Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 202342

Area Forecast Discussion
National Weather Service Green Bay WI
642 PM CDT Mon Mar 20 2017

Updated aviation portion for 00Z TAF issuance

.SHORT TERM...Tonight and Tuesday
Issued at 252 PM CDT Mon Mar 20 2017

Mid level short wave sliding through the region this afternoon
producing a band of mid level clouds along with isolated light
showers or sprinkles. Radar shows these showers were diminishing
as the surface high pressure settles into the area with clouds
decreasing across the north. Clearing and cold conditions
expected tonight with light north winds.

Deep low pressure trough tracking over Canada will send a
reinforcing shot of cold air across the Great Lakes region
Tuesday with developing northwest flow.  H850 temps fall to
around -16 C across the north and northeast Tuesday afternoon with
northwest to north winds. Lake effect clouds and snow showers
will be on the increase Tuesday morning over the far north.
Boundary layer winds may turn northeast enough in the afternoon to
produce clouds and isolated flurries along the Lake Michigan
shoreline, but more likely across Southeast Wisconsin with more of
a northeast direction. Cold air aloft with March sun likely to
produce a period of bkn050 clouds across at least east sections of
the forecast area late tuesday morning into the afternoon.

.LONG TERM...Tuesday Night Through Monday
Issued at 252 PM CDT Mon Mar 20 2017

Main forecast challenge revolves around the system arriving late
Thursday, precip timing and types, and the impact on temperatures.
Overall, long term portion of the forecast looks somewhat active.

On Tuesday night high pressure will be building in, which will
continue to clear skies and cut of the chance for any lake effect
snow in far north- central Wisconsin as winds shift north-
northeast. Lowered Wednesday morning minimum temps a few degrees
from previous forecast to account for the clearing trend and 12Z
guidance numbers coming in slightly cooler than previous runs.

Wednesday still looks quiet and dry as high pressure passes just
north of the forecast area. Highs will be a couple degrees below
average. Guidance numbers on Wednesday varied and stuck with a

High pressure moves east on Thursday and winds shift to the south,
allowing more moisture to flow in and the start of warm advection.
Will take some time to reach saturation, so expect clouds to
increase through the day, but most of the precip to hold off until
late Thursday afternoon and Thursday evening. Models vary on exact
timing, but generally support precip expanding from west to east
in the 21Z Thursday to 03Z Friday time frame. If precip starts
early enough Thursday afternoon would expect to initially see
rain in central and north- central Wisconsin. As surface
temperatures cool overnight freezing rain or a wintry mix becomes
more likely, especially north of highway 29. Mixed precipitation
is less of a concern in the southern forecast area. Precipitation
transitions back over to all rain Friday.

Precipitation chances remain persistent from Friday through
Saturday. Friday high temperatures were lowered a bit from
previous forecast to account for the cloudy and rainy conditions.
Slow progression of the surface low along with shortwave energy
keeps the chance for precipitation in most of the forecast area
through Saturday, with the exception of the far north. Added the
chance for precipitation to Sunday as well for southern and
eastern sections of the forecast area. Expect daytime types to be
rain, with overnight types as freezing rain or a wintry mix.

Early next week, models currently indicate a brief quiet period
through Monday afternoon, then another low pressure system
approaches the area. Temperatures will be be slightly below
normal through Wednesday, warm up Thursday and Friday, and then
level off close to seasonal normals for the weekend and early next

.AVIATION...for 00Z TAF Issuance
Issued at 636 PM CDT Mon Mar 20 2017

Mid and high clouds should thin out over central and east central
WI early this evening. A cold front will sweep across the region
late tonight into early Tuesday, and bring a shot of colder air,
gusty northwest winds and sct-bkn stratocumulus to the region
during the day. Scattered light snow showers or flurries are also
possible near the Upper Michigan border. Most of the ceilings
should be in the VFR category, but a brief period of MVFR ceilings
are possible in northern WI, including the RHI TAF site, late
tonight into early Tuesday morning.




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