Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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834 FXUS63 KGRB 201938 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 238 PM CDT Fri Sep 20 2024 Forecast discussion for routine afternoon forecast issuance .KEY MESSAGES... - Unseasonably warm temperatures will continue Saturday before temperatures return closer to normal Sunday into early next week. - There is a Marginal risk of severe storms with strong winds and hail across central and north central WI during the late afternoon and early evening on Saturday. && .DISCUSSION... Issued at 237 PM CDT Fri Sep 20 2024 Short Term...Tonight and Saturday Forecast concerns include fog potential tonight and a Marginal risk of severe thunderstorms across central and north central WI late Saturday afternoon. A cold front had shifted east of the region this afternoon, as evidenced by westerly winds and falling dew points at observation sites. Dry conditions prevailed, and scattered cumulus formed due to daytime heating. Temperatures ranged from the middle 70s to lower 80s. High pressure will bring clear to partly cloudy skies tonight, with generally dry conditions anticipated. Some models show a few light showers moving into north central WI late, perhaps the result of weakening elevated convection that develops upstream of the region on the nose of a low-level jet. Have opted to leave these showers out of the forecast for now. Of greater concern is the potential for some fog development, especially over far northeast WI, where models are forecasting the lowest visibilities and possibly some patchy dense fog. Lows should drop into the 50s, except upper 40s in the typical cool spots in north central WI, and around 60 in parts of Door County. Saturday will start off mostly sunny and dry, but an approaching cold front is expected to trigger thunderstorms in central and north central WI during the late afternoon, mainly after 4 pm. MUCAPE of 500-1000 j/kg, deep layer shear of 30-40 knots, and 0-3 km helicities of 150-200 support potential for a few strong to marginally severe storms with gusty winds and hail. SPC has expanded the Marginal risk into C/NC WI, and this seems reasonable. high temperatures will be in the lower to middle 80s, except mid to upper 70s near Lake Michigan. Long Term...Saturday Night Through Friday Primary period of focus for the extended forecast is Saturday night through Sunday as a cold front crossing the region returns a chance (50-60%) for showers and storms. There may be ongoing thunderstorms at the start of the period as MUCAPE peaks around 1000-1200 J/kg Saturday late afternoon. Additionally, forecast soundings show 30- 35kts of 0-6km layer shear during this time which may support stronger storms capable of producing strong wind gusts, and hail. Periods of moderate to heavy rain may also be possible as PWATS climb to 1.2-1.4" inches during this time. Showers may linger into Sunday afternoon as a short-wave trailing the initial cold front clears the area. General expecting most places to see under 1" of rain rain by Sunday evening, only 10-20% probs for greater than 1" across central and east-central WI. Do expect the region to clear out and turn dry Sunday night as dry continental air moves into the mid-levels. The passage of the cold front Saturday into Sunday will also usher in more seasonal temperatures. Highs Sunday through the middle part of next week are forecast to range from the middle 60s to low 70s with less than a 10% chance to exceed 75 degrees. Overnight nights lows will also trend about 5 to degrees cooler than the last several days. Statistical guidance is showing the chance for lows Monday morning to drop into the middle to upper 30s across the Northwoods. Will need to monitor this trend for possible frost/freeze headlines. The forecast in terms of precipitation chances during the early to middle part of next week is rather uncertain. The latest LREF run has trended drier than previous runs. This is in large part due to a southward trend of a low pressure system that is forecast to eject out of the central Plains early next week. However, there is chance (20-30%) that eastern WI sees a few showers as moisture wraps around the northern part of the low late Monday into Tuesday. Another system is then forecast to dive south toward the Ohio Valley Wednesday into Thursday which may produce a glancing shower or two, but generally expecting dry conditions during the middle of the week. && .AVIATION...for 18Z TAF Issuance Issued at 1241 PM CDT Fri Sep 20 2024 Patchy MVFR ceilings lingered along the Lake Michigan counties, where a cold front resided early this afternoon. Otherwise, SCT- BKN cumulus clouds and VFR conditions prevailed. Daytime cumulus should dissipate by around sunset, leaving mostly clear skies for the overnight period. This, combined with light winds, should allow patchy/areas of MVFR/IFR fog to form overnight, especially across far NE WI. Any fog should mix out early Saturday morning, with VFR conditions returning regionwide. A cold front will bring a chance of showers and thunderstorms late Saturday afternoon into Saturday night, but that is beyond this TAF period. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kieckbusch/GK AVIATION.......Kieckbusch