Isaar, Wisconsin Weather Forecast Discussion

190
FXUS63 KGRB 210007
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
707 PM CDT Sat Sep 20 2025
Updated aviation portion for 00Z TAF issuance
.KEY MESSAGES...
- Multiple rounds of showers and thunderstorms are expected this
  evening through Monday. Isolated strong storms with gusty
  winds, small hail, and heavy rain with localized flooding will
  be possible at times.
- An isolated severe storm with hail to one inch in diameter can`t
  be ruled through early this evening, especially across central
  and east-central WI.
- Above normal temperatures are expected for much of next week.
&&
.DISCUSSION...
Issued at 310 PM CDT Sat Sep 20 2025
SHORT TERM (This Afternoon through Sunday)
First upper level disturbance moved away from the area late this
morning, bringing a lull in the shower and storm activity early
this afternoon. The second piece of energy was moving towards the
area as of mid-afternoon. In response, scattered showers and
thunderstorms developed across central and east-central WI. The
local mesoanalysis page indicated surface based CAPE values of
1,000-1,800 J/KG across central and east-central WI. 0-6km shear
values were around 25 knots. The upper level feature is expected
to move across the area for the rest of the afternoon into this
evening, bringing scattered showers and storms to the area. The
risk of severe weather is low, however an isolated severe storm
with 1" inch hail can`t be ruled out. As the feature moves away
from the area later tonight, the shower and storm activity will
wane. With the upper trough overhead, can`t go completely dry
later tonight as a few isolated showers could pop up at times.
Also, areas of fog are possible later tonight. The HREF indicated
a 30-60% probability of visibilities dropping below one mile,
especially north and west of the Fox Valley. Any lingering fog
will burn off by mid-morning on Sunday, then the chances of
showers and storms will increase during the late morning and
afternoon. Lows tonight will drop into the middle 50s to lower 60s
with highs Sunday in the upper 60s to middle 70s.
LONG TERM (Sunday Night through next Saturday)
The 500mb trough will linger through Monday, bringing continued
chances of showers and thunderstorms. 500mb heights will begin
to rise Monday night and Tuesday as ridging develops across the
northern plains into the western Great Lakes. By the middle of
next week, ensemble height anomalies indicate a ridge will develop
over central Canada while a low-pressure system forms over the
Ozarks. This pattern will help funnel drier, more stable air into
the region, shunting most of the precipitation chances south of
the area through Thursday. The GFS model indicated a decent
rainfall event Wednesday into Thursday, but was the outlier
at the moment. Temperatures for much of next week will end up
above normal.
&&
.AVIATION...for 00Z TAF Issuance
Issued at 705 PM CDT Sat Sep 20 2025
An area of rain, with scattered thunderstorms throughout, was
lifting north/northeast across the region this evening. While the
threat for thunderstorms will gradually decrease, continued to
include thunderstorms at ATW and GRB through 01z based on radar
trends. Otherwise, showers will likely continue for all TAF sites
through roughly 06z. A few additional vicinity showers may
continue beyond 06z, but shouldn`t be impactful. What will be
impactful are dropping cigs and vsbys with fog potential between
06z and 14/15z. RHI, AUW, and CWA will see the greatest impacts
with LIFR cigs/vsbys. The signal is less impressive over the east-
central WI TAF sites, but cannot rule out the possibility for a
period of MVFR/IFR conditions through 12z.
Additional isolated showers look to develop during Sunday
afternoon. However, felt most confident to include only at RHI,
including a PROB30 for thunderstorms. The mention of showers may
need to be added at other TAF sites as models become more dialed
in.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
DISCUSSION.....Eckberg
AVIATION.......Kruk

NWS GRB Office Area Forecast Discussion