Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 170206
Area Forecast Discussion
National Weather Service Milwaukee/Sullivan WI
906 PM CDT TUE AUG 16 2016
.UPDATE...Isolated showers and storms continue to pop up and
weaken through the late afternoon and early evening over southern
WI. Updrafts and mid-level lapse rates have been weak, however
the area around Marshall in northeast Dane County has received
several periods of showers and perhaps as much as three quarters
inch of rain this evening.
Upstream mid-level short wave vicinity of WI/MN border
will continue to track east-southeast overnight as 850-700mb
moisture flux convergence continues to increase ahead of this
feature. Elevated Cape remains in the 600-1100 j/kg range as this
forcing slides souhteast. Will continue chance or scattered
wording across the eastern CWA and bump up to to a period of
likely and numerous overnight in parts of the north and west where
better elevated instability will be located.
.AVIATION/06Z TAFS/...VFR conditions expected through Wednesday
evening at TAF sites. There is a chance of thunderstorms through
early Wednesday morning. MVFR conditions are possible with any
thunderstorms. Light fog is possible in low lying areas early
Wednesday morning but should not impact TAF sites. Expect a lake
breeze Wednesday afternoon with scattered 4K ceilings.
Thunderstorm chances return late Wednesday afternoon.
.MARINE...Still a decent chance for showers and storms affecting
the near shore waters overnight, mainly after midnight and north
of North Point Light. Light southwest winds should turn south to
southeast in light flow later Wednesday morning and afternoon so
adjusted NSH forecast.
.PREV DISCUSSION... /Issued 327 PM CDT TUE AUG 16 2016/
TONIGHT AND WEDNESDAY......Forecast Confidence Is Medium.
Isolated showers have weakened across far northern portions of the
area early this afternoon, as weak 500 mb differential cyclonic
vorticity advection pushed through that area. There is another weak
500 mb vorticity maximum that should cross southern portions of the
area later this afternoon into early this evening.
In addition, there is a weak low level jet nose at 850 mb that
points into the area this evening, providing weak upward vertical
motion. The main 500 mb vorticity maximum shifts eastward through
the area later tonight into Wednesday morning.
Area forecast soundings do show modest mean layer CAPE into early
this evening, becoming more elevated tonight into early Wednesday
morning. Mean layer CAPE then increases again by Wednesday
afternoon. Deep layer shear is weak to modest into early evening,
becoming weaker later tonight into Wednesday.
Some uncertainty with areal coverage into this evening, with the
weak upward vertical motion. Think anything severe will remain west
of the area into tonight. There is a little more certainty with POPs
for later tonight into Wednesday morning, with the main 500 mb
differential cyclonic vorticity advection.
All in all, will leave the POPs spreading west to east into this
evening, with slightly higher POPs for later tonight into Wednesday
morning. Mild temperatures will continue tonight and Wednesday, with
925 mb temperatures suggesting upper 60s for lows tonight, and mid
80s for highs Wednesday.
Wednesday night through Friday night...Forecast confidence medium.
A weak swly flow will develop Wed nt and increase Thu-Fri ahead
of a cold front progressing ewd across the N Great Plains. A weak
shortwave trough will pass Wed nt so maintained slight chance PoPs
during that time. The swly flow will then lead to very warm and
humid days for Thu-Fri with 850 mb temps around 20C and sfc high
temps approaching 90F. Tstorm chances will increase mainly Fri nt
as the cold front approaches from MN.
LONG TERM...Saturday through Tuesday...Forecast confidence
The cold frontal passage will likely occur on Sat and may linger
into Sat nt. Confidence is high enough for likely PoPs on Sat with
showers and tstorm possibly lingering into Sat nt. The upper
trough that will drop swd from Canada will not pass until
Sun-Sun nt so small chances of showers for Sun along with
relatively cool temps. High pressure and pleasant temps and
humidity then forecast for Mon-Tue.
VFR category ceilings and visibilities are expected tonight and
Wednesday across TAF sites. There may be scattered thunderstorms
beginning early this evening at Madison, and across the rest of the
area later tonight into Wednesday. This is due to various troughs of
low pressure move through.
May keep vicinity thunder in TAFs for later tonight into Wednesday
morning, when the best chances will occur. Uncertainty with timing
and areal coverage remains. MVFR visibilities are possible in any
showers or storms, along with brief gusty winds.
Light fog is possible in low lying areas, but should not impact TAF
sites. Lake breeze with southeast winds at Milwaukee and Kenosha
should linger into early evening. Otherwise, light west to southwest
winds are expected tonight into Wednesday. Southeast lake breeze
Wednesday is not as certain at this time.
Light east to southeast winds will linger into early this evening
are expected with lake breeze development over Lake Michigan. Waves
will remain low. Light west to southwest winds and low waves tonight
into early Wednesday are expected. Another southeast lake breeze
Wednesday afternoon is less certain at this time. South to southwest
winds should increase a bit Thursday into Friday, with waves
TONIGHT/Wednesday AND AVIATION/MARINE...Wood
Wednesday NIGHT THROUGH Tuesday...Gehring