Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 231420
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
1020 AM EDT Sun Jul 23 2017

.SYNOPSIS...
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.

&&

.UPDATE...
Issued at 1020 AM EDT Sun Jul 23 2017

Forecast is in pretty good shape this morning with only minor
tweaks made to hourly temps/PoPs and sky cover into this
afternoon. A few weak showers/storms have developed near the US
24 corridor in IN (as of 14z) along remnant instability
axis/composite outflow. This activity will likely remain widely
scattered at best as it shifts east-southeast on the northern
fringe of a MCS tracking east near the OH River.

Mid level DCVA/height falls in advance of an approaching
mid/upper level shortwave trough may generate additional/scattered
convection by this afternoon along an associated/diffuse sfc
trough dropping southeast from southern Lake MI/lower MI. Best
chances (30-40%) will be across ne IN/nw OH, with an isolated
strong-severe storm (wind/hail) possible given adequate deeper
layer shear and potential for ~1500 j/kg of MLCAPE.

&&

.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 12Z TAFS through 12Z Monday Morning)
Issued at 632 AM EDT Sun Jul 23 2017

Fog and stratus have remained just north of terminals but a low
VFR stratocu deck did develop over the area and will be BKN-SCT
rest of this morning. Regional radars showing a few showers/tsra
developing as depicted by hires guidance. Activity should remain
widely scattered this morning and only included a VCTS in
terminals for this activity as well as expected afternoon storms
with next wave. Should see winds become northwest today and drier
air moves in tonight.


&&

.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&

$$

UPDATE...Steinwedel
SYNOPSIS...Fisher
SHORT TERM...Fisher
LONG TERM...Fisher
AVIATION...Lashley


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