Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 222002

Area Forecast Discussion
National Weather Service Green Bay WI
302 PM CDT Wed Mar 22 2017

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Thursday
Issued at 301 PM CDT Wed Mar 22 2017

Several potential pitfalls to the short-term forecast ranging from
extent of light snow late tonight/early Thursday morning, how fast
to bring precipitation back to the area Thursday afternoon and
what impact will all of this have on temperatures.

The 19z MSAS surface analysis indicated a large area of high
pressure over the Great Lakes. Several weak areas of low pressure
were located over the Rockies which will eventually organize into
one main system. Visible satellite imagery showed a dissipating
band of lake clouds over far eastern WI, but also showed the
leading edge of WAA clouds marching across the Upper Midwest.
Under these clouds, the radar mosaic had picked up on light
returns. However, there was no ground truth and most of these
returns were likely virga.

Mostly clear skies with light southeast winds will prevail this
evening, however the clouds to our west will overspread central WI
toward midnight and eastern WI during the wee hours of the morning
as WAA increases over the region. A stronger push of WAA, coupled
with a weak shortwave topping a modest upper ridge, will bring a
chance of light snow to central WI toward daybreak. Temperatures
are expected to quickly fall this evening, then stabilize as the
clouds arrive overnight. Look for readings to range in the upper
teens to around 20 degrees north, mainly 20 to 25 degrees south.

The chance of light snow will linger into early Thursday morning,
but forecast soundings do indicate a very dry air mass at low-
levels of the atmosphere, thus we may see more virga than actual
light snow. A dusting would appear to be the best we can do,
mainly across the north. Much of northeast WI could then be dry
for several hours on Thursday as the main system to still be
moving through the Rockies. That being said, increasing moisture
transport through the day, coupled with persistent WAA, could
bring increasing rain chances to the forecast area Thursday
afternoon (especially late in the day). Max temperatures are
expected to reach the middle to upper 30s north, upper 30s to
lower 40s south.

.LONG TERM...Thursday Night Through Wednesday
Issued at 301 PM CDT Wed Mar 22 2017

Pattern in the long term forecast remains active with many
challenges revolving around precipitation types through the
weekend and early next week.

Focus starts on Thursday night with the first main wave of
precipitation likely to have started, or start soon, as moisture
surges into the area. Good confidence that the south will remain
rain through the night. Locations roughly north of Hwy 29 have a
chance to see a transition to freezing rain as surface
temperatures cool overnight. Models vary on how cold it will get
Thursday night. GFS is the warmest and suggests a longer period of
rain to the north, while NAM drops temps to the north below
freezing earlier, which would result in the potential for ice
accumulations greater than a tenth of an inch, or even two tenths
in some locations. Given the uncertainly, and how dependent the
precip type is on surface and road temperatures, confidence in
amount of ice accumulation is not high. Also, would not be
surprised to hear a few claps of thunder Thursday evening, mainly
to the south and west, as lapse rates are around 6.5 to 7.5 C/km,
but the most unstable air is much further south and west and focus
remains on freezing rain potential in the north.

Good confidence that any freezing precipitation will change to
liquid by late Friday morning. For the rest of the weekend, long
term models don`t vary too much on the overall track and timing
of the main surface low. Questions still revolve around available
moisture (especially north), temperatures, and timing of precip
type changes. Expect a repeated pattern through Monday with rain
during the day and freezing/mixed precipitation possible
overnight. With colder and drier air filtering into the north this
weekend, the ice accumulation potential does not appear as high
these nights, and any accumulations look to remain minor.

The pattern next week continues to send a train of systems from
the southwest towards the Midwest and Ohio River Valley area,
however models diverge this far out with numerous track and timing
differences. Would expect the general active pattern to continue
with on and off precipitation chances.

High temperatures through the period will generally be around
or slightly above seasonal normals, with low temperatures
expected to be slightly above seasonal normals.

.AVIATION...for 18Z TAF Issuance
Issued at 1226 PM CDT Wed Mar 22 2017

High pressure over the Great Lakes is forecast to shift to the
east tonight and allow for a southerly wind to return to WI. An
increase in clouds tonight will mark the start of warmer air, but
also introduce a small chance of light snow late tonight into
Thursday morning. After a brief break in the precipitation
chances later Thursday morning, potential for light rain arrives
later Thursday afternoon ahead of a system moving across the
Rockies. This will begin a stretch of unsettled weather that is
likely to continue through the upcoming weekend. Other than the
MTW TAF site that is dealing with MVFR lake clouds this afternoon,
VFR conditions are expected through Thursday before flying
conditions deteriorate Thursday night.



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