Area Forecast Discussion
Issued by NWS Green Bay, WI

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171
FXUS63 KGRB 201911
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
211 PM CDT Sat Oct 20 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Sunday
Issued at 211 PM CDT Sat Oct 20 2018

The latest RAP analysis and satellite/radar imagery show a potent
shortwave trough moving over northeast WI early this afternoon.
Rain and snow showers are ending over east-central WI associated
with this trough. Meanwhile, cloud cover becomes more orientated in
bands behind the trough, and snow showers have become more
confined to the snow belt of north-central WI. Winds have been the
gustiest within the snow showers, with gusts up to 40 to 45 kts
reported at Marshfield to Green Bay. Winds will generally remain
gusty up to 35 kts through the afternoon, though will gradually
subside. Forecast concerns generally revolve around lingering snow
shower chances and winds tonight.

Tonight...As shortwave energy continues to move southeast across
the eastern Great Lakes, a ridge of high pressure will build into
the region from the west. Ample dry air associated with high will
rapidly push east across the area this evening, causing lake
effect cloud bands to retreat north closer to Lake Superior. A few
flurries or light snow showers may linger over northern Vilas
county in the evening. Winds will diminish with nocturnal cooling
setting in, dropping below 20 kts (except near Lake Michigan) by
8-9 pm. Temperatures will not fall too far due to the wind, with
lows ranging from the low 20s at Tomahawk to near 30 degrees along
the lakeshore.

Sunday...High pressure will quickly advance across the area during
the morning and result in mostly sunny conditions through midday.
During the afternoon, a shortwave trough moving just north of Lake
Superior will push a weak front into northwest WI. Moisture is
extremely limited along the front, but will likely see an increase
of mid-clouds across much of the area. No precip is expected
however. With a strengthening south wind, temps will warm into the
low to mid 40s at most locations.

.LONG TERM...Sunday Night Through Saturday
Issued at 211 PM CDT Sat Oct 20 2018

No major weather impacts expected through the extended portion of
the forecast.

Sunday night through Monday: A weak surface ridge will continue to
slide off to the east of the area Sunday night as a broad surface
and upper-level low pressure system shifts across northern Manitoba
into Ontario. This low will drag a surface trough/weak cold front
across the CWA from west to east late Sunday night into Monday
afternoon. The better moisture and forcing will remain north of the
CWA, main over Lake Superior into portions of the U.P. This will
keep most locations dry, with only a few extra clouds along the
MI/WI border through Monday afternoon. Overnight lows will be in the
mid 20s to low 30s with daytime highs in the upper 40s to low 50s.

Monday night into Tuesday: As the aforementioned trough axis remains
nearby, 850mb temperatures are progged to cool to around -7C to -8C.
This, along with Lake Superior surface temperatures around 6C to 7C
and northwest flow, will lead to lake effect snow potential over
north-central WI. This will be especially true over Vilas County
Monday night through Tuesday. No major system forcing is expected,
so any snow should remain fairly light with inversion
heights/moisture remaining at or below 5 kft. Only a small portion
of the convective cloud layer is expected to reach above the
-10C to -11C isotherm, so snowflake size should remain small and
give low snow to liquid ratios. Outside of some increased cloud
cover along with MI/WI border, the rest of the CWA is expected to
remain dry. Monday night lows will be in the 30s with highs expected
to be in the 40s for Tuesday.

Tuesday night through Wednesday night: High pressure will move
across the area through this time period, both aloft and at the
surface. This will allow for dry conditions, partly cloudy skies and
relatively calm winds. This will allow for some cold temperatures
Tuesday night with ideal radiational cooling conditions. Lowered
temps a few degrees to trend that way. Temperatures will remain well
below normal with overnight lows dropping into the low to mid 20s
northwest to low 30s southeast. Daytime highs will be in the upper
40s to around 50.

Thursday through Friday: Return flow will kick in on the back side
of the departing high pressure system. This will lead to increasing
moisture and cloud cover across much of the CWA ahead of the next
system, likely next weekend. There will also be a steadily
increasing chance of precipitation across the area. At this point, a
consensus of the models is the best way to handle this time period
with some model differences continuing.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1140 AM CDT Sat Oct 20 2018

Scattered to numerous rain and snow showers associated with an
intense upper disturbance will continue to impact the area through
early afternoon. MVFR and local IFR conditions will occur with
the heavier snow showers. As showers end, scattered to broken low
end vfr cigs and gusty winds to 35 kts will continue through the
afternoon. Clearing anticipated this evening along with
diminishing winds. Generally good flying weather expected for
Sunday.
&&

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

$$

SHORT TERM.....MPC
LONG TERM......Cooley
AVIATION.......MPC



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