Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
357 am CST Sat Jan 31 2015
Today...forecast confidence is high.
Will see a few peeks of sun this morning then middle-high cloud shield
with approaching storm move in. Highs reached around midday as a
weak 850 mb thermal ridge moves across the region...then temperatures
steady with a gradual cooling from north to south during the middle to
late afternoon as weak surface trough/cold front sags into southern WI.
Tonight...forecast confidence is medium.
Will time beginning of snow into the forecast area with forcing and
increasing deep layer moisture...which brings the leading edge of
the snow shield into the SW between 22z and 00z. Some hints on
forecast soundings that there could initially be a mix of rain and
snow...or even rain...in the far southwest going quickly over to all
snow with saturation in the dendrite growth zone. Low confidence in
this scenario so will leave all snow.
Steady light to moderate snow moves in across the County Warning Area as the
strongest layer frontogenesis spreads across the southern half of County Warning Area and
northern Illinois between 06z and 12z Sunday. Blended quantitative precipitation forecast amounts and consensus
snow ratios indicate 3 to 4 inches on the ground along and southwest
of a line from The Dells through southern Dane County to pleasnat prairie
by 12z Sunday.
Increasing northeast winds gusting up to 25-30 miles per hour as approaching
low deepens brings blowing snow into the picture after
06z...creating difficult driving conditons with reduced visibilities
and drifting snow.
Sunday and Sunday night... forecast confidence medium.
The snow will remain steady over all of southern WI on Sunday as a
500mb shortwave trough swings through the region. 850-600mb
frontogenesis will linger over southern WI on Sunday as well. We
will lose the forcing from the upper jet as the shortwave moves in
thus no enhancement of upward motion... just a steady 2 to 4
microbars per second. The best chance for moderate snow will be from
midnight Saturday night through noon Sunday. Snow will begin to
taper off Sunday afternoon inland from the lake.
The surface low will be crossing southern Illinois during the day
Sunday... causing a tight pressure gradient over southern WI and
resulting in blustery northeast winds and blowing snow. Winds will
remain elevated through the day and gradually diminish Sunday night.
Total snowfall amounts for the entire storm are expected to range
from 2 to 4 inches north of a line from Sheboygan to The Dells...
and 6 to 8 inches south of a line from West Bend to Madison to Lone
Rock. This is not much of a shift from the previous forecast. These
totals are over a long duration of time... from this evening through
Sunday night. If it was not for the blowing snow factor... many
areas with an advisory would not even need a headline because we are
talking about snowfall amounts of 1 to 3 inches over a couple of 6-
hour periods. But... it will be very windy on Sunday with recent
snowfall which will have a good chance of causing reduced
visibilities with blowing and drifting snow... thus supporting an
Now for the lake effect portion of the event. We went with a Winter
Storm Warning for Milwaukee-Racine-Kenosha counties due to slightly
higher expected snowfall amounts due to lake enhancement and
eventually a possible lake effect snow band. 1000-850mb flow will
change from east-northeast to north-northeast Sunday afternoon and night... just as the
system snow is pulling away from the region. The wind shift will
allow for some more enhanced convergence over the lake which could
form a heavy lake effect snow band that slides from north to south
down the Lakeshore Sunday night. This would be accompanied by gusty
north-northeast winds... a deep dendritic growth zone layer and strong upward
motion in the low levels. While this could be an intense band of
snow with high snowfall rates... it should be transient and not sit
over one area for a long period of time.
Monday through Tuesday... forecast confidence medium.
Northwest flow aloft will resume over the upper Midwest. Clippers
could bring light snow to southern WI Monday night and Tuesday night.
The Tuesday night system has the potential to drop a couple of inches.
Temperatures will be below normal during this period.
Wednesday through Friday... forecast confidence medium.
A blast of Arctic air is expected to settle over the upper Great
Lakes through this period on dry high pressure. Wind chill temperatures
will approach -20f Thursday night.
VFR conditions are expected tonight and Saturday across taf sites.
Scattered to broken middle level clouds will continue to push
southeast through the area into this evening. These clouds may push
off to the east by late evening...with a period of mostly clear
skies possible later tonight into Saturday morning.
Light winds will become southwest early this evening...then
gradually increase later tonight into early Saturday. The winds will
weaken again Saturday...before a cold front moves south into the
area mainly in the afternoon. This will bring a wind shift to the
northeast by 00z Sunday.
Will be issuing a Small Craft Advisory beginning at 03z Sunday for
the northern zones and 05z in the south as north to northeast winds
WI...Winter Weather Advisory from 9 PM this evening to 9 PM CST
Sunday for wiz056-057-062-063-067>069.
Winter Weather Advisory from midnight tonight to 3 am CST Monday
Lm...Small Craft Advisory from 11 PM this evening to noon CST Monday
Small Craft Advisory from 9 PM this evening to 9 am CST Monday
Today/tonight and aviation/marine...rem
Sunday through Friday...mrc