Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 202324
AFDGRB

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

Updated aviation portion for 00Z TAF 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 00Z TAF Issuance
Issued at 624 PM CDT Sun Aug 20 2017

A cold front will continue to sag south tonight. Doppler radar
shows very little convection associated with the front itself as
it moves through the area. With the loss of daytime heating
imminent will remove thunderstorms from all the TAF sites as
chances for activity hitting the TAF sites appears to be minimal
at best. Winds will weaken overnight with some breaks in the
clouds which would once again favor fog formation. Added fog to
the fog prone areas from the last few nites with less fog across
locations that have not fogged in recently. Thunderstorms are
again possible Monday afternoon as the front lingers across the
region with models indicating the best possibility for rain will
be across central and north-central WI TAF sites. Therefore will
place a PROB30 group for these locations Monday afternoon.
&&

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

$$

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


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