661
FXUS63 KGRB 091817
AFDGRB

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

Forecast discussion for routine afternoon forecast issuance

.KEY MESSAGES...

- Elevated fire weather conditions are expected this afternoon. Low
  afternoon humidities are also expected on 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 18Z TAF Issuance
Issued at 1208 PM CDT Sat May 9 2026

A deep upper trough will be present across the region over the
next 24 hours. High-based fair weather clouds with bases ranging
from 4.5 to 6 kft AGL early this afternoon will increase to 8-9
kft by 21-22Z. Deep mixing will result in gusty northwest winds
between 22-27 kts at all terminals through 23z.

Clearing skies are expected this evening as nocturnal cooling
sets in and winds diminish. Winds will remain light from the west
to northwest overnight. While VFR conditions will prevail at most
sites, some scattered MVFR lake effect clouds may drift into far
northern Wisconsin near the U.P. border late tonight.

On Sunday, VFR clouds will redevelop by mid-morning. Widely
scattered light showers or sprinkles are possible after 15z,
primarily north of a KRHI to KGRB line. Winds will become gusty
again from the northwest by late morning, reaching 15-20 kts.

Confidence is high in VFR flight categories through the period.

&&

.FIRE WEATHER...
Issued at 116 PM CDT Sat May 9 2026

Elevated fire weather conditions are the primary concern through
the remainder of the afternoon. A dry airmass is in place behind
the departing cold front. Deep mixing will allow dewpoints to
drop, resulting in minimum relative humidities in the 25 to 35
percent range away from the immediate Lake Michigan shoreline.
Combined with northwest wind gusts of 25 to 30 mph, conditions
will be favorable for fire development. Winds will diminish this
evening with the onset of nocturnal cooling, providing some
reprieve. Low afternoon humidities are also expected on Sunday
and Monday though winds will be less than today.

&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Frost Advisory from 3 AM to 8 AM CDT Sunday for WIZ030-031-
035>037-045.
&&

$$

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

NWS GRB Office Area Forecast Discussion