NWS-Green Bay Forecast Discussion
FXUS63 KGRB 240320
AFDGRB
Area Forecast Discussion
National Weather Service Green Bay WI
1020 PM CDT Thu Apr 23 2026
Updated aviation portion for 06Z TAF issuance
and new information added to update section
.UPDATE...
Issued at 953 PM CDT Thu Apr 23 2026
Instability is quickly waning this evening, with only a narrow
axis of SBCAPE (200-600 j/kg) just west of GRB CWA. Thus, expect
the clusters and lines of storms in western WI to weaken and
become elevated as they move into NC/C WI. Still expect wind gusts
up to 40 mph and pockets of heavy rainfall, especially in our
western counties, but the severe threat is expected to wane.
&&
.KEY MESSAGES...
- There is a chance of thunderstorms tonight. A few strong storms
with wind gusts to 40 mph are possible, and pockets of heavy
rainfall will occur, especially over north central and central
Wisconsin.
- Scattered rain and a few storms are expected to continue into
Friday. Rainfall totals around an inch are anticipated in north
central and central Wisconsin, with around a half inch in
eastern Wisconsin. Locally higher amounts between 1.5 and 2"
will be possible.
- Another round of rain and embedded storms is forecast late
Sunday into early Tuesday. Heavy rainfall between 1 and 2" will
once again be possible.
- Rivers will continue to rise into next week following several
additional rounds of heavy rain, acting to exacerbate ongoing
flooding.
&&
.DISCUSSION...
Issued at 1230 PM CDT Thu Apr 23 2026
Scattered warm advection clouds have continued to increase in
coverage this afternoon as low pressure over Manitoba deepens upon
approaching the upper Mississippi Valley. As such, temperatures
have surged into the upper 70s to low 80s for areas inland of Lake
Michigan. Influx of moisture from the south has allowed dewpoints
to rise into the mid to upper 50s along/south of Hwy 29, holding
relative humidities in the 40s and 50s.
Rain/storm chances... Scattered rain and storms are progged to
arrive late this afternoon into this evening, with trends for an
earlier arrival time still on the table across our western tiers
of counties. Best potential for any strong or severe storms looks
to be from central to north-central Wisconsin late this afternoon
when instability is maximized at around 600 to 800 J/kg MUCAPE. If
a storm or two were to develop prior to 00Z, near inverted-V
soundings with 40 to 45 knot winds at the top of the dry layer
would support a marginal wind threat, though this appears
unlikely overall. Long and skinny CAPE profiles would keep the
hail threat to a minimum. As has been the case over the past
several weeks, the main threat will come in the form of heavy rain
and exacerbated flooding concerns, especially as PWATS reach the
99th percentile relative to climo (1.25 to 1.5"). Precip amounts
have flattened out over the last couple forecast cycles, with HREF
probabilities for receiving one inch of rain currently standing
at 30 to 60% north and west of the Fox Valley through Friday
afternoon. Locally higher amounts will be possible with any
convectively enhanced precip, with a 10 to 20% signal for two
inches of rain over central Wisconsin. Best chance for heavier
rain currently looks to be near the Hwy 10 corridor, which is
already vulnerable due to ongoing flooding.
Early next week... Synoptic pattern looks to amplify later this
weekend into early next week, with split flow prominent over the
CONUS. Closed upper low will continue to sit and spin over south-
central Canada throughout the weekend, before eventually phasing
with a southern stream shortwave ejecting from the southwest. This
potential phasing will lead to rapid surface cyclogenesis over the
upper Mississippi Valley, bringing us our next chances for
widespread rain and embedded thunder. Initial thoughts are that
severe potential looks rather limited due to meager instability
and timing of FROPA, though this is subject to change in the
coming days. As it stands now, NBM shows a 40 to 70% chance for
receiving one inch of rain, with a narrow corridor of 20 to 40%
probabilities for 2 inches once again centered on Hwy 10. Much
colder air then wraps in from the northwest Tuesday night,
signaling a potential transition over to snow showers across the
Northwoods within the comma head region of the low.
Rest of the extended looks to be calmer and cooler as a blocking
upper low sits and spins over the Great Lakes. Result will be a
prolonged period of cool and cloudy weather, with highs averaging
in the mid 50s to mid 60s. Upside to this is that precip chances
look to be minimal during this time.
&&
.AVIATION...for 06Z TAF Issuance
Issued at 953 PM CDT Thu Apr 23 2026
Showers and embedded thunderstorms will continue to overspread the
forecast area overnight, but should have a tendency to weaken and
become more scattered as they move into eastern WI. Flight
conditions should deteriorate to MVFR overnight, but confidence
is a bit lower for IFR ceilings. Showers and a few storms should
taper off in our western counties Friday morning, and in eastern
WI in the early to mid afternoon. Conditions should improve to
VFR by early to mid afternoon as ceilings rise and clearing
occurs.
Southeast to south winds will continue overnight, then become
northwest as a cold front moves through late tonight into Friday
morning. Pockets of LLWS will wane overnight.
&&
.HYDROLOGY...
Issued at 1230 PM CDT Thu Apr 23 2026
Minor to moderate flooding continues on several rivers, namely the
Wolf and Menominee. While water levels have continued to recede
given a recent bout of dry weather, this is likely to change as we
get another round of moderate to heavy rain this evening through
Friday afternoon. Per RFC forecasts and HEFS guidance, it appears
that the Menominee River could return to recent crests in major
flood stage later this week into this weekend upon receiving
around 0.75 to 1" of rain, locally higher. Increasing snow melt
from the Upper Peninsula would lend some confidence for at least a
return to moderate flood stage. Additionally, levels on the Lake
Winnebago system continue to gradually rise, with minor flooding
already occurring from Lake Poygan to Winnebago and minor flooding
forecast to occur through the weekend. Those living near rivers
or streams should continue to monitor the latest Flood Warnings
and statements from the National Weather Service in Green Bay.
&&
.GRB WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE.........Kieckbusch
DISCUSSION.....Goodin
AVIATION.......Kieckbusch
HYDROLOGY......Goodin