Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Milwaukee/Sullivan WI
553 am CST sun Dec 8 2013
Short term...today and tonight. Forecast confidence high.
While radar returns would suggest light snow moving over all of
southern Wisconsin...observation indicate the dry air in place over the
region is preventing any ground truth...keeping accumulating snow
just to the west and northwest of the County Warning Area with the better 850-700
mb relative humidity and isentropic Omega...enhanced by DCVA from initial vorticity
maximum that passes by to the west and north through 12z.
Will see steady light snow spread in with more focused 850 mb warm air advection
and associated isentropic Omega. Have started advisory at 15z in
far western counties with initial light accumulations making roads
slick with cold temperatures.
Still expect to see moderate snow this afternoon and evening with
Omega maximum crossing southern WI this afternoon and evening with lift
enhanced by DCVA ahead of of main short wave.
Expect snow to taper off from southwest to northeast late tonight
with passage of middle-level trough. Some blowing and drifting after
snow ends with increasing west winds behind the deepening surface
low as it closes off over east central WI/Central Lake Michigan/or
western lower Michigan depending on model...and lifts northeast.
Consensus quantitative precipitation forecast and snow ratios still producing 3 to 4 inches over
most of the County Warning Area...with lower amounts of 2 to 3 inches along the
southeast Illinois border region.
Watching area of returns over northeast Illinois/Southern Lake
Michigan as winds become east and increase. With lake water/850 mb
temperature differentials of 15c to 18c and increasing along-shore
convergence expect this area to grow and develop...with forecast
soundings showing increasing depth of the moist unstable layer into
the dendrite growth zone as developing southeasterly 1000-850 mb winds lift
this pocket northward. Focus of the lake enhancement still looks to
be north of Milwaukee from Port Washington North and have higher
snow amounts there. Lake-effect snow flow chart supports additional
1-3 inch amounts there so will have 4 to 6 inches...with locally
Monday...forecast confidence high.
The surface low will continue to deepen as it moves into southern
Ontario on Monday. As high pressure builds into the plains...there
will be a tight pressure gradient over southern WI. Expect gusty
west winds of 15 to 25 miles per hour. These winds will blow the light fluffy
snow around...so look out for drifting or icing on
roads...especially the north-south ones. Steady cold air advection
will mean high temperatures will occur in the morning then
steady/fall through the day. Steep low level lapse rates will lead
to low clouds lingering over the region at least through the
Tuesday...forecast confidence high.
A surface ridge will move across southern WI Tuesday night. Clear
skies and lighter winds in the evening will allow for temperatures to
bottom out in the single digits by midnight. Then a middle level
shortwave trough will move across the u.P. And Lake Michigan Tuesday
morning. Temperatures will begin to warm late Monday night as the clouds move
in. Look for dry weather across southern WI but it will be windy as
this clipper moves through. Gusts to 30 miles per hour are likely.
Long term...Wednesday through Saturday...forecast confidence
Another shortwave trough will swing through late Tuesday night into Wednesday
morning. An inch of snow will be possible with this upper/surface
trough. It will usher in even colder air for Wednesday. It will be
breezy once again with the cold air advection...so expect wind
chills to drop below zero.
Temperatures look to moderate a little for next weekend as a series of
shortwaves move through the upper Midwest. Models begin to differ
about the weather pattern for next weekend.
Current VFR conditions will worsen through the morning from west
to east as warm advection-driven snow spreads across southern
Wisconsin ahead of deepening low pressure. Expect MVFR conditions
by middle- morning at kmsn and late morning at eastern taf
sites...lowering to IFR this afternoon into this evening. Expect
MVFR ceilings through the remainder of the forecast period once the
snow tapers off late this evening into the early overnight.
Gusty west winds will still cause blowing and drifting
into the morning Monday with the light powdery consistency of the
snow. With 3 to 4 inches of total accumulation expected at the taf
sites...this will cause some visibility problems but will probably have a
larger impact on keeping runways clear.
Have issued a Small Craft Advisory starting at 18z for the southern
zones and 21z for the northern zones for increasing northeast to
east winds as low pressure deepens as it moves across southern
Wisconsin to the northern Great Lakes. Waves will build to 3 to 5
feet before the winds ease as the low passes by...then turn west and
increase back to 15 to 25 knots later tonight. Some gusts to 30
knots are possible on Monday with winds easing below criteria
Winds will increase again Tuesday into Wednesday...with gale force
gusts possible Tuesday afternoon...as another low crosses Lake
Superior followed by another Arctic cold front.
WI...Winter Weather Advisory from noon today to 6 am CST Monday for
Winter Weather Advisory from 9 am this morning to 6 am CST
Monday for wiz046-056-062-067.
Lm...Small Craft Advisory from noon today to 10 PM CST Monday for
Small Craft Advisory from 3 PM this afternoon to 10 PM CST
Monday for lmz643-644.
Updated to add short term...aviation and marine sections.
Today/tonight and aviation/marine...rem
Monday through Saturday...mrc