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Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
354 PM CDT Fri Jul 19 2019

Short term...

This afternoon and tonight...forecast confidence is medium to
high...

Very hot and humid conditions are occurring across much of
central and southern Wisconsin this afternoon. Dewpoints have
climbed into the upper 70s with a few locations reporting
dewpoints in the lower 80s. This has sent heat index values into
the 105 to 115 degree range. We will continue the excessive heat
warning into the evening hours and then as temperatures begin to
cool we will let the heat warning expire for our northern tier
counties but keep it going for the rest of the area. Main
reasoning behind this is that conditions could be similar again
tomorrow but we are expecting an increase in clouds across
northern and central Wisconsin and this might keep temperatures
below criteria for tomorrow. The only changes made to the
overnight temps were a slight nudge upwards for a few locations
mainly as a result of the rich low level moisture will keep lows
from falling very far tonight.

In terms of chances for storms tonight there is a bit more
uncertainty. Models were struggling to handle the morning round of
storms and then the current redevelopment. But the general idea is
that the storms forming across central Minnesota and northwest WI will track due
east into northern WI and then start to drop southeast towards the area
late tonight into Saturday morning. Based on the wind profile
though storms may just clip our area overnight. Adjusted pops
lower for tonight but kept in chances for the northern half of the
area. The outflow from the storms tracking to our north could
allow for additional development as the boundary sags south. While
cape will be quite high with values of 3,000+ j/kg wind shear is
expected to be weaker with the stronger low level jet and jet streak aloft
positioned to our north. So, main concern with any storms will be
damaging winds and hail.

Long term...

Saturday/Saturday night...forecast confidence is medium...

Saturday will feature another very hot day with temperatures likely
reaching the mid 80s to low 90s and heat indices in the low 90s
to low 100s with the warmest temperatures along the WI/Illinois border.
Thus we have extended the excessive heat warning for areas along
and south of a line from Lone Rock to Juneau to Port Washington.
However, the temperatures still have a bit of uncertainty given
cloud cover and storm/shower potential into the afternoon hours.

The storm potential will initially be forcing from the cold front
that will push into the region by the afternoon. Some of these
storms may be strong with a few severe storms possible given a
very buoyant and unstable air mass with around 3000-4000 j/kg of
MUCAPE as well as 40-50 kts of 0-6 km bulk shear directly along
cold front. Although the shear vectors are parallel to the front
if the orientation of storms can become a bit more perpendicular
as some models suggest severe storms will be more likely. However
this will still be very dependent on the location, orientation,
track and environment, especially with respect to shear.

Into the evening and overnight hours we will see continuing chances
for more elevated showers/weak storms throughout much of the region
as the upper level wave pushes through the region. This will be in
conjunction with the more elevated portion of the boundary with
plenty of low to mid level Theta-E advection. Although instability
will be restricted primarily to the south, showers and a few
thunderstorms will likely be scattered across the region.
Showers/storms will slowly push south during the overnight hours.

Sunday/Sunday night...forecast confidence is medium...

A cooler day is expected Sunday with highs expected to reach the
upper 70s to low 80s with the elevated boundary from the overnight
period located just to the south of the WI/Illinois border. This may bring
some showers to the far south throughout part of the day especially
earlier in the morning with a very slight chance to see a few weak
storms in the afternoon/evening in the far south as the shortwave
pulls through. However, a lack of much low level forcing with
decreased low to mid level moisture may prevent the area from seeing
any storms.

Monday through Friday...forecast confidence is high/medium...

This period looks to be a cooler and drier period as high pressure
will dominate the region for most of the week with high temperatures
in the upper 70s to mid 80s with much lesser humidity. There is
potential for a few showers in areas in the middle of the week but
the region definitely looks more likely to remain dry throughout the
week.

&&

Aviation(18z tafs)...

A scattered/broken deck of clouds between 2,500 and 3,500 feet continues to
linger over southern Wisconsin this afternoon. This should thin
into the evening hours resulting in VFR conditions. Storms well
north of the area will bring an increase in mainly high level
clouds overnight. Towards 12z Saturday a boundary nearing the area
will start to lower cigs into MVFR. Confidence in storms impacting
any of the terminals overnight remains low and have kept a probability 30
in the forecast. More widespread showers and storms are expected
to impact the terminals towards 18z Saturday.

&&

Marine...

A push of higher dewpoint air into the region could allow for
patchy dense fog to develop through Saturday. South to
southwesterly winds will continue into the overnight hours with
brief gusts of 15 to 20kts still possible. Thunderstorm chances
increase overnight mainly for the north half of the lake. Storm
chances shift south on Saturday as a cold front sweeps across the
area. Cooler and drier air will arrive for Sunday and continue for
much of next week.

&&

Mkx watches/warnings/advisories...
WI...excessive heat warning until 8 PM CDT Saturday for wiz058>060-
062>072.

Excessive heat warning until 9 PM CDT this evening for wiz046-
047-051-052-056-057.

Lm...none.
&&

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