Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 211749

Area Forecast Discussion
National Weather Service Green Bay WI
1249 PM CDT SUN AUG 21 2016

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Monday
Issued at 330 AM CDT Sun Aug 21 2016

Dominate weather feature in the short-term will continue to be
pronounced upper-level trough axis forecast to steadily progress
east across the western Great Lakes today. WV imagery and RAP
analysis indicated primary embedded shortwave impulse now working
its way across northern Wisconsin. Associated band of low and
mid-level cloudiness pretty much cover the entire forecast area
early this morning with scattered light shower activity generally
confined to north of highway 29. 06Z HRRR seemed to have a
respectable handle on the current situation, thus will lean on its
short-term forecast into the afternoon.

Scattered showers across northern Wisconsin will continue to
drift southeast across the remainder of the forecast area during
the morning hours. The bulk of this activity should be southeast
of the forecast area around 15 UTC. Shower activity expected to
be light with amounts generally less than a tenth of an inch.
Looking further upstream, WV imagery also indicates another weak
upper-level impulse moving into western Minnesota. Thus far only
broken area of mid-level clouds associated with this feature. Both
the HRRR and RAP seem to have latched onto this and bring it quickly
southeast into the central Wisconsin around mid-day and even generate
isolated light shower activity primarily over central Wisconsin. No
reason to dispute this signal, thus continued to carry low chance
pops across pretty much the entire forecast area until early this
afternoon. Probably will not see any notable decrease in clouds
until mid afternoon with highs generally in the upper 60s to lower

By early this evening, surface ridge will quickly build into the
area with clearing skies and diminishing winds. Lows will fall to
a little below normal for a change, generally in the 40s north to
the lower 50s elsewhere.

Upper heights will quickly rebound on Monday while surface high
pressure ridge moves east of the forecast area. Rather robust
southwesterly return flow will quickly become established over the
northern Plains and northern Mississippi Valley by Monday morning.
Airmass over the Plains will still be somewhat moisture deficient,
thus rapid increase in low-level WAA upstream will likely result
in mainly a band of mid-level clouds over northern Minnesota which
should quickly advect east across upper Michigan and perhaps
northern Wisconsin before mid-day Monday. Appears any shower or
thunderstorm activity associated with aforementioned WAA should be
confined to north of Lake Superior. Daytime highs on Monday should
rebound nicely with readings closer to normal for mid August with
breezy southwesterly winds developing by afternoon.

.LONG TERM...Monday Night Through Saturday
Issued at 330 AM CDT Sun Aug 21 2016

00Z models continued to place QPF across some part of northern
Wisconsin on Monday night, associated with weak mid level short
wave energy and warm advection. The location and exact amounts
vary so went with a large area of slight chance POPs for showers
during that period. Left out any mention of rain on Tuesday since
the NAM, ECMWF and Canadian were all dry.

An approaching surface system and a more significant mid level
short wave will bring showers and thunderstorms to the forecast
area starting Tuesday night. There were some timing differences
with the onset of the rain, but all bring QPF to at least part of
the area by 12Z Wednesday. Thunderstorm chances will continue
through Wednesday night as the front and short wave pass. There is
a slight chance for showers on Thursday in cyclonic flow behind
the departing system. After that, dry weather can be expected
Thursday night through Friday night with surface high pressure
over the Great Lakes Region. Another chance for thunderstorms
arrives in central and north central Wisconsin on Saturday, ahead
of the next approaching system.

High temperatures should be much warmer than normal on Tuesday,
a few degrees above normal Wednesday and Thursday, and near
normal Friday and Saturday.

.AVIATION...for 18Z TAF Issuance
Issued at 1249 PM CDT Sun Aug 21 2016

Moist cyclonic flow behind a departing low pressure system
combined with daytime heating will keep plenty of clouds across
the area through the afternoon hours, with scattered to isolated
showers also expected. Look for mainly vfr cigs/vsbys through
early evening, with brief mvfr conditions possible in any heavier
shower. Clouds and any shower activity will diminish late this
afternoon and evening.

Met/mav guidance not showing any fog tonight; however, overall
setup pretty good for fog development overnight. Light winds,
clear skies, recent rains, and moisture trapped under an inversion
should allow fog, some dense, to form especially in the low lying
areas. Other than the fog, mostly clear skies are expected
overnight into Monday.



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