Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Green Bay WI
552 am CST Monday Jan 26 2015
Updated aviation portion for 12z taf issuance
Short term...today...tonight...and Tuesday
issued at 453 am CST Monday Jan 26 2015
Precipitation trends...snowfall amounts and potential for freezing drizzle
through tonight are the main forecast concerns.
A clipper low pressure system was moving into far SW Ontario early
this morning...and strong pressure falls over northern and central
Minnesota suggested a continued quick southeastward movement. The system was being
driven by the lfq of a 150 knots jet streak and a short wave trough. Strong
warm air advection ahead of the low was combining with the upper forcing to
generate an area of snow over eastern Minnesota and northwest/west
central WI...though the eastern edge of the snow band was aloft
due to a lingering dry wedge around 850 mb.
Best forcing due to the lfq of the upper jet...warm air advection and frontogenetic
forcing is expected to move through the SW half of the forecast area
this morning and early afternoon...bringing brief pockets of
moderate snow...and a quick accumulation up to 2 inches. The snow
will begin during the morning commute in parts of NC/c WI...then
shift eastward into eastern WI during the late morning and early
afternoon. Snow intensity should wane farther east due to weaker
forcing...so daytime accums of only a half inch to an inch are
expected over NE/ec WI. Patchy freezing drizzle is possible in our
far SW counties late in the day...as moisture gradually Shallows
out. Highs temperatures will be in the 20s.
Additional short-wave energy will pass through the region tonight...
and an inverted surface trough will linger over the forecast area. Mesoscale
models support some lake-enhancment over eastern WI as low level winds
back from southeast through northeast during the night. Instability
is marginal...with lake-800 mb Delta-t's only 12-14 c...but still
sufficient for some enhancement...and there should be a well-
defined convergence zone over eastern WI through the night. Have
kept likely probability of precipitation for the most of the night over NE/ec WI...with
additional accums of 1 to 1.5 inches most places. Farther west...
precipitation will gradually taper off to patchy light snow and freezing
drizzle...though the travel impacts of the fzdz should be lessened
somewhat as it falls on snow covered or treated roads. Low temperatures
are expected to settle into the upper teens or lower 20s.
Weak high pressure will build into the region on Tuesday...causing
any lingering light precipitation to end...and result in a gradual decrease
in clouds during the day. High temperatures should reach the upper 20s
or lower 30s.
Long term...Tuesday night through Sunday
issued at 453 am CST Monday Jan 26 2015
Mean 500mb flow will be dominated by western North America ridge
and eastern trough. High pressure will dominate the weather
pattern Tuesday night into Wednesday as clipper system approaches
from the northwest. The clipper system should affect the area
late Wednesday afternoon into Thursday. Some timing differences
noted with system among the models... but trended toward the slower
Canadian/European model (ecmwf) solution. Dry air ahead of the system could also
delay the onset of precipitation.
This system should bring a few inches of snow to the region by
Thursday morning. High pressure will then build into the region
Thursday night...then east of the area on Friday. Arctic cold
front will swing across the area late Friday night and Saturday
morning. The front will be accompanied by some snow shower activity
and probably falling temperatures. Later shifts may need to raise
high temperatures a few degrees since European model (ecmwf) is slower with the
arrival of the front. Sunday should be considerably colder than
Aviation...for 12z taf issuance
issued at 541 am CST Monday Jan 26 2015
Snow was developing over NC/c WI early this morning...and is
expected to spread east to Lake Michigan by around midday.
Conditions will deteriorate to IFR as the snow increases...
with local LIFR visibilities in central WI during the middle to late
morning. The snow will taper off to patchy light snow/freezing
drizzle in central WI late this afternoon...and over much of
NC/c WI tonight. Light snow will continue over eastern WI
tonight...and may be enhanced due to east flow off Lake