Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 140141 AAB
AFDMKX

Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
841 PM CDT Sun Aug 13 2017

.UPDATE...

Quiet weather is expected into the overnight hours across the
area. The low level jet and warm air advection will remain to the
west of the area during this time, where the current shower and
thunderstorm activity is located. This activity will be rather
slow to push eastward, and should not start to move toward the
area until sometime Monday morning. Scattered to broken middle to
high clouds will remain over the area.

Some mesoscale models are showing some weakening showers and
storms moving into the western counties Monday morning, with lead
500 mb vorticity maximum. Better shot will be Monday afternoon
into the evening, as weak low level jet nose pivots across the
area, with main 500 mb shortwave trough passage and some warm air
advection. Upward vertical motion fields are modest, so would
expect scattered activity during this time.

Temperatures look to remain near seasonal normals into Monday
night. Dewpoints will increase into the lower to middle 60s by
later Monday afternoon into Monday night. This will bring somewhat
more humid conditions, and may bring some fog to the area Monday
night.

Wood

&&

.MARINE...

Light winds are expected overnight into Monday across the
nearshore waters of Lake Michigan, as high pressure moves east of
the region. A southeast lake breeze is expected by late morning or
early afternoon Monday. Wave heights will be low during this time.
Winds and waves should remain low into Tuesday.

South winds may increase for a time Wednesday into Wednesday
night, as low pressure moves through the region. Chances for
showers and thunderstorms exist Monday afternoon and night as
well. A better chance will be on Wednesday into Wednesday night.

Wood

&&

.PREV DISCUSSION... (Issued 648 PM CDT Sun Aug 13 2017)

UPDATE...

AVIATION(00Z TAFS)...

Isolated showers may affect southwestern portions of the area
into early this evening. Otherwise, expect light winds with
scattered to broken middle to high clouds lingering over the area
tonight into Monday. There may be some breaks at times, especially
on Monday toward the southeastern portions of the area.

Scattered diurnal cumulus clouds are anticipated by Monday
afternoon. A lake breeze with southeast winds will develop by
afternoon as well near Lake Michigan.

Chances for showers and thunderstorms will increase across south
central Wisconsin Monday, with the best chances toward the
Wisconsin Dells area. These chances should push across the rest of
the area Monday night. Fog may develop Monday night, with
visibilities down to alternate minimums possible later in the
night.

Wood

PREV DISCUSSION... (Issued 255 PM CDT SUN AUG 13 2017)

TONIGHT AND MONDAY - Forecast Confidence...Medium.

High clouds associated with a weak shortwave trough will continue to
stream across southern WI through the evening. Light showers in
eastern Iowa due to 850-700mb warm air and moisture advection will
likely remain to the south of the WI/IL border this afternoon and
evening due to dry air in the low levels.

A stationary upper trough over the Upper Great Lakes will sweep
another shortwave trough through southern WI on Monday. The first
round of forcing will encounter dry air in south central and
southeast WI, so chances for showers are fairly low during the late
morning and early afternoon hours.

By late afternoon there will be a little extra forcing from warm air
advection, right entrance region of upper jet streak, and nose of
low level jet to support some scattered showers and storms. Models
disagree about the amount of instability Monday afternoon/evening,
with some suggesting less than 500 j/kg of CAPE and others up to
1000. Limited deep moisture will limit our storm coverage and severe
potential. SPC just has us in an area of general thunder.

MONDAY NIGHT THROUGH WEDNESDAY - Forecast Confidence...Low to
Medium.

Will continue showers and t-storms chances Monday night tapering off
late in the night as mid-level short wave moves east of the area,
and weak 15 to 25 knot low level jet pivots off to the east. Despite
impressive bulk shear values around 40 kts, drier atmosphere will
limit instability to around 500 j or less Monday evening. Tuesday
could easily be dry due to short wave ridging as stronger mid level
wave moves into the upper midwest.  12Z NAM showing considerable
instability over southern WI on Tuesday while latest GFS much less
so with less low level moisture.  Also 12Z NAM appears to be outlier
with stronger low pressure moving through northern WI resulting in
faster eastward progress of sfc front through southern WI Wednesday
aftn.  Hence wl lean more on blend of GFS and ECMWF which are in
better agreement of stronger warm front located well south of WI not
pushing into the area until later Wednesday into Wed night. Moisture
not a problem by Wednesday as pwat values climb to over 1.5.  Will
need to watch for potential of heavy rainfall as forward propagation
expected to slow for a few hours Wednesday evening.

Will hang onto low pops on Thursday due to slower eastward
progression of surface trof from GFS and GEM solutions.  Most of
Thursday likely to be dry however.

EXTENDED PERIOD...

WEDNESDAY NIGHT THROUGH SUNDAY - Forecast Confidence...Low to Medium.

Large discrepancy continues with short wave trof passing through the
western Great Lakes early in the period.  ECMWF remains weaker and
more progressive with mid-level trof while GFS and GEM show higher
amplitude trof over southern Canada extending into the upper midwest
and western Great Lakes.  Following ECMWF solution would have best
threat of more widespread showers and storms Wednesday into
Wednesday evening, while other Medium range guidance favors more
Wednesday night.  WPC used a blend of the GFS and ECMWF so wl have
highest pops Wednesday afternoon (as mentioned above) into Wednesday
evening. Thursday could turn out to be dry as first short wave trof
moves off to the east, however dry conditions will be short-lived.

Medium range in better agreement on secondary short wave tracking
southeast from the northern plains in large scale troffing and will
move through the area later Friday and Friday night. Precipitable
water values will still be in the 1-1.5" range by the time of the
second event on Friday.  High pressure will move across the area
resulting in dry conditions at least for a portion of the weekend.

Digging long wave trof over the far western CONUS late in the
weekend may result in deeper moisture and warmer air located to the
south of the area moving slowly northward late next weekend into
early the following week.  End result will be clouds from
approaching warm front possibly impacting partial Eclipse viewing
across southern WI Monday afternoon.

AVIATION(21Z TAFS)...Few to Sct cumulus clouds developed beneath
thickening high clouds today. Southern WI will remain dry through
the night and probably Monday morning. Scattered showers and storms
will approach MSN from the west during the late morning, but they
will most likely hold off until the afternoon due to dry air over
the area.

A lake breeze is expected once again Monday. VFR conditions outside
of any thunderstorms.

MARINE...A lake breeze will develop again Monday afternoon.
Otherwise, look for light winds and low wave heights for much of the
week. However, there are chances for thunderstorms that could
produce gusty winds each day this week.

&&

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

$$

Update...Wood
Tonight/Monday and Aviation/Marine...Cronce
Monday Night through Sunday...MBK


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