NWS-Green Bay Forecast Discussion

						FXUS63 KGRB 161900
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
200 PM CDT Thu Apr 16 2026

.KEY MESSAGES...

- Minor to major flooding will continue into next week with the
  greatest impacts expected on the Menominee and Wolf Rivers
  where major or record breaking flooding has been observed.

- Severe storms with a risk of tornadoes (possibly strong), large
  hail and damaging winds are increasingly likely Friday
  afternoon and evening, with the highest risk across central
  Wisconsin.

- Thunderstorms Friday will produce locally heavy rainfall. If this
  occurs over the flood sensitive areas of central and east-
  central WI additional flooding may occur.

- No significant precipitation is expected from Sunday through
  at least the middle of next week.

&&

.DISCUSSION...
Issued at 200 PM CDT Thu Apr 16 2026

Tonight: Areas of fog

Clouds have slowly been eroding from the northwest this
afternoon. However, additional fog may develop this evening,
especially across eastern Wisconsin and lakeshore areas. This
fog may become dense in spots.


Friday-Friday Night: Severe Storm / Heavy Rain Risk

The active period of weather continues later Friday night as a
strong mid-level trough and associated cold front move across the
area. This system will bring a variety of hazards, including severe
storms and locally heavy rainfall.

Severe Storm Risk:

A southerly 50 kt low-level jet ahead of the trough will promote
gusty southerly winds by afternoon on Friday along with robust
northward moisture transport, helping to enhance instability.
Although there is some spread in the quality and northern extent
of moisture, HREF mean dew points are forecast to reach at
least 60F with an axis of at least 1000-2000 J/kg of surface-
based CAPE across central Wisconsin. It is noteworthy that the
instability axis is rather narrow, with a gradient in
instability noted eastward towards Lake Michigan.

HRRR/RAP hodographs show substantial curvature in the unstable
sector with strong low-level shear across central Wisconsin.
This environment would be quite favorable for tornadoes,
including a strong tornado risk with any more semi discrete
storms. Supercells would also pose a large to very large hail
risk (2"+).

There is some uncertainty on the surface low/warm front
placement, which would impact the northward extent of the more
unstable air and the favored area for locally backed flow/higher
low-level shear. In addition, convective evolution remains
somewhat unclear with convection allowing models showing a range
of prefrontal and frontal storms, with mixed storm modes,
before storms begin to grow upscale with embedded line
segments/bows. The HREF shows a robust signal for
rotating/severe storm (mid- level updraft helicity) across
central Wisconsin with a more muted signal eastward towards Lake
Michigan in the less unstable air.

The most favorable window for severe storms looks to be during
the later afternoon and evening hours with the greatest risk
over central Wisconsin.

Heavy Rain Risk:

MRMS FLASH soil moisture continues to highlight high soil moisture
values across parts of central Wisconsin through far eastern
Wisconsin, where the heavier rains have occurred. Precipitable water
values remain near the top end of seasonal climatology, so although
the system will remain progressive, any thunderstorms will be
capable of high rain rates with high end (90% percentile) amounts
exceeding 2 inches. The 16.12Z local probability matched mean also
shows variable rain amounts, but localized corridors of 2-3+ inches.
Given the saturated ground, especially from central into eastern
Wisconsin, any rain will quickly run-off. One hour flash flood
guidance is just over 1 inch across the urban Fox Valley
corridor, so flash flooding is a concern where higher rain rates
persist. Additional areal flood concerns may develop where
higher rain amounts (1-2"+) overlap areas with saturated soils.
Given these concerns, a flood watch was issued for much of the
area, except parts of north-central Wisconsin.


Weekend: Drier and cooler

The cold front and any storms will have cleared by Saturday morning
with deep troughing over the Great Lakes. Much cooler below average
temperatures will move in for the weekend with gusty northwest winds
and a strong push of low-level cold advection Saturday morning.
Highs will struggle to exceed the 40s through the weekend. A very
dry airmass will move in late in the weekend with precipitable water
values falling below the 10th percentile relative to climo as
surface high pressure approaches.


Next Week:

A dry northwest flow pattern will set up through at least the first
half of the week with the western Great Lakes largely remaining
under the influence of surface high pressure. This will provide a
much needed respite from the heavier rains over the past week. After
a seasonably cool start to the week, temperatures will trend back
above average for midweek, although significant spread is evident
for temps in the model suite heading through mid-week.

&&

.AVIATION /18Z TAFS THROUGH 12Z FRIDAY/...
Issued at 1148 AM CDT Thu Apr 16 2026

Skies will gradually clear from the north and west this
afternoon. However, there are medium to high chances (40-80%)
for additional fog development this evening and overnight across
eastern Wisconsin. The fog will persist into Friday morning.
LIFR visibilities may occur for a time.

Winds will become southeasterly tonight and become gusty from
the south during the day on Friday. Beyond this TAF period,
gusts may exceed 25 to 30+ kts during the afternoon. Before
surface winds increase, a period of LLWS may occur early
Friday.

Thunderstorm chances will increase on Friday afternoon beyond
this TAF period.

&&

.HYDROLOGY...
Issued at 200 PM CDT Thu Apr 16 2026

Flooding continues along multiple rivers due to the combination of
snow melt and recent heavy rainfall, including major flooding along
the Wolf and Menominee Rivers. 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.

Additional thunderstorms will occur later Friday and Friday night.
Although amounts will be variable, localized high end amounts
exceeding 2 to 3" may occur where repeated storms occur. This may
lead to additional rises for impacted river basins, in addition to
exacerbating flood concerns in areas that received higher rain
amounts already this week and in urban areas.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
WI...Flood Watch from Friday afternoon through Saturday morning for
     WIZ011>013-019>022-030-031-035>040-045-048>050-073-074.
MARINE...None.

&&

$$

DISCUSSION...JM
AVIATION...JM
HYDROLOGY...JM