Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 080306
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
906 PM CST Thu Dec 7 2017

.UPDATE...The forecast is on track for tonight through Friday
night.


&&

.MARINE...A Small Craft Advisory is in effect tonight through 4 PM
Fri due to brisk wly winds.


&&

.PREV DISCUSSION... (Issued 613 PM CST Thu Dec 7 2017)

UPDATE...Warm advection will increase late tnt into Fri on wly
winds. Enough moisture may arrive within a low level thermal ridge
to produce stratus for Fri AM and possibly lingering into the
afternoon. Afterward, a fast moving amplifying shortwave trough
will move swd from Canada to the Upper MS River Valley on a nly
130 kt jet. As it amplifies it will shift ewd across the Ohio
River Valley and Great Lakes through Sat-Sat nt. PVA and warm
advection at the jet level should produce a period of light snow
Fri eve into the overnight. The frontogenesis is rather weak but
the mid level frontogenesis may become more organized over ern WI
as the upper wave amplifies. Overall, we are forecasting 1-3
inches with the higher amounts in ern WI.

AVIATION(00Z TAFS)...VFR conditions tnt with stratus developing
around and just after sunrise. Prevailing Cigs will range from
3.5-5.0 kft but there is the potential for MVFR Cigs during this
time as well. The stratus will continue into the afternoon with
the snow arriving Fri eve. Cigs will eventually fall to 1-2 kft
with the snow and Vsbys down to 1 mile.

PREV DISCUSSION... (Issued 259 PM CST Thu Dec 7 2017)

Tonight And Friday...Forecast Confidence Is Medium.

Some middle level clouds will push southeast through the area into
early evening, as weak differential cyclonic vorticity advection
at 500 mb shifts through. These clouds have some breaks in them,
and they may continue to break up as they move through.

More middle level clouds should move southeast through the area
later tonight into Friday morning, with additional weak 500 mb
differential cyclonic vorticity advection. The pressure gradient
should remain rather tight tonight into Friday morning, with winds
backing to the southwest. It should then weaken later on Friday.
Below normal temperatures are expected tonight and Friday.
Lowered lows a few degrees below blended short term models for
tonight.

Added some flurries in the northwest Friday morning, with some
weak frontogenesis response in the low levels with some low level
moisture. It looks like the best moisture and upward vertical
motion with the approaching strong 500 mb shortwave trough will
remain to the northwest of the area Friday afternoon. For now,
continued to mention some lower end PoPs, highest in the north for
Friday afternoon.

Friday night...Forecast confidence is high.

A fast hitting, potent mid level short wave, and an accompanying
decent surface trough/cold front with the deepening surface low,
will push southeast across the area Friday night. This is all
consistent with the previous forecast and expected snow amounts
remain largely unchanged. The snow will start north of Milwaukee
and Madison between 6-7 PM and south of Milwaukee Madison by 8-9
PM. The peak snowfall will be in the mid to late evening period,
then diminishing quickly from northwest to southeast by midnight.
The snow may end by midnight in the Sauk/Columbia county area and
in the Milwaukee/Madison area by 2-4 am Saturday. Total
accumulations will generally be in the 1 to 2 inch range, but
some local reports of 3 inches are possible. This will be a dry
snow with the cold temperatures.

The weather pattern through the weekend into next week shows cold
and persistent northwest upper level flow with periodic embedded
short waves diving southeast across the area. Some of those could
result in some light snow from time to time.

Saturday and Sunday...Forecast confidence is high.

The weekend is looking dry right now as a narrow high pressure
ridge pushes across the area in the wake of the departing low.
Some guidance is suggesting we could see a little light snow
Sunday afternoon with a weak short wave pushing through, but right
now, the atmosphere looks too dry to support that. So, dry for
now. Temps on Saturday will be cold, only in the mid 20s, warming
into the lower 30s for Sunday.

Monday through Thursday...Forecast confidence is medium.

The models are in pretty agreement in bringing a short wave and
decent surface low through here late Sunday night and Monday.
This could bring another inch of snow. Any snow should more or
less be over by Monday evening.

For Tuesday and beyond, it becomes rather uncertain as the timing
or existence of any short wave energy for the middle of next week
is difficult to resolve with confidence at this point.

AVIATION(18Z TAFS)...

Area of scattered to broken middle level clouds should continue
to slide southeast through parts of the area into early this
evening. Gusty westerly winds should linger during this time,
especially near Lake Michigan.

The winds will back to the southwest tonight, and linger into
Friday morning. Gusty winds may linger near the lake during this
time. Gusty southwest to west winds should return later in the
morning and afternoon near Lake Michigan, though should gradually
weaken elsewhere. Middle clouds overnight into Friday morning
should lower to around 3000 feet above ground level later in the
day from north to south.

Any snow is expected to hold off until early Friday evening,
moving quickly southeastward into the area. It should linger into
the overnight hours, before ending later Friday night from
northwest to southeast. A 1 to 3 inch fluffy/powdery snowfall is
forecast at this time, with the highest amounts in the far eastern
portions of the area. We should get a better idea on hourly rates
as the event draws closer.

Ceilings and visibilities should lower to IFR or below
categories, perhaps down to or below alternate minimums at times.
Light winds should veer northwest and become gusty later Friday
night into Saturday. This may lead to some blowing snow on
runways.

MARINE...

The pressure gradient will remain rather tight tonight into
Friday afternoon across the area. There are some gusts already
reaching at or above 22 knots at Sheboygan and Kenosha. Westerly
to southwesterly gusts should reach up to 25 knots at times during
this period, especially by later this evening.

Thus, a Small Craft Advisory has been issued from 03Z until 22Z
Friday. This may need to be started sooner, if the current gusts
remain high enough. High waves will remain over the open waters of
Lake Michigan.

Gusty winds may reach Small Craft Advisory levels again at times
Saturday into Sunday, as a tight pressure gradient lingers in the
wake of low pressure moving to the east of the region. Gusts will
approach gale force Saturday morning. High waves may occur toward
the open waters of Lake Michigan.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 PM CST Friday for LMZ643>646.

&&

$$

Update...Gehring
Tonight/Friday and Aviation/Marine...Wood
Friday Night through Thursday...Davis



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