Area Forecast Discussion
Issued by NWS Green Bay, WI
Issued by NWS Green Bay, WI
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029 FXUS63 KGRB 301718 AFDGRB Area Forecast Discussion National Weather Service Green Bay WI 1218 PM CDT Sun Jun 30 2024 Updated aviation portion for 18Z TAF issuance .KEY MESSAGES... - The cold spots over north-central Wisconsin could see low temperatures in the 30s tonight. Widespread frost is not expected, but protecting cold sensitive plants are encouraged. - Periods of heavy rain will be possible from late Monday night through Tuesday night. There is a 40 to 70 percent chance of rainfall greater than 1 inch over central to east-central Wisconsin. - The next chance of widespread rain will arrive late on July 4 into July 5. && .DISCUSSION... Issued at 229 AM CDT Sun Jun 30 2024 Short Term...Today...Tonight...and Monday Cold air advection into the region will setup a fairly robust area of high pressure over the western Great Lakes for the latter half of the weekend through Monday. As result, expect clear skies and cooler temperatures for both today and Monday. High temperatures will run below normal as well, with highs in the upper 60s to middle 70s today, and in the lower to middle 70s on Monday. The only concern weather- wise for this early week period will be temperatures tonight, as a few of the colder spots may drop into the middle to upper 30s tonight. While this is unlikely to support any widespread frost, cold sensitive plants may need some additional protection. Long Term...Monday Night Through Saturday Focus of this forecast continues to revolve around the thunderstorm and heavy rainfall potential from Monday night through Tuesday night. Secondary focus is weather for the Independence Day holiday. Monday night through Tuesday night...As a large high pressure system shifts from the eastern Great Lakes to the northeast coast on Monday night, return flow will rapidly increase including a 35 to 45 kt low level jet that will lead to surge of elevated moisture into the region from the west. The strong moisture advection and convergence will lead to a large area of rain spreading across the region from west to east. Instability is lacking and less than 200 j/kg, so severe weather is not expected despite decent wind fields. But probabilities appear to have increased (30-50%) over central to east- central Wisconsin for 1+ inches of rainfall by midday Tuesday. Isolated amounts to 1.5 inches appear possible over central WI. After the first push of precip exits across the area on Tuesday morning, indications continue to suggest a relative lull in the precip on later Tuesday morning or Tuesday afternoon. This is a little slower than guidance was showing yesterday. Then precip chances ramp up again on Tuesday evening along the cold front. The ensemble means continue to show precipitable water values (pwats) approaching their daily high and in excess of 2 inches. Like the previous shift mentioned, chances of heavy rain have shifted south somewhat over the past 24 hours closer to the higher instability. Chances of an additional 0.50 inches of rain lie around 20 to 30% over central Wisconsin. To summarize, probabilistic data continues to show potential for 1-2 inches of rain over central to east-central Wisconsin from late Monday night through Tuesday night. Given the marginal instability, the severe weather risk remains lower than heavy rainfall. Thursday thru Friday (July 4-5)...Low pressure will be moving into the northern Mississippi Valley on Thursday and into the western Great Lakes on Friday. The latest data suggest timing of rain will hold off until late on Thursday night, and heavy rain will be possible again on Friday. Considering the timeframe, details could certainly change. Temperatures are forecast to be near normal on Independence Day. && .AVIATION...for 18Z TAF Issuance Issued at 1217 PM CDT Sun Jun 30 2024 VFR flying conditions are expected at all terminals through the TAF period as a high pressure system settles in over the region. A few isolated areas of fair weather cumulus clouds may develop this afternoon, but should have minimal aviation impacts. Only potential concern would be fog development overnight as winds become calm, but was not confidence enough to include fog in the TAFs at this time. Otherwise, winds will veer around and increase Monday morning ahead of the next low pressure system. Flying conditions will likely deteriorate Monday afternoon/evening as the aforementioned low is forecast to bring periods of heavy rain to the region through Tuesday. && .GRB WATCHES/WARNINGS/ADVISORIES... None. && $$ DISCUSSION.....Uhlmann/MPC AVIATION.......GK