991
FXUS63 KGRB 092355
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
655 PM CDT Sat May 9 2026

Updated aviation portion for 00Z TAF issuance

.KEY MESSAGES...

- Low afternoon humidities are expected Sunday and Monday.

- A Frost Advisory has been issued for areas over central
  Wisconsin and west of the Fox Valley for early Sunday morning.
  Additional frost is likely Sunday night into early Monday
  morning.

- High probability of rain on Tuesday (greater than 80%). A few
  isolated thunderstorms are possible over central and northeast
  Wisconsin as the system passes.

&&

.DISCUSSION...
Issued at 116 PM CDT Sat May 9 2026

The latest RAP analysis and satellite/radar imagery show a deep
upper trough centered from Hudson Bay to the central Great Lakes
early this afternoon. Embedded shortwave energy is pushing a cold
front across Lake Michigan with scattered light shower activity
exiting to the east. Partial clearing is spreading across
northwest Wisconsin and this clearing trend should continue east
through the rest of the afternoon. Looking further upstream, a
ridge of high pressure is positioned over the Plains and is
gradually shifting eastward. Forecast concerns revolve around
fire weather potential, frost potential, and light rain chances.

As skies clear this evening and winds become light under the
influence of the approaching surface ridge, favorable radiational
cooling conditions will develop. This will set the stage for
frost development. While there is some concern that the pressure
gradient may stay tight enough to keep temperatures up slightly,
consensus guidance is insistent on lows in the middle 30s for
areas west of the Fox Valley. Consequently, a Frost Advisory has
been issued for much of central Wisconsin and west of Outagamie
and Winnebago counties.

On Sunday, clouds will redevelop with the heat of the day.
Marginally unstable conditions off Lake Superior combined with
weak shortwave impulses could lead to widely scattered light
showers or sprinkles across far north- central and northeast
Wisconsin Sunday afternoon, though amounts will be negligible.
Another round of frost appears likely Sunday night as high
pressure settles directly over the state.

The next significant weather maker arrives on Tuesday in the form
of a dynamic clipper system. Confidence in precipitation has
increased significantly, with rain chances now exceeding 80
percent. Mid-level lapse rates of 6.5 to 7 C/km will support
modest instability, making isolated thunderstorms a possibility
over central and northeast Wisconsin. Showers may linger into
Tuesday night, particularly across the far north, before the
system exits to the east.

A shift in the large-scale pattern is expected late next week as
the persistent eastern trough flattens and a warming ridge over
the western United States shifts eastward. This will result in a
pronounced warming trend starting Thursday, with high temperatures
likely reaching the 70s to near 80 degrees by next Saturday. This
warmer airmass will lead to increasing instability by the end of
next weekend, though uncertainty remains regarding the timing of
the next round of organized precipitation.

&&

.AVIATION...for 00Z TAF Issuance
Issued at 652 PM CDT Sat May 9 2026

Primary low pressure resides over Quebec this evening, leaving
northeast WI within a cool, moist northwest flow aloft. Weak waves
within the pattern through Sunday will result in SCT-BKN high-
based (cigs 050-100) stratocu clouds with small chances (037-045.
&&

$$

DISCUSSION.....MPC
AVIATION.......JLA
FIRE WEATHER...MPC

NWS GRB Office Area Forecast Discussion