Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 171724
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1124 AM CST Sat Feb 17 2018

.UPDATE...No significant changes to forecast. Upstream snow
continues to push into the area. Looks like better returns staying
to our south in se IA heading into nrn/cntrl IL. Expecting our
quick hitting light snowfall to push out of the east from mid to
late afternoon.

PC

&&

.AVIATION(18Z TAFS)...Will lower ceilings down to MVFR levels with
the snow moving through this afternoon. Radar showing heavier
returns may end up staying south moving into nrn/cntrl IL from se
IA. Already seeing clearing working steadily into se MN and nc IA.
So that will slide across here this evening.

PC

&&

.PREV DISCUSSION... (Issued 943 AM CST Sat Feb 17 2018)

UPDATE...Round of snowfall still knocking on the doorstep with
some vsbys largely in the 1 1/2sm to 2 1/2sm across srn MN and
nrn IA though some pockets of <1sm noted. The meso models continue
to bring this across starting in the west from later in the morning
and ending mid to late afternoon in the east.

PC

MARINE...Winds starting to increase though not yet to criteria
levels. Overall expect enough of a tightening of the pressure
gradient to support the small craft. So will leave the SCA
intact through 6 pm.

PC

PREV DISCUSSION... (Issued 543 AM CST Sat Feb 17 2018)

UPDATE...The forecast is on track for today. The clouds have
increased and a few hours of light snow is expected for the
afternoon.

AVIATION(12Z TAFS)...A 2-4 hour period of light snow will occur
from west to east across srn WI from the late morning hours
through the afternoon. Areas of MVFR Cigs and Vsbys of 2-5SM are
expected during the snowfall. Clearing skies then expected early
this evening.

PREV DISCUSSION... (Issued 345 AM CST Sat Feb 17 2018)

SHORT TERM...

Today And Tonight...Forecast Confidence Is High.

Swly winds and warm advection will continue until the cold front
passes from the middle to late afternoon. A shortwave trough will
pass during this time along with weak frontogenesis in the low to
mid levels. Forecast soundings and meso models are suggesting a
2-4 hour period of light snow will occur with snow accums around
one half inch or less. Sfc temps will warm into the lower to
middle 30s ahead of the snow, with little to no impact with the
minor snow accum. Clearing skies this evening with a sfc ridge to
shift quickly ewd across the state late tnt.

Sunday Through Tuesday...Forecast Confidence Is High.

Models show warm air advection developing Sunday, with increasing
south winds. Any precipitation will remain over northern
Wisconsin, with some clouds over the area. Mild temperatures are
expected, with values around 40 expected at this time.

Main issue will be precipitation types and amounts for Monday
into Tuesday across the area. GFS/ECMWF/Canadian models remain
rather consistent with bringing one round of low pressure
northeast along a baroclinic zone into far southern or
southeastern Wisconsin late Monday afternoon.

These models bring a low level jet nose into the area Monday,
providing strong upward vertical motion. Strong low level
frontogenesis also moves through the area Monday into Monday
evening. NAM model is slower and not nearly as robust with upward
vertical motion during this period. Sided more with the
GFS/ECMWF/Canadian solutions. Thus, high PoPs are forecast Monday
into Monday evening.

Temperature profiles suggest that there likely will be a period of
light freezing rain Monday morning in far northern parts of the
area. Lack of ice crystals with surface temperatures below
freezing will allow for this to occur. The precipitation will
change to rain by midday here. Elsewhere, rain is expected with
rather warm temperatures in far southern parts of the area, within
the tight baroclinic zone. Kept small chances for thunder in the
far southeast and far south Monday into Monday evening, with very
weak elevated CAPE.

Another round of fairly strong upward vertical motion is forecast
later Monday night into Tuesday, as a secondary low slides
northeast along the baroclinic zone through northeast Illinois.
NAM is once again the outlier solution, so will side with the
GFS/ECMWF/Canadian models. The 850 mb trough moves toward and
into the area as well Tuesday.

This period will see surface temperatures fall, with the surface
low to the south of the area. This will bring a period of freezing
rain in northern and western portions of the area, with a lack of
ice crystals in the air column. Ice accumulations may be on the
order of 0.10 to 0.20 inches or higher in these areas. This
certainly would impact travel. Will highlight the freezing rain
risks Monday morning and again Monday night into Tuesday in our
product messaging.

Rather robust QPF amounts of 1 to 2 inches or higher are shown on
the models somewhere in the northeast Illinois into far southeast
Wisconsin area Monday into Tuesday. This may lead to issues with
runoff and cause rivers and streams to rise. Localized flooding is
possible. This will also be messaged.

LONG TERM...

Tuesday Night Through Friday...Forecast Confidence Is Medium.

Kept chance PoPs going for Tuesday night into Wednesday, as the
models are in some disagreement with when the precipitation with
the passing system will exit the area. This would mainly be light
snow.

High pressure should move east through the region Wednesday into
Thursday, which would bring quiet weather. Temperatures look to be
near seasonal normals. Next chances for precipitation tries to
push into the area Friday.

AVIATION(09Z TAFS)...

A 2-4 hour period of light snow will occur from west to east
across srn WI from the late morning hours through the afternoon.
Areas of MVFR Cigs and Vsbys of 2-5SM are expected during the
snowfall. Clearing skies then expected early this evening.

MARINE...

A Small Craft Advisory is in effect today for brisk swly winds.
Waves will build to 2-4 feet north of Port Washington.

Another Small Craft Advisory will likely be needed Sun afternoon
and night for breezy sly winds and high waves. A few gale force
wind gusts could occur north of Port Washington.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 6 PM CST this evening for LMZ643>646.

&&

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


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