280
FXUS63 KGRB 301130
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
630 AM CDT Mon Mar 30 2026

Updated aviation portion for 12Z TAF issuance

.KEY MESSAGES...

- Mild temperatures today. Greatest potential for highs in the
  60s or even low 70s from central WI to the southern Fox Valley.

- Potential for isolated strong thunderstorms with hail tonight.
  If clearing occurs, strong thunderstorms could also develop over
  east-central WI through mid-afternoon Tuesday.

- Winter weather impacts becoming more likely Wednesday night
  through Thursday night. There is a 50-80 percent chance for more
  than 2 inches of snow across northeast Wisconsin, along with a
  30-60% chance of 0.10 inch or more of ice.

&&

.DISCUSSION...
Issued at 208 AM CDT Mon Mar 30 2026

Warm today inland from Lake Michigan. Then, low pressure system
and a warm front brings round of showers and storms tonight with
another round on Tuesday as cold front crosses. Southern stream
low pressure system moving in late Wednesday will bring winter
weather impacts back to Wisconsin Wednesday night through Thursday
night.

Changes to the going forecast themes are small. Dry air
entrainment tonight leads to questions regarding how widespread
coverage of storms will be. But, even so, effective shear 1-6km of
50 kts and mid-level lapse rates up to 8c/km, MUCAPE up to 1k
J/kg tonight (especially 00z-06z) support risk of severe hail.
Decent agreement after 06z, main push of showers and storms in
warm air advection regime shifts east into lower Michigan. Small
window still remains open for sfc based convection initiation on
Tuesday mid morning into mid afternoon over south-central to
southeast cwa on the western edge of the day2 marginal risk from
SPC. Otherwise, northern stream wave arriving mid morning will
support clusters of showers and some thunder with still a hail
risk.

Additionally, still appears that light icing (mainly on elevated
surfaces) is possible toward daybreak and into Tuesday morning near
the Michigan border due to persistent northeast flow and surface
temperatures near freezing. Just not sure extent of precip during
the time the temps are most favorable.

A brief break in precipitation still in forecast for Wednesday as
high pressure builds in and front slides to the south. Southern
stream system quickly arrives later Wednesday night, through
Thursday, before exiting Thursday night. System is gaining steam
and has a lot of Gulf moisture to interact with as it moves
through. Warm layer aloft will lead to host of ptypes, especially
on Thursday and Thursday night. In some areas the precip may
eventually change to rain. During the event though, could be
looking at snow and ice. Probabilities for 2+ inches of snow as
high as 80% (up from 40% previously) while probabilities of 4+
inches now sit at 25-35%. In terms of ice, probabilities of a
coating of ice are as high as 75%, while seeing 0.10" or more has
climbed to 30-60%. A lot of numbers here to assess the potential,
but the main takeaway is this system is trending toward having
bigger impact over our region beginning Wednesday night and
lasting through Thursday night. WSSI-p showing this too, with
trends upward in minor, moderate impacts, and even some weak
signal for major impacts. Caution though as it is a warm system,
so sfc and warm layer aloft thermals will be very critical in
assessing the impact potential. Best advice now is to stay tuned
for later updates.

No changes to the previous thinking for system that follows as yet
another potent storm system is forecast to approach the region
Friday night to Saturday timeframe. Unlike the mid-week system,
this feature looks to be much warmer, suggesting a transition to
primarily rain. We will be monitoring this period for additional
thunderstorm potential and the risk for heavy rainfall as the low-
pressure center tracks toward the Great Lakes.

&&

.AVIATION...for 12Z TAF Issuance
Issued at 628 AM CDT Mon Mar 30 2026

Conditions will be VFR today, but deteriorate to MVFR this
evening and eventually IFR later tonight as sfc low and warm front
shift over the area bringing a chance of showers and some storms.
However, potential/coverage of storms tonight is uncertain due to
dry air that will be around to start the evening. Went with
prevailing showers and prob30 group for thunder over eastern TAF
sites 03z-07z where there is at least loose agreement in some
showers and thunderstorms. However, given trends in models that
are very sparse in shower and storm coverage tonight, wouldn`t be
a surprise if most of the terminals remain dry majority of tonight.

Better agreement that disturbance arriving from the northwest
kicks off round of showers and some storms very late tonight over
central and north-central WI, spreading to rest of the terminals
through the morning and early afternoon hours on Tuesday. Put a
mention of showers in at the very end of the TAF period at RHI/AUW/CWA.

Warm front close by on Tuesday morning should lead to continuation
and/or expansion of IFR-MVFR cigs/vsby late tonight through Tuesday
morning. Surface winds will be variable this morning, before becoming
easterly and gusty this afternoon and evening. Winds will remain from
the NE-E later tonight, but diminish.

&&

.HYDROLOGY...
Issued at 208 AM CDT Mon Mar 30 2026

Localized flooding is possible tonight through Tuesday where more
concentrated storms and heavy rain occur, especially if locations
impacted still have snow cover. Also, any higher rainfall rates
with storms could lead to minor flooding in low-lying, poor
drainage and urban areas.

Otherwise, signal showing up for many rivers to potentially reach
minor flood stage starting next weekend following the two moisture
laden systems late this week.

&&

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

&&

$$

DISCUSSION.....JLA
AVIATION.......JLA
HYDROLOGY......JLA

NWS GRB Office Area Forecast Discussion