Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 250837
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
337 AM CDT Mon Sep 25 2017

Forecast discussion for routine morning forecast issuance

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 337 AM CDT Mon Sep 25 2017

As a cold front slowly tracks across the state today into
Tuesday, temperatures will be on the decrease while precipitation
chances will be on the increase.

Early this morning, the cold front extended from near Bayfield to
Rice Lake to far southeast Minnesota. Scattered mainly post
frontal showers and isolated storms were noted over far northwest
Wisconsin into Minnesota. The previous day, showers and storms
develop along and just ahead of the front over the Northern
Plains. With available instability and PWATS increasing this
afternoon, anticipate showers and storms developing just ahead of
the front over north central and central Wisconsin in the
afternoon and evening, then precipitation returns to mainly post
frontal overnight.

The front continues to drift east overnight along with mainly post
frontal precipitation. Precipitation expected to begin reaching
eastern areas toward early Tuesday morning. A more widespread rain
is likely late tonight into Tuesday as a surface wave moves along
the front. The ECMWF and NAM were more west with this low vs the
GFS. Expect more rain to be northwest of this track.

Eastern sections of the state today will remain in the continued
warm south flow and can expect afternoon high temperatures well
into the 80s.  Warm start early Tuesday morning will provide
another day of temperatures 5 to 15 degrees above normal.

.LONG TERM...Tuesday Night Through Sunday
Issued at 337 AM CDT Mon Sep 25 2017

500mb ridge that brought the record heat to the area over the
weekend will continue to flatten through the middle of the week.
Later in the week, a sharp 500mb trough will move across the
western Great Lakes region Thursday afternoon into Friday morning.
500mb ridge will then spread eastward across the region next
weekend.

Showers and thunderstorms will taper off Tuesday evening for
much of the area. Showers will linger across the north late
Tuesday night into Wednesday morning. Otherwise, high pressure
will dominate the weather pattern Wednesday afternoon into
Thursday morning.

The next upper level disturbance and associated cold front will
approach the area from the northwest Thursday morning, and then
move across the area Thursday afternoon/evening. This system
looks a little more interesting this morning. Steep mid level
lapse rates, low wet bulb zero heights around eight thousand feet
combined with lifted indices drop to near 0C along with 0-6km
shear values of 35 to 40 knots support adding thunderstorms to
the forecast. GFS sounding indicated an inverted V structure as
well. It is possible some of the storms Thursday afternoon and
evening could produce wind gusts to 40 mph and small hail.
Will mention this scenario in the Area Forecast Discussion (AFD),
but will not introduce gusty winds and hail in the Hazardous
Weather Outlook since it is still pretty far out with respect to
timing.

High pressure will dominate the weather pattern next weekend,
bringing clear night and mostly sunny days along with large
diurnal temperature ranges. Frost is possible Saturday morning
across the north. Suspect there will be colder guidance values
across the north Sunday morning as well, thus may need to
think about frost for this period as well as we get closer.
&&

.AVIATION...for 06Z TAF Issuance
Issued at 1135 PM CDT Sun Sep 24 2017

VFR conditions to prevail for much of the TAF period. The
exception tonight would be some patchy late night fog which could
brief lower vsbys into the MVFR range. Have kept the LLWS
potential for the RHI, AUW and CWA TAF sites tonight as southwest
winds just above the surface reach 30 to 35 knots. Mid and high
clouds are forecast to increase over the region on Monday with a
chance for showers/thunderstorms reaching central and north-
central WI Monday afternoon and evening. The heavier
showers/thunderstorms could reduce conditions to MVFR at times.
Kept thunderstorms in a window where instability is maximized in
the afternoon and early evening hours. Activity is expected to
mainly stay out west through the TAF period with the slow moving
front.
&&

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

$$

SHORT TERM.....TDH
LONG TERM......Eckberg
AVIATION.......Kurimski



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