NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 150741
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
241 AM CDT Wed Apr 15 2026

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Another round of showers and thunderstorms are expected late
  this afternoon and evening. 1+ inch hail is the main severe
  hazard.

- Additional rainfall will continue to exacerbate any ongoing
  flooding. If thunderstorms train over areas that have seen
  multiple inches of rain the last two days flash flooding would
  be likely.

- Minor to moderate river flooding is ongoing or forecast to occur
  on several area rivers. Expect many rivers to rise this week due
  to additional rain and runoff from Upper Michigan, with the
  greatest impacts expected on the Menominee River, where some
  locations may see major flooding during the mid to late part of
  the week.

- Addtioanl rounds of rain and thunderstorms are expected Friday
  through this weekend.

&&

.DISCUSSION...
Issued at 240 AM CDT Wed Apr 15 2026

Short Term...Today...Tonight...and Thursday

Fog this morning..

Dense fog with visibilities as low as 1/4 mile has spread across
much of the lake and bayshore counties overnight, while dense fog
is more patchy further west. The coverage of fog will continue to
expand over the next few hours before fog starts to dissipate. Fog
will be quicker to burn off across central WI compared to eastern
and northern WI. Areas along the lake and bay as well as far
northern WI may see fog linger into the early afternoon.

Rain and Thunderstorm Chances Today...

A stalled frontal boundary snaking from east-central WI back
toward central IA will continue to spur on isolated showers this
morning, however, most locations should remain dry. Chance for
precipitation increases again this afternoon as a surface low
lifts into the region. Main concern with this next round of
precipitation is how additional rainfall will exacerbate ongoing
flooding or lead to new flood concerns given soils are saturated
and rivers and streams continue to run high. REFS LPMM shows
another 0.25-0.5" of rain with this system through Thursday
morning south of a Stevens Point to to Marinette line. However, if
more persistent convection is able to develop over this area
could see rainfall totals closer to REFS 90th percentiles of
1-1.5" in localized areas. If those higher end amounts do play
out in areas with ongoing flooding or areas that have had
flooding issues over the past two days flash flooding would be
likely.

The severe storm threat late this afternoon and evening is more
muted compared to the past two days. Forecast soundings do show
elevated MUCAPEs of 200-400 J/kg late this afternoon along with
50-60 kts of unidirectional 0-6km shear. This may lead to a
marginal risk for 1+ inch hail across part of central and east-
central WI. The risk for damaging wind gusts or tornados is very
low given a stable boundary layer.

Long Term...Thursday Night Through Tuesday

The latest ensemble means continue to indicate a break in this
incredibly wet pattern is forecast this weekend into the middle of
next week. Until this time range, the final system to move through
the region arrives late Friday afternoon and departs on Saturday.

A brief lull in the rainfall is likely on Thursday night into
Friday morning as the region will reside between systems. However,
that changes by late Friday afternoon when a 35 to 45 kt low level
jet advects precipitable water values up to the 99 percentile into
the northern Mississippi Valley. Models show precipitation is
forecast into expand on Friday afternoon as large scale ascent and
moisture increases over the course of the day. Instability
increases between 400-700 j/kg on Friday night when the surface
low pressure and pwat axis moves through. Because instability
peaks at night, the severe risk will likely be muted somewhat due
to a capping inversion. But given the wind profiles and some
instability, small hail and gusty winds in excess of 40 mph appear
possible.

Greater concern revolves around rainfall and flooding potential.
Probabilities for a 1/2 inch of rain ranges from 40-60% while
probabilities for 1 inch of rain ranges from 5-20%. So, most
likely looking at precipitation of 1/2 to 1 inch of rain, with
locally higher amounts where thunderstorms occur. Given the
moisture laded soils, the most flood prone areas may see renewed
flooding potential.

After the system passes, much colder air arrives on Saturday. A
change over of precip from rain to snow remains possible. The
probability of a 1/2 inch of snow over Vilas county ranges from 20
to 40% on Saturday, so little to no impacts are expected. But
gusty winds in excess of 30 mph appear possible.

Thereafter, high pressure will move across the region late in the
weekend into early next week. This should result in a period of
little to no precipitation into Wednesday.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1205 AM CDT Wed Apr 15 2026

A stationary warm front remains positioned across the southern
Fox Valley tonight. Scattered showers and isolated thunderstorms
continue to impact northeast Wisconsin, primarily affecting KGRB,
KATW, and KMTW through 08z. While the severe threat has
diminished, brief reductions in visibility remain possible in any
stronger cells.

Following the departure of the precipitation, low-level moisture
and stratus will expand across the region from the northeast.
Flight conditions are expected to deteriorate rapidly to LIFR or
VLIFR at all terminals overnight. Dense fog is anticipated over
areas which received rain this evening, from central to east-
central WI, with visibilities frequently dropping to 1/2SM or less.
Confidence is high in these poor flight conditions persisting
through at least 14z-15z Wednesday.

Conditions will be slow to improve Wednesday morning. Fog and
ceilings are forecast to lift more quickly over north-central
Wisconsin (KRHI) than areas further south and east. Persistent
MVFR ceilings are expected to linger through Wednesday afternoon
across east-central Wisconsin, while KMTW may remain IFR for much
of the day due to onshore flow. Another round of showers and
thunderstorms is possible Wednesday night as additional energy
moves into central Wisconsin, likely leading to a return of IFR
conditions.

&&

.HYDROLOGY...
Issued at 240 AM CDT Wed Apr 15 2026

Widespread flooding continues across parts of central and east-
central WI, where flood warning remain in place, due to multiple
rounds of thunderstorms that have produced 3 to 6 inches of rain
over the last 48 hours. Extensive road closure remain where the
heaviest rain has fallen. Multiple dams have also been over topped
at times due to high flows on rivers and streams. Runoff from
snow melt in Upper Michigan is also still expected to bring
moderate to major flooding on the Menominee River, especially
during the mid to late part of the week. If you live near a river
or stream, keep a close eye on water levels this week and monitor
the latest Flood Warnings from the National Weather Service in
Green Bay.

&&

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

&&

$$

DISCUSSION.....GK/MPC
AVIATION.......MPC
HYDROLOGY......GK