Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 251745
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1245 PM CDT SUN SEP 25 2016

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Monday
Issued at 405 AM CDT Sun Sep 25 2016

Main forecast concerns today and this evening are flooding
concerns and severe weather potential as a low pressure system
tracks through the western Great Lakes region.

A low pressure system is forecast to track through the western
Great Lakes today, bringing an occluded front through the cwa this
afternoon and this evening. Although conditions do not look that
favorable at first blush for a Flash Flood Watch given expected
QPF amounts of 0.5 to 1 inch, PWAT values do soar to around 2
inches this afternoon which could allow some slow moving storms to
overachieve the expected NWP values. In addition, the extreme
southwestern portion of the cwa received 3 to 4 inches of rain
last week, making for very saturated soil conditions. Therefore
will continue the Flash Flood Watch for the 3 southwestern
counties given the antecedent conditions and the watch already
being in place.

Attention then turns to the severe weather potential this
afternoon and early this evening as MUCAPEs soar to 500 to 1000
J/kg across the extreme southern cwa with 0-6 km shear values of
25 to 35 knots. The best instability this this system is to our
south, where the warm sector survives across southern Wisconsin
and northern Illinois. As was noted earlier this area will get an
occluded front instead of a classic warm then cold front.
Therefore not much in the way of severe weather is expected across
the area this afternoon and evening. However a few storms could be
strong, producing gusty winds over 40 knots and small hail across
the extreme southern cwa with the strongest storms.

Behind this system windy conditions are expected to start the work
week on Monday, as winds gust to around 30 mph at times. The low
will also bring a surge of cold air, with daytime highs ranging
from the middle 50s across north-central, with highs around 60
across east-central and northeast Wisconsin. Wrap-around moisture
will continue the chance for showers across the area on Monday,
with the best chances across the northern cwa closer to the mid
level low and deeper moisture.

.LONG TERM...Monday Night Through Saturday
Issued at 405 AM CDT Sun Sep 25 2016

Main concern for this period will be the upper low at the
beginning of the period, and then the new development in the
ECMWF solution for late this week into next weekend.

The 00z ECMWF solution last night trended with a further west
solution Monday night through Tuesday night. The ECMWF continued
with this trend with the gfs/canadian model converging on this
solution. This has led to an increased confidence in increasing
cloud cover and rain chances Monday night through Tuesday night.
The combination of the wind and cool temperatures will definitely
make it feel like fall.

For Wednesday, the main question is how quick to end the rain and
decrease cloud cover. Continued with a morning chance of rain with
dry conditions during the afternoon. High pressure will dominate
the weather pattern Wednesday night into Thursday night. For
Friday into next weekend, the latest ECMWF model solution now
showing the upper low that moved east of the area now retrograding
northwestward and bringing precipitation into eastern Wisconsin
Friday afternoon into Saturday afternoon. The gfs/canadian model
did not depict this solution. Since this is a new development in
the ECMWF model, will hold off on adding rain for this period.
Below normal temperatures are expected at the beginning of the
period but should return closer to normal by next weekend.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1245 PM CDT Sun Sep 25 2016

Scattered showers/isolated thunderstorms will continue to affect
northeast WI this afternoon ahead of an eastward moving cold
front. Brief clearing to VFR conditions in the east will give way
to IFR/MVFR conditions as the front approaches. Precipitation
chances are expected to diminish behind the cold front with again
a brief rise in the cigs to VFR this evening. However, a strong
mid-level trough is forecast to move into the region later tonight
and send cigs down into the IFR/MVFR range late tonight. A
cyclonic flow around this trough is expected to keep plenty of
clouds around (mainly MVFR-based) on Monday along with a chance of
additional showers. In addition to the clouds and rain, west winds
could gust to 30 knots at times.
&&

.MARINE...
Issued at 405 AM CDT Sun Sep 25 2016

Gusty southerly winds ahead of an approaching low pressure system
will cause high wind gusts and elevated waves across the nearshore
waters today and tonight.

Behind the cold front, gusty west to northwest winds are expected
Monday into Tuesday. Gale force gusts are possible at times
Monday afternoon into Tuesday afternoon across the coastal waters
of northern Door County. Winds should begin to decrease later
Tuesday afternoon and Tuesday night.
&&

.HYDROLOGY...
Issued at 405 AM CDT Sun Sep 25 2016

Another round of showers, with some embedded thunderstorms, can
be expected today and this evening as a cold front moves through
the region. Even though rainfall amounts are forecast to be under
an inch with this system, parts of central Wisconsin are still
recovering from very heavy rains from earlier in the week. PWAT
values are forecast to approach 2.0 inches, which is nearly off
the charts for late September, thus locally heavy rainfall is
possible today. Therefore, a Flash Flood Watch will continue for
Wood, Portage, and Waushara counties.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......Eckberg
AVIATION.......Kallas
MARINE.........Kurimski
HYDROLOGY......Kurimski


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