209
FXUS63 KGRB 151717
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1217 PM CDT Sun Jun 15 2025

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Isolated showers and sprinkles possible today and tonight,
  especially west and north of the Fox Valley/lakeshore areas.

- A warm, humid and stormy period expected for the early to mid
  part of the next work week, and again toward Friday/Saturday.
  Strong to severe storms and heavy rainfall will be possible at
  times.

&&

.DISCUSSION...
Issued at 259 AM CDT Sun Jun 15 2025

A band of light showers and sprinkles was noted across northern
Wisconsin early this morning. Precipitation chances the rest of
today into this evening will be difficult to diagnose given the
fairly weak dynamics in place across the region. Therefore, will
continue with low chances (10-20 percent) as activity will be
isolated and light in nature. Less shower activity should allow
temperatures to warm up from yesterday, especially across north-
central Wisconsin.

The area will get into the warm sector on Monday 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 pre-frontal showers and a few thunderstorms
ahead of the approaching cold front during the day on Monday.
SBCAPEs will be less than 1000 J/kg on Monday with 20 knots of
bulk shear; therefore, these storms are not expected to be severe.

An MCS developing across Minnesota Monday afternoon is progged to
push east coincident with the cold front Monday night. This
activity is slated to track through central and north-central
Wisconsin late Monday evening and the rest of the area overnight
on Monday. MUCAPEs across central and north-central Wisconsin will
still be 1500-2000 J/kg Monday evening as the storms move through
the region. Therefore, some strong to severe storms will be
possible if the storms hold together mainly west of the Fox
Valley. The threat for these storms to hold together appears a bit
higher this run as the marginal risk has been pushes slightly
eastward with the caveat that there is still not high confidence
in this scenario.

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 2000 to 3000 J/kg with 30-40 knots of effective
shear late Tuesday afternoon. Although these values do wane
Tuesday evening, the region will still be close to the CAPE
gradient. This could lead to some strong to severe storms Tuesday
night depending on how close the MCS gets to the area and if the
instability or reservoir of instability will be close enough for
storms to tap into it.

The middle to late part of the week is difficult to pin down as
models indicate there will be several additional opportunities for
the generation of MCSs that track through the western Great Lakes
region. The region will generally be in a warm humid airmass with
unstable conditions. The main question will be what other features
like mid level shortwaves in the zonal flow track through and
when. The longer range models are in some kind of agreement that a
system could affect the region Friday night as a shortwave tracks
through the western Great Lakes with substantial instability and
shear. However, subsequent runs could alter the timing or
trajectory of this system.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1217 PM CDT Sun Jun 15 2025

Cigs have risen to VFR over the Fox Valley and eastern WI, while
MVFR cigs continue over central and north-central WI. Expect these
lower clouds to gradually rise this afternoon with primarily VFR
conditions late this afternoon and evening.

Expect MVFR clouds to reestablish tonight, mainly over central and
northern WI. Forecast soundings also show some indication a period
of IFR cigs is possible early Monday morning, however, confidence in
these lower cigs occurring is low so went with low-end MVFR at
AUW/CWA/RHI. Models also show a chance (20-30%) for light showers
overnight across central and northern WI, but aviation impacts from
any showers should be minor.

Light easterly winds will remain for the rest of today before
veering around to the south early Monday morning.

Beyond the TAF period there is an increase chance for an area of
thunderstorms to move into central and northern WI late Monday
afternoon/evening. Some stronger thunderstorms are possible with
strong wind gusts (40-50 mph) the main expected hazard.

&&

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

&&

$$

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