441
FXUS63 KGRB 261734
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1234 PM CDT Sun Apr 26 2026

Updated aviation portion for 18Z TAF issuance

.KEY MESSAGES...

- Moderate to heavy rain with embedded storms is expected Monday
  and Monday night. Locally heavy rainfall between 1 and 2" will
  be possible.

- Rivers are expected to rise next week after a round of moderate
  to heavy rain early in the week.

- Strong to severe storms are possible Monday afternoon and Monday
  evening. The primary threat would be large hail.

&&

.DISCUSSION...
Issued at 108 AM CDT Sun Apr 26 2026

Dry weather today:

Dry weather is expected for the back half of the weekend as high
pressure slowly drifts off to the east. Despite the dry weather,
there will be quite a bit of clouds across the region as a
shortwave tracks through the Minnesota arrowhead with a band of
showers, currently seen ongoing on radar imagery.

A round of moderate to heavy rain early in the week:

Meanwhile, a low pressure system developing across the central
Plains will deepen and move northeast towards the western Great
Lakes tonight. The low is tracking into the region a bit faster
then previous runs, making it into western portions of central
Wisconsin late Sunday night into early Monday morning. The bulk of
the rain from this system is slated to fall during the day on
Monday into Monday night as the low lifts northeast through
western and northern Wisconsin. Although some light rain showers
could linger into Tuesday, the bulk of the moderate to heavy rain
will be over late Monday night into early Tuesday morning, which
tracks with the quicker onset time on the front end of the
system.

Rainfall amounts:

NBM probabilities for one inch or more of rain continue to slowly
climb, with the latest run inching upward to 40 to 80%. The
probability for more than 2 inches is holding steady at 15 to 35%.
The highest probabilities continue to be in the highway 29 to
highway 10 corridors.

Severe weather risk:

There will be a marginal risk for severe weather Monday afternoon
into Monday evening, mainly south of a line from Rhinelander to
Sturgeon Bay. Although a steep low level inversion will mean
storms are expected to be elevated, there is substantial MUCAPEs
of 1000 to 1500 J/kg across this region. The elevated nature of
the storms means winds are not expected to be the primary threat;
however, model soundings show CAPE profiles are thick in the hail
growth zone. Therefore, large hail is expected to be the primary
threat from any strong to severe storms with this system. In
addition to the severe threat, PWATs as high as 1.2 to 1.4 will
mean heavy rain will be possible with any thunderstorms.

Another period of dry weather from mid week into the weekend:

After this system clears the region, dry weather is expected from
Tuesday afternoon through next weekend. Cooler temperatures are
expected for the rest of the week, with a slight warmup expected
next weekend. Some embedded shortwaves could bring a small chance
(10-20%) for light precipitation at times during this period;
however, the impact would be rather low as QPF amounts are only a
few hundredths of an inch. Despite this stretch of quiet weather,
area rivers may continue to rise during the middle to late part
of next week as precipitation works its way through the river
basins. The dry conditions could also cause an uptick in fire
weather concerns late next week.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1227 PM CDT Sun Apr 26 2026

MVFR/IFR CIGS from KMTW/KATW/KGRB northward to KEZS/KCLI and
KOCQ will burn off by 20z. Otherwise, VFR conditions should
prevail into late tonight. Will need to watch for MVFR/IFR CIGS
late tonight, but more likely Monday morning as southerly flow
increases. Low level wind shear develops late tonight and continue
into Monday evening until a cold front passes. Winds off the
deck in the 60-70 knot range at 2-3 thousand feet tomorrow
afternoon into the evening. Showers and scattered storms expected
Monday with strong or severe storms possible south of a
Rhinelander to Sturgeon Bay line. Strong winds and hail
are the main risks. Conditions will gradually improve Monday
night.

&&

.HYDROLOGY...
Issued at 108 AM CDT Sun Apr 26 2026

Minor flooding continues on several rivers, namely the Wolf,
Menominee, and the Fox River at Oshkosh. Dry conditions should
prevail through this evening, with increasing chances of rain
late tonight into Monday. Widespread rainfall amounts of 0.75 to
1.25 inches is expected with locally higher amounts. There is a
40-80% chance of more than 1" of rain across much of the region,
with a 15 to 35% chance of more than 2" across central Wisconsin.

Per RFC forecasts and HEFS guidance, several points along the
Menominee River could return to moderate flood stage. 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