Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 121733

Area Forecast Discussion
National Weather Service Green Bay WI
1233 PM CDT Thu Oct 12 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 326 AM CDT Thu Oct 12 2017

Low clouds continue to advect in across the area early this
morning as the lower atmosphere slowly moistens up. Although some
drizzle was noted to the southwest, model soundings indicate
conditions will not be conducive for drizzle until later this
afternoon and into the overnight hours when the moisture deepens
to a 4k ft layer and isentropic lift at the 295K level develops.
Hi-res models seem to capture this phenomena rather well, with
the drizzle moving from southwest to northeast this afternoon and
into the overnight hours. Therefore will add drizzle to the
forecast to account for the deeper moisture and lift during these
periods. A cold front will bring a better chance for showers on
Friday as it tracks through the western Great Lakes region.

Highs today will be around 60 degrees with mostly cloudy skies.
Lows tonight will be around 50. By Friday highs will range from
around 60 across the north, with lower to middle 60s across the
south ahead of the cold front.

.LONG TERM...Friday Night Through Wednesday
Issued at 326 AM CDT Thu Oct 12 2017

Main focus to be on the timing of an upper trough that is forecast
to move across the western Great Lakes this weekend. An
intensifying area of low pressure will precede the upper trough,
although the models differ a bit on exactly how strong this low
will get. Once this system departs, the mean flow attempts to go
zonal across the CONUs early next week before a new upper trough
heads toward the western CONUS mid-week. Unsettled/breezy
conditions are expected through Sunday morning, then mainly dry
conditions to take over. Temperatures to be above normal Saturday,
drop below normal Sunday/Monday, then return above normal for

Shower chances look to continue over roughly the southeast half of
the forecast area into Friday evening as the cold front to still
be in the process of exiting the region. As the front begins to
stall over the WI/IL border later Friday night, cannot rule out a
few showers lingering over our southeastern most counties.
Meanwhile, high pressure over northern sections of the Great Lakes
should bring mostly clear to partly cloudy skies to northern WI
during the overnight hours. This set-up would lead to a large
temperature variation across northeast WI with lower to middle 30s
over parts of Vilas county, but only around 50 degrees across
east-central WI.

As the upper trough swings eastward through the Rockies on
Saturday, an area of low pressure is expected to move from the
central Plains into the Midwest and intensify in the process. As
this occurs, the stalled boundary is forecast to slowly lift north
as a warm front. A prevailing south flow just above the surface
will draw gulf moisture into WI with PW values rising into the
1.0-1.5 inch range by 00z Sunday. Anticipate a chance of showers
Saturday morning across our southern counties (roughly Marshfield
to Kewaunee), then a gradual northward shift of the precipitation
Saturday afternoon as lift increases (aided by the right entrance
region of the upper jet) and mid-level frontogenesis increases.
Northern WI should see increasing clouds through the day with
shower chances arriving by late in the day. Max temperatures to
mainly be in the upper 50s to lower 60s.

Saturday night looks to be soggy and breezy as the low pressure
tracks across WI, pulling a cold front along. The main question is
the exact track of the surface low takes as a more northern track
could place parts of the forecast area in the warm sector for a
brief period of time. While time of year and time of day are
negatives for thunder, the strength of the lift, coupled with
modest instability and ample shear, should be enough to bring at
least a slight chance of thunderstorms to at least east-central WI
(mainly during the evening hours). Due to the strength of the
shear, cannot rule out a few stronger storms with gusty winds.
Otherwise, ample moisture in place could bring locally heavy rain
(PW values in the 1.25-1.75 inch range) to much of the region. Min
temperatures to be in the upper 30s to lower 40s north-central,
upper 40s to around 50 degrees east-central.

Models have picked up the forward speed of this system with the
surface low well to our northeast by Sunday morning and the
passage of the trailing upper trough around the midday hour. If
this new trend is correct, there may not be enough moisture left
over WI to generate any further precipitation, even with the
passage of the upper trough. Prefer to trend pops down Sunday
morning and go dry for Sunday afternoon. It will be a breezy day
on gusty northwest winds and with CAA over the region,
temperatures will be below normal. Look for readings around 50
degrees north-central, middle to upper 50s east-central.

A weak surface ridge moves into the western Great Lakes region
Sunday night which typically signals clearing skies/quiet weather.
However, the models show a weak shortwave trough dropping
southeast into the region as well Sunday night. If there is enough
moisture left behind, perhaps a few light rain or mixed snow
showers would be possible, primarily over northern WI where mid-
level forcing is stronger. This feature quickly zips east-
southeast Monday morning with any precipitation ending by midday.
The rest of Monday will be dry with high pressure to our south
beginning to pull warmer air into WI. Look for max temperatures to
generally be in the middle to upper 50s.

A system passing across southern Canada Monday night/Tuesday will
bring a weak cold front through WI. However, a lack of moisture
and the weakness of the cold front would preclude the need to
carry any pops. Instead, the near zonal flow aloft with west winds
at the surface will bring warmer air into WI. Max temperatures by
Tuesday could reach the lower 60s north/near Lake MI, middle 60s
south. Dry and mild conditions should persist through Wednesday as
the region gets on the backside of the retreating surface high. 8H
temperatures climb to around +10C, which would bring temperatures
close to 10 degrees above normal. This would translate to lower to
middle 60s north, middle to upper 60s south.

.AVIATION...for 18Z TAF Issuance
Issued at 1229 PM CDT Thu Oct 12 2017

Low-end MVFR ceilings were predominant across the area at mid-day,
with a few sites reporting IFR/LIFR conditions. SSE flow above the
surface may bring a little drier air into the east and allow for a
brief improvement at MTW, but winds are forecast to begin veering
this afternoon. That will bring the main mass of the clouds back
across the area. So overall, ceiling trends will probably be
dominated by the typical diurnal oscillation of bases edging
down during the night and then rising tomorrow morning.



SHORT TERM.....Kurimski
LONG TERM......Kallas
AVIATION.......Skowronski is the U.S. government's official web portal to all federal, state and local government web resources and services.