Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 190441
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
1141 PM CDT Fri Aug 18 2017

.UPDATE...Needed to add fog to more of western CWA for the late
night as mid-clouds will affect mainly eastern half. Dewpoints
also staying a few degrees higher in the west and boundary layer
winds decreasing faster than originally expected. Fog likely to
become locally dense.

&&

.AVIATION(06Z TAFS)...Noted some lower cigs have developed over
central WI. A mix of low clouds and fog may spread into western
CWA overnight as boundary layer mixing decreasing faster than
expected and mid-clouds look to affect mainly eastern CWA. Held
off on low cigs with new TAF issuance but introduced some lower
vsbys in fog at KMSN.

&&

.PREV DISCUSSION... (Issued 926 PM CDT Fri Aug 18 2017)

UPDATE...Despite compact, sharp mid-level short wave passing
through, limited moisture and instability preventing any
significant shower activity. Hence removed mention for the rest of
the night. Beefed up fog in the Wisconsin River Valley overnight
but due to uncertainty regarding late night cloud cover and
boundary layer mixing, wl hold off from introducing fog elsewhere.
Think some patchy shallow fog likely in low areas however.

Think there is a better chance for fog Saturday night with
clear to partly cloudy skies and light low level winds.

MARINE...West to northwest winds 5 to 10 knots will persist
tonight as high pressure edges closer to Lake Michigan. As the
high pressure passes through the area on Saturday, light west
winds will turn onshore late in the morning and remain south to
southeast through the afternoon. Light winds will persist through
the rest of the weekend.

PREV DISCUSSION... (Issued 631 PM CDT Fri Aug 18 2017)

UPDATE...A few light showers have developed around KDLL moving
east in response to mid-level short wave trof moving through
central WI. Likely these light showers will carry eastwarn next
several hours across northern CWA, and a few more may develop
farther south. Instability negligible so not expecting any
thunder. Some question as to amount of clearing expected later
tonight, but upstream convection may spread some high cloudiness
back in. WI River valley likely to see some late night fog, but
boundary layer mixing should prevent thicker fog elsewhere.

AVIATION(00Z TAFS)...VFR conditions expected for the bulk of this
forecast period. Expect lake breeze to develop late Saturday
morning into the afternoon due to light winds and increasing
temperature gradient along the lakeshore. Possible some light fog
may briefly affect some taf sites late tonight. Better chance for
fog Saturday night into early Sunday.

PREV DISCUSSION... (Issued 217 PM CDT Fri Aug 18 2017)

SHORT TERM...

Tonight and Saturday...Forecast confidence is high:

A decent shortwave will move through this evening. Moisture looks
like it will be confined to a shallow layer centered around 10
kft though. Kept precip chances on the low end, as a few showers
or sprinkles are the best this wave will probably produce given
the limited moisture.

Should see clearing northwest to southeast later tonight into
Saturday morning as high pressure moves in. If clearing moves in
early enough, could see a little fog in the Wisconsin River
valley.

It will be a great start to the weekend Saturday, with mostly
sunny skies and near normal temps.

Saturday night and Sunday... Forecast confidence is High.

The upper level flow becomes zonal, as a lead speed max in the
jet north of the Dakotas pushes east, to just northwest of lake
Superior. Weak upper level divergence and 700 mb upward motion
occurs across southern Wisconsin. The 700 mb upward motion
increases Sunday afternoon. A 20 degree 850 celsius thermal ridge
pushes into southern Wisconsin Sunday afternoon with a 25 knot
southwest 850 mb wind.

Surface high pressure will move across the Great Lakes with some
weak warm air advection beginning Sunday. Zero to 1 km mixed
layer CAPE rises to 1000 Joules/kg southeast, and near 2000
Joules/kg south central. However there is a fairly strong cap just
below 850 mb. Only the GFS brings light rain into south central
Wisconsin. Prefer the dry ECMWF and NAM due to the cap.

LONG TERM...

Monday through Tuesday... Forecast confidence is Medium.

The zonal flow becomes more southwest Monday night and Tuesday
ahead of a shortwave across south central Canada.

The shortwave will push across Wisconsin Tuesday night.

A surface trough/warm front will be near southern Wisconsin later
Monday and Tuesday. The ECMWF is just a little slower in bringing
precipitation, holding off until Monday afternoon far southeast.
The GFS is faster with showers and thunderstorms through the day
Monday. Also The GFS/ECMWF and NAM all have a large MCS in
eastern Iowa Monday morning. Therefore clouds will likely affect
viewing the eclipse in southern WI on Monday. Stay tuned.

Conditions will remain favorable for showers and scattered storms
through Tuesday evening until a cold front drops south.

Wednesday through friday...Forecast confidence is High.

A large mid/upper level trough is expected over the eastern Great
Lakes Wednesday, that slowly reaches the northeast U.S. Thursday
night.

A brisk cool north wind is expected Wednesday, with high pressure
and cooler air Thursday. The high is expected to be over the
Great Lakes Friday.

AVIATION(18Z TAFS)...

Lingering MVFR locations are expected to improve to VFR by mid to
late afternoon.

A shortwave may bring a shower or a few sprinkles to the area late
afternoon into the evening. VFR ceilings are expected with this
system.

Could see a little fog in the Wisconsin River valley later
tonight into Sat morning under light winds and clearing skies.
High pressure should then bring mostly sunny skies to the area
Saturday.

MARINE...

Quiet weather is expected this weekend under high pressure.

&&

.MKX WATCHES/WARNINGS/ADVISORIES...
WI...None.
LM...None.
&&

$$

Update...99
Tonight/Saturday and Aviation/Marine...99
Saturday Night through Friday...99



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