Green Bay, Wisconsin 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

520
FXUS63 KGRB 190416
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1116 PM CDT Fri Apr 18 2025

Updated aviation portion for 06Z TAF issuance

.UPDATE...
Issued at 719 PM CDT Fri Apr 18 2025

Conditions have become more stable in wake of the cold front that
has shifted south and east of northeast WI. Had isolated thunder
earlier this evening, but focus for this has moved into lower
Michigan. Elevated instability that is still present (200-400
j/kg of MUCAPE) seems to be just helping to enhance the light rain
and showers over the area. An isolated lightning strike may still
occur through late evening over Calumet and Manitowoc counties as
spotty convection in southern WI on northern edge of higher sfc
based CAPES eases east-northeast, but this too will be minimal in
coverage. Thus have dialed back thunder mention to far southeast
CWA and went with murkier light rain/light fog idea over the area
the rest of the evening. Updated HWO to remove any mention of
strong thunderstorms. That all lines up with latest SPC Day1
outlook which now has the marginal risk line (level 1 of 5) to the
southeast of GRB forecast area.

&&

.KEY MESSAGES...

- Next chances for widespread precipitation arrive Sunday night
  into Monday. Mixed precip types possible, mainly across north-
  central Wisconsin.

&&

.DISCUSSION...
Issued at 234 PM CDT Fri Apr 18 2025

Cloudy to mostly cloudy skies and low ceilings continue to plague
the forecast area late this afternoon. Despite these conditions,
CAMs models continue to develop showers, and a few thunderstorms,
across the area late this afternoon and this evening. Mesoanalysis
shows that despite very strong shear across the region, with bulk
shear values of 75 knots, instability is wanting across our area
with the best instability well to our south in northern Illinois
and only a few hundred J/kg of MUCAPE across our area. Therefore,
while thunderstorms will be possible, severe weather is not
anticipated across our area this evening as any thunderstorms that
develop should be elevated in nature.

High pressure will provide a break in the active pattern late
tonight through Sunday morning as it tracks across the northern
Great Lakes. Meanwhile, a low pressure system developing across
the southern Plains will track north-northeast towards the western
Great Lakes region Sunday night and Monday. Some light rain is
possible Sunday afternoon ahead of the main low with isentropic
lift across the region; however, the main swath of precipitation
is expected to hold off until Sunday night and Monday.
Precipitation with this system should mainly be rain across much
of the area, with a mix of rain and snow across north-central
Wisconsin. The latest probabilistic guidance has cut back on the
amount of snow quite a bit this run with only a 10-20% chance of 2
inches or more of snow across far north-central Wisconsin and a
20-40% chance of an inch or more of snow.

After a brief break in the action late Monday night into Tuesday
morning, the next system will track through the region Tuesday
afternoon into Tuesday night. This system will have fairly weak
dynamics; therefore, only light rain is expected from this next
low pressure system. Yet another low pressure system looks to
affect the area Wednesday night through Thursday night. Beyond
this part of the forecast there is quite a bit of uncertainty as
there are discrepancies on if a Canadian high pressure can keep
the weather dry to end next week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1115 PM CDT Fri Apr 18 2025

Lingering scattered showers, mist and light fog (IFR to MVFR
visibility) will gradually diminish overnight as northwest winds
usher in drier air. Mainly dry conditions are expected Saturday
through Saturday evening. Cigs will be IFR to MVFR overnight,
lifting to MVFR on Saturday morning, before scattering out to VFR
on Saturday afternoon.

As winds turn southeast Saturday night, scattered MVFR clouds
may form from the lakeshore to the Fox Valley. VFR conditions
will occur elsewhere.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE.........JLA
DISCUSSION.....Kurimski
AVIATION.......JLA