Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 171723
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1123 AM CST Wed Jan 17 2018

.UPDATE...Southwest wind gusts of 30 to 35 mph with sustained
winds of 20 mph are expected this afternoon in Sheboygan County
where a fresh powdery snowcover of 6 to 12 inches is located.
Widespread drifting is expected on north-south roads and some of
the snow will become lofted, reducing visibility in open, rural
areas. This will have an impact in some areas on the afternoon
commute, so posted Winter Weather Advisory into the evening. Will
be keeping an eye on Ozaukee County as well, however winds are not
expected to be quite as strong.

&&

.AVIATION(18Z TAFS)...VFR conditions for this forecast period.
Main concern is southwest wind gusts as high as 30kts this
afternoon. This will cause areas of blowing and drifting snow. The
blowing snow may reduce visibilities in some areas. Strong low
level winds developing over southern WI tonight will result in low
level wind shear for a time.

&&

.PREV DISCUSSION... (Issued 858 AM CST Wed Jan 17 2018)

UPDATE...Leading edge of mid-level warm air advection causing
area of mid clouds which will sweep across southern WI rest of
the morning. Main concern is increasing southwest winds during the
afternoon and eve. Winds will likely gust to 28 to 32 knots for a
time in the Sheboygan area which will cause drifting snow. With
sustained winds getting to 17kts in this area, some of the fresh
snowpack may get lofted causing some visibility restrictions. The
blowing and drifting will cause slippery roads to develop in the
northeast CWA this aftn.

MARINE...Increasing southwest winds will develop this morning and
continue into Thursday. May need to upgrade to a Gale Warning as
latest soundings show a better chance for wind gusts to 35 knots
for a time later this aftn and eve. Will see how winds increase
through the early afternoon before making final decision.

PREV DISCUSSION... (Issued 500 AM CST Wed Jan 17 2018)

UPDATE...

The one concern will be the increasing west to southwest winds.
We should see sustained winds of 15 to 20 mph with gusts to 30
and possibly 35 mph up toward Sheboygan for this afternoon into
Thursday. This should result in drifting snow, causing some
problems, especially in the more north/south oriented roads.

Temperatures will be in the lower 20s, but with the winds, wind
chills will keep values in the single digits this afternoon.

AVIATION(12Z TAFS)...

VFR conditions should prevail. The main concern will be
increasing southwest winds this morning and afternoon, with gusts
between 25 and 30 kts at times during the afternoon hours. This
wind will likely result in areas of drifting snow, and while
widespread visibility restrictions aren`t especially likely,
airport surfaces may need to be cleared of drifting snow.

LLWS is expected across the area tonight into early Thursday.

PREV DISCUSSION... (Issued 330 AM CST Wed Jan 17 2018)

SHORT TERM...

Today And Tonight...Forecast Confidence Is Medium.

A northwest upper flow with an upper ridge moving across
Wisconsin this evening. 700 mb warm air advection should bring
scattered altocumulus across southern Wisconsin today. The
increased mid level moisture is rather shallow.

Generally quiet weather is expected. The one concern will be the
increasing west to southwest winds. Low pressure to our north and
high pressure to the south, puts us squarely in a tight pressure
gradient. We should see sustained winds of 15 to 20 mph with gusts
to 30 and possibly 35 mph up toward Sheboygan for this afternoon
into Thursday. This should result in drifting snow, causing some
problems, especially in the more north/south oriented roads.

Temperatures will be in the lower to 20s, but with the winds,
wind chills will keep values in the single digits this afternoon.

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

Models are in good agreement with showing warm air advection
taking hold over the region during this period. The pressure
gradient should gradually become tighter during this time, with
south to southwest winds bringing warmer air into the area.

The models also bring a strong 500 mb shortwave trough southeast
through the region on Thursday. However, the airmass is quite dry,
so not expecting anything more than some clouds with this
feature. The flow at 500 mb is expected to shift to a more zonal
look Friday into Friday night.

One complicating issue with the warm air advection will be the
strong inversion around 1500 feet above ground level, which will
limit the mixing and subsequent warming somewhat. Some
uncertainty here, so went near blended model temperatures for
now. This should bring highs into the lower 30s Thursday, and the
upper 30s to around 40 on Friday.

LONG TERM...

Saturday Through Tuesday...Forecast Confidence Is Medium.

Main feature this period will continue to be the low pressure
system moving northeast through the region Sunday into Monday.
There continues to be uncertainty with the track of the low, with
the GFS taking the low northeast across the area around 12Z
Monday. The Canadian is well north at this time, with the ECMWF
slower and in south central Iowa. The ECMWF does take the low
across the area Monday afternoon.

All of these low tracks are accompanied by a rather deep 500 mb
low and associated differential cyclonic vorticity advection.
Using the GFS/ECMWF track would bring the warm sector into the
area Saturday night into Sunday night, before colder air filters
back into the area Monday into Monday night. This would bring a
mainly rain scenario for Sunday into Sunday night, before mixing
with and changing to snow Monday. This would bring light
accumulations later Sunday night into Monday.

GFS forecast soundings also show some risk for freezing
rain/drizzle Saturday night, if temperatures remain below
freezing. For now, used the consensus blended PoPs and
temperatures, given the uncertainty in the models this far out.
Certainly a system to watch as is gets closer.

AVIATION(09Z TAFS)...

VFR conditions should prevail. The main concern will be
increasing southwest winds this morning and afternoon, with gusts
between 25 and 30 kts at times during the afternoon hours. This
wind will likely result in areas of drifting snow, and while
widespread visibility restrictions aren`t especially likely,
airport surfaces may need to be cleared of drifting snow.

LLWS is expected across the area tonight into early Thursday.

MARINE...

Winds will increase from the southwest this morning, with
frequent gusts around 30 knots through the day. A few gale force
gusts are also possible. A Small Craft Advisory will be in effect
from mid morning through Thursday afternoon.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...Winter Weather Advisory until 9 PM CST this evening for WIZ052.

LM...Small Craft Advisory until 3 PM CST Thursday for LMZ643>646.

&&

$$

Update...99
Today/Tonight and Aviation/Marine...99
Thursday THROUGH Tuesday...99


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