Area Forecast Discussion
Issued by NWS Green Bay, WI

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000
FXUS63 KGRB 172246
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
546 PM CDT WED AUG 17 2016

Updated aviation portion for 00Z TAF issuance

.SYNOPSIS...
Issued at 220 PM CDT Wed Aug 17 2016

Seasonably warm and humid the next couple days, then wet weather
for the end of the work week and at least the start of the upcoming
weekend.

The large scale pattern is expected to remain modestly progressive
and undergo fairly substantial amplification during the next
several days, as a strengthening trough swings through the
northern Plains and Great Lakes region. Some flattening of the
flow is likely next week, with the mean trough position lingering
from Hudson Bay to the northern Plains.

Seasonably warm and humid conditions at the start of the period
will give way to cooler weather for late in the weekend and early
next week as an early autumn-like air mass sweeps into the area.
The cool down is likely to be short-lived however, with
temperatures bouncing back to a few degrees above normal by the
middle of next week. With ample moisture in place, the
combination of the large scale trough and significant cold front
crossing the region should result in above normal precipitation.
&&

.SHORT TERM...Tonight and Thursday
Issued at 220 PM CDT Wed Aug 17 2016

The latest RAP analysis and satellite/radar imagery show weak
surface high pressure stretching across the northern Mississippi
Valley early this afternoon.  The shortwave that brought widespread
rainfall to parts of central and northeast WI last night is moving
over Lake Huron, but served to stabilize much of the area judging by
the 12z GRB sounding.  Although cu formation has not been nearly as
widespread as the past few days, isolated showers have developed
along the lake breeze over the western Upper Peninsula and far
northern WI early this afternoon.  Expect these showers to persist
into early this evening across the north.  Otherwise, fog potential
tonight and cloud trends are the main forecast concerns.

Tonight...Weak high pressure will reside at the surface.  No signs
of any shortwaves which could trigger showers, but a couple isolated
showers may linger for the first couple hours into the evening over
far northern WI. Once these showers die off, skies should turn clear
and promote good radiational cooling conditions.  Patchy to areas of
fog should develop since low temps are projected to fall below this
afternoons crossover temp.  Fog should be most dense in the sandy
soil areas of northern WI. Lows ranging from the upper 50s north to
mid 60s south.

Thursday...High pressure slides east of the region, while low
pressure travels east over the northern Great Plains.  Should have a
southerly wind which will boost temps up a couple degrees from
todays readings.  Progged soundings show potential for scattered to
broken diurnal cu again, but mid-level heights are a little warmer
than today, so think will stick with a dry forecast.  Highs in the
low to mid 80s.

.LONG TERM...Thursday Night Through Wednesday
Issued at 220 PM CDT Wed Aug 17 2016

Consensus among the numerical models is probably a little poorer
than typical for this time frame--especially with the timing of
the main frontal wave forecast to lift northeast along the front.
That tends to lead to lower confidence in the timing of the
precipitation chances, and increases the likelihood that
substantial adjustments will be necessary in later forecasts. For
the most part, leaned toward the ECMWF for the timing and track of
the system as it typically verifies toward the top of the pack
and it/s solution seems quite reasonable.

Storms developing to the west will move toward the area Thursday
night. Timing is uncertain, but they will probably be weakening
by the time they arrive here. If a highly organized MCS develops
to the west, it might still pose a threat of strong winds and hail
when it reaches the area. SPC has accounted for this by outlooking
the southwest part of the forecast area with a marginal risk of
severe storms in the day 2 outlook, and this seems on target.

The cold front will probably begin to sag into the area Friday as
a weak wave riding up the front departs to the northeast. That
combined with the remnants of the MCS that will likely be across
the area early in the day suggest destabilization will be limited.
Although questions remain about the severe potential, there seem
to be more factors working against severe than working for severe.
Will attempt to convey this thinking in the HWO, while still
acknowledging things could change.

The main frontal wave will lift through the region Saturday. The
heaviest/steadiest precipitation is likely to be across the
northern part of the forecast area. The best estimate is that 1-2
inches of rain will occur across the north. The 12Z ECMWF backed
down some on the QPF compared to its 00Z run, though its 3+ inch
totals are still a high outlier. Given current river levels, feel
that we can handle up to 2 inches of rain fairly well. If totals
end up exceeding 3 inches, some minor flooding will likely occur
in low-lying areas and some rivers would probably reach bankfull.

Scattered showers will likely linger Sunday as the cooler Canadian
air mass surges across the area.
&&

.AVIATION...for 00Z TAF Issuance
Issued at 546 PM CDT Wed Aug 17 2016

Isolated showers will linger over northern wisconsin, with
isolated to scattered showers toward the Lake Superior lake
breeze boundary. After the showers end this evening...vfr skies
are expected for the rest of the evening. Clear skies, light
winds and a relatively moist boundary will again lead to patchy
to areas of fog late tonight. After fog dissipates Thursday
morning, vfr conditions expected for rest of Thursday.
&&

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

$$

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



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