657
FXUS63 KGRB 170415
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1115 PM CDT Wed Jul 16 2025

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- The warm and humid weather will come to an end tonight. Cooler
  and less humid on Thursday and Friday.

- Small craft should exercise caution on the bay of Green Bay through
  late this afternoon. A Small Craft Advisory is in effect for
  the bay and nearshore areas of Lake Michigan tonight into
  Thursday morning.

- An active pattern is expected Friday night through the middle
  of  next week with periodic chances of thunderstorms. Stronger
  storms and heavy rain are possible at times.

&&

.DISCUSSION...
Issued at 219 PM CDT Wed Jul 16 2025

A Mesoscale Convective Vortex continues to move across the region
this afternoon, bringing showers and scattered thunderstorms to
the region. Some of the strongest storms could produce strong
or damaging winds, an isolated tornado and torrential rainfall
across central and east-central WI. This feature will also bring
in additional moisture as precipitable water values at Green Bay
are expected to increase to 2.11 inches late this afternoon or
near the daily record supporting the likelihood of heavy rainfall.
The movement of the mesoscale convective vortex will support a
nearly west to east band of heavy rain across portions of central
into east-central Wisconsin. The greatest rainfall is expected to
fall in a corridor from Marshfield to Wisconsin Rapids to Waupaca
and Wautoma to Appleton and Oshkosh east to Kewaunee and
Manitowoc. For locations south of Highway 29, HREF probabilities
indicated a 50-90% chance of 1 inch of rain, 30-60% chance of 2
inches and a 10-30% chance of 3 inches. The greatest risk of heavy
rain and flooding will continue for the remainder of the
afternoon into early this evening. Rainfall rates in the heavier
showers and storms could be as high as 1 to 3 inches per hour,
resulting in urban street flooding and ponding of water on area
roads while creeks and ditches may rise rapidly. Fishermen and
boaters on rivers should anticipate river rises and faster flows
from runoff Thursday and Friday.

On the backside of the vortex, gusty northerly winds and building
waves will result in hazardous conditions for small craft into
Thursday morning. Also, low stratus is expected tonight, combined
with northerly winds should keep any dense fog away. The big
change will be the cooler weather and much less humid conditions.
Highs on Thursday will only be in the upper 60s to middle 70s. The
dewpoints will continue on Friday and then will increase again
over the weekend.

The westerlies will linger along the U.S./Canadian border through
the rest of the forecast period. This will result in an active
period with periodic chances of showers/storms next week. The
potential exists for stronger storms and heavy rainfall at times.
The first round of storms arrive Friday night into Saturday
morning with dry conditions expected Saturday night into Sunday
night. The chances of showers and storms return Tuesday and
Wednesday. Temperatures will be close to normal this weekend, then
rise above normal for much of next week.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1113 PM CDT Wed Jul 16 2025

Lingering IFR/MVFR ceilings will continue tonight, along with some
isolated to scattered light showers and sprinkles. Improvements
in flying conditions expected Thursday morning. Clouds could
linger a little longer than the models have due to the low-level
moisture from the recent rain and/or add to the cu field during
the day. Ceilings will rise to VFR by Thursday afternoon.

&&

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

&&

$$

DISCUSSION.....Eckberg
AVIATION.......Bersch

NWS GRB Office Area Forecast Discussion