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Area forecast discussion 
National Weather Service Green Bay WI
604 am CST Monday Dec 22 2014

Updated aviation portion for 12z taf issuance

Short Tuesday
issued at 418 am CST Monday Dec 22 2014

Precipitation trends/type...snowfall amounts and winter weather headlines are
the main forecast concerns.

Precipitation has diminished across the region as a dry wedge in the middle-levels
moved over the region. This dry wedge is expected to remain for much
of the have backed off on probability of precipitation compared to the previous forecast.
Precipitation type should be a mix of light rain/snow...though patchy light
freezing rain could occur early in the day over north central WI.
Increasing warm air advection/isent lift will eventually lead to better saturation
and some steadier precipitation over c/ec WI by late afternoon.

An upper level low is expected to move into southeast Iowa tonight...then
lift NE through WI on Tuesday. Increasing warm air advection and a strong
deformation zone will set up over the region tonight...with the
deformation zone remaining over the northwest half of the forecast area on
Tuesday. Precipitation type will remain mainly snow over NC/far NE WI through
the period...with a mix of rain/snow elsewhere...changing to rain over
our southeast counties late tonight into Tuesday. A dry slot will cause precipitation
to taper off over ec WI as the day progresses on Tuesday.

After finalizing snowfall amounts and coordinating with surrounding
offices...have opted to issue a Winter Weather Advisory for snow
across roughly the northwest half of the forecast area. Snowfall totals of
4 to 6 inches are expected over the advisory area between 9 PM
Monday and 6 PM Tuesday.

Long term...Tuesday night through Sunday
issued at 418 am CST Monday Dec 22 2014

The latest GFS and European model (ecmwf) ensemble means indicate a pattern change
will take place by next weekend when a deep eastern noam trough
becomes entrenched across the Great Lakes. This is a typical
pattern for the winter months...which will lead to a period of below
normal temperatures. Until this pattern change active
week of weather will impact the region. The GFS ensemble mean has
nudged the track of a cyclone due to move across the central Great
Lakes a little to the east on Wednesday...while the operational runs
have made bigger eastward adjustments to the track over the past 24
hours. The spread in the guidance remains substantial even if there
is a greater likelihood of the primary impacts being felt east of
the state. Will go with a general model compromise for this
system. Models also continue to hint at another weak cyclone to
move through the region during the Friday-Saturday time period.
Will side with the European model (ecmwf) which has support from its ensemble mean.

Tuesday night through Wednesday night...occluded low pressure will
be moving to the northeast Tuesday night from central Wisconsin to
the Eastern Upper Peninsula. Light rain and snow will likely continue
north of the surface low until it crosses the u.P. Border.
However...models continue to point towards middle-level moisture
peeling out through through the night...which would lead to a ptype
transition to drizzle/freezing drizzle by late Tuesday night. Not
expecting much snow accumulation across the north due to this dry
slotting. Nuisant drizzly/flurry weather will likely carry over into
Wednesday morning but should see the threat gradually diminish
through the day. Will be watching low pressure track towards the
Detroit/Cleveland area Wednesday afternoon. The back edge of the
snow from this cyclone may graze the Lakeshore counties but not
expecting significant accumulations unless models shift the track
back to the west. The storm will pull out Wednesday night...but
hard to say if any clearing will take place. Little change to temperatures
over the period.

Rest of the forecast...after a quiet and seasonable day on
Christmas...the next low pressure system will move across the Great
Lakes Christmas night into Friday. A positively tilted wave
combined with a weakening cyclone leads ME to think that only small
accumulations will be the potential (1-2 inches...locally 3
inches). Mainly quiet next weekend but turning colder (below normal

Aviation...for 12z taf issuance
issued at 551 am CST Monday Dec 22 2014

A dry wedge of air in the middle-levels has caused precipitation to taper off
over much of the region this morning. Patchy mixed rain/snow will
still occur through the day...with a small chance of light freezing
rain in north central WI this morning. Precipitation will increase again
during the late afternoon and a developing low
pressure system approaches the region. Precipitation will fall as mainly
snow over NC/far NE WI...with a rain/snow mix expected farther

Current MVFR/IFR conditions should improve a bit during the middle
part of the day...then deteriorate again as the steadier precipitation
arrives this evening.

Low level wind shear is expected to develop tonight...especially at the western
taf east winds aloft increase to 35 to 40 kts.

issued at 418 am CST Monday Dec 22 2014

A winter storm will track over the Great Lakes region tonight
into Tuesday...and is expected to bring rain and mild temperatures
into parts of central and east central Wisconsin on Tuesday.
The rain and warm temperatures will produce some runoff...and
may also result in changing ice conditions on area rivers and
lakes. Minor flooding due to ice jams is possible.

Grb watches/warnings/advisories...
Winter Weather Advisory from 9 PM this evening to 6 PM CST
Tuesday for wiz005-010>013-018>021-030-031.


Short term.....Kieckbusch
long term......mpc

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