Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

FXUS63 KMKX 031649

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1049 AM CST Sat Dec 3 2016


Overcast skies and dry weather expected through midnight. A midlevel
trough will approach the region later tonight becoming negatively
tilted and passing through the region on Sunday. QPF looks a tad
higher with the latest model runs. We are strongly considering a
winter weather advisory for our western counties since it looks like
it will be 3-4 inches. We are still evaluating for the eastern
counties where amounts may be a little less.

There is good synoptic lift and soundings show decent omega in the
dendrite growth zone for a 4-6 hour period from late morning to late
afternoon. There is broad, weak warm air advection and weak
frontogensis across southern WI. There is strong upper level
divergence from a 140 knt upper jet during the morning then it
weakens as the jet moves east during the afternoon. Models are in
good agreement with 1000-500mb thicknesses of 532 NW to 534 SE
resulting in 14:1 to 12:1 snow ratios. Road temperatures this
morning are in the low to mid 30s so with little increase in
temperatures expected today, we think snowfall rates will be high
enough to overcome "warm" roads and accumulate.



Ceilings are improving to 3500-4000 ft across SW WI and this trend
is expected to move west to east across southern WI today. They may
become scattered for a time. Ceilings will continue to lift this
evening, then mid level clouds will move into the region ahead of
the next weather system.

On Sunday morning ceilings will quickly drop to IFR as snow moves
into the region. 2-4 inches of snow is expected by Sunday evening,
with the highest amounts occuring from Madison and southwest. Road
temperatures are currently in the low to mid 30s and with little
increase in temperature today we think there snowfall rates will be
high enough to overcome these "warm" temperatures and it should
accumulate on pavement.



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.


.PREV DISCUSSION... /Issued 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.


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.


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.







Sunday THROUGH Friday...DDV is the U.S. government's official web portal to all federal, state and local government web resources and services.