642
FXUS63 KGRB 110023
AFDGRB

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

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Showers and thunderstorms are possible at times from this
  afternoon 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 00Z TAF Issuance
Issued at 719 PM CDT Thu Jul 10 2025

Showers and embedded thunderstorms will persist over central WI
(CWA/AUW) through 02z. Showers may lift into RHI before dark,
but may struggle to reach the Fox Valley to the lakeshore. VFR
conditions, except brief MVFR beneath the heavier showers and
storms. After shower activity ends late this evening, expect some
clearing for portions of central and north-central WI overnight.
The clearing and the evening rainfall could lead to fog late
tonight/early Friday morning. Based on the greater coverage of
rain this evening, have carried prevailing MVFR VSBY with TEMPO
IFR VSBY at CWA and AUW. Kept MVFR VSBY for the fog at RHI.

MVFR cigs are anticipated to spread eastward Friday morning with
the potential for additional shower activity. Due to uncertainty
in where and when this shower activity will occur, retained the
PROB30 groups for only CWA/AUW with this TAF issuance. However,
latest trends indicate the showers may even stay south of those
sites. Does appear that terminals across eastern WI may be stuck
in MVFR stratus much of the day with a flow off Lake Michigan.

&&

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

&&

$$

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