Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 221502 AAA
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1002 AM CDT FRI JUL 22 2016

.UPDATE...

Could see a few storms pop this afternoon along the
moisture/instability gradient in the southwest forecast area. Will
keep some low pops there for now, though most guidance is showing
dry weather across the forecast area through the afternoon hours.

Quite a bit of clouds across the southwest half of the forecast
area, though should see coverage go more scattered as daytime
mixing increases. Given temps aloft and increasing sunshine,
should see high temps similar to what`s in the forecast. Dewpoints
are expected to continue to come up a bit into the afternoon, so
heat headlines still look good.

&&

.AVIATION/18Z TAFS/...

Some MVFR ceilings are lingering in the southwest this morning,
but should mix to VFR by late morning or early afternoon. VFR
conditions are then expected into the evening, with some patchy
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...

Light offshore winds will become onshore late this morning and early
afternoon.  Wind speeds are expected to remain mostly at or below 10
knots.  Yesterday`s thunderstorms and strong winds resulted in
upwelling of cooler waters in the near shore waters.  Atwater Buoy
measuring lake surface temps in the 50s this morning.  These patchy
cooler waters and lingering high dew points should result in patchy
fog developing through tonight, possibly lingering into Saturday.
Next chance form more widespread thunderstorms is Saturday night
into Sunday.

&&

.PREV DISCUSSION... /Issued 418 AM CDT FRI JUL 22 2016/

SHORT TERM...Weak high pressure over nrn WI will move into srn WI
later today and tonight. Beforehand, a weak frontal boundary between
the high and the mesohigh over north central IL will pass south
through srn WI later this morning. The front with weak sfc
convergence will stall from ern IA into nrn IL for the afternoon and
evening. More thunderstorm development is possible along it but it
should mainly stay south. Only went with slight chance PoPs in the
far sw CWA for late afternoon and early evening.

The large MCS from last night has lowered the dewpoints into the
middle to upper 60s. Evaporation should boost the dewpoints by
several degrees but not to as high as yesterday. High temps in the
lower 90s and dewpoints in the lower to middle 70s over the srn half
of the CWA is yielding heat index values of 95-100F over the heat
advisory area and 100-105F in the excessive heat warning area. Will
maintain the headlines as is for today.

LONG TERM...

SATURDAY AND SATURDAY NIGHT... Forecast confidence is medium.

Warm air advection (WAA), the nose of a low level jet (LLJ) and weak
shortwave activity will bring a chance for showers and thunderstorms
to southern WI Saturday afternoon. There should be high CAPE, but
low shear, so most of the MKX forecast area is still in a marginal
risk for severe on Day 2. However, SPC nosed the slight risk a
little farther southeast now.

Saturday is looking like another warm day. 925mb temps should reach
26c over the area, yielding max temps around 90. If thunderstorms
hold off until later in the afternoon, then heat indices will be
able to get into the mid to upper 90s.

A thunderstorm complex is expected to develop over northern MN
(NAM/ECMWF solution) or southern MN (GFS solution) on the nose of
the LLJ Sat afternoon/evening. This complex should slide across
central and south or southeast WI Sat night. Of course, there is
plenty of uncertainty about its development and track, but went with
likely PoPs for our area.

SUNDAY... Forecast confidence is medium.

We are not sure how Sunday is going to play out quite yet. If we get
the Sat night convection, it will take a while for temperatures to
recover after clouds clear, and dewpoints might not recover either.
I went with the conservative blend of models with highs in the upper
80s to around 90 and max heat indices similar to Saturday, in the
mid to upper 90s.

More thunderstorms will be possible Sunday morning (depending on
what Sat night convection does) within an area of warm air
advection, just ahead of a shortwave trough and associated cold
front. The surface cold front will slide across southern WI late Sun
afternoon. Strong instability ahead of this front and decent shear
will give us a chance for severe storms on Sunday, but it is still
uncertain what the trigger will be (models are not in great
agreement). SPC includes eastern WI in their Day 3 marginal risk
area.

MONDAY THROUGH TUESDAY... Forecast confidence is high.

It looks like a cooler and quieter weather pattern is in store for
southern WI for the first part of next week with high pressure over
the Great Lakes. High temperatures are expected in the mid 80s with
dewpoints in the lower 60s.

Wednesday through Friday... Forecast confidence is medium.

Both the GFS and ECMWF are showing a potent shortwave tracking
through the Upper Great Lakes for the middle of the week which will
bring our next chance for storms. The problem is that each model
brings this shortwave through the area at different times. It looks
like weak shortwaves will also interact with diurnal heating in
slightly cyclonic flow to keep small chances for showers and
thunderstorms across southern WI for this whole period.  The weekend
is also looking like there will be active weather.

AVIATION/12Z TAFS/...The thick cirrus field is thinning which may
allow enough cooling for patchy fog and low stratus this morning.
Otherwise few-sct cumulus today and dry. Areas of fog will develop
late tnt within the humid airmass. Vsbys will generally range from 1-
3sm BR. The TAF sites are expected to see the fog late tnt with the
exception of MKE.

MARINE...Areas of fog may develop over the nearshore waters of Lake
MI as a very moist airmass will reside over the relatively cooler
waters of Lake MI. This will remain possible from today through Sat
nt. Otherwise light winds and low wave heights will prevail today
through Sat nt.

&&

.MKX Watches/Warnings/Advisories...
WI...EXCESSIVE HEAT WARNING until 7 PM CDT this evening for WIZ062-
     067-068.

     HEAT ADVISORY until 7 PM CDT this evening for WIZ056-063>066-
     069>072.

LM...None.
&&

$$

UPDATE...DDV/MBK
TODAY/TONIGHT AND AVIATION/MARINE...Gehring
Saturday THROUGH Thursday...MRC


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