Scientific Forecaster Discussion
Area forecast discussion...corrected
National Weather Service Milwaukee/Sullivan WI
236 PM CDT sun Mar 9 2014
Tonight and Monday..forecast confidence...high
Middle and high level clouds will persist through much of the
night...thus low temperatures were kept on the milder end of model
Temperatures aloft will be fairly mild Monday...with 925 mb temperatures of
9-11c in the afternoon. Without snow cover on the ground...these
temperatures aloft would normally result in highs in the low 60s with
decent mixing. Even with the extensive snowpack though...still think
highs will get up around 50 given how well the European model (ecmwf) and Canadian
have performed in previous warm up events this winter. The NAM and
GFS low level temperatures continue to be overly influenced by the
snowpack. With a good amount of sunshine expected...tomorrow will
likely be the nicest day in quite a while...as the last time it hit
50 was early December.
Monday night and Tuesday...forecast confidence...medium
Middle/upper flow is zonal Monday night and Tuesday. As the 250 mb
jet maximum moves across the Great Lakes...southern Wisconsin becomes
located in the right entrance region of the departing jet. There
is some weak upper divergence and the 700 mb upward motion increases
across the the south by sunrise...but then moves more over the far
south Tuesday afternoon. The 700 mb layer is nearly saturated by
sunrise...but sags to more near the Illinois border by evening...
where the relative humidity lowers quickly across northern portions from The
Dells to Sheboygan.
The NAM brings around 0.20 inches over areas from Lone Rock to
just south of Madison...with lighter amounts north and east. The
Fond Du Lac and Sheboygan areas remain dry...with only around 0.05
towards Kenosha. The 00z European model (ecmwf) has a more broad area of around
0.15 inches over much of southern Wisconsin. Thickness values
would trend toward a rain snow mix and mainly rain along the
Illinois border initially...with the precipitation trending
towards more snow later during the day. Boundary level
temperatures are rather warm and should keep precipitation as
mainly rain longer.
The GFS is more of a NAM/European model (ecmwf) blend. Will therefore use the
consensus precipitation values.
Tuesday night and Wednesday...forecast confidence...medium
A shortwave drops into the upper and middle Mississippi Valley
Tuesday night and reaches the western Great Lakes Wednesday.
Weak 700 mb upward motion early Tuesday evening becoming downward
by midnight as the 700 mb relative humidity lowers. Higher relative humidity exists in the
925/850 mb layer.
Some spotty light precipitation extends over southern Wisconsin
Tuesday night...but dries on Wednesday as the main surface low
moves across the Kentucky area with weak high pressure across
Wisconsin. With the proximity of the middle level trough there could
still be some instability snow showers on Wednesday.
Thursday and Friday...forecast confidence...high
The main trough exits the eastern U.S. Thursday with a second
northern stream shortwave moving into the upper Great Lakes
Warm advection begins Thursday as low pressure moves across south
central Canada. Most models have a around a hundreth of
precipitation Thursday morning. The mex MOS is a little cooler
with the clouds and somewhat slower start to the warmer air.
Friday morning should start mild before weak cold advection
Friday afternoon as the low moves into southeast Canada.
Saturday and Sunday...forecast confidence...high
A large upper level trough extends over the Hudson Bay area that
extends farther south into the Great Lakes and upper Ohio Valley
Weak surface high pressure extends into the Great Lakes...with
colder temperatures. The 12zgfs brings precipitation into southern
Wisconsin Sunday...but the 00z European model (ecmwf) and 06z dgex are both slower
or farther south...and are dry. Prefer the drier scenario.
Middle to high level clouds will continue through much of
tonight...with clearing expected later tonight into Monday morning.
VFR conditions will thus persist through Monday.
Low level wind shear is just ramping up and will continue into the
Wind gusts of 25 to 30 knots are likely into tonight...with the
winds slowly easing late evening and overnight. The 08z ending time
for the Small Craft Advisory still looks reasonable. Waves will be
very limited due to extensive ice coverage.
Lm...Small Craft Advisory until 3 am CDT Monday for lmz643>646.
Tonight/Monday and aviation/marine...ddv
Monday night through Sunday...hentz