Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 131119

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
519 AM CST Mon Nov 13 2017


Widespread dense fog and freezing fog continues across the
southern 3/4 or so of the forecast area, with the most widespread
and dense fog southwest of a line from Baraboo to Watertown to
Burlington. Even where fog isn`t that all widespread, patchy dense
fog is expected, with rapid changes in visibility.

Temperatures are of considerable concern with this fog event, with
readings in the 20s--low 20s in some cases--in many locations.
Temperatures like this, combined with dense fog, should be
supportive of significant frost formation on roadways and elevated
surfaces, especially bridges and overpasses. Between reduced
visibility and the potential for slick spots, caution should be
exercised when driving this morning.



Fog/freezing fog remains the main aviation hazard this morning.
KMSN has seen the most widespread fog this morning of the terminal
sites, and will likely stay in LIFR range for the next couple of
hours. For the other terminals, the most significant fog has
stayed just south and west of the sites, with just MVFR being
experienced so far. KENW and KUES may see some more significant
fog build in before sunrise, though confidence is low. For KMKE,
it appears for now that fog will stay just west. Again, however,
confidence is on the low side.

Fog should lift by mid morning today, with VFR conditions then
expected. Light west winds will become southerly tonight, with
some increase in speeds heading into Tuesday.


.PREV DISCUSSION... (Issued 326 AM CST Mon Nov 13 2017)


Early This Morning Through This Afternoon...Forecast Confidence
Is High.

Dense fog and freezing fog continue over a good portion of the
forecast area early this morning. Recently expanded the Advisory
north into Dodge and Washington Counties, and additional expansion
north and east isn`t out of the question through daybreak. Fog
has certainly been most dense and widespread across the southern
portion of the forecast area, but even along/north of I-94, some
patchy dense fog is likely occurring.

In addition to the obvious reduction in visibility, this fog is
occurring with temperatures in the mid to upper 20s in many areas,
which tends to be favorable for road frost/slick spots
developing. Bridges and overpasses will be most susceptible.

After the fog lifts, today should be a decent day, with highs a
degree or two on either side of 40 degrees. Some sun is expected
this morning, before high clouds begin to move in later this
afternoon, especially across the west.

Tonight Through Wednesday Night...Forecast Confidence Is Medium.

Models are showing warm air advection gradually developing
tonight, then becoming more robust on Tuesday. Models are not
handling the low stratus clouds to the south of the region well,
and does not move it into the far western counties until around
12Z Tuesday.

Given their current location and expected movement, they should
move northeastward into the western counties after midnight
tonight, spreading across the rest of the area Tuesday. Still may
be a little slow with bringing them into the area tonight in the
current forecast.

As low clouds spread into the area Tuesday, area forecast
soundings gradually saturate in the 800 mb and below layer. The
air column remains dry above it. The upward vertical motion
associated with the warm air advection is modest to weak Tuesday.
Some of the models are producing a broad 0.01 inches of QPF over
the area Tuesday, which can hint at drizzle.

Thus, it seems like there will be more of a drizzle potential
than rain for Tuesday. Temperatures should rise steadily Tuesday
morning, which should limit any freezing drizzle potential to the
far western portions of the area early in the morning.

Models try to saturate a deeper portion of the air column for
Tuesday night into Wednesday morning, as more focused warm air
advection and some low level frontogenesis with the passing cold
front move through the area. A 500 mb shortwave trough passes
through the area as well Wednesday morning. Continued the highest
PoPs for this period in the forecast. Temperatures look warm
enough for all rain during this period.

High pressure then slides southeast into the area later Wednesday
into Wednesday night. This should bring a period of dry
conditions. Cool temperatures should return Wednesday night,
resulting from earlier cold air advection.


Thursday Through Sunday...Forecast Confidence Is Medium.

After the high moves east of the region Thursday morning, low
pressure will approach the region from the southwest. The GFS and
ECMWF/Canadian models continue to differ with the timing of this
system through the region Friday into Saturday. The GFS continues
to be the quickest, taking the low northeast through southern
Wisconsin Friday. The ECMWF/Canadian models are slower, taking the
low northeast through southern Wisconsin Friday night, about 12
hours slower than the GFS.

All models are showing the low undergoing cyclogenesis as it
shifts northeast away from the area. This should bring a period of
strong west to northwest winds behind the passing low and cold
front, lingering into at least Saturday night. Upward vertical
motion should be rather robust with the warm air advection ahead
of the low, as well as the frontogenesis response with the passing
cold front.

Temperature profiles later Thursday night into Friday morning may
allow for some light snow or mixed precipitation to occur. There
is still uncertainty here with this, depending on how quickly the
models saturate the air column. The main area of rain should move
through later Friday morning into the evening. Left a small
thunder mention Friday afternoon in the southeast, closest to the
warm sector.

As the precipitation winds down Saturday, may see a changeover
back to light snow. This is also uncertain, as the air column may
be drying out by this time. Left consensus blended model PoPs for
now for Thursday night into Saturday night.



Light northwest to west winds today will become southerly tonight
into Tuesday. Expect southerly winds and waves to increase
through the day Tuesday into Tuesday night. A Small Craft
Advisory may eventually be needed later Tuesday into Wednesday.


WI...Dense Fog Advisory until 10 AM CST this morning for WIZ056>059-



Today and Aviation/Marine...Boxell
Tonight THROUGH Sunday...Wood is the U.S. government's official web portal to all federal, state and local government web resources and services.