Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 230830

Area Forecast Discussion
National Weather Service Northern Indiana
430 AM EDT Sun Jul 23 2017

Issued at 410 AM EDT Sun Jul 23 2017

A series of disturbances will bring chances for showers and storms
to the region through this evening. Isolated strong to severe
storms will be possible through early evening before drier and
less humid air settles in to start the work week. Highs will reach
into the 80s today with lows in the 60s.


.SHORT TERM...(Today and Tonight)
Issued at 410 AM EDT Sun Jul 23 2017

Several challenges exist in the period with possible brief impacts
from stratus/fog in Lower Michigan and then chances for
showers/storms as early as 12Z through early evening.

Partial clearing and abundant low level moisture has helped produced
stratus deck across mainly central/southern Lower Michigan.
Stratus has been slowly working south and now into portions of
northern Indiana with highly variable visibilities (BEH settled in
at quarter mile for a bit now). Have introduced areas of fog US 6
north and then a narrow band of patchy fog just south of it
through 12Z. No headlines, but may need SPS if pockets of locally
dense fog expand.

Focus then shifts to the first of what may be 2 chances for widely
scattered to maybe scattered showers/storms. Somewhat diffuse
trough/windshift was noted from NE Iowa into NE Lower Michigan as of
6Z. Widely scattered showers and storms were occurring from
central Lake Michigan into northeastern Lower MI. A few returns
starting to show up west of Chicago as well. HRRR seems to be best
initialized of hi res models. That being said the evolution of
what may be widely scattered to maybe scattered showers and
storms still varies, leading to a low confidence setup. Enough
signals exist to increase pops into the slgt chc to chc range
through 18Z. Elevated CAPE on the order of 500 - 1000 J/KG exists
in the NW by 12Z with instability slowly increasing with SE
progression as diurnal heating takes place. Bulk shear parameters
in the 35 to 40 kt range could cause some issues if convection can
organize sufficiently to tap this (0-3 km shear at best 20 kts).

Little in the way of impacts will be seen behind the front with
dewpoints remaining well into the 60s to near 70 and clearing skies
to allow for increase in instability as main upper low and
associated lobe of energy rotate through late this afternoon. Flow
will become more west and northwest but strong heating and 5 to 10
kt wind should keep lake breeze near shoreline areas. If a lake
breeze can develop, this could pose yet another focus to aid
development with approaching wave and expected instability. Non-
zero severe threat will exist until passage of the energy. Rather
than get fancy timing out what may or may not occur left blanket
30 pops everywhere. Could concede that SW areas may be far enough
away from upper level support to warrant lower pops, but signals
in HRRR still show some potential.

Once the upper level energy departs by late evening, cooler and less
humid conditions begin to settle in overnight.


.LONG TERM...(Monday through Saturday)
Issued at 410 AM EDT Sun Jul 23 2017

High pressure will drift across the region through Weds bringing
cooler and less humid conditions to start. More seasonable
temperatures and humidity values will start to return in the wake of
the high as upper level trough begins dig somewhat into the northern
Lakes by Thursday. This will force a cold front back south starting
late Weds ngt into Thursday. Models have begun to converge on what
looks like a decent shot at a period of showers and storms moving
into NW areas Weds ngt and points SE Thurs. Blend of models has
increased to likely pops and while not normally a big fan enough
signals (model agreement, favorable timing of front in SE and
available instability/moisture) all lean towards increase to likely
pops mainly SE half Thurs. Too early to pin down any severe threat
but something that will have to be at least monitored.

Dry weather returns for the remainder of the period, but with only
limited southward penetration of the front any cool off will be
short lived with seasonable conditions back by the weekend.


.AVIATION...(For the 06Z TAFS through 06Z Sunday Night)
Issued at 132 AM EDT Sun Jul 23 2017

Several aviation concerns this package beginning with fog/stratus
potential through daybreak followed by two mid level disturbances,
one shortly after daybreak and a second later this afternoon and
evening. Fog satellite product and surface obs show widespread fog
and stratus across central lower Michigan and some movement
southward. Winds have decoupled and latest HRRR keeps wind calm or
under 5 knots through daybreak. Short range guidance varies on how
far south stratus will develop but HRRR keeps it north of
terminals and for now prefer to lean this way but did introduce
some MVFR vis restrictions along with a SCT010 group given
proximity. Last several runs of HRRR has been consistent in
bringing a few TSRA into KSBN toward 12z and KFWA near 15z with
first short wave currently over central WI. This feature has been
producing some shra/tsra and HRRR seems to have caught on.
Introduced a VCTS given limited coverage and will monitor.
Second short wave currently over MN will drop in late afternoon
and evening. Instability grows with decent deep layer shear. Still
too much uncertainty on how much, if any, convection will develop
with this wave so did not introduce into TAFs at this time.




LONG TERM...Fisher

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