Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 201932
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
232 PM CDT Sun Aug 20 2017

Forecast discussion for routine afternoon forecast issuance

.SYNOPSIS...
Issued at 226 PM CDT Sun Aug 20 2017

Warm and humid with thunderstorms at times through tomorrow night,
then cooler and drier for the rest of the upcoming work week.

A seasonably strong band of westerlies will persist across the
northern CONUS and southern Canada throughout the period. A
gradual amplification of the flow is anticipated as an upper
trough deepens over eastern North America. The period will begin
with above normal temperatures, readings will drop back to a
little below normal for several days, then moderate late in the
period. The main opportunities for rain will be early and late in
the period, likely resulting in amounts AOA seasonal normals.
&&

.SHORT TERM...Tonight and Monday
Issued at 226 PM CDT Sun Aug 20 2017

Determining the timing and intensity of convection continues to
be the main short-term forecast challenge.

A cold front has entered northwest Wisconsin. It will make some
additional progress to the south and east before basically
stalling out across the area late tonight. The front will also
become increasingly diffuse with time. Large scale forcing for
ascent will also be somewhat ill-defined until late tomorrow.
These factors suggest it would be unwise to attempt to add too
much detail to the precipitation forecast. So after an increase in
PoPs from NW to SE this evening to account for the arrival of the
front into a modestly unstable air mass, opted to settle PoPs
back into the chance/slight chance range through tomorrow. The
most likely time period for widespread convection will be at the
start of the long- term part of the forecast, so trended PoPs up
late tomorrow afternoon as a lead in to that.

CAPES around 2000 J/kg along with 20-30 kts of deep-layer shear
suggest a low-end severe threat will persist though this evening
near the front. That threat will wane overnight as the atmosphere
stabilizes, then redevelop tomorrow. The SPC Day 1 and 2
Convective Outlooks seem to handle the situation well. Will also
mention the heavy rain threat in the HWO.

Models are perhaps a little less optimistic in terms of showing
sky conditions that will allow viewing of the eclipse tomorrow.
But with the front in the area, it will still come down to when
and where there are breaks in the clouds near the front.

.LONG TERM...Monday Night Through Sunday
Issued at 226 PM CDT Sun Aug 20 2017

The chance for heavy showers and thunderstorms will persist
throughout Northeast Wisconsin Monday night and end as a cold
front moves through the region on Tuesday. Temperatures will cool
into the upper 40s to mid 50s Tuesday night as high pressure
moves in. Temperatures will then be a little below normal for a
few days, providing for a pleasant second half of the week under
mostly sunny skies. The next chance for precipitation arrives
Saturday as a low pressure system traveling east along the
Canadian border approaches Wisconsin.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1246 PM CDT Sun Aug 20 2017

A cold front will sag south into the area late today and tonight.
Scattered thunderstorms will accompany the front. Other that with
the storms, VFR conditions are anticipated. The front may sag far
enough south to allow winds over central and north-central
Wisconsin to weaken overnight. That favors fog formation. Added
some fog to the central and north-central WI TAF sites for now,
but may need to lower visibilities further in later TAFs,
especially in any areas that receive rain this afternoon.
&&

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

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......ML
AVIATION.......Skowronski


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