808
FXUS63 KGRB 271646
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1146 AM CDT Mon Apr 27 2026

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Strong to severe storms are possible this afternoon and evening,
  especially south of a line from Rhinelander to Sturgeon Bay. The
  primary threats would be large hail and damaging winds.

- Moderate to heavy rain with embedded storms is expected today
  and tonight. Locally heavy rainfall between 0.75 to 1.5" is
  expected at most locations.

- Rivers are expected to rise this week after a round of moderate
  to heavy rain on Monday.

&&

.DISCUSSION...
Issued at 110 AM CDT Mon Apr 27 2026

Severe Weather Risk and moderate to heavy rain today and tonight:

Showers and a few thunderstorms will move in from the west this
morning as a low pressure system tracks towards the western Great
Lakes region. The main period of concern will be this afternoon
into this evening as a cold front sweeps through the region with
strong shear and instability. MUCAPEs during this period will
generally be around 1000 J/kg with 40 to 60 knots of bulk shear,
however effective shear will be a more modest 20 to 40 knots,
which is a better indicator as storms will be elevated. The best
chance for severe weather will be south of a line from Rhinelander
to Sturgeon Bay from about 4 to 9 pm. The main threat from any
storms would be damaging winds and large hail as very strong winds
of 60 knots will exist a few thousand feet off the surface, which
could be brought down to the surface despite the expected
elevated nature of the storms. In addition, large hail is possible
given the thick CAPE profile in the hail growth zone. In addition
to the strong to severe storm threat, abundant moisture, lift,
and stretched out CAPE profiles will mean moderate to heavy rain
will be possible with any storms. Showers will then linger behind
the cold front overnight and ending by early Tuesday morning.

Rest of the week into the weekend:

Except for a small chance of rain on Thursday (15-25%), dry
conditions should prevail for the rest of the week and into the
weekend, allowing for river levels to recede after the rain today
and tonight. Several afternoons will also feature low humidity
readings, which could lead to an increase risk of fires heading
into next weekend.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1135 AM CDT Mon Apr 27 2026

Showers and isolated thunderstorms will move across the area
during the early to mid afternoon, through 21z, before the risk of
stronger storms arrive along and south of Highway 29 late this
afternoon into the evening. Some of the stronger storms will be
capable of strong gusty winds. The risk of thunderstorms will
come to an end by 03z Tue. CIGS will fall into the MVFR or IFR
category along and behind the front. Isolated to scattered showers
are possible behind the front, with the showers ending late
tonight. CIGS will improve on Tuesday, reaching the VFR category
by late morning or early afternoon. West/northwest winds will
still gust to 25 to 30 knots Tuesday morning, then gradually relax
during the afternoon.

&&

.HYDROLOGY...
Issued at 110 AM CDT Mon Apr 27 2026

Minor flooding continues on several rivers, namely the Wolf,
Menominee, and the Fox River at Oshkosh. Widespread rainfall
amounts of 0.75 to 1.50 inches are expected with locally higher
amounts possible today and tonight. NBM probabilities for more
than an inch continue at a steady 40-80%, with a 15-40% chance of
more than 2 inches. However, the NBM probabilities are biased
corrected and likely suffer a high bias due to the recent heavy
rainfall this month. The non-biased corrected LREF precipitation
probabilities are a bit lower and seem more representative of the
actual probabilities based on the current raw and ensemble model
QPF amounts. Current LREF probabilities for more than an inch are
generally 20-50%, with less than 10% of exceeding 2 inches.

Per RFC forecasts and HEFS guidance, several points along the
Menominee River could return to moderate flood stage; however,
probabilities of reaching moderate have fallen to less than 10%.
Continuing snow melt from the Upper Peninsula would lend some
confidence for at least a return to moderate flood stage.

The Wolf River is expected to stay below moderate flood stage
during this event, with some points rising back to minor flood
stage. Levels on the Lake Winnebago system continue to rise due
to inflow from the Wolf and Fox Rivers, with minor flooding
already occurring from Lake Poygan to Winnebago and minor
flooding forecast to occur through the weekend. Those living near
rivers or streams should continue to monitor the latest Flood
Warnings and statements from the National Weather Service in
Green Bay.

&&

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

&&

$$

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

NWS GRB Office Area Forecast Discussion