Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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000
FXUS63 KMKX 280227
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
927 PM CDT SAT AUG 27 2016

.UPDATE...

Adjusted PoPs and weather to reflect southeast shift of showers
and thunderstorms in region of low level moisture convergence that
hi-res/rapid update models show will stay to the south and east
of the forecast area.

Starting to see fog develop in the western CWA as clouds clear to
the north and east, and given light winds and moist boundary
layer, should see fog expand overnight with widespread
visibilities falling to between 1 and 2 miles and some locally
dense fog especially in the river valleys. Widespread dense fog not
expected at this time as model guidance suggest low stratus to the
north will drop back down over the CWA limiting radiational
cooling, but will bear watching.

&&

.AVIATION/06Z TAFS/...

Watching development of fog over the forecast area begin with
widespread 1 to 2 mile vsbys expected after 05Z with locally
dense fog and 1/4 mile vsbys especially in the river valleys.
IFR stratus ceiling hanging just to the north and guidance is
split as to how far south it will drop overnight. Will await all
of 00Z guidance but plan is to keep the current IFR conditions
starting between 05Z and 09Z due to vsbys and/or cigs until mid-
morning Sunday and then improve to VFR with morning mix-out. Winds
will be light through the period with low-level moisture bringing
another good chance for fog Sunday night into Monday morning.

&&

.MARINE...

Band of showers with an isolated thunderstorm or two has pushed
east of mid-lake and little chance of further development the rest
of tonight and Sunday. Will see areas of fog as rich low-level
moisture moves over the cooler waters of the lake, with a few
pockets of dense fog possible depending on amount of clearing over
the lake.

&&

.PREV DISCUSSION... /Issued 340 PM CDT SAT AUG 27 2016/

TONIGHT AND SUNDAY - Forecast Confidence...Low.

Weak surface low and warm front continue to push northeast into
southern Wisconsin. These features are expected to slide
northeastward across the area into this evening. There has been some
mixing out of the low stratus clouds in mainly the southeast half of
the forecast area so far this afternoon. This should allow for some
mean layer CAPES of 5000 to 1000 J/kg to work into far southern and
southeastern portions of the area. 0-6 km bulk shear is still fairly
robust, in the 30 to 40 knot range.

Some concern here for a strong storm to occur, if there is enough
upward vertical motion in this rather weak forcing environment. For
now, will mention scattered showers with isolated thunder into this
evening, mainly in the eastern 2/3 of the forecast area.

Next issues are low clouds and fog trends for tonight into Sunday
morning. Weak high pressure will slide east across the area later
tonight into Sunday. Dew points remaining in the 60s with decoupling
winds tonight should result in at least areas of fog.

The question is if the low clouds will completely mix out across the
rest of the area by this evening. If so, then dense fog with
possible low stratus may occur later tonight into Sunday morning. If
the clouds hang around in the northwest half of the area, there
would be less in the way of fog. Uncertainty here with these
scenarios. At this time, the southeast half would be more at risk
for dense fog and low stratus development. Kept areas of fog for
later tonight into early Sunday morning.

Any low stratus should mix out by late morning, which should give
scattered to broken cumulus, and a warm and humid day. Light winds
will become easterly during the afternoon near Lake Michigan. Went
with lower 80s inland, and mid to upper 70s lakeside for highs
Sunday.

SUNDAY NIGHT THROUGH TUESDAY - Forecast Confidence...Medium.

Quiet weather should persist through Sunday night as increasing
short wave ridging affects the area.  Will continue small pops on
Monday as short term guidance not showing much agreement in
placement and strength of convectively enhanced mid-level short wave
progressing eastward across northern Wisconsin.  In fact, the ECMWF
is well north with the short wave over northern MN.  High
precipitable water air not really going anywhere next several days
and should stick around through Tuesday before column drying. With
dewpoints in the mid to upper 60s on Monday, sfc based Cape to
exceed 1000 j/kg.

A mix of low clouds and late night fog is expected Sunday night due
to light boundary layer winds and lingering low level moisture.

Little better synoptic setup for Tuesday as second weaker short wave
teams up with passing cold front.  0-6km shear not overly impressive
but afternoon Cape values may get close to 3000 j/kg as humid air
mass lingers.

Influx of drier, less humid air and subsidence will end
precipitation threat Tuesday night.

EXTENDED PERIOD...

TUESDAY NIGHT THROUGH SATURDAY - Forecast Confidence...Medium
to High.

Much of this period is looking quiet with temperatures near or
slightly below seasonal normal for the start of September. The
coolest days are expected to be Wednesday and Thursday.  Medium
range guidance remains in reasonable agreement on more amplified
upper air pattern developing around Tuesday across the CONUS and
continue through the remainder of the work week.  Long wave troffing
expanding across the eastern Pacific and western CONUS will cause
large ridge to expand downstream across the central US by mid-week.
Eventually, upstream trof will weaken later in the week and cause
ridging to collapse resulting in increasing southwest mid-level
steering winds spreading into the western GTLakes.  Expect dry and
pleasant conditions for most of this period.  Increasing column
moisture and passing weak wave will result in an increasing chance
for showers and storms Fri night through Sat night.

AVIATION/00Z TAFS/...

Low stratus finally mixing out, with ceilings rising to MVFR/VFR
category across eastern TAF sites. This should continue into the
evening. Madison may take a little longer to mix out, but upstream
conditions suggest that they will as well before sunset.

Weak low and warm front, moving northeast through the area into
early this evening, should bring scattered showers with a few
thunderstorms. Kept vicinity thunder mention in TAFs until around
03Z Sunday, in case any storms develop. A strong storm with gusty
winds is possible.

East winds will continue to veer to the south/southwest by early
this evening, with the warm front moving through the area.

High pressure moving east across the area later tonight into Sunday
should bring a period of quiet weather. Should see MVFR/IFR category
fog at TAF sites tonight into Sunday morning, mainly between 06Z and
13Z Sunday, with light winds and moist airmass lingering. May see
dense fog develop with LIFR stratus as well, depending on if low
clouds remain mixed out into the evening. Uncertainty exists here
with the fog and low cloud trends.

Easterly winds are expected Sunday afternoon at Milwaukee and
Kenosha, with southeast to south winds inland. Scattered diurnal
cumulus clouds are possible as well by Sunday afternoon.

MARINE...

Expect patchy fog to develop across the lake this evening, with
areas of fog later tonight into Sunday morning. This is a result of
light winds and a moist airmass over the region, especially in areas
where cool waters exist from upwelling from a few days ago. Dense
fog is possible later tonight, depending on if low clouds mix out
into this evening. Uncertainty exists here with the fog and cloud
trends.

Winds and waves will remain light into early next week. Another
round of fog may occur Sunday night into Monday morning, with a
similar light wind/moist airmass setup.

MKX WATCHES/WARNINGS/ADVISORIES...

WI...None.
LM...None.

$$
TONIGHT AND SUNDAY/AVIATION/MARINE...Wood

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...None.
&&

$$

UPDATE...REM
TONIGHT/Sunday AND AVIATION/MARINE...Wood
Sunday NIGHT THROUGH Saturday...MBK


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