Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 030907
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
307 AM CST Sat Dec 3 2016

.TODAY AND TONIGHT...Forecast confidence - Medium to High.

Main forecast concern is increasing likelihood for snow spreading
into parts of south central WI late tonight.  For majority of today,
expect low clouds to persist due to lighter wind regime and high low
level moisture caught beneath strong inversion around 4K ft.  Clouds
may erode later this afternoon into this evening as low level mixing
begins to increase and thermal trof slides off to the east.  Not
expecting any light precipitation with passing weak mid-level short
wave as increasing subsidence causing wave to shear and further
weaken.  Plus air mass remains very dry above 5K ft.

Strong upstream piece of short wave energy will track ENE and
approach WI late tonight.  Strong warm air advection aloft and
increasing upper level divergence associated with strengthening 300H
jet will cause -sn to break out across IA this evening, spreading
eastward into parts of south central WI by late tonight.  Hence
bumped up pops to categorical as 0.5-1.0 inch may be on the ground
already by 12Z west of Madison.

.SUNDAY...Forecast Confidence...High

Models are in good agreement in swinging the strong wave through
on Sunday. Plenty of moisture/lift with this system and models
have been trending upward with QPF, so raised pops and snowfall
amounts even more. New forecast totals are up to 2-4 inches. Not
out of the question to see a few spots as high as 5 given some of
the higher model QPF, particularly in the southwest forecast area.

Given expected temps in the 20s most places at daybreak, the snow
should have no problem accumulating on all surfaces initially. As
it warms up during the day and dewpoints come up as well, there
will probably be a little bit of melting, hopefully making it
easier to keep roads clean by afternoon.

A couple models are aggressive bringing mid level dry air in
toward the tail end of the precip, which would result in a loss of
ice crystals and thus a little drizzle. Not completely sold on
this yet though, so just went with all snow for the duration of
the event for now.

.MONDAY...Forecast Confidence...High

High pressure will move through briefly on Monday. May actually
see breaks in the clouds in the morning, though clouds will likely
be on the increase by afternoon ahead of the next approaching
trough. Bumped high temps down a tad from the consensus of models,
as the fresh snow cover will keep temps from warming up much.
Probably some room to go even lower with highs based on colder
GFS/NAM temps.

.TUESDAY THROUGH FRIDAY...Forecast Confidence...Medium

Models are in overall better agreement with storm tracks mid to
late week, though still some differences to sort through. On the
other hand, seeing pretty decent agreement among models with the
arrival of the coldest air of the season thus far.

Have some pops in Tue mainly per the Canadian bringing the surface
low and precip farther north, though the ECMWF does bring the
precip right to the border.

Looks dry Wednesday between systems, with models swinging another
trough through Wed night into Thu. The ECMWF is developing a
surface low ahead of the wave and lifting it into the region,
clipping the forecast area with some light snow. The GFS/Canadian
solutions don`t develop the surface low and keep the precip to
the south at the base of the trough. Kept some low pops in due to
the uncertainty.

Strong high pressure is expected to build in behind the departing
trough, bringing below normal temps to the area. Highs may
struggle to reach 20 both Thu and Fri given latest model runs.

&&

.AVIATION/12Z TAFS/...

Strong inversion aloft and lack of significant low level drying
should result in MVFR stratus continuing across southern WI much of
the day.  IR imagery showing signs of stratus eroding on back side
of passing high pressure system where a bit more low level mixing is
taking place over SW IA into SW MN.  Hence stratus may become
scattered late today into tonight as mid-level clouds increase ahead
of approaching low pressure.  Expect -sn to overspread southern WI
late tonight through Sunday morning with visibility restrictions
falling to low MVFR/IFR for a time.

&&

.MARINE...

Lighter winds will continue over the near shore waters through
tonight as high pressure passes by to the south. Winds will
eventually back to the south to southeast later tonight and Sunday
morning and then veer back to the southwest late Sunday into Sunday
night as a low pressure trof passes through.  Wind speeds will
approach Small Craft Advisory levels Sunday night.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.

&&

$$

TODAY/TONIGHT AND AVIATION/MARINE...MBK
Sunday THROUGH Friday...DDV



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