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569
FXUS63 KGRB 191106
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
606 AM CDT Sat Aug 19 2017

Updated aviation portion for 12Z TAF issuance

.SHORT TERM...Today...Tonight...and Sunday
Issued at 321 AM CDT Sat Aug 19 2017

An isolated storm crossed Lake Superior and reached the Upper
Michigan Keweenaw Peninsula region early this morning. This
convection was associated with a region of higher pwats moisture
with a piece of energy in the northwest flow. Radar trends
suggests this storm will slide by north of the Wisconsin/Upper
Michigan border this morning. Will keep an eye on north central
Wisconsin during the early morning hours as total totals values
were in the lower 50s. Otherwise clearing skies from the west were
creating areas of fog and low stratus early this morning. Dense
fog was not widespread at this time so will likely issue a SPS
for central and north central areas.

Progs continue to hint for a slight chance of afternoon or early
evening convection over far northeast Wisconsin. Weak low
pressure drops into the area along with possible initiation with
lake breeze boundaries. Some weak CAPE develops along with steep
low level lapse rates. Upper heights do increase for a limiting
factor. Do note some convection up stream in the Lake of the Woods
area.

Otherwise a quiet weather regime expected through most of Sunday
until precipitation chances begin to increase Sunday afternoon as
a frontal boundary approaches form the northwest.

.LONG TERM...Sunday Night Through Friday
Issued at 321 AM CDT Sat Aug 19 2017

The active weather system continues to be focal point for the
extended forecast Sunday night through Tuesday morning. Drier
conditions return through the midweek and towards the end of the
week

Warm air advection through Sunday will setup ample moisture for
Sunday evening as a weak cold front approaches the region. Spotty
convection is expected to develop across central Wisconsin and the
northeast. Current severe potential looks marginal, although if
shear and CAPE values increase towards us, a few stronger
thunderstorms will be possible. Overnight rainfall will then
linger in the area as the frontal system stalls out. Additional
development is expected to arrive Monday, with a bit more
organization as an upper level shortwave lends a helping hand.
Main threat will be locally heavy rainfall, although shear values
around 30-40 knots around the Fox Valley may aid in the
development of marginally severe thunderstorms, provided lingering
morning convection doesn`t ruin the instability. In either case,
things don`t look good for those wanting to catch the eclipse
Monday morning.

The 500 mb ridge then begins to amplify towards the middle of next
week, pushing in drier conditions across the region. A weak
shortwave will be the last chance to see some rain in far
northeastern Wisconsin on Wednesday before drier conditions move
back into the area.

Temperatures will be above normal through the end of the weekend
before heading closer to normal as the ridge establishes itself
next week.
&&

.AVIATION...for 12Z TAF Issuance
Issued at 606 AM CDT Sat Aug 19 2017

Areas of LIFR/IFR ceilings and patchy IFR/MVFR vsbys due to fog
developed early this morning where clouds departed earlier.
Expect conditions to improve to vfr later morning and continuing
into tonight. Clear skies and light southwest winds may lead to
patchy IFR/MVFR fog again late tonight.
&&

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

$$

SHORT TERM.....TDH
LONG TERM......Uhlmann
AVIATION.......TDH