Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 011819
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1219 PM CST Wed Mar 1 2017

.UPDATE...

Shortwave trough axis is shifting from Minnesota and Iowa into
western Wisconsin this morning, with surface low pressure to our
east over Michigan. Cold air wrapping in behind the low allowed
for a quick change over from rain to all snow earlier this
morning.

An area of moderate, to at times heavy, snow continues working
through our northeast late this morning. This first batch of snow
was aided by an area of mid-level frontogenesis and differential
cyclonic vorticity (DCVA) advection preceding the upper wave. This
area will continue pushing east through early this afternoon.

Light snow will continue this afternoon as the upper trough swings
through with some additional DCVA. Additional snow accumulations
should mostly be on the light side.

&&

.AVIATION/18Z TAFS/...

Periods of moderate snow will continue north of Milwaukee and
Madison this afternoon, with light snow elsewhere. We`ll see a mix
of MVFR and IFR ceilings and visibilities, with periodic drops
during the snow. The wet, slushy snow should at least partially
melt given the relatively warm pavement temperatures this
afternoon. The snow will end from west to east this evening, with
temperatures remaining below freezing tonight. Northwest winds
will persist this afternoon, with periodic gusts to around 20
knots.

&&

.MARINE...

The Small Craft Advisory continues through later tonight. A tight
pressure gradient will linger into tonight across the area, as low
pressure moves to the east of the region. This will continue to
bring gusty northwest winds to the area, along with high waves
toward the open waters of Lake Michigan. Frequent gusts to 30 knots
are expected this afternoon into this evening, with a few gusts
possibly reaching 35 knots. Not enough confidence to issue a Gale
Warning at this time.

&&

.PREV DISCUSSION... /Issued 320 AM CST Wed Mar 1 2017/

SHORT TERM...

TODAY AND TONIGHT...Forecast confidence is Medium.

Confidence in this forecast remains middling at best. Unreliable NAM
has shifted axis of heavier precipitation across northern WI today.
GFS and ECMWF more consistent but still having issues with strength
of synoptic scale forcing.  Never the less, used a blend of these
two short term models for today.  Still expect low pressure to
strengthen over central and eastern Great Lakes today with
sharpening trof at around 10k feet.  Increasing northerly winds in
the wake of this trof will pull colder air southward across southern
WI today. This will change the bulk of the precipitation over to
snow or a rain/snow mix.  Several upstream short wave trofs will
provide necessary lift to generate areas of mostly light rain and
snow this morning across southern WI.  A period of mid-level
deformation swings through this afternoon generating more light snow
before tapering off from west to east during the mid to late
afternoon. Used a blend of forecast guidance and came up with lower
QPF and resultant snowfall across the area today with amounts of 2
to 4 inches across the northern half of the CWA and from one half to
2 inches across the southern half.  Wl keep Winter Weather Advisory
going for north but drop southern tier from Iowa County east to
Milwaukee County including Dane, Jefferson and Waukesha counties as
well.  Main snow for the Milwaukee metro will be this afternoon but
with lesser amounts and with the likelihood of pavement
temperatures remaining above freezing, had enough confidence to
drop advisory in this area.

A period of gusty winds this afternoon and evening may result in
patchy blowing snow as the temperature dewpoint depressions and snow
liquid ratios increase.

Snow and any lingering rain will end early this evening but a
resurgence of low level warm air advection and lingering high rh may
result in light snow redeveloping late tonight, mainly western CWA.

LONG TERM...

THURSDAY... Forecast confidence is medium.

A shortwave trough is expected to slide through eastern Iowa and
northern IL or southern WI on Thu. Steep lapse rates and brief
strong omega could cause a quick inch of snow, along with reduced
visibilities. This event would impact travel, especially if it
happens during the afternoon commute. Timing, track and strength are
still uncertain.

Temperatures are going to remain cold, I mean around seasonal
normal, through the end of the work week.  We could see another
clipper system bring light snow Fri night.

SATURDAY THROUGH SUNDAY... Forecast confidence is high.

Temperatures will warm to well above normal once again this weekend
after a warm front lifts all the way to Lake Superior. Forcing and
moisture with this warm front are not too impressive, so not
expecting storms or any precip. There should be a fair amount of mid
level clouds though. Southerly winds could become fairly breezy
on Sunday.

MONDAY THROUGH TUESDAY... Forecast confidence is medium.

A deep upper trough will approach from the Pacific Northwest
early next week. This will help to draw moisture up into WI
ahead of a strong cold front. The synoptic pattern favors
thunderstorms Monday. The cold front is expected to cross southern
WI Mon afternoon or night, there is still a lot of model
uncertainty.

AVIATION/12Z TAFS/...

Increasing low level winds helping to thin areas of dense fog across
southern WI overnight.  A few pockets remain in the south but these
should continue to thin through the early morning. Occasional light
rain should transition to periods of light snow later this morning
and early afternoon with cigs remaining mostly MVFR to IFR. The snow
will cause visibility restrictions later this morning and
afternoon as well.

MARINE...

Tightening pressure gradient associated strengthening low pressure
over the central Great Lakes has caused gusty winds to rapidly
develop overnight, after 06z over the near shore waters.  Gusty
winds will continue today into tonight so Small Craft Advisory will
remain in effect.  Strongest winds expected from mid-afternoon
through early evening when wind gusts could approach Gale levels.
Too much uncertainty to upgrade at this point but wind gusts likely
to reach at least 30 knots for a time.

Also, increasing winds helping to thin and dissipate the dense fog
that had been over the near shore waters.  Patchy fog may linger
early this morning, but should continue to thin.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 6 PM CST this evening for WIZ046-
     047-051-052-056>060.

LM...Small Craft Advisory until 4 AM CST Thursday for LMZ643>646.

&&

$$

UPDATE...SPM/WOOD
TODAY/TONIGHT AND AVIATION/MARINE...MBK
Thursday THROUGH Tuesday...MRC


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