NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 182046
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
346 PM CDT Fri Jul 18 2025

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Showers and scattered thunderstorms expected late tonight into
  Saturday, then pleasant conditions return Saturday night through
  Monday. Smoke from Canadian wildfires returns Saturday night
  into Sunday.

- An active pattern is expected during the middle of next week,
  with periodic chances of showers and thunderstorms. Strong
  storms and heavy rain will be possible at times.

&&

.DISCUSSION...
Issued at 346 PM CDT Fri Jul 18 2025

Skies were mostly cloudy over NC WI this afternoon, while partly
cloudy conditions were observed elsewhere. A short-wave was
tracking through far northern WI, bringing a few light sprinkles
or virga to areas near the U.P. border. Temperatures were
seasonably cool; ranging from the upper 60s far north and near
Lake Michigan to the lower to middle 70s elsewhere.

Expect mainly dry conditions to prevail this evening. H8 WAA
developing ahead of an approaching cold front, and upper forcing
from a weak short-wave or jet streak, should generate showers and
scattered thunderstorms late tonight, mainly west of the Fox
Valley/lakeshore areas. MUCAPE (all elevated) is only expected to
be 300-700 j/kg, so severe weather is not expected. The cold
front will track southeast through the forecast area on Saturday,
with showers and embedded storms continuing until it shifts south
of the region late in the day. Think there may be enough cloud
cover and showers around to limit the severe threat, but CAPE of
1000-1500 j/kg across C/EC WI bears watching, as suggested by the
small sliver of a Marginal severe risk seen on the SPC Day 2
Outlook.

High pressure brings dry and pleasant conditions Saturday night
through Monday. Smoke from Canadian wildfires will push into
the forecast area Saturday night into Sunday. While the initial
surge should be aloft, there is some potential for surface-based
smoke on Sunday. As such, have increased sky cover a bit Saturday
night, and added patchy smoke to the forecast on Sunday.

Zonal flow sets up across the region for the rest of the work
week, with very warm and more humid conditions returning to the
forecast area. Timing and location of individual disturbances
(possibly convectively-induced MCVs) will be very difficult, so
specific details on pops will be initially lacking. There is some
consensus that a couple rounds of convection could develop as a
warm front lifts toward the region Tuesday into Tuesday night,
followed by a cold frontal passage sometime during the Wednesday
to Thursday time frame. During this mid-week period, CAPE is
expected to increase to 2-3K j/kg, so a period or two of severe
storms could occur. In addition, with PWATs increasing to around 2
inches and surface dew points rising into the middle 60s to
middle 70s, heavy rainfall will also be a distinct possibility.
Look for highs to reach well into the 80s, and heat indices could
get as high as the upper 80s to lower 90s in parts of C/EC WI.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 113 PM CDT Fri Jul 18 2025

As previously forecast, a FEW/SCT cu field with bases of 3500-5000
ft AGL developed early this afternoon south of a GRB to ISW line.
Mid and high clouds also moved into north-central WI early this
afternoon ahead of a developing low pressure system. This system
is expected to slowly track across the state through the end of
this TAF period, bringing isolated to scattered showers, MVFR/IFR
cigs, and MVFR vsbys from northwest to southeast. Meso models are
not in agreement with the timing or placement of the showers,
leaving low confidence in when the showers will move over a
specific TAF site. However, a general consensus has the showers
arriving sometime after 06z Sat for all TAF sites. Mainly used
PROB30 groups at all TAF sites for the showers with anticipated
timing. There is also potential for thunder at times, but given
the lack in confidence in timing/placement, opted to not include
thunder, except at RHI with a PROB30 where confidence is slightly
higher for thunder to occur.

The passing system is expected to cause a wind shift from the
prevailing south/southeast to west/northwest during Saturday
morning, but winds will remain around 5-15 kts.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......Kruk