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Area forecast discussion 
National Weather Service Green Bay WI
558 am CST sun Nov 23 2014

Updated aviation portion for 12z taf issuance

Short Monday
issued at 459 am CST sun Nov 23 2014

The phasing of two upper systems will produce an
intensifying storm system tonight. These type of systems give the
numerical weather prediction models and forecasters some of our
bigger challenges. This situation is no exception as there is a
wide range of model solutions. The European model (ecmwf) and GFS phase the systems
the least while the NAM and Gem are slower and more phased. The
NAM and Gem are finer scale models and take into account the
effects of the Great Lakes better than the others so does that
give them an advantage? Maybe. Since there is still such a big
difference between the models we decided it would be prudent to
wait before issuing any possible watches or advisories.

Warm...moist air moving north over the snow covered ground was
producing dense fog in central and northern Wisconsin. This should
diminish by midday. Some drizzle is expected this morning with
rain arriving this afternoon as the low pressure systems begin to
organize over Illinois. Periods of rain expected tonight with
areas of fog as well. Highs today will be well above normal.

The rain will change to snow from west to east Monday as low pressure
deepens over lower Michigan if the NAM and Gem are correct or
north of Lake Huron if the GFS and European model (ecmwf) are correct. Significant
snow is likely if the NAM and Gem are right with only minimal snow
accumulations if the GFS or European model (ecmwf) are more correct. Issued a
Special Weather Statement saying the snow accumulations are
possible Monday afternoon and evening. In addition to the snow...a
more vigorous storm could produce considerable blowing and
drifting snow.

Long term...Monday night through Saturday
issued at 459 am CST sun Nov 23 2014

The medium range models continue to struggle with the details for
this upcoming they try to determine whether the northern
stream or southern stream will dominate the northern part of the
lower 48. Will take a blend of the European model (ecmwf) and GFS for the Monday
night through Tuesday night period...then use the superblend
thereafter given the uncertainty. Looking ahead into the first week
of December...the GFS ensemble mean points toward above normal
heights and temperatures across the region.

Monday night through Tuesday night...the deep cyclone will be
rapidly moving into Quebec Monday night...but northern stream
shortwave energy will be moving through the region. Moderate
forcing within the cyclonic flow will keep widespread light snow
going for much of the night. Think an additional half inch to an
inch and a half is possible...locally higher over Vilas County where
wind trajectories will be favorable until late in the night. Could
see an additional 2-4 inches there. Any lingering snow will be
pulling out of NE Wisconsin early Tuesday morning...and also ending
over Vilas County as winds back to the west. Surface ridge axis
will move across the state for the rest of the day...which will
promote at least partial clearing. The next clipper will be moving
quickly into the northern Mississippi Valley Tuesday night. Clouds
will be increasing through the night with a chance of snow pushing
into north-c Wisconsin by 12z.

Rest of the forecast...the clipper will move across the region
Wednesday into Wednesday night. Plenty of details to get sorted out
since the European model (ecmwf) and GFS are on opposite ends of the spectrum in
terms of strength of the system. The strength of the incoming jet
streak...which the shortwave will reside in the left exit
region...would argue for a stronger system. So think a conservative
approach would call for a widespread 1-2 inch event...locally higher
(possibly significant) within the snow belts of Vilas where wind trajectories
will become favorable for lake enhancement once again. Arctic high
pressure will build in for Thursday and Friday but it may take until
Thursday night until the lake effect machine diminishes. Quiet and
cold weather could linger into the start of next weekend though the
GFS is considerably more active.

Aviation...for 12z taf issuance
issued at 558 am CST sun Nov 23 2014

Mild and moist air moving north over cold and snow
covered ground will produce IFR conditions through tonight.
Ceilings and visibilities will be near Airport minima in some
areas. Rain will be on the increase today as a deepening low
pressure system lifts northeast from the middle Mississippi Valley
region into the lower Great Lakes tonight. The rain will change to
snow from west to east Monday.

Grb watches/warnings/advisories...
dense fog advisory until 9 am CST this morning for wiz005-


Short term.....Rdm
long term......mpc

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