Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 230235
AFDMKX

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
935 PM CDT FRI JUL 22 2016

.UPDATE...

Have removed the slight chance PoPs for tonight as strong capping
in the 850-800mb layer on AMDAR soundings has prevented much from
getting going. Convection along weak convergence/warm front in
northeast Iowa earlier struggled to survive, with an isolated cell
or two currently near DVN showing the same tendencies. Hi-
res/rapid update models showing a lack of showers/storms
developing in the CWA until forcing ahead of short wave trough,
currently over sw South Dakota/panhandle of Nebraska, approaches
for mainly the late afternoon and evening into tomorrow night.

Still looking for areas of fog to develop overnight in the humid
airmass over the forecast area. Signals are for 1 to 2 mile fog
with some patchy dense in the river valleys and low-lying rural
locations.

&&

.AVIATION/06Z TAFS/...

Light winds and a humid airmass means areas of MVFR/IFR fog around
or shortly after midnight. 1 to 2 mile vsbys at worst though some
patchy dense fog with vsbys down to 1/4 mile in low-lying rural
areas and river valleys. Will keep TAF sites no lower than 2 miles
for now even at eastern locations where a light land breeze will
keep the cooling affects of Lake Michigan away from land areas.

Should be dry until late afternoon/evening Saturday when
chances for thunderstorms with MVFR cigs/vsbys increase from west
to east with a warm front passage ahead of low pressure crossing
the northern Plains. Storm chances continue overnight with a
complex moving across the forecast area between 06Z and 12Z
Sunday ahead of a trailing cold front as the low tracks north of
Lake Superior.

&&

.MARINE...

Issued a marine dense fog advisory from Port Washington north to
Sheboygan until 15Z Saturday. Web cams indicated fog with vsbys of
1 nm or less at the Sheboygan shore with a fog bank visible
offshore of the Port washington web cams. This is in line with
remaining cool pocket of 60 degree lake water after upwelling with
strong offshore winds with Thursday convective lines. Will monitor
for a southward expansion with overnight cooling but signals are
for visibilities to remain around 2 miles elsewhere overnight.

&&

.PREV DISCUSSION... /Issued 310 PM CDT FRI JUL 22 2016/

TONIGHT AND SATURDAY - Forecast Confidence...Medium.

Will convert the Excessive Heat Warning to a Heat Advisory into
early evening given how the clouds have held back the heat indices.
Will leave ongoing Heat Advisory as is.

Could see a storm or two in the southwest forecast area late this
afternoon into the evening within moisture/instability gradient.
Pretty quiet on the radar for now though. Looks dry then overnight,
with precip chances increasing from west to east on Saturday as
deeper moisture begins to advect eastward and a shortwave
approaches. Just stuck with chance pops through Sat afternoon for
now, due to uncertainty among models in timing of the wave and
resultant storm placement. There are solutions that would bring
storms into at least the west by late afternoon.

Should stay pretty mild tonight. Could see some fog overnight into
early Saturday morning due to light winds, recent rainfall, and high
low level moisture. MOS and soundings support the fog potential,
though will depend on extent of cloud cover.

Highs on Saturday will be up near 90 most places. The exceptions to
this will likely be in the east due to onshore winds and maybe in
the southwest due to higher possible cloud cover or earlier arrival
of showers/storms. Will be another hot and humid one, with heat
indices in the 95-99 range most places, except for near Lake
Michigan.

SATURDAY NIGHT THROUGH MONDAY - Forecast Confidence...Medium.

The very warm temperatures will continue into Sunday until drier and
slightly cooler air invades southern WI behind passing cold front.
At this time, enough clearing is expected to help temperatures climb
back into the upper 80s to lower 90s on Sunday.  The combination of
hot temperatures and lingering dewpoints in the lower 70s is
expected to push the Heat Index back into the 95 to 100 degree range
for the fourth day in a row across much of southern WI. There is
some uncertainty regarding amount of lingering cloud cover and
timing of frontal passage.  If confidence increases on hot and humid
conditions continuing Sat and Sun, then next forecast shift may be
issuing a Heat Advisory for four consecutive days of Heat Indicies
reaching the mid 90s to around 100.

Will continue likely wording for thunderstorms Saturday night as
tilting low level jet ushers strong surge of moisture advection
across WI.  Better upper level synoptic lift and nose of llj favors
areas to the north, but thinking convection likely to carry along
instability gradient toward the southeast into srn WI overnight.
Corfidi Vectors favor southeast movement and do drop off during the
night.  In addition, heights at both 500 and 700 levels drop
slightly overnight on short term guidance indicating weak mid-level
trof passage.  After 12z Sunday, GFS and NAM coming into better
agreement on carry surface cold front across southern WI during the
morning and early aftn.  Atmosphere may have enough time to recover
but veering low level winds and drier air arrival should limit
redevelopment.  Hence wl only carry low chance pops on Sunday. More
comfortable and dry conditions will settle in Sunday night and carry
through Monday.

EXTENDED PERIOD...

MONDAY NIGHT THROUGH FRIDAY - Forecast Confidence...Medium.

Drier more zonal flow looks to continue for at least the first part
of the extended period.  Temperatures and humidity levels will be
more seasonal.  Medium range guidance in fair agreement on zonal
flow carrying short wave trof across the upper midwest around
Wednesday or Thursday.  Short wave also amplifies slightly as it
moves across the region. Enough atmospheric moisture will be
available to continue small pops for thunder as weak surface
boundary moves through the area.

AVIATION/00Z TAFS/...A few MVFR ceilings are lingering in the west
this afternoon, but most places have mixed to VFR. VFR conditions
are then expected into the evening, with some patchy/areas fog then
possible overnight.

May see a few storms at times in the west or southwest forecast area
this afternoon through Saturday. Better chance for storms across
southern Wisconsin looks to be Sat evening and overnight.

MARINE...

Could see some fog at times through Saturday due to higher moisture
lingering over cooler Lake Michigan waters. Webcams and satellite
currently not showing fog...but certainly something to keep an eye
on.

Will likely see storms return by Saturday evening or night, with a
chance lingering into at least Sunday morning.

MKX WATCHES/WARNINGS/ADVISORIES...

WI...HEAT ADVISORY until 7 PM CDT this evening for WIZ056-062>072.
LM...None.

$$
TONIGHT AND SATURDAY/AVIATION/MARINE...DDV

&&

.MKX Watches/Warnings/Advisories...
WI...None.
LM...DENSE FOG ADVISORY until 10 AM CDT Saturday for LMZ643.

&&

$$

UPDATE...REM
TONIGHT/Saturday AND AVIATION/MARINE...DDV
Saturday NIGHT THROUGH Friday...MBK


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