION.......Kieckbusch