Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 150324 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
924 PM CST Sat Jan 14 2017

.UPDATE...

Most of the high clouds have pushed out of the area this evening,
with the majority of these clouds expected to remain just south of
the area overnight into Sunday morning. These clouds will
eventually push back northward into the area Sunday afternoon and
night, ahead of the next system affecting the area later Sunday
night into Tuesday.

High pressure and the clear skies over the area should allow for
temperatures to drop a decent amount overnight. Already seeing
temperatures drop quickly just to the north of the forecast area.
Kept lows in the single digits above zero in most areas, with lows
in the 10 to 13 degree range in the far south and near Lake
Michigan.

&&

.AVIATION/06Z TAFS/...

High pressure moving through the region overnight into Sunday
will allow for light winds and clear skies. High clouds to the
south of the area will gradually shift northward into the area
Sunday afternoon and night, ahead of the next system that will
affect the area later Sunday night into Tuesday.

&&

.MARINE...

High pressure moving through the region will bring light winds
overnight into Sunday. Winds will remain rather light Sunday night
into Monday, before increasing Monday night. A Small Craft
Advisory may be needed for Monday night in later forecasts.

Low pressure moving northeast through far southeast Wisconsin
early on Tuesday should bring lower winds once again. Gusty west
winds are possible Tuesday night into Wednesday, as the low moves
out of the area.

&&

.PREV DISCUSSION... /Issued 330 PM CST SAT JAN 14 2017/

TONIGHT AND SUNDAY - Forecast Confidence...Medium.

Quiet conditions are expected for tonight with surface high pressure
in control. High level cloud cover will increase ahead of the next
weather system approaching from the southwest. Lows should range
from the single digits in our northern service area, to around 15 in
the southeast.

Clouds will thicken on Sunday as jet-level moisture streams into
southern Wisconsin. Surface high pressure slowly slides to our east
during the afternoon and evening, but will maintain enough influence
for fair conditions. Highs will range from the 20s north, to lower
30s south.

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

Still expecting unsettled wintery weather to return to southern
Wisconsin for Monday and Monday night.  Closed low over Baja
Peninsula area will get nudged northeast over the next 72 hours by
large amplitude ridge approaching west coast.  Short term guidance
continues to come into better agreement with track of this low as it
ejects northeast across central Plains on Monday and across srn WI
Monday night.  NAM remains outlier with farther west track of
sfc low while GFS, ECMWF and GEM in good agreement on carrying low
across se WI late Monday night and early Tuesday.  By no means is
this a classic winter storm as this system will have little cold air
to tap into.  Hence focus on wintery mix and not snow. Strong low
level jet will develop ahead of the wave and transport deep moisture
and warmer air currently causing problems across central CONUS
rapidly northward Sunday night and Monday.  Column precipitable
water triples in a 12 hour period as nose of low level jet passes
across srn WI/nrn IL on Monday, and then shifts off to the east
Monday night. However expect precipitation to continue into Monday
night as upper wave and area of enhanced synoptic forcing passes
through.

Critical thicknesses and Top Down precipitation method still shows a
wintery mix of light freezing rain, sleet and snow affecting
southern WI from late Sunday night through Monday.  Soundings show
the predominant ptype changing to liquid in the morning but surface
and pavement temps will lag ptype changeover, especially in south
central into east central WI.  Far southeast WI may escape glaze
potential as sfc temps warm more rapidly in this area during the
morning.

Also a concern that light freezing rain may linger over northern
parts of CWA into Monday night.  Winter Weather Advisory likely to
be issued on Sunday but wl need to watch that northwest corner
closely.

GFS hangs onto stronger mid-level deformation and secondary mid-
level wave passing through while ECMWF and NAM weaker with this
secondary feature on Tuesday.  For now, will continue lower chances
for light rain possibly transitioning to light snow before ending.

EXTENDED PERIOD...

TUESDAY NIGHT THROUGH SATURDAY - Forecast Confidence...Medium.

Discrepancy shows up right away in Medium Range guidance as GFS
slowing low pressure eastward progression Tue night with more
amplified system over central Great Lakes while ECMWF more
progressive and drier.  Due to GFS earlier success handling
this system, will keep in low pops for parts of the area this
period with possibly some accumulating light snow in some areas
during the evening.

Otherwise, no significant push of colder air with early week system
so temperatures will rebound to near or above seasonal normal for
much of the period.  Brief period of zonal flow on Wednesday will
transition to southwest steering flow at mid-levels as several
higher amplitude low pressure waves move across the eastern Pacific
and western CONUS during this period.  Southwest flow eventually
ushers into the midwest and western Great Lakes a piece of short
energy ejected from upstream amplifying long wave trof late in the
week. Low level atmosphere would favor a liquid scenario once again
but air mass looks even warmer initially so less of a freezing
rain/ice threat on Friday and Saturday.

Large positive 500mb height anomoly over the Great Lakes through
next weekend still expected to flatten and become more neutral by
early in the week of the 22nd.  Until then, temps to remain near or
above seasonal normal most periods.

AVIATION/00Z TAFS/...

Low clouds have scattered out, with prevailing VFR conditions
expected into tonight. Scattered to broken high clouds should
persist into Sunday. Quiet weather through the period with high
pressure in control.

MARINE...

Light winds and low waves through Sunday. Low pressure will bring
increasing winds by Monday evening, with Small Craft Advisory
conditions possible. Another period of higher winds and waves is
expected for Tuesday afternoon into Wednesday.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

UPDATE...Wood
TONIGHT/Sunday AND AVIATION/MARINE...SPM
Sunday NIGHT THROUGH Saturday...MBK


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