NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 151900
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
200 PM CDT Wed Apr 15 2026

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Another round of rain/storm arrives from the south later this
  afternoon and evening. One inch hail would be the main hazard
  with any stronger storms.

- Additional rainfall will continue to exacerbate ongoing areal
  flooding. Flash flooding would be possible in areas that have
  already received multiple inches of rainfall, or over areas
  that see training storms.

- Minor to moderate flooding is ongoing or forecast to occur on
  several rivers. Expect many rivers to continue rising this week,
  with the greatest impacts expected on the Menominee River where
  major flooding has been observed.

- Widespread rain/storms will again be possible on Friday. Some
  storms could become strong or severe.

&&

.DISCUSSION...
Issued at 143 PM CDT Wed Apr 15 2026

Rain/storm chances today... Frontal boundary remains stalled out
over southern Wisconsin as of early this afternoon, which will
bring our next chances for rain and storms later this afternoon
into this evening. Par for the course, the main concern will be
how any additional rainfall will exacerbate ongoing flooding,
especially in areas that are already vulnerable. Overall, we're
looking at receiving an additional 0.25 to 0.5" of QPF through
tonight, with probabilistic guidance showing a 30 to 50% signal
for 0.5" of rain over the southern Fox Valley. Reasonable high-
end scenario (90 to 95th percentile) would bring amounts in excess
of one inch from the Fox Valley to the lakeshore, though this
would most likely occur with a slight northward shift of the
boundary and training storms. If these amounts were to be
realized, flash flood thresholds would likely be met over east-
central Wisconsin where soils are already saturated and areal
flooding is ongoing.

Severe threat for this afternoon looks less distinguished than
yesterday given unfavorable placement north of the front and
stable easterly boundary layer flow. Elevated instability (300 to
500 J/kg MUCAPE) and appreciable deep-layer shear (50+ knots)
sneak into our southern tier of counties late this afternoon,
though the threat for any surface-based storms is low. Cannot rule
out the possibility for an elevated hailer or two given elongated
hodographs and decent lapse rates, though suspect that severe
potential would be rather limited.

Strong/severe storms late week... Following a brief lull in precip
Thursday into Friday, 500 mb pattern then re-amplifies toward the
end of the week. Robust trough approaches from the Intermountain
West on Saturday as a deepening surface low ejects from the
central Plains, bringing with them yet more chances for widespread
heavy rain and strong or severe storms. Southerly flow regime
would support decent moisture transport from an open Gulf, with a
narrow corridor of 60 dewpoints possible along the leading edge of
cold FROPA. Decent instability (~1,000 J/kg CAPE) would favor
linear ascent along the front, resulting in likely upscale
development into a QLCS storm mode Friday evening and overnight.
Main source of uncertainty at this time centers around timing of
the front, which currently looks to be late Friday night into
early Saturday morning. Regardless, this system looks to be much
more dynamic than what we've seen this week thus far, especially
with the influence of a 50+ knot LLJ and favorable deep layer
shear.

Given an ample supply of Gulf moisture, heavy rain once again
becomes a concern Friday into Saturday. Probabilistic guidance
currently shows a widespread 30 to 50% chance for receiving 1
inch of rain, with a signal (10 to 30% chance) for exceeding 1.5".
Locally higher amounts would be possible within convection. As
such, flash flood potential would once again come into play Friday
into Saturday, where WPC currently highlights most of the state
in a marginal Day 4 risk for excessive rainfall.

Muc colder air wraps in from the northwest on the back end of the
departing surface low on Saturday, resulting in a probable
transition from rain to snow across the far north. Probabilities
for half an inch of snow currently stand at 20 to 40% mainly over
Vilas, so little to no impacts are expected. Temperatures then
drop off steeply by Saturday afternoon, bringing highs down into
the 30s and 40s for most. High pressure then settles in over the
CONUS late this weekend and into early next week, affording us a
much needed dry spell.

&&

.AVIATION...for 18Z TAF Issuance
Issued at 1208 PM CDT Wed Apr 15 2026

Low IFR/LIFR stratus has lingered over much of the forecast area
as of early this afternoon, with patchy BR and reduced vsbys
persisting over east-central Wisconsin. Some clearing has begun
to work its way into north-central Wisconsin, with the potential
for RHI to go VFR in the next hour or two. Rain/storm chances then
arrive from the south late this afternoon, lasting through
Thursday morning. A strong hail-producing storm or two cannot be
ruled out during this time, though severe potential should be
limited. This being said, have opted to include a PROB30 mention
for -TSRA in the east-central TAFs for when thunder seems most
likely. Vsbys may drop into IFR or LIFR territory within any
heavier rain.

Light winds and recent rainfall may result in areas of fog/low
stratus development late tonight into early Thursday morning.
Locally dense fog with vsbys below 1 SM will be possible, though
was not confident enough to provide exact timing resolution as of
yet.

&&

.HYDROLOGY...
Issued at 143 PM CDT Wed Apr 15 2026

Following another bout of heavy rain and storms yesterday,
widespread flooding continues across portions of central to east-
central Wisconsin where an areal Flood Warning remains in effect.
Several roads remain closed, especially in areas that received
between 3 and 6 inches of convectively-enhanced precip over the
past 48 hours. Multiple rivers, namely the Wolf, Menominee, and
Wisconsin Rivers, continue to read in minor to moderate flood
stage, with the Menominee River now in major flood stage due to
the additional influence of snow melt from the Upper Peninsula.
Home evacuations are ongoing along the Wolf River. High flows and
rising water levels have also resulted in several dams being
compromised or overtopped. If you live near a river or stream,
continue to monitor the latest hydro forecasts and Flood Warnings
from the National Weather Service in Green Bay.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory from 11 PM this evening to 10 AM CDT Thursday
for WIZ005-010>013-018>022-030-031-035>040-045-048>050-073-074.
&&

$$

DISCUSSION.....Goodin
AVIATION.......Goodin
HYDROLOGY......Goodin