Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 161753
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
1253 PM CDT Thu Mar 16 2017

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Friday
Issued at 317 AM CDT Thu Mar 16 2017

The forecast starts out fairly quiet as mostly clear skies and
light winds rule over the forecast area for much of today. Highs
pressure pushing off to the south will bring southerly surface
winds, as highs soar into the upper 30s to around 40 which will be
right around normal for this time of year.

Most of the attention for this portion of the forecast will be
the on the clipper system tracking through the western Great Lakes
tonight and Friday. 00Z NWP models have all trended a bit slower
with the progression of the precipitation shield tonight,
including the previously faster GFS, with precipitation not
reaching the Lake Michigan shoreline until around midnight or so.
The models have also trended a bit cooler this run, with model
soundings indicating less wintry precipitation and more snow
across the area tonight. There is a chance for icy precipitation
later tonight and early Friday morning as the area loses some mid
level moisture, however given the timing of this dry air near or
just after sunrise, icy precipitation should be minimized given
the solar radiation hitting area roadways. The low pulls out
rather quickly on Friday, with only light rain or drizzle in place
by the afternoon hours.

The system itself will have fairly strong dynamics with the left
front quad of the upper level jet over the western Great Lakes and
a potent PV anomaly tracking through the region. There will also
be quite a bit of isentropic lift in the 295K to 300K layers
tonight with winds just about perpendicular to the isentropic
surfaces. However the amount of time this exists is fairly short,
on the order of 6 hours. In addition the 00Z KGRB RAOB sounding
shows a very dry atmosphere in place, with only 0.11 inches of
precipitable water as surface observations noting many dew points
in the area in or near the single digits above zero. Given the
speed of this system and the dry air in place only expecting
around 2 inches of snow with this system north of highway 29 with
around an inch or a few tenths along and south of highway 29 with
lesser amounts as you head south.

.LONG TERM...Friday Night Through Wednesday
Issued at 317 AM CDT Thu Mar 16 2017

Forecast concerns revolve around precip chances Friday night into
early Saturday, and also late in the weekend.  Models continue to
have some timing differences with both of these systems, so will try
a blend of the gfs/ecmwf to mitigate these differences.

Friday night through Saturday night...Dry slotting will be in place
over eastern WI at the start of Friday evening, but deeper moisture
will return through the night as the upper trough digs overhead.
Temps will likely be too warm for much snow at the start of the
evening, but weak cold advection will likely support precip changing
over to snow through the night from west to east.  Potential accums
look pretty meager, perhaps a dusting over the east to a half inch
across the north.  Any lingering light snow will likely end early
Saturday morning as subsidence causing moisture above 850mb to scour
out. But clouds will likely hang around into the afternoon before
drier air arrives from the west.  Surface high pressure will move in
for Saturday night.  Incoming mid and high clouds will prevent temps
from plummeting.

Rest of the forecast...Sunday continues to look dry with the next
front pushing into Minnesota by late in the afternoon.  This front
will quickly move across the area Sunday night into early Monday,
providing the next chance of precipitation.  The gfs is considerably
wetter with this system than the ecmwf, but think the gfs is
overdone with the moisture availability due to the previous high
pressure system extending into the Gulf of Mexico, and the right
front quad of a jetstreak overhead.  This system also looks
considerably warmer than the previous system, so precip type should
be mostly liquid, except with a little snow possible across the
north. A strong Canadian high will build into the region in the wake
of the system through midweek, causing temps to fall below normal by
Tuesday.  The next weather system will arrive late in the work week.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1253 PM CDT Thu Mar 16 2017

VFR conditions will prevail throughout the daytime hours and into
at least early evening as 12Z models have trended slower with the
approaching system. Forecasts of the vertical temperature profile
from the models would suggest snow overnight, changing to rain
during the morning on Friday, with a period of freezing rain or
mixed precipitation in between. MVFR conditions should hold off
until after 06Z or 07Z, with IFR conditions after about 09Z or
10Z. IFR should then last through 18Z.
&&

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

$$

SHORT TERM.....Kurimski
LONG TERM......MPC
AVIATION.......MG



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