848
FXUS63 KGRB 161117
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
617 AM CDT Mon Jun 16 2025

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- A warm, humid, and stormy period is expected through mid-week,
  and again toward Friday/Saturday. Strong to severe storms and
  heavy rainfall will be possible at times. Any areas that receive
  multiple rounds of heavy rainfall will be under the threat for
  flooding.

&&

.DISCUSSION...
Issued at 306 AM CDT Mon Jun 16 2025

The area will get into the warm sector today as a low pressure
system develops across the northern CONUS. This will allow
temperatures to soar as dew points rise into the 60s, providing
for a warm and humid air mass across the western Great Lakes.
There may be some showers and a few thunderstorms ahead of the
approaching warm front this morning. Another round of showers and
thunderstorms is then possible later this afternoon into the
overnight hours as the cold front tracks through the region.
MUCAPEs will only around 500 J/kg this morning with 10 knots of
bulk shear; therefore, these storms are not expected to be
severe.

An MCS developing across the Dakotas and Minnesota today is
progged to push east coincident with the cold front tonight.
Recent model runs take the bulk of this activity northeast over
Lake Superior tonight with some models tracking the storms through
northern Wisconsin. This recent trend from the models diverging
from each other lends itself to very low confidence that the area
will get these storms. If storms can make it into the area the
best chance for strong to severe storms will be west of the Fox
Valley this evening with 1000-2000 J/kg along with 30-40 knots of
bulk shear.

Another MCS is forecast to develop on Tuesday and track east
Tuesday night. While the models generally take this system to our
south, there are some models that do graze portions of central and
east-central Wisconsin with this system Tuesday night as MUCAPEs
will be as high as 1000 J/kg with 30 knots of effective shear.
Given the model trends in keeping this system south of the area
for the most part confidence in strong to severe storms reaching
the area this period is also low.

There will be another chance for strong to severe storms Wednesday
into Wednesday night as a low pressure system tracks from Iowa
through the central Great Lakes. The threat for severe weather
will once again depend on the timing and track of the low with the
best chance for strong to severe storms from the Fox Valley east
to the lakeshore as these areas will be closer to the best
instability and forcing.

There will be additional opportunities for showers and
thunderstorms through the rest of the week into the weekend as
several additional lows track through the zonal flow in place
across the northern CONUS. The next best chance for strong to
severe storms appears to still be Friday night as the models are
honing in on a complex of storms developing ahead of a surging
warm front with MUCAPEs around 1000 J/kg and 50 to 60 knots of
effective shear. Despite this being at the very end of the week,
the models have been keying in on this period for several runs.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 617 AM CDT Mon Jun 16 2025

Mainly dry conditions were observed across the forecast area early
this morning with showers developing upstream across the west and
south. VFR conditions prevailed over the southeast half of the
forecast area, with MVFR observed northwest.

Expect VFR conditions to prevail at the eastern TAF sites through
much the TAF period. MVFR conditions remain likely at the western
TAF sites, with a possible lowering to IFR early this morning,
followed by improvement to VFR after a warm front moves through in
the late morning/early afternoon. Regarding precipitation
chances, overall confidence has decreased due to a lack of
agreement with the latest model runs. Will continue with our
previous thinking, starting with a chance of showers and possibly
a thunderstorm in C/NC WI as an MCV in MN moves through this
morning, which is supported by current upstream radar trends.
There is less confidence farther east, so will continue with a
Prob30 for showers at the eastern sites during the late
morning/early afternoon. Still think it is possible for a round of
thunderstorms arriving in NC/C WI early this evening, then
tracking into the eastern TAF sites toward the end of the period
which is supported by some of the CAMs models.

Light southeasterly winds will gradually become a bit gusty from
the south after the warm front moves through later today.

&&

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

&&

$$

DISCUSSION.....Kurimski
AVIATION.......Kurimski