NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 130038
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
738 PM CDT Sun Apr 12 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Showers and isolated thunder will track across the southeast
  part of the area this evening.

- Potential for severe thunderstorms with large hail and damaging
  winds has increased for Monday evening and overnight, with much
  of the area in an Enhanced Risk (level 3 or 5).

- Rain and thunderstorms chances continue at times Tuesday and
  Wednesday. Some severe storms may also occur. More precip is
  possible Friday through this weekend.

- Minor to moderate flooding is ongoing or forecast on several
  area rivers. Expect many rivers to rise this week due to
  additional rain and runoff from Upper Michigan.

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

&&

.DISCUSSION...
Issued at 434 PM CDT Sun Apr 12 2026

Rain and thunderstorms from earlier today have exited to the east,
however more development in southwest WI is tracking to the
northeast. Initial indications showed this batch of rain just
brushing the far southeast portion of the GRB forecast area, but
current radar trends indicate this round of rain may impact the
Fox Valley as well. Some lightning is also present, but do not
expect any strong or severe storms. This round of rain/thunder
will depart by mid to late evening.

A surface cold front drops south across WI on Monday, and then
stalls out somewhere in central to southern WI. An initially
capped environment during the afternoon will break down via
increasing low level jet Monday evening, setting the stage for
thunderstorm development. Initially individual cells will grow
into a complex and progress eastward. MUCAPEs of 1000 to 2500 J/kg
along with steep mid level lapse rates indicate mainly elevated
storms with large hail (up to ~2") and damaging winds (~60 mph) as
the main threats. However, any storm in proximity to the warm
front could tap into some surface based instability resulting in
a small tornado threat, mainly for central WI, but this will also
depend on where the front stalls out. Heavy rain and localized
flooding will also be a concern, with pwats of 1.0-1.4", and many
rivers and soils already saturated from the recent wet pattern.
Best timing for severe potential is from 6PM Monday to 1AM
Tuesday, which has trended slightly early with recent model runs.

Expect a lull late Monday night into Tuesday morning, but as the
surface boundary will still be draped across WI more showers and
thunderstorms are expected to develop along this feature Tuesday
afternoon and evening. The severe threat is lower, but hail and
damaging winds are possible, especially south of Hwy 29.

The pattern remains active Wednesday, as a surface low tracks
along the front, and then finally pushes eastward Wednesday
night. Severe thunderstorm potential will come down to the exact
track of this low/location of the front, but at the moment remains
low.

Deep upper trough tracks towards the Plains and Midwest Friday
and this weekend, bringing more opportunities for rain,
thunderstorms, and possibly even snow by Sunday.

Meanwhile, milder temperatures are expected through Friday with
daily highs in the 60s and 70s. Readings return to near normal by
this weekend.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 738 PM CDT Sun Apr 12 2026

Showers will continue across east-central WI this evening, mainly
impacting MTW but clipping ATW/GRB for a time. Main issue will be
gusty winds up to ~35 kts in/around the showers. A stray shower
is also possible in far north-central WI late this evening, but
no impacts are expected at RHI. The VFR/MVFR clouds are expected
to lower to mainly MVFR/IFR later this evening and overnight,
along with some fog which will reduce visibilities. The southwest
winds should help keep the fog from becoming dense, but as winds
diminish early Monday morning across central and north-central
WI, some denser fog is possible, along with some LIFR ceilings.

During the mid-late morning on Monday, conditions will begin to
improve as fog dissipates and clouds lift and/or scattered out.
Quiet weather is likely for the early-mid afternoon followed by
thunderstorms, some likely strong to severe, Monday evening and
overnight.

Winds will be SW through the evening, then gradually veer W
overnight. Gust of 15 to 30 knots are expected at times tonight,
locally higher near/in the showers. Lighter winds are expected on
Monday, shifting to the south/southeast Monday afternoon.
Additionally, LLWS at 2kft will continue through early Monday
morning due to a strong LLJ overhead.

&&

.HYDROLOGY...
Issued at 434 PM CDT Sun Apr 12 2026

Additional rainfall from Monday through Wednesday is likely to be
at least 1" (50-90% chance), but lower potential for more than 2"
(10-30%). However, rain amounts will be highly variable based on
where various rounds of convective storms track. Additional rain
is expected late in the week and into the weekend, but it is too
early to hone in on specific amounts.

Based on the most likely current forecast, minor flooding will
continue on the Wolf River through the next week. Runoff from
Upper Michigan along with additional rain will bring minor and
moderate flooding on the Menominee River early this week, too.
Minor flooding is also ongoing or possible on other area rivers,
with flood warnings currently out for the Oconto River and a small
portion of the Wisconsin River.

&&

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

&&

$$

DISCUSSION.....KLJ
AVIATION.......Bersch
HYDROLOGY......KLJ