Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 122122
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
322 PM CST THU JAN 12 2017

.TONIGHT - Forecast Confidence...Medium to High.

Water vapor/rap combo shows nicely defined shortwave trekking east
north of Lake Superior. The surface low is will drag a reinforcing
cold front through this evening resulting in a period of caa and
some gusty nw winds, esp in the ne cwa where gradient tightens up
the longest. Temps will drop into the single digits with some
subzero readings possible in the nw cwa closer to slackening
gradient with approaching surface high. Wind chills will be biting
with some of the northern counties getting close to hitting
criteria.

.FRIDAY - Confidence...Medium to High.

Surface high proggd to waffle across cntrl WI. Cold airmass remains
in place with 925 temps in the -10c to -13c range with a north/south
gradient and likely a bit further enhanced in areas in our north
with a snow field. 700 millibar RH increases with some mid level
waa. Low levels remain dry.

.FRIDAY NIGHT THROUGH SUNDAY - Forecast Confidence...Medium to
High.

Weak isentropic upglide on 295 theta surface shows period of
lower condensation pressure deficits passing across srn WI
Friday night.  Isentropic omega remains weak but CPD do lower to
less than 10mb with 20-25kts of upglide.  Thoughts are to keep small
chance for -sn as low level rh remains lower below 5k feet.  However
noticing trend toward deeper low level rh so later shifts may be
bumping up pops for Fri night with the potential for snowfall less
than 1 inch.

Otherwise, a mostly quiet period with nearly stationary high
pressure over the northern Plains and Great Lakes suppressing
deep moisture and baroclinic zone to the south. Not expecting
any Lake Effect snow over eastern areas as light winds /less than
10kts/ veer to the southeast later Friday into Friday night but can
not rule out a few flurries and lower clouds.

Light snow and wintery mix from southern Plains low pressure looks to
hold off from affecting southern WI until Sunday night.

.EXTENDED PERIOD...

SUNDAY NIGHT THROUGH THURSDAY - Forecast Confidence...Medium.

Medium range guidance in reasonable agreement on cut off low
over Baja Peninsula and northern old Mexico filling and getting
ejected northeast into the southern Plains on Sunday and into
the central Plains Sunday night and Monday.  Some differences
regarding how this system phases with northern stream short wave
moving into the northern Plains early in the period.  But general
agreement is that the southern system will pivot northeast into the
upper Midwest and Wisconsin around Tuesday.  The GFS is trending a
little slower than the ECMWF and Canadian but by 18z Tuesday, all
Medium range guidance has around 1000mb Low over southern WI.
Strong low level jet will accompany this feature and will transport
deeper moisture and warmer air rapidly northward.  Once again, it
looks like southern WI will see warmer air transported into southern
WI resulting in a mostly liquid scenario starting Sunday night or
Monday, possibly changing to snow as the low pressure moves away
from the region later Tue or Tue night.  Forecast soundings and
critical thicknesses show the potential for a period of freezing
rain Sunday night into Monday with glazing potential looking to
remain less than one quarter inch.  This would cause hazardous
travel conditions on Monday so advisory headlines may eventually be
needed.

Steering winds remain more zonal to southwesterly after early week
system moves off to the northeast so no significant push of cold
air.  Long wave troffing spreading toward west coast will cause
downstream short wave to amplify somewhere across the southern
plains into the eastern Great Lakes around Wed and Thu.  At this
point, precipitation from this system looks to remain well east
and southeast of the area.  Potential for another rain/wintery
weather event over the weekend.

&&

.AVIATION/00Z TAFS/...

Mid deck moving out with plenty of SKC moving in. A period of caa
and nw winds this evening expected with reinforcing cold front
dropping in. Surface high settles in for Friday with a lighter wind
regime. 700 RH increases Friday so an increase in mid clouds
expected. Low levels to remain dry.

&&

.MARINE...Expect secondary surge of cold air advection tonight
across the near shore waters behind passing cold front. Colder air
over relatively warmer waters of Lake Michigan will create steep low
level lapse rate which may allow wind gusts to approach 25 knots
tonight, especially over northern marine zones. A Small Craft
Advisory has been issued for the northern two zones for much of the
night to account for some of the higher gust potential.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...

WI...None.
LM...SMALL CRAFT ADVISORY LMZ643>644 from 7 pm CST this evening
through 6 am CST Friday.

$$
TONIGHT AND FRIDAY/AVIATION/MARINE...PC
FRIDAY NIGHT THROUGH THURSDAY...MBK


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