Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 091547 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
947 AM CST Sat Dec 9 2017

.UPDATE...

The snow is beginning to wind down in the east, and should come to
an end by late morning. A big gap in the cloud cover has formed
across northwest and central parts of the forecast area. Most
places should see some breaks in the clouds at times today, though
given the cyclonic flow and extensive cloudiness just to the
west, sunny skies aren`t expect to prevail. High temps for the
afternoon still look generally on track.

&&

.MARINE...

The timing of the current Small Craft Advisory still looks
reasonable, though there might be some room to extend a couple
hours given lingering higher waves in the south late this evening.

Gusty winds will return later Monday into Tuesday as another low
pressure system moves through the area. Another Small Craft
Advisory is likely for this period.

&&

.PREV DISCUSSION... (Issued 553 AM CST Sat Dec 9 2017)

UPDATE...The snow is decreasing in intensity and coverage as the
upper trough and low move ewd. The stratus will linger but will
scatter out this afternoon.

AVIATION(12Z TAFS)...
Light snow with Cigs of 1-3 kft and Vsbys of 1-3SM will gradually
diminish from northwest to southeast across srn WI through
14-15z. Stratus will remain but scatter out for the afternoon.
Brisk nnwly winds will prevail through the day with lessening this
evening. Mid level clouds for tnt.

PREV DISCUSSION... (Issued 355 AM CST Sat Dec 9 2017)

SHORT TERM...

Today And Tonight...Forecast Confidence Is Medium.

Light to moderate snow over the eastern half of srn WI will end
around sunrise with total snow accum of 1-2 inches. The low
pressure area and upper trough will move away this morning with
brisk nnwly winds and cold advection in its wake. A stratus deck
extends well north and nwwd but model soundings do scatter out
stratus for the afternoon via subsidence and drying. Some
uncertainty if subsidence and drying will be enough but will go
with partly cloudy conditions for the afternoon.

For tnt, a weak sfc ridge moves ewd across srn WI with light swly
flow afterward. An approaching weak vorticity maximum and mid
level warm advection will bring increasing clouds this evening.
The clouds will keep temps from plummeting with lows in the teens.

Sunday Through Monday Night...Forecast Confidence Is Medium.

Models are showing a surface trough pushing southeast through the
area Sunday morning, with trailing 500 mb differential cyclonic
vorticity advection lingering into the afternoon. Deep moisture is
questionable with these features, so just some clouds may pass
through the area. Highs in the upper 20s to lower 30s look
reasonable.

Main impact will be chances for light snow later Sunday night into
Monday evening across the area. GFS/ECMWF are now in better
agreement with trends during this period, and leaned toward them
with this system. The Canadian is somewhat similar to them, with
the NAM remaining a bit of an outlier with its QPF.

There is a shot of focused warm air advection and low level
frontogenesis response later Sunday night across the area, along
with some differential cyclonic vorticity advection. The main 500
mb shortwave trough then slides southeast through the area Monday
morning and early afternoon. The GFS forecast soundings have
relatively deep moisture to work with Sunday night into Monday
morning, before ice crystals start to erode from the dendrite
snow growth zone.

Went with higher end chance PoPs for Sunday night into Monday
morning, mainly in the north, with lower PoPs to the south. If
GFS/ECMWF remain consistent, may need to raise PoPs in later
forecasts. There is some potential for light freezing rain or
drizzle to occur later Monday morning into the afternoon, as the
ice crystals in the dendrite zone may mix out. Still uncertainty
here, so left in some light freezing rain wording in spots for
Monday afternoon at this time.

Strong cold air advection then occurs later Monday into Monday
night, as gusty northwest winds develop. The drier air working
into the area should help end any lingering light snow. Lows in
the 12 to 18 degree range Monday night may not be cold enough, if
there is snow on the ground.

LONG TERM...

Tuesday Through Friday...Forecast Confidence Is Medium.

Models are generally showing northwest flow at 500 mb lingering
across the region during this period. They are having some timing
and placement differences with the passing 500 mb shortwave trough
Wednesday into Wednesday night. The GFS brings it through the
area, with the ECMWF staying to the southwest. A secondary
shortwave trough then slides through on Thursday, with more
differences in timing and placement.

The GFS/Canadian have light QPF across all or parts of the area
Wednesday, with the ECMWF dry. There are also differences here
with features for Wednesday night and Thursday, before warm air
advection and some QPF develops on Friday. For now, kept consensus
blended PoPs for now for the long term period. Cold temperatures
Tuesday into Tuesday night may be lower than currently forecast,
with snow covering the ground. Wind chills may dip a little below
zero Tuesday night. Temperatures may moderate for Wednesday, then
fluctuate later in the week.

AVIATION(09Z TAFS)...
Light snow with Cigs of 1-3 kft and Vsbys of 1-3SM will gradually
diminish from west to east across srn WI through 13-14z. Stratus
will remain but scatter out for the afternoon. Brisk nnwly winds
will prevail through the day with lessening this evening. Mid
level clouds for tnt.

MARINE...

A Small Craft Advisory remains in effect for today into this
evening. Brisk nnwly winds will develop this morning and continue
through the day. Waves will build to 5 to 9 feet by early
afternoon. The brisk winds and high waves will gradually subside
during the evening.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 9 PM CST this evening for LMZ643>646.

&&

$$

Update...DDV
Today/Tonight and Aviation/Marine...Gehring
Sunday THROUGH Friday...Wood



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