813
FXUS63 KGRB 110400
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1100 PM CDT Thu Jul 10 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Showers and thunderstorms are possible at times through
  Saturday. Heavy downpours are possible within any thunderstorms.
  A few strong to severe storms will also be possible on
  Saturday.

- Next round of active weather arrives during the middle of next
  week.

&&

.DISCUSSION...
Issued at 428 PM CDT Thu Jul 10 2025

A mid-level shortwave over eastern MN/western WI producing
scattered showers and thunderstorms is progged to make eastward
progress through this evening before weakening with time
overnight. This will allow the scattered showers and thunderstorms
to move into portions of central, north-central, and east-central
WI this afternoon through this evening. The potential for strong
or severe storms is low, but PWATs will be nearing 2 inches
leaving the potential for heavy downpours within any thunderstorm.
Later this evening, the weakening of the shortwave and loss of
daytime heating will cause the coverage to decrease or remain
mainly across southern WI.

Meanwhile, another shortwave will be on its tail that is progged to
phase/overcome the leading shortwave overnight. However, the
evolution of this second shortwave has much uncertainty revolving
around it. Models are still not in agreement with the timing,
placement, or intensity of the shortwave/precip axis for Friday, but
there is decent agreement Friday morning will be dry under some
cloud cover. Overall, there appears to be a southern trend with the
shortwave/precip axis for Friday afternoon and evening, but there
are still indications that portions of eastern WI could see some of
the main precip swath. If the latter is correct, these areas would
be more likely to see higher rainfall totals (1-2+ inches),
especially with a juicy atmosphere in place (PWATs around 2 inches).
Otherwise, if the more southern solution occurs, much of the
forecast area could see much lower rainfall amounts (less than 0.75
inches) for Friday/Friday night. Given the low confidence and much
uncertainty, the potential for strong or severe storms has also
decreased.

Additional showers and thunderstorms are possible on Saturday with
the main upper-level trough and leading surface cold front sweeping
across the region. The severe potential Saturday afternoon and
evening will depend on what happens Friday afternoon/night and how
much cloud cover sticks around. Cannot rule it out at the moment
given a tongue of 1000-2000 J/kg of MUCAPE ahead of the cold front,
deep layer shear around 35-40 kts, and steeper mid-level lapse
rates. SPC has included almost the entire forecast area in a
Marginal Risk for severe storms, which reflects these features.

The remainder of the weekend will be dry, but there are subtle
indications of a weak boundary sweeping across the area on Monday,
which could bring light rain and a chance of thunderstorms. A higher
chance for widespread showers and thunderstorms is shaping up for
midweek with an upper-level trough moving across the northern
CONUS.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1058 PM CDT Thu Jul 10 2025

Showers from the evening will give way to clearing skies and some
fog over central WI overnight. Also could see patchy fog over
north-central WI. Have continued to carry MVFR VSBY with TEMPO
groups for IFR VSBY at AUW/CWA and RHI. Though fog will lift
around daybreak, IFR stratus could linger into mid morning.
Over east-central WI, no fog is expected, but a small chance of
some showers may arrive after 07-08z as steadier showers over
southern WI graze the area while lifting across south half of Lake
Michigan. The showers will be done shortly after daybreak. In
wake of any showers, expect MVFR CIGS to prevail much of the day
as easterly flow keeps stratus persistent, except over far north-
central WI with only scattered to broken mid and high clouds are
expected.

Based on recent model trends for Friday, have refreshed TAFs to
keep all sites dry through early afternoon. Did intro PROB30 for
some thunderstorms over central WI terminals (AUW/CWA) late in the
day as next wave arrives with increasing instability. By Friday
evening, most of the area will see scattered showers with small
chance of thunder. Conditions on Friday evening will mainly be
VFR central WI to north-central WI, while MVFR will grudgingly
hold over east-central WI sites (GRB/ATW/MTW).

&&

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

&&

$$

DISCUSSION.....Kruk
AVIATION.......JLA