Area Forecast Discussion
Issued by NWS Green Bay, WI

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836
FXUS63 KGRB 181728
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1228 PM CDT Wed Sep 18 2019

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 409 AM CDT Wed Sep 18 2019

Very warm and rather humid weather weather will persist into the
weekend. Scattered showers and thunderstorms are likely at times.

A highly amplified upper pattern will persist across North
America for several more days. The pattern was anchored by a deep
trough across the West and mid-continent ridging. The strong
positive upper height anomaly with the ridge will persist in the
Hudson Bay vicinity into the weekend, then quickly weaken and
shift off to the east. A lower amplitude pattern with some
splitting of the main westerlies is expected to develop during the
latter part of the forecast period.

Southwest upper flow between the trough to the west and the ridge
will maintain a feed of warm, moist air into the area, resulting
in well above normal temperatures and rather humid conditions
through the first half of the upcoming weekend. Readings will
trend down a bit thereafter, but remain above normal. There will
be numerous opportunities for precipitation, likely resulting in
above normal amounts for the period.
&&

.SHORT TERM...Today...Tonight...and Thursday
Issued at 409 AM CDT Wed Sep 18 2019

Convection forming near the nose of the LLJ and aided by a weak
shortwave riding NE out of the western trough was over MN early
this morning. The models were very consistent in showing the MN
convection weakening and dissipating prior to reaching the
forecast area. That makes sense given the drier air aloft that
circulated back into the forecast area from the departing
anticyclone.

Convection will likely re-fire across eastern MN and western WI
this afternoon as a cold front advances in from the west. That
area of convection should slowly advance east across the area
tonight into Thursday as the front reaches the area and then
stalls. The ability to add details to the PoP forecast diminishes
with time, so advanced the rain chance into the area from the west
tonight, taking PoPs up to likely over the SW part of the area
for a time. Then gradually transitioned to broad-brushed 25-40
percent PoPs across the area for Thursday. Deep-layer shear will
be very weak (10-20 kts), but PWATs will be high (> 1.50 inches).
So the severe threat will be low, with the main threats being
locally heavy rainfall and sub-severe gusty winds with the
strongest storms.

Backed down a bit on temperatures for today across north-central
Wisconsin where stratus was expanding pretty quickly early this
morning. Also edged back a bit on temperatures tomorrow with the
expectation that there will be a lot of clouds around.

.LONG TERM...Thursday Night Through Tuesday
Issued at 409 AM CDT Wed Sep 18 2019

A mid level ridge over the eastern CONUS is expected to break
down over the weekend, as a trough over the Pacific Northwest
passes through the Great Lakes region.

Much warmer than normal temperatures are expected for the end of
the work week, but there are small chances or slight chances for
showers and storms in the warm and humid air mass. A cold front
and some mid level short wave energy, ahead of the main trough,
will bring the best chance for showers and storms to the area
Saturday and Saturday night. Cooler temperatures are in store for
the start of the upcoming week, but highs should still be a
little warmer than normal for this time of year.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1227 PM CDT Wed Sep 18 2019

Some MVFR in place over the western TAF sites early this
afternoon, will likely improve over the next couple of hours. A
front will approach central Wisconsin this evening, bringing the
next chance of showers and thunderstorms. This bring the next
chance of MVFR/IFR conditions, which will linger into the day
Thursday. The eastern TAF sites will be farther away from the
front and have a bit more stable conditions, so opted to keep
thunder out of those TAFs at this point. Some showers will likely
approach the eastern TAF sites late in the evening into the
overnight hours. The scattered showers and thunderstorms will
linger intermittently through the day Thursday.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 7 PM CDT this evening for WIZ022.
&&

$$

SYNOPSIS.......Skowronski
SHORT TERM.....Skowronski
LONG TERM......MG
AVIATION.......Cooley



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