931 
FXUS63 KGRB 061802
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
102 PM CDT Mon Sep 6 2021

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 409 AM CDT Mon Sep 6 2021

High pressure was building into the forecast area early this
morning. Mostly clear skies and light winds were causing patchy
fog to develop over north central and parts of central WI.

Partly cloudy skies and lighter winds are anticipated across the
region today, as the surface high moves through. Have bumped up
temperatures a couple degrees, with highs expected to reach the
lower to middle 70s at most locations.

After a mainly dry evening, expect elevated showers and
thunderstorms to form in north central WI toward midnight, as a 
40 knot LLJ develops coincident with the arrival of elevated
instability. The LLJ will veer west overnight, causing the 
thunderstorm activity to shift into northeast WI late tonight into
early Tuesday. With strong deep layer shear of 40 to 50 knots,
moderate elevated instability (H8 LI's of -3 to -6 C) and wet bulb
zero heights of 9-10.5 K feet, will likely see a threat of hail
with the stronger storms. SPC has placed far northern WI in a
Marginal Risk, and this seems reasonable. Lows tonight will be in
the 50s to lower 60s.

On Tuesday, a deepening low pressure system moving through Lake 
Superior will drag a cold front through the forecast area in the 
morning and early afternoon. Though the initial round of convection
should exit northeast WI in the morning, it is possible for 
scattered storms to redevelop along the cold front around midday 
in eastern WI. With CAPE increasing to 1000-1500 j/kg and deep 
layer shear of 45 to 60 knots, it is plausible that a few strong 
to severe storms could form near the lakeshore before exiting 
the forecast area in the early afternoon. Once again, SPC has 
this area in a Marginal Risk. Highs should reach the upper 60s far
north, and 70s elsewhere.

.LONG TERM...Tuesday Night Through Sunday
Issued at 409 AM CDT Mon Sep 6 2021

500mb ridge across western North America will shift eastward and
flatten as its moves into the central plains towards next 
weekend. The northwest flow pattern aloft should allow temps to 
be close too or little bit below normal at the start of the 
period. As the pattern flattens next week, temperatures should
trend warmer than normal. 

For Tuesday night, a gusty northwest flow pattern will continue
across the area. Have increased rain chances across the far north
with the northwest flow off Lake Superior. The cool cyclonic flow
aloft will continue across the western Great Lakes on Wednesday. 
With day time heating, there is the potential for additional 
chances of showers during the day across the north. The remainder
of the period should be tranquil as high pressure builds into the
region Wednesday night. The next system will bring a chance of 
rain to the area Friday night into Saturday. 
 
Temperatures overall will be close to normal for the first half of
the week, then trend warmer than normal for the end of the work
week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 102 PM CDT Mon Sep 6 2021

VFR conditions prevailed this morning and early afternoon as
scattered high clouds along with some daytime cu pushed across 
the area. The VFR conditions will prevail into the this evening,
then scattered showers and storms are expected to develop
overnight into Tuesday morning as strong warm air advection occurs
over the western Great Lakes and ahead of a cold front and upper
level disturbance. Best chance to see this activity will be at
RHI, but the other sites could see a brief period of showers and
possibly a storm. Stuck with mainly VCTS/VCSH as there still 
remains some minor timing differences on when the best chance for 
the showers/storms will arrive. Most of the showers/storms should 
have fairly high cloud bases, but did lower CIGs a bit. A few 
storms could be strong, with vsbys briefly reduced to MVFR. Expect
some LLWS overnight into early Tuesday as a low level jet 
develops. Most of the shower and storm activity will exit east of
the area by 18z, but a few additional showers will be possible, 
mainly over northern WI, in the afternoon.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kieckbusch
LONG TERM......Eckberg
AVIATION.......Bersch