Area Forecast Discussion
Issued by NWS Northern Indiana

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FXUS63 KIWX 300019

Area Forecast Discussion
National Weather Service Northern Indiana
819 PM EDT Sat Apr 29 2017

Issued at 258 PM EDT Sat Apr 29 2017

A frontal boundary will bring periods of rain and chances for
thunderstorms tonight through Sunday night. Heavy rainfall is
possible, especially over northwest Indiana and southwest Lower
Michigan. It will be cool into tonight with temperatures in the
40s to low 50s. Temperatures will trend warmer on Sunday,
especially across northeast Indiana and northwest Ohio where highs
will reach the mid to upper 70s. Breezy and cooler conditions are
expected behind this system Monday into Tuesday.


Issued at 808 PM EDT Sat Apr 29 2017

Showers and a few thunderstorms are developing over NW IN and SW
MI this evening. Large area of rain over eastern IL associated
with convective MCV should continue to move northeast for much of
the evening into overnight hours. Hires models struggling with
convective trends but surface observations and analysis shows low
level stable layer sinking southward and well into central Indiana
at 00z. Sfc temps into the upper 40s and lower 50s which should
preclude any severe threat but elevated instability may allow for
some small hail over the south especially with residual convective
line exiting east central IL. Overall going forecast on track and
no significant changes made other than tweaking timing of pops
and temps. Subsidence behind northeast moving MCV may allow for
brief end to pcpn but will wait for radar to reveal such trends
before slashing pops too much later tonight.


.SHORT TERM...(This Evening through Sunday Night)
Issued at 258 PM EDT Sat Apr 29 2017

Occasional rain/storms and some concern for heavy rain/flooding will
be the story tonight through Sunday night as tropical moisture
overspreads a strong frontal zone lifting into the local area. This
will occur in advance of deepening low pressure expected to eject
slowly northeast from New Mexico into the Central US. Showers/Storms
will impact areas mainly west of I-69 into tonight as a
convectively induced mid level disturbance lifts through focusing
pcpn along the 850-700 mb portion of the front. The sfc portion of
the front will gradually lift north from near the OH River to
just south of our area toward daybreak Sunday keeping cool/strong
easterly low level feed in place and limiting the severe threat
(though marginal hail could accompany stronger cells). Locally
heavy rain/lowland flooding will be possible given influx of deep
moisture and deep/warm cloud layer to 10-12 kft.

The near surface portion of the front should edge north into at
least portions of our ne IN/nw OH counties on Sunday, though
confidence is low on how far north warmer/unstable mixed layer
reaches given the potential for convection to retard northward
progress. Areas that do briefly get into the warm sector will likely
see temperatures reach the 70s to near 80, while nw IN/lower MI
may struggle to reach the 60s. This thermal/instability gradient
will continue to support periods of showers/storms as additional
small scale/convectively enhanced waves lift through in advance of
meandering deep low into the Central Plains. In between waves
coverage/intensity will tend to wane, focusing more along the near
surface portion of the front. Best chances will continue to
reside west of I-69, with non-zero chances for an isolated strong-
severe storm as convection possibly becomes more surface based
into our IN/OH zones. The bigger concern otherwise will continue
to be localized heavy rain/flooding given high PWAT airmass and
stalled out nature to forcing. Narrowing warm conveyor belt/strong
frontal occlusion will likely bring additional rounds of
rain/embedded thunder into Sunday night. Cannot rule out some
stronger winds with this activity given a favorable shear profile.


.LONG TERM...(Monday through Saturday)
Issued at 258 PM EDT Sat Apr 29 2017

Mid level dry slot will bring an end to more organized shower
activity post-frontal on Monday as filling deep tropospheric
circulation meanders ne into the Upper Midwest/Northern Great Lakes.
Cyclonic flow/wrap around moisture/cold advection on the
southeastern fringe will keep skies mainly cloudy with a few light
showers not out of the question. Windy otherwise with temps steady
or falling into the 50s.

The rest of the week will feature below normal temperatures as mean
longwave troughing becomes established across the Eastern US. Strong
upper jet/shortwave amplifying into this trough will allow the next
mid lat cyclone to take a more southerly route through the OH or TN
Valley around Thursday or Friday. Continued with chance PoPs on the
northern fringe during this time, though confidence is low given
large solution spread in medium range guidance.


.AVIATION...(For the 00Z TAFS through 00Z Sunday Evening)
Issued at 808 PM EDT Sat Apr 29 2017

Difficult aviation forecast with chaotic atmosphere and variable
cigs and vis. Expect showers and a few tsra at KSBN this evening
given latest radar trends and approaching convective short wave.
Eastward extent of pcpn more difficult as significantly drier low
level air continues to feed into NE Indiana on NE winds. Some
elevated instability may allow showers and a little thunder to
make it to KFWA late evening into early overnight hours with left
over convective line currently in eastern IL. Warm front is
progged to finally lift north of KFWA Sunday as main upper system
approaches. This could set the stage for afternoon or evening
thunderstorms at KFWA but too much uncertainty for timing so kept
mention out of TAF for now.


IN...Flash Flood Watch through Monday morning for INZ003-004-012.

MI...Flash Flood Watch through Monday morning for MIZ077-078.

LM...Small Craft Advisory until 4 PM EDT Sunday for LMZ043-046.



SHORT TERM...Steinwedel
LONG TERM...Steinwedel

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