772
FXUS63 KGRB 290527
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1227 AM CDT Sun Mar 29 2026

Updated aviation portion for 06Z TAF issuance

.KEY MESSAGES...

- Mild temperatures are expected on Sunday and Monday. Greatest
  potential for highs in the 60s or even low 70s from central WI
  to the southern Fox Valley.

- Potential for strong thunderstorms Monday Night into Tuesday
  morning, then drying out Wednesday into Thursday.

- Many rivers at or above bankfull into next week. Isolated
  instances of minor flooding may still occur on some rivers.

&&

.DISCUSSION...
Issued at 1222 PM CDT Sat Mar 28 2026

The latest RAP analysis and satellite imagery show a ridge of
high pressure shifting southeast of the region as a surface low
develops over the central High Plains. Warm advection is currently
occurring ahead of shortwave energy embedded within northwest
flow aloft, resulting in thickening mid and high clouds across
eastern Minnesota and northwest Wisconsin. While some light radar
returns are noted over western Lake Superior and northwest
Wisconsin, dry air in the low levels is preventing precipitation
from reaching the ground thus far. Have added a slight chance of
light snow near the U.P. border this afternoon as cloud bases are
expected to lower to around 6000 ft.

Mid-level heights will rise tonight as the current shortwave
lifts northeast, leading to a quiet night. The jet stream will
continue to push in scattered to broken mid and high clouds at
times, but low level saturation will be confined to areas over
northern Lake Superior. Lowered min temps over the northwoods
tonight due to a combination of light winds and some lingering
snow pack.

Mostly dry conditions will prevail through Sunday before a
complex frontal system arrives late in the day on Monday. Highs
on Sunday will reach the mid 50s to mid 60s under mild southerly
flow. However, a weak frontal boundary will drape itself across
the region Sunday night into Monday. With northeast winds
developing behind the boundary, a significant temperature gradient
will set up on Monday. Highs will struggle to reach the lower 40s
near the lakeshore and far northeast Wisconsin, while central
Wisconsin manages to reach the middle 60s to lower 70s. Lowered
highs slightly on Monday due to cloud cover and northeast winds,
which is usually conducive for temps underperforming.

Focus then turns to thunderstorm potential late Monday night.
Ahead of a more potent shortwave, a low-level jet will develop and
point into northeast Wisconsin by Monday evening. This feature
will usher in a surge of warm air and moisture aloft, with
precipitable water values climbing to 200 percent of normal. While
a strong low-level inversion caused by the cool northeast winds
will likely keep storms elevated, mid-level lapse rates of 7.5 to
8 C/km and instability exceeding 1000 J/kg could support
marginally strong storms. Much of the instability is rooted above
700mb so believe the threat of severe storms is relatively low. The
primary threat with these storms will be hail. While moisture is
abundant, dry air in the 850-700mb layer may limit the overall
heavy rain threat. The chance of greater than a half inch of rain
is less than 20% from Monday night through Tuesday.

The surface low will cross southern Wisconsin Tuesday morning,
bringing lingering light rain and drizzle before colder air
returns in the afternoon. A robust Canadian high pressure system
will build in for Wednesday and Thursday, ensuring dry but much
cooler conditions with highs returning to the 30s and 40s. Another
trough is forecast to move into the Northwest by Thursday,
eventually pulling additional moisture into the Midwest by Friday.
This could result in another round of precipitation late in the
week, with thermal profiles potentially cold enough to support a
mix of rain and snow.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1227 AM CDT Sun Mar 29 2026

The primary aviation concern will be LLWS through mid-morning.
Southwest winds at 2000 feet will be around 40 knots, creating
shear concerns for all terminals. Wind shear should dissipate by
mid-morning Sunday as surface mixing increases.

Surface winds will remain S to SW between 5-10 knots through the
TAF period. Some occasional gusts up to 20 knots are possible
during the daylight hours.

Meanwhile, scattered to broken mid level clouds will drift
through from time to time.

Outlook...VFR conditions continue after 06Z Monday. A frontal
boundary brings a chance for thunderstorms and MVFR conditions
Monday night.

&&

.HYDROLOGY...
Issued at 1222 PM CDT Sat Mar 28 2026

No changes to previous thoughts. Several rivers will remain at or
above bankfull into next week due to recent/ongoing melting snow
along with rainfall late in the week. Ensemble river probability
forecasts still show some potential for isolated points on a few
rivers to reach minor flood stage next week, but trends for
multiple locations to see potential for minor flooding are not as
bullish. If heavy rainfall ends up being more widespread instead
of tied to smaller complexes of thunderstorms, the risk for
flooding would increase over more of the area as the grounds are
more saturated and rivers are already running higher.

&&

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

&&

$$

DISCUSSION.....MPC
AVIATION.......KLJ
HYDROLOGY......MPC

NWS GRB Office Area Forecast Discussion