Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 191745

Area Forecast Discussion
National Weather Service Green Bay WI
1145 AM CST Fri Jan 19 2018

Updated aviation portion for 18Z TAF issuance

.SHORT TERM...Today...Tonight...and Saturday
Issued at 349 AM CST Fri Jan 19 2018

High heights and zonal flow favors mild and dry weather and that
is what we expect for the next couple days. Should be mild today
with 900 mb temperatures of +10C. Some middle and high clouds
will inhibit mixing and keep it from getting warmer than it could
be. We still expect high temperatures of 10 to 15 degrees above

The mild weather will continue tonight with some middle or high
clouds and mild boundary layer temperatures. Lows should be 15
degrees or more above normal.

Fair weather will continue Saturday. Light winds and mild
temperatures should make for a good conditions for winter sports
or melting snow and ice from the roads and sidewalks.

.LONG TERM...Saturday Night Through Thursday
Issued at 349 AM CST Fri Jan 19 2018

The primary forecast concern continues to revolve around the
elusive details in regards to the next winter storm due to
impact the region late this weekend into early next week. The
latest models have trended slightly south with the track of the
system over the past 24 hours. Furthermore, the GFS and Canadian
have trended slower, closer to the timing of the ECMWF. Will
therefore put more weight into the ECMWF solution.

Saturday night through Sunday night...Low level moisture will be
increasing across the mid-Mississippi Valley and southern Great
Lakes on Saturday night, as low pressure emerges into the central
Plains.  Across central and northern WI, will have enough dry air
wedged below 700mb to keep most of the area dry, except for
possibly far northern WI. In this area, mid-level fgen will be
present within the right rear quad of a jet streak, which may
provide enough forcing/saturation for a chance of light snow or
flurries. The low makes some progress to the east on Sunday while
low level moisture creeps farther north into central WI by late in
the afternoon. The mid-level convergence zone holds pretty steady
over far northern WI, so think the best chance of precip will
probably occur there. Perhaps a dusting to a half inch of
accumulations are possible. The start of widespread precip will
likely occur on Sunday night as upper divergence and isentropic
ascent increases. Precip should be light to start out due to
lingering dry wedges in the mid-layers. Thermal profiles suggest a
wintry mix north and west of the Fox Valley, where 1 to 3 inches
of snow to go along with minor ice accumulations are possible.
Temps will be close to freezing in eastern WI, so cant rule out
some ice, but thinking mainly rain through 12z Mon.

Rest of the forecast...The low pressure system will travel across
Iowa to southeast or east-central WI on Monday and Monday night.
On the northern flank of the cyclone, a large swath of precip
will lift northeast across the region during this time, and exit
the area on late Monday night into Tuesday. Models continue to
point towards an ample surge of warm air ahead of the low into
central and northeast WI for precip type to be a real headache to
forecast. Most likely looking at a wintry mix to rain scenario
shaping up for Monday in this area before precip turns back to
snow once the low passes on Monday night. North-central WI stands
the best chance of seeing mostly snow, where could see significant
accumulations. CIPS analogs suggest a corridor of mixed precip in
between these areas, which could result in ice accumulations. All
this said, the track of the cyclone has not settled down yet in
the forecast models so details like those listed above will
undoubtedly change as we draw closer to the event. The main take
away is that travel is likely to be significantly impacted across
most of the region on Sunday night through Monday night.

In the wake of the cyclone, generally quiet and seasonable weather
is expected during the middle of next week. There are some
indications that another storm system will impact the area late
next week.

.AVIATION...for 18Z TAF Issuance
Issued at 1144 AM CST Fri Jan 19 2018

VFR conditions expected through Saturday, as mid-upper level
clouds continue to push across the region. Some models showing low
cloud/fog development tonight, but those models have been over-
doing low-level moisture, so will not include any low clouds or
fog. Increasing low level moisture arrives Saturday night and
Sunday, so there is a better chance of lower clouds and possible
fog then.

Low level wind shear is expected through late this evening as
west/southwest winds of 35 to 45 knots at 2000 ft with southwest
winds at the surface around 10 knots.



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