Area Forecast Discussion
Issued by NWS Green Bay, WI

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371
FXUS63 KGRB 260347
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1047 PM CDT Mon Sep 25 2017

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 243 PM CDT Mon Sep 25 2017

The main forecast focus to be on precipitation trends both tonight
and Tuesday as a slow-moving cold front shifts across the state.

The 19z MSAS surface analysis showed the cold front stretched from
roughly Ironwood south-southwest to La Crosse and then farther
southwest through central IA. All the showers/thunderstorms have
been along and behind the frontal boundary with one cluster of
storms that will impact central WI by late afternoon. Temperatures
were once again unseasonably warm with record or near record high
temperatures over eastern WI.

The stalled synoptic pattern across the CONUS finally begins to
move starting tonight as the upper trough over the western CONUS
lifts northeastward toward the northern Plains and helps shove the
cold front into central WI. Models also show a weak surface wave
lifting north along the frontal boundary tonight which would tend
to slow the front down or even briefly stall its eastward
progress. Deeper moisture and stronger forcing to remain behind
the front, thus highest pops will be placed across north-central
WI where the front should reach first. Eastern WI may see a stray
shower toward daybreak, but anticipate a mainly dry night. One
more mild night can be expected with min temperatures around 60
degrees north-central WI, lower to middle 60s east-central WI.

The upper trough is forecast to move from the northern Plains
toward northern sections of the Upper MS Valley/southwest Ontario
on Tuesday and gradually weaken in the process. Meanwhile, the
slow-moving cold front edges farther east and should reach Lake MI
by 00z Wednesday. The deeper moisture/modest instability finally
overspreads the rest of northeast WI on Tuesday, therefore showers
should become more likely. Since forcing is weak, thunderstorms
should be scattered about, but no severe weather is anticipated.
Max temperatures will be noticeably cooler with readings around 70
degrees north-central, upper 70s to around 80 degrees east-central
WI.

.LONG TERM...Tuesday Night Through Monday
Issued at 243 PM CDT Mon Sep 25 2017

Cooler and less humid air will return to Wisconsin
Wednesday night and continue through the end of the week, as upper
flow becomes northwest and a surface high drops south from
central Canada into the Great Lakes. A shortwave trough moving
through the upper flow should produce enough upper support to
produce scattered showers and thunderstorms Thursday afternoon and
evening. Temperatures will be close to normal Thursday through
Saturday.

Warmer temperatures will return Sunday and Monday as heights rise
and winds become southerly as the large surface high moves east.
There should be some showers and thunderstorms Monday as upper
flow becomes southwest and a weak surface front approaches from
the west.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1047 PM CDT Mon Sep 25 2017

An approaching cold front will bring an increased chance for
showers and thunderstorms during the TAF period as it slowly
tracks east through the western Great Lakes. The best chance for
thunderstorms will be Tuesday afternoon, save for RHI where there
will be less instability. Otherwise showers are mainly expected
as this front moves to the east. The eastern TAF sites should stay
dry until later tonight or early Tuesday morning given the later
arrival of the front. Conditions are expected to drop to MVFR,
with IFR possible as the front moves through. Behind the front
conditions are expected to remain at MVFR as winds turn to the
west later Tuesday afternoon and into Tuesday evening.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM.....Kallas
LONG TERM......RDM
AVIATION.......Kurimski



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