Area Forecast Discussion
Issued by NWS Milwaukee/Sullivan, WI
FXUS63 KMKX 171558 AAA
Area Forecast Discussion...UPDATED
National Weather Service Milwaukee/Sullivan WI
1058 AM CDT WED AUG 17 2016
500 mb shortwave trough is currently shifting eastward through the
area, with associated showers to the east. Should see scattered to
broken diurnal cumulus develop by early afternoon with daytime
Highs in the mid 80s look on track, with humid conditions with
dew points in the mid to upper 60s. A lake breeze may develop
along the lakeshore this afternoon. but there is some uncertainty
here with how far the lake breeze will push inland. This would
cool down these areas somewhat.
Lots of uncertainty with if and how much in the way of showers
and thunderstorms will develop this afternoon and evening. There
is not much in the way of forcing for upward vertical motion
during this period. Outflow boundary from early morning convection
may lay out across the far southern portions of the area, or may
sink into northern Illinois.
Adjusted area forecast soundings suggest that the airmass will be
uncapped, so a subtle surface confluent boundary may be enough to
generate a few showers and storms this afternoon into early
evening. Mesoscale models seem to favor northern Illinois with
areal coverage of showers/storms, but some do bring this activity
into southern Wisconsin. 00Z synoptic models also bring light QPF
across southern Wisconsin.
Not expecting anything severe, with mean layer CAPE modest at
best, and deep layer shear weak. For now, will leave chance POPs
going in the south this afternoon and this evening, with lower
POPs in the north.
Mainly VFR conditions are expected across TAF sites this
afternoon, tonight and Thursday. Scattered showers and storms are
possible this afternoon and early evening, but there is a lot of
uncertainty with areal coverage. May continue with vicinity
thunder in TAFs for this period. Could see brief MVFR/IFR
visibilities and gusty winds with any storms.
Otherwise, scattered to broken diurnal cumulus clouds are expected
this afternoon. Light west to northwest winds this afternoon
should remain, with winds possibly shifting southeast at Milwaukee
and Kenosha later this afternoon with a lake breeze. Not sure if
the lake breeze will reach these locations or remain east of
Light southwest winds tonight should remain on Thursday, with
southeast winds developing at Milwaukee and Kenosha with lake
breeze Thursday afternoon. After some clearing later tonight,
more scattered to broken diurnal cumulus is expected by Thursday
Southeast lake breeze may develop this afternoon, and should
develop Thursday afternoon, over the nearshore waters of Lake
Michigan. Light southwest to south winds are expected tonight.
South winds will increase somewhat Friday into Saturday, before
cold front moves southeast through the area Saturday night. Winds
should veer northwest and become gusty on Sunday. Low waves are
expected into Saturday night, building to 2 to 3 feet Sunday.
Chances for showers and thunderstorms linger this afternoon and
early evening, but uncertainty remains with how much activity will
occur. Chances return for Friday into Friday night, becoming
likely Saturday into Saturday evening with the cold front moving
southeast through the region.
.PREV DISCUSSION... /Issued 317 AM CDT WED AUG 17 2016/
TODAY AND TONIGHT...Forecast Confidence Is Medium.
Showers and thunderstorms rolling across the area early this morning
are associated with a decent mid level wave moving through. The low
level pattern is very weak with weak wind flow. But, there is
enough moisture and instability to keep this stuff active. An axis
of mostly elevated marginal instability stretches across southern
Wisconsin and should help support this stuff as it moves into
eastern Wisconsin. However, as usual this season, some of the
guidance suggests it will diminish by the time it reaches the
southeast and that would be about right given the late timing and
Look for most of the showers and storms to end by 8 am or so, with a
quiet period expected into the early afternoon. Thereafter, there is
a plethora of scenarios for this afternoon into the evening. The NAM
is likely suffering from too much CAPE and is firing off some
excessive convection this afternoon. It`s likely this morning`s
convection will lay out a boundary that "could" be a focus for more
storms this afternoon into the evening. Just where that boundary
ends up is in question. Very possible it pushes into northern
Illinois. With that uncertainty, will hang onto small pops this
afternoon and evening, mainly over the southern tier of counties.
Then dry after midnight.
Look for a warm and humid day with highs in the mid 80s.
THURSDAY...Forecast confidence is medium.
Brief upper level ridging, a weak cap, and lack of a trigger will
give us a quiet weather day with hot and humid conditions. The
Canadian model and HiResWRFnmm are showing thunderstorm development
along the lake breeze while most other models keep it dry. Given the
general southerly winds, we are not expecting a strong lake breeze,
so this appears a little overdone.
The 925mb temps rise to 25C by Thu afternoon, yielding max temps in
the upper 80s. Dewpoints will begin in the lower 70s Thu morning,
but mix out into the upper 60s later in the afternoon. Max heat
indices will end up in the lower 90s.
The low level jet will be pointed into east central MN Fri evening
and then veer east across central WI overnight. Storms are expected
to focus over northwest WI, closer to the upper jet. If they gain
momentum, a thunderstorm complex could skirt the northern portion of
the MKX forecast area overnight.
FRIDAY AND SATURDAY... Forecast confidence is medium.
A longwave trough will slowly make its way across the Upper Midwest
and Great Lakes region late in the week. Weather should be fairly
quiet in southern WI on Friday unless there is a convective complex
Thu night that could place an outflow boundary over the area. We
will still be in the warm and humid air mass, so expect similar max
temps and heat indices as Thu.
A leading shortwave trough tied to the right entrance region of the
upper jet and the nose of the low level jet will lead to increasing
thunderstorm chances over central WI Friday night.
By Saturday morning, the main upper trough and associated surface
low will arrive in southwest WI. The ECMWF is showing more of a
phased upper trough and stronger surface low, while the GFS has a
less organized look. CAPE and shear will be weak to moderate, so
widespread severe thunderstorms are not anticipated.
SUNDAY... Forecast confidence is medium.
Cyclonic flow will linger over the Great Lakes through Sunday night
leading to plenty of cloud cover, a chance for light showers, and
temperatures topping out in the lower 70s.
MONDAY AND BEYOND... Forecast confidence is medium.
Ridging and warmer air will begin making a comeback on Monday and
continue into the middle of next week. The next chance for showers
and weak storms will be Wed and Thu as the next upper trough
approaches. Temperatures will be closer to normal, in the mid to
upper 70s, for most of the week.
The early morning showers and storms should dissipate or exit
eastern Wisconsin by 13z this morning. Brief MVFR or IFR conditions
are always possible in the heavier activity. Otherwise, look for
VFR conditions through the remainder of the TAF period. This
morning`s activity could leave a few boundaries across the area that
could be the focus for isolated showers and storms this afternoon
and evening. But, the chances are probably low enough to keep it as
vicinity thunderstorms in the TAFs. Winds will remain below 10kts,
away from thunderstorms, through the TAF period.
Winds and waves will remain well below small craft advisory levels
TODAY/TONIGHT AND AVIATION/MARINE...Davis
Thursday THROUGH Tuesday...MRC