Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI

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FXUS63 KMKX 292039

Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
340 PM CDT MON AUG 29 2016

.TONIGHT AND TUESDAY - Forecast Confidence...Medium.

Scattered showers and thunderstorms continue to develop to the south
and west of the forecast area. Weak 500 mb differential cyclonic
vorticity advection, an inverted surface trough and some weak
850/700 mb moisture pooling helping to generate these showers and
storms. Mesoscale models suggest that the southwest counties may get
clipped by these showers and storms into the early evening hours.
Continued with the lower end POPs in this area.

Kept lower end POPs going for the rest of the night, as low level
moisture and resultant instability linger. However, mesoscale models
are not showing much activity for this period. There is not much
forcing for upward vertical motion, besides the weak 500 mb
differential cyclonic vorticity advection with the ridge axis. This
period could end up dry, but will need to watch trends from the
south and west before removing POPs later tonight.

Better chances for showers and storms comes Tuesday, as cold front
slides southeast toward the area. Area forecast soundings suggest
that the cap will mix out, with weak deep layer shear but modest
mean layer CAPE. Think that any convection should be more scattered
about along and ahead of the front, as the forcing for upward
vertical motion is not very strong. SPC removed the marginal risk of
severe storms for Tuesday, which seems reasonable given the lack of
deep layer shear. Could still see brief gusty winds and locally
heavy rainfall with any storms.

Patchy fog is expected later tonight into Tuesday morning, though
clouds should limit anything dense from developing. Warm and humid
conditions are expected tonight into Tuesday. Lows tonight should
remain in the upper 60s, with lower to mid 80s on Tuesday. Onshore
winds in the afternoon should bring slightly cooler temperatures
near Lake Michigan.

.TUESDAY NIGHT THROUGH THURSDAY - Forecast Confidence...Medium
trending to High.

Small chance for showers and thunderstorms will linger into Tuesday
night as low level baroclinic zone and frontogenetical forcing moves
across southeast Wisconsin.  Also, some enhanced forcing from right
entrance region of upper jet before it sags farther south and east.

Shift in upper level steering winds behind passing trof and front
will usher cooler and drier air across southern WI Tuesday night and
Wednesday.  925H temps fall to around 17C on Wednesday.  Sunshine
and cool north breezes should result in a comfortable, pleasant day.

A reinforcing push of cooler air spreads southward Wednesday night,
further dropping 925H temps to around 13C.  Breezes will be more
north to northeast off of Lake Michigan as the cooler air settles
in.  The cooler air and some low level moisture should result in a
period of sct to bkn CU on Thursday as the winds pick up some
additional moisture from Lake Michigan.  Delta-T increases to around
10 degrees on Thursday using an average lake surface temperature in
the mid 60s. However NAM and GFS soundings show only a shallow
moisture layer less than 1k feet in depth. Hence wl continue dry
wording near the lake on Thursday.


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

Southern Wisconsin will be in the midst of a quiet, cooler period
for the first portion of this extended period.  Large amplitude high
pressure over the Upper Midwest will begin to move slowly eastward
through the first part of the holiday weekend as upstream long wave
trof weakens and pushes northeast through southern Canada. Upper
level ridge axis moves east of WI Friday night allowing increasing
low level southerly winds to pull warmer, more humid air back into
the region for the weekend.  This surge and piece of short wave
energy moving northeast from the central Plains will return the
chance for showers and storms to the area late in the holiday
weekend into Labor Day.  At this time, Saturday looks to be the best
day of the holiday weekend with less humidity and little chance of
precipitation but the trend for Sunday is improving.

GFS 5-day 500h means transitions to upstream broadscale troffing
over northern plains and Northwest CONUS with heights falling to
near normal by 00Z/06.  Hence expect cooler weather to settle in the
week following Labor Day with more clouds and an occasional
precipitation threat.



Middle to high clouds from thunderstorms to the west should continue
to spread east across TAF sites into this evening. Scattered to
broken diurnal cumulus should dissipate by early evening. An
isolated shower or storm may affect Madison into early evening,
though not enough confidence to mention in TAFs at this time. Light
east to southeast winds are expected.

Small chances for showers/storms are forecast for the rest of
tonight, though chances are too low to mention in TAFs. A better
chance for showers and storms comes Tuesday into Tuesday evening,
with a cold front passing southeast through the area.

Will carry mainly VFR category ceilings and visibilities into
Tuesday, with a possible vicinity thunder mention Tuesday afternoon.
Any storms should be scattered in nature, with brief gusty winds,
locally heavy rainfall and MVFR/IFR visibilities possible.

Should see light fog later tonight into early Tuesday morning, with
light winds and a moist airmass lingering. Presence of middle to
high clouds should limit dense fog chances to low lying areas. Winds
will become southwest to west on Tuesday, remaining rather light.
Lake breeze may turn winds southeast at Milwaukee and Kenosha later
in the afternoon.



Recent MODIS imagery from Sunday continued to show the effect of
recent upwelling of cooler waters in the nearshore waters. MODIS
estimated lake surface temperatures mostly in the low to mid 60s,
while mid-lake temperatures were measured in the low to mid 70s.

Light wind regime will continue through tonight. Lingering warm,
humid air over cooler nearshore waters should continue to produce
patchy fog and haze until cold front passes through Tuesday night.

May see winds and waves reach Small Craft Advisory levels at times
later Wednesday into Wednesday night, as cooler and drier air pushes
southward into the region. North to northeast winds may gust to near
22 knots at times, with waves building to 3 to 4 feet.




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