Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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133 FXUS63 KGRB 200914 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 414 AM CDT Thu Jun 20 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - There is a chance of thunderstorms in central and east central Wisconsin this afternoon and tonight. Severe storms are unlikely. - Thunderstorms with gusty winds and locally heavy rain are possible Friday and Friday night. The rain could produce small stream and urban flooding. - Strong to severe thunderstorms with damaging winds, hail and heavy rain are possible Saturday. Heavy rains may cause rivers to rise rapidly. && .DISCUSSION... Issued at 412 AM CDT Thu Jun 20 2024 Short Term...Today...Tonight...and Friday The right entrance region of an upper jet was producing light rain showers across east central Wisconsin at 09 UTC this morning. This jet will exit the forecast area this morning. Another jet streak will approach central and northcentral Wisconsin during the afternoon, and could produce scattered showers and isolated thunderstorms. A surface high centered over Lake Superior will bring a northeast flow of cooler air today with high temperatures five to ten degrees below average on the first day of summer. There is a chance of a shower or thunderstorm tonight in association with weak upper support, but most areas will likely remain dry. Cloud cover will limit how cool it will get, but temperatures should still drop to normal levels for this time of the year. The likelihood of showers and thunderstorms will increase Friday ahead of a warm front moving north from the Illinois border. There will be a lot of moisture in the atmosphere above the stable surface layer, so locally heavy rain is possible with the thunderstorms. Clouds, rain and an east northeast will make for a cool day with highs in the middle 60s to low 70s. Long Term...Friday Night Through Wednesday Main focus of the extended period will be the potential for heavy rain and stronger thunderstorms Saturday as a low pressure system moves across the region. Confidence in the flood risk is increasing, especially for low-laying and urban areas. Friday Night through Saturday...Moderate to heavy rain will likely be ongoing Friday night with widespread isentropic ascent over the region as a warm front slowly lifts north. The heaviest band of rainfall fall Friday night into Saturday morning will likely be focused across northern WI along the noise of developing 30-40kt low- level jet. Periods of heavy rainfall are progged to continue into Saturday afternoon as models show a deepening low pressure system propagating across the Dakotas toward the Minnesota Arrowhead. The axis of heaviest rainfall during this period will likely be focused along the axis of greater frontogenetic lift which is currently forecast to develop generally along a line from east-central MN to central WI. In combination with the abundant lift, the expected heavy rain is the result of an anomalously moist air mass moving over the region. Medium range guidance is showing PWATS ranging from 2- 2.5 inches which is in the 99th percentile of the CFSR climatology database. In terms of total QPF Friday through Sunday, ensemble models are showing a 15-40 percent chance for greater than 2.5 inches of rain with the highest chances in central and north-central WI. Deterministic models are more bullish with the GFS, ECMWF, and Canadian all showing high end amounts of 3-4 inches. There is more uncertainty with the severe weather potential Saturday, compared to the heavy rain potential. A few stronger discrete cells may develop over central WI Saturday morning, however the better chance for stronger to severe thunderstorms looks to come Saturday afternoon and evening as a cold front sweeps across the region. However, with relatively modest low and mid-level lapse rates forecast sounding show tall skinny CAPE profiles with MUCAPE values up to about 500 J/kg in central WI which is not necessarily an environment that would favor quickly accelerating updrafts. Effective shear values of 35-45 kts are expected along the cold front which could help to sustain any updrafts that are able to develop. If stronger storms are able to develop strong wind gusts and hail would likely be the main concern. Sunday through Wednesday...Once the cold front passes through the region the risk for heavy rain will diminish, however, a few showers and storms may linger into Sunday as moisture wraps around around the departing low. Ensemble models then favor a high pressure system taking over Monday returning dry conditions to the region. The upper- level is then forecast to flatten out toward the middle of next week allowing a few chances for showers and storms to cross the area Tuesday and Wednesday. Temperatures are expected to start warming back up next week with highest on Tuesday expected to peak in the middle to upper 80s. && .AVIATION...for 06Z TAF Issuance Issued at 1045 PM CDT Wed Jun 19 2024 Cold front has settled south and east of the area so stronger showers and thunderstorms have ended for the night. Still could be waves of lighter showers crossing the area at times overnight into Thursday with best chances late tonight into midday Thursday over east-central WI. At this point, it does not look like the showers on Thursday will be widespread. Meanwhile it will remain mostly dry at AUW/CWA/RHI until late Thursday afternoon as a warm front shifts in from the southwest and an upper disturbance crosses the northern plains. Conditions will be mostly VFR this evening, but will trend MVFR overnight into much of Thursday at east-central WI terminals as a cooler/moist NE flow develops to the north of the front. Cigs will drop to IFR near the lakeshore at times with some fog as well, including at MTW. Cigs will improve to VFR late on Thursday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....RDM/GK AVIATION.......JLA