Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 171817 AAB
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1217 PM CST Fri Nov 17 2017

.UPDATE...

Ran first draft of the forecast for tomorrow morning, and am
getting more of a mix than all snow in my precipitation types
across all but the southeast portions of the area. Will try to
adjust my temperature threshold for rain and snow warmer a degree
or two, to get more of a snow or rain/snow wording in the
forecast.

Wood

&&

.AVIATION(18Z TAFS)...

May see some rain showers move through the area early this
afternoon. Rain will then gradually spread eastward and/or
develop across the area during the middle to late afternoon hours.
Gusty south winds are expected to linger this afternoon into this
evening.

Rain is then expected into the middle to late evening hours in the
eastern counties, tapering off from west to east by or soon after
midnight. The gusty south winds should taper off as well by later
this evening.

The cold front will move east through the area later tonight,
exiting the southeast counties between 09Z and 12Z Saturday. Gusty
northwest winds are then expected to develop soon after the
frontal passage, lingering through Saturday and into Saturday
night.

A band of rain and snow, or perhaps all snow, will affect portions
of the area Saturday morning. The best shot should be centered
across a Fond du Lac, to Watertown, to Darlington line. Madison
would be on the fringe of this area, with the Milwaukee area and
points to the south mainly rain.

A quick 1/2 to 1 inch of slushy accumulation is possible where
the snow can linger. Road temperatures suggest that pavement areas
may remain wet, but a quick burst of snow could still bring the
above mentioned slushy accumulation. There remains a fair amount
of uncertainty on where the best chances for this will be located,
so stay tuned for later forecast updates.

Wood

&&

.PREV DISCUSSION... (Issued 1020 AM CST Fri Nov 17 2017)

UPDATE...

The going forecast generally looks on track at this time. May have
to push back the beginning times for the rain early this afternoon
several hours, as 12Z models are showing the dry air lingering a
bit longer. Mesoscale models are showing rain becoming more
widespread later this afternoon, especially in the eastern
portions of the area, as warm air and moisture advection increase
and help saturate the air column. There may be a rumble of
thunder or two in the southeastern counties as well later this
afternoon and early this evening.

There should then be a relative lull in the rain overnight, as the
cold front pushes through the area. An area of 850 mb to 700 mb
frontogenesis response then pushes into the southeastern half of
the forecast area Saturday morning. The forecast soundings are
showing potential for a period of snow to occur, as the saturated
air column gets mostly below freezing. The dendrite snow crystal
growth zone also gets tapped during this period.

Thus, there could be a quick 1/2 to 1 inch or so of slushy snow
accumulation Saturday morning, before it changes back to rain.
This may impact travelers and hunters during this period. Still
looking at 12Z models and may have to message this potential in
Weather Story and other outreach products this afternoon.

Wood

MARINE...

A Small Craft Advisory continues until later tonight across the
nearshore waters of Lake Michigan. A tight pressure gradient and
good low level mixing will allow for gusty south winds to occur
into this afternoon and early this evening. These winds will bring
high waves, especially north of North Point Lighthouse. The
pressure gradient should weaken later this evening and overnight,
as a cold front moves through the area. High waves will be slow to
subside during this period.

After the cold front passes through the area early Saturday
morning, winds will quickly shift to the northwest. A tight
pressure gradient and good low level mixing will allow for gale
force gusts to 35 knots at times Saturday into Saturday evening.
High waves are expected toward and over the open waters of Lake
Michigan. A Gale Warning is in effect for this period.

A Small Craft Advisory will be needed for later Saturday night
into Sunday, as the strong northwest winds and high waves toward
the open waters gradually weaken.

Wood

PREV DISCUSSION... (Issued 517 AM CST Fri Nov 17 2017)

UPDATE...

The forecast remains on track early this morning. No changes at
this time.

AVIATION(12Z TAFS)...

The MVFR CIGS across the area early this morning are still
expected to lift to VFR levels by about mid morning as drier air
surges north ahead of approaching trough. However, these improved
conditions will only last for about 4-6 hours as moisture will
surge back in from west to east. Look for CIGS to drop to MVFR
levels again between 18-22z across southern WI, with IFR
CIGS/VSBYS tonight into Saturday morning. The CIGS/VSBYS will be
lowering in response to rain spreading across the area this
afternoon and continuing through tonight.

Southerly winds will increase rapidly this morning with gusts by
mid morning pushing 24-28kts. The winds will diminish tonight as
a trough of low pressure moves overhead. Then strong northwest
winds kick in for Saturday.

PREV DISCUSSION... (Issued 253 AM CST Fri Nov 17 2017)

SHORT TERM...

Today...Forecast confidence is high.

We`ll see fairly rapid column saturation this afternoon due to
steady warm advection and isentropic lift ahead of the approaching
trough of low pressure. Much of the morning should stay dry across
southern Wisconsin, though we could see some showers push into
areas west of Madison after about 11 am. The rain will become
widespread by mid afternoon, continuing into the evening. The
consensus has the rain reaching Madison by noon-1 pm and Milwaukee
about 2-3 pm. There is some very minor, and very elevated CAPE in
the soundings, but doesn`t look sufficient to include thunder at
this time.

Tonight through Saturday...Forecast confidence is high:

Strengthening low pressure is expected to move through central or
northern IL tonight, heading northeast into Ontario Saturday.
Decent moisture surge with this low, as precipitable water values
will be around an inch this evening. The first round of rain will
continue during the evening hours, but it looks mostly dry then
overnight between areas of better forcing. Rain will then pick
back up Saturday morning across the forecast area, winding down
west to east during the afternoon.

Still looks like the rain could mix with or change over to snow
for a time late Sat morning into the afternoon before the precip
comes to an end. Not expecting any accumulations though, as the
window of opportunity for snow will be short lived and any snow
that does fall will likely melt quickly.

Gusty winds are expected on the back side of the low Saturday.

LONG TERM...

Sunday through Thursday...Forecast confidence is high:

High pressure will be in place for much of the time Sunday through
the middle of next week. Models do bring a wave through Monday
night into early Tuesday, but kept the dry forecast going due to
limited available moisture.

Temps are expected to be chilly Sunday behind the departing low,
but then will likely recover nicely on Monday with temps
approaching or hitting the 50 degree mark. Cooler temps will
return for mid-week behind the departing trough.

AVIATION(09Z TAFS)...

The MVFR CIGS across the area early this morning will lift to VFR
levels by about mid morning as drier air surges north ahead of
approaching trough. However, these improved conditions will only
last for about 4-6 hours as moisture will surge back in from west
to east. Look for CIGS to drop to MVFR levels again between 18-22z
across southern WI, with IFR CIGS/VSBYS tonight. The CIGS/VSBYS
will be lowering in response to rain spreading across the area
this afternoon and continuing through tonight.

Southerly winds will increase rapidly this morning with gusts by
mid morning pushing 24-28kts. The winds will diminish tonight as
a trough of low pressure moves overhead. Then strong northwest
winds kick in for Saturday.

MARINE...

A small craft advisory remains in effect today and tonight due to
strong southerly winds and rapidly building waves ahead of an
approaching trough of low pressure. Winds will veer to the
northwest by Saturday and increase rapidly. A gale warning has
been posted for mid morning on Saturday through Saturday evening.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...Small Craft Advisory until 4 AM CST Saturday for LMZ643>646.

     Gale Warning from 9 AM Saturday to midnight CST Saturday night
     for LMZ643>646.

&&

$$

Update...Wood
Today/Tonight and Aviation/Marine...Davis
Saturday THROUGH Thursday...DDV



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