Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 170334
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
934 PM CST Thu Nov 16 2017

.UPDATE...

Stratus continues to spread NW and has overspread all but a few
counties in central WI. It will continue to envelop the rest of
the area overnight. No other changes made to the fcst.

&&

.MARINE...

Winds will increase significantly out of the south Friday morning
with waves building through the afternoon. Winds will begin to
diminish Friday evening but waves are expected to last into the
night. Waves will be slowest to diminish near the Sheboygan area.
A small craft advisory is in effect.

Winds will become northwesterly and increase behind a cold front
Saturday morning with gale force gusts possible by noon. Winds
are forecast to remain elevated into Sunday. A headline will be
needed for this period. Not confident yet that gale criteria will
be met.

&&

.PREV DISCUSSION... (Issued 550 PM CST Thu Nov 16 2017)

UPDATE...

Not much change. The low clouds across southern and eastern
portions of the FA that were in the process of dissipating this
aftn have stopped that trend with the loss of insolation and
mixing. There is a large expanse of stratus across N IL, Lake MI,
N IN and ;lower MI. Expect these clouds to slowly spread NW this
evng due to low level E/SE flow. Uncertain as to how far/fast they
will move though. Otherwise, expect temps to hold in the low/mid
30s this evng with increasing mid/high clouds from the NW.

AVIATION(00Z TAFS)...

Main fcst challenge this evng will be stratus trends. Existing
low clouds that failed to dissipate this aftn across S/E WI will
slowly work to the NW overnight due to E/SE low level flow. And
there is currently an impressive existing stratus deck to our SE
poised to move into the area. Beyond that, a strong storm system
will move through the region Fri and Sat producing IFR conditions
and gusty winds. CIGs should lower through the day on Fri with
drizzle dvlpng late mrng into the aftn with rain moving in later
in the aftn. CIGs will eventually fall to IFR by evng. VSBYs will
at least be MVFR by Fri evng as well...and possibly lower.

PREV DISCUSSION... (Issued 331 PM CST Thu Nov 16 2017)

SHORT TERM...

Tonight and Friday... Forecast confidence is medium.

Skies cleared out nicely across southern WI this afternoon as
drier air mixed into the low levels. Light winds are turning
around to the east. Mid and high clouds are slowly spreading into
WI this afternoon. These are due to an approaching upper jet and
mid level vorticity advection.

South winds will increase quickly Friday morning as the pressure
gradient strengthens over southern WI, a shortwave trough
approaches, and the low level jet slides overhead. Isentropic lift
will bring increasing clouds to the low levels through the
morning. There should be some drizzle developing by late morning.
Strong theta-e advection spreads into southern WI early Fri
afternoon. This and increasing precipitable water values of around
an inch and deeper forcing will bring periods of rain to the area
Fri afternoon. There is still a little uncertainty about timing of
that deeper moisture, so I kept the pops in the likely category
rather than "definite" for now.

Friday night and Saturday... Forecast confidence is medium.

Rain is expected across southern WI Friday evening. There could be
a break in the widespread rain after midnight as that initial
round of warm air advection within the inverted trough shifts
east.

The surface low will slide from northeast IL to northern IN/OH
Saturday morning in response to the left exit region of the upper
jet shifting east. The 500mb trough will be a little slower to
cross southern WI, so another surge of lift is expected to spread
into southern WI Saturday morning. Although surface temperatures
should remain above freezing, dynamic cooling aloft may allow for
rain to change over to snow for a period of time Sat morning. The
NAM is showing the coldest solution at this time, but the GFS and
ECMWF are hinting at the possibility. For now, trended colder and
mentioned rain and snow in forecast.

The precip will taper off across southeast WI through Sat
afternoon. Winds will be gusty out of the northwest. Dry and cold
expected Saturday night.

LONG TERM...

Sunday through Wednesday... Forecast confidence is medium.

Quiet and cool weather is expected Sunday. Temperatures will
modify Monday and through the middle of next week with southerly
flow. An upper low and associated surface cold front will swing
through the southern Ontario and Lake Superior area on Tuesday,
but southern WI should remain dry with this system. We will just
have some increased winds. The next chance for precip will hold
off until Thu.

AVIATION(21Z TAFS)...

The low clouds with bases in the 2000-3000 ft range cleared across
all but far southern and eastern WI this afternoon. Mid level
clouds will spread into southern WI this evening. Lake clouds
should remain over the lakeshore counties as winds turn around to
the east through the late evening hours. Uncertain about when
these clouds will scour out, but it could be late tonight.

Look for MVFR ceilings and drizzle to develop Friday morning, then
evolve into steadier rain for the afternoon/evening hours. There
is a chance for snow on Saturday in southern WI (except the
lakeshore counties), but there is still uncertainty.

MARINE...

Look for winds to increase rapidly out of the south-southwest
Friday morning, with waves building through the evening. Winds
will diminish Friday evening, but waves will persist through late
Friday night. A small craft advisory is in effect.

Winds will switch to the northwest behind a cold front Saturday
morning. Gale force gusts are possible. A headline will be needed
for this time period, but there is still uncertainty about
reaching gale criteria.

&&

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

&&

$$

Update...BM
Tonight/Friday and Aviation/Marine...BM
Friday Night through Thursday...Cronce



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