Area Forecast Discussion
Issued by NWS Green Bay, WI

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523
FXUS63 KGRB 270844
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
344 AM CDT SAT AUG 27 2016

Forecast discussion for routine morning forecast issuance

.SYNOPSIS...
Issued at 329 AM CDT Sat Aug 27 2016

Wet over all but north-central Wisconsin today, then more
sunshine, warmer, and rather humid on Sunday.

The large-scale trough over the Northern Plains will quickly
weaken as the bulk of the energy within it shifts off to the
northeast. That will leave a fairly zonal band of westerlies
across the northern CONUS and southern Canada by the start of the
work week. The zonal regime won`t last long, as a sharp/fairly
deep trough is expected to quickly develop just off the West
Coast. That will lead to downstream amplification over NOAM. But
the amplitude/position of the downstream ridge and the next
downstream trough remain rather uncertain, and that has
considerable impact on the forecast for Wisconsin.

Rain and clouds will hold temperatures down today, but the air
mass is still rather mild so readings should return to modestly
above normal for Sunday and at least the early part of next week.
Uncertainty increases thereafter as the position/amplitude of the
eastern NOAM upper trough are unclear. Today`s rainfall will be
significant for all but the far northwest part of the forecast
area. Outside of that, precipitation events will probably be
somewhat limited during the period.
&&

.SHORT TERM...Today...Tonight...and Sunday
Issued at 329 AM CDT Sat Aug 27 2016

A widespread soaking rainfall is expected for all but far north-
central Wisconsin today, with the bulk of the rain falling this
morning. Models still differed considerably on where the axis of
the heaviest rain would occur. Based on the latest satellite and
radar, it looks like it will be across the southeast part of the
forecast area. A little concerned that a small scale flooding
threat could emerge if a heavy rain band pivots on the northwest
flank of frontal wave tracking toward southeast Wisconsin. But
instability looks limited, and P-groups on METARS to the south
have not revealed any heavy amounts thus far. Will continue to
monitor. SPC has outlooked the southeast 1/4 of the forecast area
for a marginal risk of severe weather, for 5% wind and 2% tornado
risks. The threat would be of damaging wind gusts from a wet
microburst, or of a tornado forming with a storm near the frontal
boundary, if the boundary can creep far enough north this
afternoon. Although the likelihood of either of those things
occurring is rather low, they can`t be ruled out either.

Although the northwest part of the area may miss out on the bulk
of the rain this morning, it is possible some shra from northwest
Wisconsin could move into that area this afternoon or evening.
Otherwise, tapered Pops down this afternoon and evening, ending
the rain chance overnight. Added patchy fog to the forecast for
all but lakeshore areas tonight as winds will die off, clouds will
decrease, and there will be plenty of lingering moisture from
today`s rains.

A rather warm and somewhat humid day is expected Sunday. Kept
slight chance PoPs for north-central Wisconsin in case some
convection firing to the west manages to bleed into that area.

.LONG TERM...Sunday Night Through Friday
Issued at 329 AM CDT Sat Aug 27 2016

Zonal flow at 500mb will continue early next week, then deep upper
trough is expected to develop across eastern Canada. This will
result in a northwest flow pattern across the western Great Lakes
region with the first substantial cool down of the season across
the eastern Great Lakes into New England. At this point, Wisconsin
will see a glancing blow from Canadian air mass.

For Sunday night, models show high pressure across the western
Great Lakes region with dry conditions expected across eastern
Wisconsin. Models do depict some precipitation breaking on the
backside of the high with return flow, thus will have small
chances of showers and storms across portions of north-central
Wisconsin. Do you have small chances of showers and storms
spreading eastward into eastern Wisconsin on Monday. The better
chance for storms will be on Monday night into Tuesday morning as
a cold front moves across the region. Dry conditions will prevail
Tuesday night into Friday. The next chance for showers and storms
would be later Friday into Friday night. Above normal temperatures
are expected at the beginning of the period, but should return
closer to normal by the end of next week.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 329 AM CDT Sat Aug 27 2016

Ceilings across the area have held up pretty well this far despite
the rain. But expect them to lower as the rain continues. Not real
confident how far down they will go. Best guess now is for IFR
ceilings over all but north-central Wisconsin for a time this
morning, but will make issuance time decision for the 12Z TAFs.
Ceilings may edge up some this afternoon, but will likely drop off
again tonight.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......Eckberg
AVIATION.......Skowronski



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