Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 101714
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1214 PM CDT Thu Aug 10 2017

Updated aviation portion for 18Z TAF issuance

.SYNOPSIS...
Issued at 356 AM CDT Thu Aug 10 2017

Showery today, then a couple days of cooler weather before
temperatures moderate.

The persistent large-scale western ridge will consolidate at high
latitudes and shift east across Canada, eventually settling in
over eastern Canada. The ridge building through to its north will
cause at least a portion of the trough over eastern North America
to get locked in place well into next week--keeping upper heights
across the forecast area a little below normal.

Clouds and precipitation will keep temperatures a little cooler
today, but the coolest day will be Friday as northerly flow brings
in a surge of air from Canada. Readings will begin to rebound
during the weekend. They will probably end up at least a little
above normal by the middle of next week, in large part due to
limited clouds and precipitation. The most significant
precipitation event will be one today into this evening. There
will probably be some additional opportunities for precipitation
during the rest of the forecast period, but none of them look
substantial at this point. So discounting what falls through this
evening, precipitation totals for the period are likely to end up
below normal.
&&

.SHORT TERM...Today...Tonight...and Friday
Issued at 356 AM CDT Thu Aug 10 2017

Plenty of details to work out in the short-term part of the
forecast. The mid-level wave crossing the region contains several
embedded smaller scale impulses. So the precipitation will
probably occur in surges tied to the impulses, with lulls in
between. The most significant lull is likely to occur over the
southeast half of the area sometime during the mid-day to early
afternoon hours, before the main vort arrives from the west. This
should allow for some recovery of the atmosphere prior to the
arrival of the vort, and will probably result in a greater
potential for thunderstorms than earlier expected. The area most
at risk of strong storms will be east-central Wisconsin, during
the mid-afternoon to early evening. SPC extended the marginal
risk into this area on the Day 1 Convective Outlook. That seems
reasonable given this area has the greatest potential to
destabilize and will be closest to the wind max on the south side
of the mid-level wave. Provided the mid-day break in the
precipitation materializes and there are at least a few breaks in
the clouds, MUCAPES approaching 1500 J/kg and 30 knots of 0-6 km
shear will be in place prior to the arrival of the vort, and will
support a low-end severe threat.

While it was possible to work some of the expected timing into
the grids, the resulting trends were somewhat muted by the need to
keep at least some mention of precipitation at all times since
even the lulls will probably not be completely dry.

The main area of convection should be east of the area by mid-
evening, though some isolated showers could linger behind that.
Additional showers are possible Friday as a secondary cool front
drops south across the area.

Stayed close to a blend of top performing guidance products for
temperatures.

South winds flowing up the length of Lake Michigan are expected to
result in waves sufficient to warrant a Beach Hazard Statement
for today.

.LONG TERM...Friday Night Through Wednesday
Issued at 356 AM CDT Thu Aug 10 2017

Models had surface high pressure moving into the region, bringing
drier conditions to the forecast area. The high was forecast to
remain in the region through the middle of next week, though a
mid level short wave trough is expected to pass through Wisconsin
late in the weekend/early next week. Diurnally driven showers may
develop during the afternoon on Monday and Tuesday, but Wednesday
looks to be dry with a mid level ridge passing through the state.

Cooler than normal daytime temperatures are expected Friday
through Sunday. Highs should be near or a little above normal for
the upcoming work week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1213 PM CDT Thu Aug 10 2017

Scattered showers and isolated storms are expected to pass over
much of the forecast area this afternoon and early evening before
tapering off this evening. MVFR cigs over northern Wisconsin will
gradually expand southeastward and lower to a mix IFR/MVFR cigs
overnight into Friday morning with little improvement through late
Friday morning.
&&

.GRB WATCHES/WARNINGS/ADVISORIES...
Beach Hazards Statement until 10 PM CDT this evening for WIZ022-
040-050.
&&

$$

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



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