Area Forecast Discussion
Issued by NWS Northern Indiana

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000
FXUS63 KIWX 260800
AFDIWX

Area Forecast Discussion
National Weather Service Northern Indiana
400 AM EDT Wed Jul 26 2017

.SYNOPSIS...
Issued at 346 AM EDT Wed Jul 26 2017

Dry weather will continue today with temperatures moderating into
the lower to mid 80s. Chances of showers and thunderstorms will
increase late tonight into Thursday as a disturbance approaches
from the Plains. Some locally heavy rainfall is possible late
tonight into Thursday, especially along and south of Route 30.
Another system will approach from the Upper Midwest Thursday night
into Friday providing an additional chance of showers and
thunderstorms. Cooler and less humid conditions can then be
expected behind this system for the weekend.

&&

.SHORT TERM...(Today through Thursday)
Issued at 346 AM EDT Wed Jul 26 2017

Quiet weather to continue today into the first part of tonight, with
focus for late tonight and into Thursday on increasing chances of
showers and thunderstorms.

Western periphery of low level ridge axis will slowly lose its
influence on local area today with return southwesterly low level
flow developing. Pocket of relatively dry low level air persists
across the region this morning with 00Z RAOBS from ILX/DTX with
PWATs of 0.96 and 0.69 inches respectively. An area of showers
across west central Lower Michigan early this morning will
continue to rapidly erode through daybreak due to more of an
influence from the stable air mass across the region. Humidity
levels will begin to creep up later this afternoon into this
evening in response to return flow, with focus for tonight
shifting to next upper level short wave which has enhanced
overnight convection across Nebraska. At least southern portions
of the forecast area southward across Ohio Valley appear to be in
favorable track with this short wave. However, as is the case in
many of these types of setups, details regarding timing/strength
of short wave will be modulated by upstream convective enhancement
over the next 24 hours. Otherwise for this afternoon, onset of
low level WAA and expected decent amount of sun should allow for
moderating temps back into the low to mid 80s.

Stronger low level theta-e advective push should occur in the 21Z-
06Z this afternoon/tonight from west to east as a fairly weak
westerly low level jet pushes strong low level theta-e gradient
eastward. Some of the steepest lapse rates this forecast period
could be just after onset of this stronger low level theta-e push
before more pronounced mid level moistening takes place late tonight
into Thursday morning. Greatest precip coverage is expected post 09Z
tonight as upstream convectively enhanced vort max approaches the
area with a likely accompanying pocket of stronger low level
moisture convergence. However, will need to maintain low to mid
chance PoPs in the early portion of the overnight hours given more
favorable elevated instability profiles during this time. Given late
timing and marginal nature to shear, overall severe threat looks to
be minimal. Cannot completely discount some low end wind
potential across the far west/southwest late tonight,
particularly if some smaller scale more substantial shear can be
realized with the upstream convective vort. However, greater
concern for tonight into Thursday will be potential for some
localized heavier rainfall. PWATS should increase to around 2
inches late tonight into Thursday. Current indications suggest
areas south of Route 30 would stand best chances of localized
heavier rainfall given initial indications of more favorable
convective vort/low level moisture convergence track. Will have to
watch this potential closely, as these general locations have
been harder hit by heavier recent rainfall.

General model consensus would suggest passage of this convective
vort max Thursday afternoon would temporarily lower precip
chances across northern half of the area, but lingering low level
convergence axis argues for maintaining low to mid range chance
PoPs through the afternoon across central/northern locations. Weak
lagging mid level troughiness also may aid in some convective
redevelopment in the afternoon. Not expecting much in the way of
severe potential Thursday afternoon given anticipated marginal
shear/instability. Still alot of mesoscale details to resolve
between now and then however regarding how overnight/earlier
morning convection impact instability/kinematic profiles. If some
better pooled moisture can be realized along weak sfc trough, may
have a few afternoon strong storms but confidence in appreciable
instability is on the low side.

&&

.LONG TERM...(Thursday Night through Tuesday)
Issued at 346 AM EDT Wed Jul 26 2017

By Thursday night, local area will become increasingly influenced by
more vigorous upper level wave dropping southeast from the western
Great Lakes. Approach of this wave should tend to sharpen inverted
sfc trough and provide some enhancement to deeper moisture
convergence, particularly late Thursday night into early Friday.
With a good deal of spread in guidance, did slightly increase PoPs
to low to mid range chance range (highest across the northeast) for
this time period. Low chance of showers and thunderstorms to
continue across the east through Friday, with precip potential
finally ending by Friday evening as this upper trough pushes
southeast. The weekend still appears to be shaping up as pleasant,
with slightly below normal temps and comfortable humidity values.

Western CONUS upper ridging is expected to undergo some
amplification late weekend/early next week with primary short wave
track across northern Great Lakes/Ontario/Quebec. Still some
indications in medium range guidance of weak frontal boundary
approaching late Monday/Tuesday where have maintained low chance
PoPs. Without much upper support, this front should tend to wash
out across the region toward the end of this forecast valid
period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
Issued at 1240 AM EDT Wed Jul 26 2017

VFR conditions should cont through the taf period as sfc ridge
slowly departs to the east. Cirrus blowing se from thunderstorms
along shrtwv/cdfnt over the upr midwest should cont to spread
over the tafs through the period while low level winds veering
southerly will advect in some low level moisture, which may allow
a few cu to develop over the area today, lingering into this eve
as shrtwv/front approaches. This system will likely cause some
tstms in our area as it moves through, but, timing prbly will be
beyond the end of this taf period.

&&

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

$$

SYNOPSIS...Marsili
SHORT TERM...Marsili
LONG TERM...Marsili
AVIATION...JT


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