375
FXUS63 KGRB 300911
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
411 AM CDT Mon Sep 30 2024

Forecast discussion for routine morning forecast issuance

.KEY MESSAGES...

- Well above normal temperatures will continue today. A strong
  cold front will bring windy conditions and much cooler
  temperatures on Tuesday. Frost is likely Tuesday night, mainly
  across northern WI.

- Gusty winds and building waves late tonight into Tuesday, and
  again Wednesday into Wednesday night, will create hazardous
  conditions for small craft.

- Gusty winds, low humidity and persistent dry conditions may lead
  to elevated fire weather concerns on Tuesday and Wednesday.

&&

.DISCUSSION...
Issued at 410 AM CDT Mon Sep 30 2024

Short Term...Today...Tonight...and Tuesday

Forecast concerns include precipitation chances, gusty winds and
cooler temperatures in association with a strong cold frontal
passage tonight into Tuesday. Marine headlines and possible
elevated fire weather conditions in the wake of the frontal
passage are also of concern.

High pressure centered east of Lake Superior still extended into
NE WI early this morning. Though fog was less of a concern than
previous mornings, patchy fog was still reported in far NE WI.
Under clear skies, early morning temperatures ranged from the
upper 30s and lower 40s in the cold spots of NC WI to the 50s and
lower 60s in the Fox Valley and lakeshore areas.

Today: High pressure will slide east of the region, with south
winds developing as a cold front moves from MN into western WI.
Another unseasonably warm day is anticipated, with high
temperatures in the upper 70s and lower 80s, except lower to
middle 70s near Lake Michigan (due to SE onshore flow.

Tonight/Tuesday: A strong cold front will move through the
forecast area during the late evening and overnight hours. This
system is expected to be moisture-starved, with precipitation
chances mainly confined to northern WI, and rainfall amounts of
0.05 inch or less. Considered the possibility of a few rumbles of
thunder, as there will be steep mid-level lapse rates ahead of the
front, but confidence was too low to include at this time. Strong
CAA and mixing in the wake of the frontal passage should result
in a period of 25 to 30 mph gusts late tonight into Tuesday
morning, with deep mixing to 800-750 mb allowing gusts to 20 to
25 mph to persist into the afternoon. A much cooler and drier air
mass arrives on Tuesday, with highs only reaching the upper 50s
and 60s. Relative humidity is expected to drop into the 25 to 30
percent range in the sandy soil regions, which combined with the
gusty northwest winds, may result in elevated fire danger during
the afternoon.

Gusts to 25+ knots on Lake Michigan will produce hazardous
conditions for small craft late tonight into Tuesday. A Small
Craft Advisory has been issued.

Long Term...Tuesday Night Through Sunday

Generally dry conditions are expected through the extended period
with only slight chances (10-20%) for scattered showers Thursday
night and again Sunday. With the recent drought development, mostly
dry forecast, and gusty winds Wednesday there will likely be fire
weather concerns, especially across northern and northeast WI.

Precipitation...Upper-flow is expected to become zonal behind a
departing trough late Tuesday through the middle part of this week.
This along with surface high pressure will lead to dry conditions
across the region through Thursday afternoon. The next chance for
rain comes late Thursday into Friday morning as another quick moving
trough moves over the region along with the development of a
nocturnal low-level jet. With little to no instability during this
period the chance for any thunderstorms is low. Rainfall amounts
will this system will likely have little impact on the current
drought conditions with the majority of LREF ensemble members only
showing up to a few hundreths of an inch.

Beyond Friday morning the next chance for precipitation comes late
into the weekend as models show a low pressure system riding along
the US/Canadian border.

Fire Weather/Wind...Expected blustery conditions Wednesday as the
pressure gradient tightens across the area along with favorable
conditions to mix down stronger winds from an upper-level jet that
is anticipated to be over the region. Peak gusts are likely (70-80%
chance) to reach 20-30mph with a 40-50% chance of greater than 35
mph gusts across northern WI during the afternoon. Along with the
strong winds a dry air mass in place over the region (dew points in
the middle 30s) will raise fire weather concerns, especially across
portions of northern and northeast WI where fuels are relatively dry
due to the recent lack of precipitation.

The strong southwest winds Wednesday may also pose marine concerns an
waves are forecast to exceed 4ft which may make conditions hazardous
to small craft.

Temperatures...A chilly start to the extended forecast Wednesday
morning with as lows behind a departing cold front are forecast to
range from the low 30s across northern WI to the middle 40s along
the lakeshore. This makes areas of frost possible across portions of
northern and central WI Wednesday morning. As winds back to the
southwest temperatures will warm back above normal for Wednesday and
Thursday with highs back in the middle 60s to low 70s for most
locations. Another cold front Friday will bring temperatures back
toward normal for the weekend with chances for frost Friday and
Saturday morning across north-central WI.

&&

.AVIATION...for 06Z TAF Issuance
Issued at 1041 PM CDT Sun Sep 29 2024

Clear skies and VFR conditions overnight with only a slight increase
of high clouds on Monday. The only exception to VFR conditions will
be from 08z to 13z Monday with possible patchy ground fog from north-
central to east-central Wisconsin with IFR/MVFR conditions are possible.
Mid clouds will slowly increase from the west on Monday night with small
chances for rain showers, mainly over northern WI.

Winds are expected to veer to the southeast or south on Monday,
with gusts of 15 to 25 knots Monday afternoon. Highest wind gusts
will be across central and north-central Wisconsin.

&&

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

&&

$$

DISCUSSION.....Kieckbusch/GK
AVIATION.......JLA