Area Forecast Discussion
Issued by NWS Green Bay, WI

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129
FXUS63 KGRB 182134
AFDGRB

Area Forecast Discussion
National Weather Service Green Bay WI
334 PM CST Thu Jan 18 2018

Forecast discussion for routine afternoon forecast issuance

.SHORT TERM...Tonight and Friday
Issued at 334 PM CST Thu Jan 18 2018

Main weather concern tonight will be if any low clouds develop.
MET/SREF guidance showing high probabilities of low clouds across
parts of central WI and much of northern WI later this evening
into Friday morning. MAV guidance not as aggressive with the low
clouds, but the GFS-LAMP data is showing the potential for lower
clouds. Strong inversion will trap low level moisture tonight,
especially across central and northern WI. With temps in the 30s
this afternoon, any melted snow will add to the low level
moisture. Also, some low clouds were observed upstream early this
morning. So thinking is that moisture should be sufficient to get
low clouds to develop over northern WI. A little more questionable
as you work south away from the stronger inversion and higher low
level moisture. Otherwise, a dry night is expected with winds
under 10-15 mph. Temperatures will fall through the evening
hours, then level off or rise slightly as clouds develop (for
some) and weak warm air advection takes place. Looking for most
spots to drop into the upper teens to lower 20s.

Any low clouds that develop tonight will linger into Friday, but
should mix/lift through the morning hours. However, plenty of
moisture above 15,000 ft so expect a good deal of mid-upper level
clouds. 850mb temps climb to near/slightly above 10C on Friday,
and with full mixing, we would expect highs in the 70s!
Unfortunately, it is the middle of January and a strong inversion
remains in place, so highs are expected to reach the upper 30s to
around 40 for most locations.

.LONG TERM...Friday Night Through Thursday
Issued at 334 PM CST Thu Jan 18 2018

The main forecast concern continues to be the path of a surface
low and mid level cyclone late this weekend into early next week.

Of the 12Z versions of the GFS, Canadian and ECMWF, the GFS was
the fastest, had the northern most path of the system, and was
generally strongest with both the surface and mid level cyclones.
The ECMWF was farthest south, slower, and weakest with these
features.

A cold front moving into Wisconsin from the north will bring a
small chance for snow to the northern part of the state Saturday
night into Sunday. The blended model solution brings precipitation
chances into the area from the south later in the day on Sunday.
The southern part of the forecast area should be warm enough for
rain, but snow and maybe even a little freezing rain is possible
across the north. There may be a wintry mix between the two rather
than a sharp rain/snow line, but where this occurs remains in
question. Precipitation chances increase Sunday night, with most
of the area getting snow as the boundary layer cools. On Monday,
warmer air ahead of the approaching surface low will result in a
change back to mainly rain in parts of central and eastern
Wisconsin before colder air behind the departing system results in
a transition to all snow Monday evening. Confidence in any
specific snow totals is low since there is too much uncertainty
due to model differences.

Temperatures look to be much warmer than normal through Monday
before colder air behind the departing system arrives. Near normal
temperatures are in store for Tuesday and Wednesday before
slightly warmer air moves in on Thursday.
&&

.AVIATION...for 18Z TAF Issuance
Issued at 1157 AM CST Thu Jan 18 2018

VFR conditions are expected this afternoon with mid-level clouds
exiting the area. A few lower clouds are possible closer to the MI
border. Lower clouds across northern MN and northwest WI will try
to drop southeast toward north central WI this evening, but
should dissipate before impacting RHI.

Later tonight, MET/SREF guidance showing IFR/LIFR ceilings across
central and northern WI as moisture gets trapped under a strong
inversion. Low clouds were observed upstream, plus there should
be a little added low level moisture from melting snow, so the
idea of some low clouds developing is not too far fetched.
However, MAV guidance not showing any low cloud development, so
confidence is not very high, but high enough to add the low clouds
for RHI and a tempo group for AUW and CWA. Will keep the low
clouds out of the Fox Valley and lakeshore.

Any low clouds should burn off / lift Thursday morning, but a
mid-deck will be spreading over the area.
&&

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

$$

SHORT TERM.....Bersch
LONG TERM......MG
AVIATION.......Bersch



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