Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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456 FXUS63 KGRB 271108 AFDGRB FXUS63 KGRB 270812 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 312 AM CDT Thu Jun 27 2024 Forecast discussion for routine morning forecast issuance .KEY MESSAGES... - Showers and thunderstorms may bring locally heavy rainfall to the region Friday and Friday night. Small hail is possible with some storms on Friday night, but the severe weather threat is low. - Small Craft Advisory may be needed from Friday morning through Friday night on Lake Michigan. - Some rivers and streams will remain above bankfull and near flood stage into the middle of the week. && .DISCUSSION... Issued at 312 AM CDT Thu Jun 27 2024 Short Term...Today...Tonight...and Friday Cool weather will continue across northeast Wisconsin today as high pressure drifts off to the east. A deck of mid clouds will persist across central and north-central Wisconsin early this morning before giving way to mostly sunny skies later this morning. Later in the day clouds will increase from the west as a low pressure system develops across the northern Plains. Highs today are expected to mainly be in the upper 60s to lower 70s. Clouds will continue to thicken and lower tonight as the aforementioned low pressure system tracks east towards the upper Mississippi Valley tonight. While much of the area will remain dry for most of tonight, some precipitation could make it into central and north-central Wisconsin late tonight. Lows tonight will be a bit warmer given the abundant cloud cover; with temperatures mainly in the 50s. The main surface low slows down and stalls across Minnesota on Friday as two mid level PV anomalies track through northern Wisconsin and Illinois. These shortwaves and some modest warm air advection will bring widespread light rain showers and isolated thunderstorms on Friday, with the best chance for thunder on Friday afternoon due to the increased instability. Model soundings indicate thunderstorms will mainly be elevated, with MUCAPEs of only 300 to 600 J/kg Friday afternoon. Therefore, severe weather is not expected during the day on Friday. Highs on Friday are expected to range from the upper 60s across north-central Wisconsin, to the middle 70s across east-central Wisconsin away from the lake. Given the fairly meager forcing, heavy rainfall is not expected on Friday as QPF amounts should generally be one half of an inch or less. The probability for greater than one half of an inch of rain is fairly low and at most 20-30 percent across far western central and north-central Wisconsin. Long Term...Friday Night Through Wednesday Focus of this forecast continues to revolve around the thunderstorm and severe potential for Friday night. Friday night into Saturday... A relatively potent shortwave trough will push a cold front across the region on late Friday night into early Saturday morning. Strong to severe thunderstorms will likely be ongoing upstream and along the front over Minnesota within a instability axis of 1500-2500 j/kg. As the front moves east, most unstable capes within the instability axis weaken to 600-1000 j/kg by the time it moves into north-central Wisconsin around 1 am Saturday. Forecast soundings indicate storms will be elevated by this time with a stout inversion present around 850-800mb. While surface to 6 km shear will be increasing with the approaching front, effective bulk shear values are only around 20 kts due to the inversion present. Therefore think there will be an elevated hail threat with storms, and perhaps an isolated large hail threat should a storm acquire a rotating updraft. Despite precipitable water values upwards of 1.75 inches, the threat of excessive rainfall appears low on Friday night. The percent chance of greater than 0.25 inches of rainfall is only around 10% from 7 pm Fri to 7 am Sat. Therefore dont think there is a significant risk of flooding with storms on Friday night. The chance of showers and a few storms will continue on Saturday morning until the front clears. Behind the front, the boundary layer remains modestly moist beneath troughing aloft. Forecast soundings indicate deep mixing over north-central WI with skinny cape values up to around 700 j/kg. Could see additional shower and isolated storm development on Saturday afternoon that could bring a gusty wind threat. Rest of the forecast...After quiet weather on Sunday and Monday, strong warm advection will bring a widespread thunderstorm chance to the region on Monday night into Tuesday. Wind fields are fairly robust, so will need to monitor for a severe thunderstorm chance. && .AVIATION...for 06Z TAF Issuance Issued at 1110 PM CDT Wed Jun 26 2024 VFR conditions are expected through the TAF period. Late evening mid-level clouds will linger over east-central WI tonight, with additional clouds arriving across central and north-central WI. Some of these clouds may linger into Thursday morning, with additional daytime cumulus clouds developing on Thursday as well. There will also be high clouds spreading across the region ahead of the next system. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Kurimski/MPC AVIATION.......Bersch