364
FXUS63 KGRB 111149
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
649 AM CDT Sat Apr 11 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Periods of heavy rainfall and thunderstorms expected from
  Saturday night through the middle of next week. There is a
  80-100% chance of rainfall greater than 1 inch, and a 40-60%
  chance of greater than 2 inches.

- A round or two of strong to severe thunderstorms will be
  possible during the early to mid part of next week, with the
  best chance occurring Monday night, and additional chances
  Tuesday afternoon/evening and Wednesday afternoon.

- Much above normal temperatures expected, with highs in the 60s
  and 70s from Sunday through Friday.

- Minor flooding will continue along the Wolf River through at
  least early next week. Combined runoff from melting snow in the
  Upper Peninsula and heavy rain will likely result in flooding
  on the Menominee River by Tuesday, with moderate to major
  flooding possible during the mid to late part of the week.

- More heavy rainfall and storms possible late in the week.

&&

.DISCUSSION...
Issued at 239 AM CDT Sat Apr 11 2026

Aside from some stratocumulus clouds in far northern WI, clear
skies were observed across the forecast area. Temperatures ranged
from the middle 20s to middle 30s.

High pressure will shift east today, so morning sunshine will
give way to increasing clouds as WAA increases this afternoon.
Scattered showers will work their way into NC and central WI late
in the day. Highs should reach well into the 50s, except near lake
Michigan, where readings will be in the mid to upper 40s.

A prolonged period of active weather arrives tonight and
continues through the middle of next week. Periodic showers and
thunderstorms, and potential for heavy rainfall, can be expected
through the period.

The first batch of heavy rainfall arrives tonight into early Sunday,
as a warm front lifts north into the region and a 45 to 50 knot
southerly low-level jet brings a surge of Gulf moisture (PWATs
1-1.4 inches) and marginal instability. Given the marginal
instability, not expecting organized severe storms during this
first episode. Models show a decrease in precipitation after the
warm front lifts north Sunday afternoon. The lull continues Sunday
night into Monday, as H8 flow turns westerly (parallel to the
baroclinic zone), PWATs drop to less than 1 inch and instability
wanes.

The front sags south and stalls across the area Monday into
Tuesday, and potentially lifts back to the north as a low
pressure system approaches Tuesday night into Wednesday. This
front will interact with a persistent flow of Gulf moisture and
instability. Instability peaks across the forecast area Monday
evening, with mid-level lapse rates of 7.5-9 C/km and H8 LI`s
of -4 to -8 C expected. A southerly low-level jet redevelops and
increases to 40-50 kts, setting the stage for strong to severe
thunderstorms with large hail and damaging winds. Additional
strong to severe storms could develop as the front starts to lift
back to the north Tuesday afternoon and evening. If the surface
low tracks far enough west on Wednesday, we could see a surge of
instability across eastern WI as the cold front moves through in
the afternoon, so cannot rule out additional severe potential
(especially damaging winds) then. See the Hydrology section for
information on heavy rainfall and flooding potential.

Milder temperatures are expected through the period, with highs
reaching into the 60s and 70s from Sunday through Friday.

Long-range models show another frontal system approaching late in
the week, with potential for additional storms and heavy rainfall.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 636 AM CDT Sat Apr 11 2026

Clear skies covered the forecast area this morning, but mid-level
clouds were already moving into western WI, and showers were
pushing across SW MN and IA.

Mid-level clouds will increase this morning and early afternoon,
then gradually lower as showers arrive in the afternoon and
evening. Flight conditions will deteriorate to MVFR/IFR tonight
as heavier and steadier rain arrives. Elevated thunderstorms are
expected at times, and have used CAMs and trends with the low-
level jet to firm up a 4-hour favored window for storms at each
TAF site.

Winds become S-SE today, and continue into tonight, gusting to
20 kts at times. LLWS develops by mid-evening in NC/C WI, and
toward midnight in the Fox Valley/lakeshore areas.
&&

.HYDROLOGY...
Issued at 239 AM CDT Sat Apr 11 2026

Minor flooding is expected to continue on the Wolf River through
at least early next week. Periods of heavy rain and thunderstorms
arrive tonight and continue through the middle of next week.
During this upcoming period, probabilities for rainfall in excess
of 1 inch are 80-100%, with a 40-60% chance of amounts in excess
of 2 inches and a 10-20% chance of 3 inches or more. Current
forecasts call for 1.50 to 2.50 inches of rain in most areas.
Runoff from this rainfall, combined with rapid snowmelt in the
Upper Peninsula, is expected to bring potential for flooding on
the Menominee River by Tuesday, with moderate to major flooding
possible during the middle to late part of the week.

&&

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

&&

$$

DISCUSSION.....Kieckbusch
AVIATION.......Kieckbusch
HYDROLOGY......Kieckbusch

NWS GRB Office Area Forecast Discussion