NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 210810
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
310 AM CDT Tue Apr 21 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Water levels have crested in most areas, and due to an extended
  period of dry weather, a gradually drop is anticipated with
  flooding expected to continue through the week.

- Showers and thunderstorms are expected Thursday night into
  Friday. Heavy rainfall may accompany any thunderstorms, with a
  20-30% chance of exceeding an inch of rain.

- Temperatures will well above normal through Friday, with highs
  in the 60s and 70s expected away from Lake Michigan.

&&

.DISCUSSION...
Issued at 1243 AM CDT Tue Apr 21 2026

Dry weather is expected through the middle of the week, which
will allow area rivers to continue to slowly subside. A weak
surface low/trough will move through the region with no
precipitation today. Much warmer gets drawn into the region ahead
of the trough, with high temperatures rising into the 60s and
lower 70s, except 50s and lower 60s due to a lake/bay breeze. High
pressure returns tonight into Wednesday, with continued dry and
mild conditions inland from Lake Michigan. Throughout this period,
low afternoon humidity is anticipated (20-30 percent range),
which may result in an uptick in wildfire potential.

South winds develop Wednesday night and gusts to 20 to 30 mph on
Thursday, resulting in an increase in Gulf moisture over the
region. There is a 20 percent chance of showers in our far western
counties late Thursday afternoon, but showers and embedded storms
become more numerous Thursday night, as a cold front moves
through the region. Rain will continue into Friday as the front
slowly moves through the region. PWATs increase to 1.2 to 1.5
inches during this period with modest instability (MUCAPEs of
500-1000 J/kg). The long, skinny CAPE profiles and increased
moisture will mean locally heavy rainfall will be possible. NBM
probabilities of exceeding an inch are currently 20-30% with a
less than 10% chance of exceeding 2 inches, which appears to be
the high end amount for this event. Once the rain ends Friday
afternoon/evening a period of dry weather is then anticipated for
the upcoming weekend.

A low pressure system lifting north from the Plains is then
expected to bring another round of rain to the region during the
early part of next week. This system looks similar to the late
week system with modest MUCAPE values of 500-1000 J/kg with the
90th percentile for rainfall amounts around 2 inches.

Above normal temperatures are anticipated through Friday, with
the cold frontal passage only bringing modest cooling for the
weekend into early next week.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 310 AM CDT Tue Apr 21 2026

VFR conditions are expected through the TAF period. Mid and high
clouds will move through the area early this morning, with mostly
sunny skies expected later this morning and through the afternoon.
Some fair weather cumulus will develop across eastern Wisconsin
during the mid to late afternoon. Mostly clear skies are then
expected across all TAF sites tonight.

A weak cold front will move across the area this morning,
shifting winds to the northwest. During the afternoon, a lake
breeze boundary will develop around 18z at KMTW/KSUE, spreading
westward to KGRB/KATW/KOSH between 21z Tue and 00z Wed. There also
could be a bay breeze that would impact KGRB. Given the lake and
bay breezed, there is uncertainty regarding wind direction at
KGRB; however, current thinking is winds will switch to the
northeast this afternoon then east during the evening as the lake
breeze moves inland.

&&

.HYDROLOGY...
Issued at 1243 AM CDT Tue Apr 21 2026

Minor to moderate flooding continues on many rivers, with major
flooding expected to persist on parts of the Wolf River through
tonight. Most of the river levels have crested, and with a
prolonged stretch of dry weather anticipated through Thursday,
water levels should gradually subside through the week.

Those living near rivers should continue to monitor the latest
Flood Warnings and statements from the National Weather Service
in Green Bay.

See the discussion section above for information pertaining to
precipitation forecasts for the Thursday to Friday period.

&&

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

&&

$$

DISCUSSION.....Kurimski
AVIATION.......Kurimski
HYDROLOGY......Kurimski