Area Forecast Discussion
Issued by NWS Green Bay, WI

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FXUS63 KGRB 120908

Area Forecast Discussion
National Weather Service Green Bay WI
408 AM CDT Mon Mar 12 2018

Forecast discussion for routine morning forecast issuance

Issued at 404 AM CDT Mon Mar 12 2018

Some snow showers and flurries at times through Tuesday, but
overall, relatively quiet March weather likely at least through
the end of the work week.

Large scale amplification is underway and will peak the next
couple days, with strong troughs near 140W and 80W and a sharp
ridge around 110W. After that, the eastern trough will lift into
Canada and the Atlantic. The ridge will begin to progress east and
flatten as energy ejects out of the western trough. There will
also be a tendency for the flow over western and central North
America to split during the latter half of the period. The medium
range models are now struggling to determine which stream of the
split will dominate the forecast area late in the period.

Amplification of the eastern trough will drive a shot of colder
air into the area beginning today. Once that passes through,
temperatures will rebound and are likely to remain reasonably
close to seasonal normals for the rest of the period. The pattern
will be unfavorable for significant precipitation through the end
of the week. What happens after that depends on to what extent the
southern stream affects the area.

.SHORT TERM...Today...Tonight...and Tuesday
Issued at 404 AM CDT Mon Mar 12 2018

The weather the next couple days will likely mirror what happened
with a similar southward intrusion of cold air last week. The
main difference this time will that be the recent dissipation of
the snow cover over the southern part of the forecast area will
allow more/quicker modification of the incoming cold air.

A strong upper level speed max digging southeast across the area
today will be the main factor forcing reamplification of the
eastern North American longwave trough. A band of snow showers
driven by forcing in the LFQ of the speed max developed over the
north/east part of the area overnight, but was now off to the
east. North flow off Lake Superior will continue to generate snow
showers and flurries in the Lake Superior snowbelt today, but
considerable ice on the lake will limit the accumulation
potential. Temperatures today will get off to a warmer start than
most guidance indicated, so edged maxes up a bit despite CAA.

A series of small scale shortwaves will continue to drop
southeast across the area on the cyclonic shear side of the strong
jet today into tonight. The most significant of these will cross
the area tonight, with the NAM/GFS/ECMWF all sweeping an area of
QC forcing through the northeast part of the forecast area during
the night. Raised PoPs accordingly, and added flurries to the rest
of the forecast area. Although large scale forcing will be more
subtle on Tuesday, deep cyclonic flow and steep low-level lapse
rates suggest flurries or snow showers will be possible. The
negative will be quite dry air at low-levels. Settled for nudging
PoPs up and carrying flurries for most areas for now. Later
forecasts can take another look at the SHSN potential.
Temperatures aloft will be cold enough for snow throughout, but
the precipitation could still be a mix or even a little rain at
times when the boundary layer is a few degrees above freezing.

Stayed close to a blend of top performing guidance products for
temperatures tonight and Tuesday, but tweaked them a bit to
reflect the diminished snow cover over the southern part of the
forecast area.

.LONG TERM...Tuesday Night Through Sunday
Issued at 404 AM CDT Mon Mar 12 2018

At the beginning of the forecast period, a 500mb ridge will
dominate western North America while a closed upper low is
positioned across the eastern Great Lakes. The upper low is
expected to gradually shift eastward while the western North
America ridge is expected to flatten next weekend. There are
still many questions in how the evolution of the upper pattern
will affect the potential for a weekend system across the western
Great Lakes.

For Tuesday night, it will be cold with lows in the single digits
to around 10 above zero north to the teens across the Fox Valley
and lakeshore region. Despite a cold start to the day, high
temperatures at most places will climb into the upper 30s to
middle 40s. A weak disturbance and associated surface boundary is
expected to bring a small chance of light snow showers to the far
north on Thursday. Tranquil conditions will prevail Thursday
night through Friday evening.

The models diverge on the system for Saturday into Saturday night.
The Canadian and GFS model bring precipitation into the area
while the ECMWF solutions remained dry. The ECMWF solution had
systems passing to the north and south of us and we remained dry.
The Canadian model brings an upper low across the region. However,
the Canadian model is such a significant change from last nights
run with a Hudson Bay high prevailing across the northern United
States. Forecast builder has small chances of rain/snow for
Saturday. This seems reasonable with such uncertainty in the
models at this time. No changes made to the Sunday period due to
the uncertainty in the pattern. Only minor changes made to max/min
temperatures to account for our warm bias sites during the day
and the cold bias sites across the north where there is a deeper

.AVIATION...for 12Z TAF Issuance
Issued at 404 AM CDT Mon Mar 12 2018

Expect primarily VFR conditions during the next 24 hours. The
exception will be some MVFR conditions across the north at times
with clouds off Lake Superior, and briefly lower visibilities in
snow showers.



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