Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
424 am CST Monday Dec 22 2014
Today and tonight...forecast confidence medium to high.
Scattered rain and snow showers moving northward across the area with precipitation type
more rain near the Illinois border. The precipitation will remain spotty into the
early afternoon while the 925 mb 0c isotherm will gradually shift
northward through southern WI. The upper trough over the central USA will
continue to deepen today and tonight as shortwave troughs dig into that
region from The Rockies. Cyclogenesis will quickly evolve to
occlusion from MO into eastern Iowa and northern Illinois for tonight. The nose of the
low level jet and associated thetae advection and frontogenesis...aided by
increasing positive vorticity advection aloft will bring widespread precipitation from south to north
from middle to late afternoon. This precipitation should start as all rain in
the southern County Warning Area and will either be a mixture or briefly starting as snow
in the north. Light to MDT rainfall is then expected much of the night
with the dry slot moving into southeast WI by 12z Tuesday.
Tuesday through Christmas day... forecast confidence medium.
Surface low pressure will track from northeast Iowa to northeast
Wisconsin during the day Tuesday and weaken overnight as it drifts
into eastern Ontario. This is in response to the Midwest 500mb
closed upper low weakening and lifting northeast. Southeast
Wisconsin will end up in the dry slot for the day on Tuesday. This
means middle levels will dry out and low levels will remain moist... so
we can generally expect cloudy skies with periods of drizzle and
A secondary upper low will develop at the base of the elongated
trough over the Arkansas/MO area on Wednesday and track northeast through
lower Michigan Wednesday evening. A 150 knots upper jet streak will lead to
surface cyclogenesis over the eastern Great Lakes. Southeast WI will
be on the far western periphery of this system. I lowered the precipitation
chances to slight chance for Wednesday and Wednesday night and winds should not
even be very strong except for over Lake Michigan.
925mb temperatures will fall below 0c in southeast WI Tuesday evening but will
remain warmer than -5c through Wednesday night. We will be hovering around
the freezing mark at the surface... so this will mean a rain or snow
mix for any light precipitation we get.
Middle level ridging will allow for quiet weather in southern
WI Christmas day.
Friday through Saturday... forecast confidence medium.
Surface low pressure... in response to a digging upper trough over
the intermountain west... will develop in the Central Plains Thursday
night and track northeast across southern WI Friday afternoon/evening.
Models are now showing southern WI in the dry area for Friday with a
chance of light snow Friday night with the cold front. Surface high
pressure and dry weather will dominate for the weekend into
Monday... but temperatures will be below average.
Aviation/12z tafs/...scattered rain and snow showers will continue into
the early afternoon with 3-5sm visibilities in some of the showers. Low
pressure will develop over the Great Plains today and move into SW
WI Tuesday am. Widespread rain will move northward into southern WI this afternoon
with light to MDT rain all night. Some fog will also develop
especially Tuesday am when the low moves across the area.
Ceilings of 1-3 kft at kmsn and kues will transition to 3.5-5.0 kft by
14-15z with visibilities mainly staying above 5sm. Kmke and kenw will
continue to see VFR ceilings this am as well with visibilities around 5-6sm at
kenw this am. When the widespread rain arrives by the middle of the
afternoon the ceilings will fall back to 1.0-3.0 kft and eventually
below 1kft tonight. The visibilities will also drop with the rain and any fog
from 3-5sm this afternoon to 1-2sm for tonight but locally lower visibilities
are possible. The better chances for fog and very low visibilities will be
Marine...a Small Craft Advisory is in effect today and tonight for
breezy east-southeasterly winds and high waves as low pressure over the Great
Plains strengthens and moves to eastern Iowa by 12z Tuesday. Subsiding winds
and waves are expected on Tuesday and Tuesday nt as the low weakens northeastward
Lm...Small Craft Advisory until 3 am CST Tuesday for lmz644>646.
Small Craft Advisory until 6 am CST Tuesday for lmz643.
Today/tonight and aviation/marine...gehring
Tuesday through Sunday...mrc