Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 240327

Area Forecast Discussion
National Weather Service Green Bay WI
1027 PM CDT Fri Mar 23 2018

Updated aviation portion for 06Z TAF issuance

.SHORT TERM...Tonight and Saturday
Issued at 248 PM CDT Fri Mar 23 2018

The latest RAP analysis and satellite/radar imagery show high
pressure stretching from Hudson Bay, across the western Great
Lakes, and to the Gulf Coast early this afternoon. Dry air
emanating out of the high is supporting falling humidities into
the 20 to 25 pct range over central and north-central WI. Meanwhile,
warm advection is occurring over the central to the northern
Plains, which is generating an arcing band of rain and snow from
North Dakota to Missouri. As this storm system slides southwest of
the region tonight, temperatures and humidities are the main
forecast concerns.

Tonight...Precipitation will continue to shift southeast across
Minnesota, Iowa, and Illinois. Slight cold advection will be
occurring further north across Wisconsin, with a tight pressure
gradient generating breezy northeast to east winds. Will have some
cirrus invade the region from the west on the edge of the storm
system, but think far NE WI will remain mostly clear through much
of the night. The combo of cirrus and breezy winds off the Lake
should lead to a warmer night at most locations. Low temps ranging
from the low to mid teens over Vilas county to the middle or upper
20s over the southern Valley and Lakeshore.

Saturday...The Hudson Bay high will continue to be dominant across
northern Wisconsin. A blanket of cirrus will persist over central
and east-central WI, on the northern fringes of the slow moving
storm system. Under filtered sunshine, gusty east winds will make
temperatures in the middle 30s to near 40 feel colder. Humidities
are forecast to not fall as far as they did today, and bottom out
in the 27-37 pct range over central to far northeast WI.

.LONG TERM...Saturday Night Through Friday
Issued at 248 PM CDT Fri Mar 23 2018

Mean flow to remain amplified, but slowly progressive next week.
The main features to consist of: an eastern Pacific upper ridge,
an eastward moving longwave trough across the CONUS and an east-
ward moving upper ridge from the eastern CONUS into the western
Atlantic. The main system of interest remains from Monday
afternoon through Tuesday night as a cold front slowly pushes
through WI, accompanied by a couple waves of low pressure. There
will be other small precipitation chances later next week as the
longwave trough arrives. Temperatures are expected to go above
normal early next week as the mean flow turns southwest.
Temperatures should then drop closer to normal by late week as the
flow turns northwest behind the trough.

High pressure over Quebec will extend southwest through the Great
Lakes into the Midwest Saturday night. Clear skies and diminishing
winds should bring yet another cold night to the region with min
temperatures around 10 above zero north-central WI, to the lower
20s across east-central WI. Quiet and seasonal conditions are
expected through Sunday as the region to remain on the southwest
flank of the high pressure. A slight wind shift from east-
northeast to east-southeast will also help raise temperatures a
bit. Under sunny skies, look for max temperatures to range from
the upper 30s to around 40 degrees near Lake MI/Bay of Green Bay,
mainly lower to middle 40s elsewhere although a couple sites west
of the Fox Valley could reach the upper 40s.

The high pressure is forecast to start losing its influence on our
weather Sunday night as a southwest flow aloft takes over the
central CONUS. Anticipate some increase in at least high clouds
into central WI after midnight, while eastern WI remains mostly
clear. The combination of these clouds and boundary layer winds at
around 30 knots will prevent temperatures from falling as far as
previous nights. Look for readings in the upper teens to lower 20s
far north, middle to upper 20s south. Clouds will continue to
thicken, overspread northeast WI on Monday as a new system
organizes over the central Plains. This system is expected to tap
gulf moisture and quickly transport this moisture into WI,
especially by the afternoon hours. The onset of WAA, combined with
pieces of shortwave energy moving through the southwest flow
aloft, will bring a chance of light rain to parts of northeast WI
primarily in the afternoon. Max temperatures to range from the
lower to middle 40s north/near Lake MI, middle to upper 40s south.

Precipitation will become more widespread Monday night as a cold
front pushes across the Upper MS Valley toward far western WI by
12z Tuesday. Plenty of moisture to be in place over WI with PW
values surpassing 1" over central/east-central WI. Not sure if we
have enough instability to justify carrying a thunder threat, but
will leave it in the forecast for now to avoid any yo-yo effect.
Precipitation type is also an issue as temperatures cool
overnight. Northern WI should see rain become mixed with snow
after midnight with the far north changing to all snow toward
daybreak. Any snow or mixed precipitation is expected to
transition back to rain Tuesday morning as temperatures warm. The
cold front is forecast to steadily move across the rest of WI on
Tuesday, thus higher end pops will continue over most of the
forecast area. As for thunder, there is better instability with a
little CAPE/LI`s approaching zero over east-central WI. Max
temperatures to range from the middle to upper 40s north/lakeside,
lower to middle 50s east-central WI.

Precipitation chances will continue into Tuesday evening over all
of northeast WI, then focuses more over eastern WI Tuesday night.
Precipitation type may be an issue once again depending on how
quick the precipitation diminishes and how fast cooler air pushes
into WI. Any lingering clouds in the east Wednesday morning should
quickly exit as a weak area of high pressure moves into the
western Great Lakes. Anticipate mostly sunny skies for most of the
day with max temperatures in the middle to upper 40s north/near
Lake MI, upper 40s to lower 50s south.

Another cold front is progged to push into the region Wednesday
night, however gulf moisture appears to be lacking due to a
stalled frontal boundary over the Gulf Coast states. Cannot
completely rule out a few rain and/or snow showers across
northeast WI later Wednesday night into Thursday. Models are
having timing issues with regards to a northern stream shortwave
trough Thursday night (ECMWF) or Friday (GFS). There is a pretty
good surge of CAA, along with mid-level forcing, but moisture is
again lacking. For now, have followed the model consensus which
brings a small chance of rain/snow showers to north-central WI on
Thursday, followed by a low-end chance pop for the entire forecast
area Thursday night. Max temperatures for late next week to be
near seasonal normals for late March.

.AVIATION...for 06Z TAF Issuance
Issued at 1026 PM CDT Fri Mar 23 2018

The main aviation concern will be northeast winds, which will be
gusty at times, especially in east-central Wisconsin. Given the
very dry air at low-levels, will continue to downplay the
potential for any low clouds tomorrow morning.



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