Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 171810

Area Forecast Discussion
National Weather Service Indianapolis IN
210 PM EDT Sun Sep 17 2017

The LONG TERM Section has been updated below.


Issued at 223 AM EDT Sun Sep 17 2017

High Pressure east of Central Indiana will continue to keep dry
weather across the area this morning. A frontal boundary over the
plains states will push east toward Indiana this afternoon. This
will result in chances for showers and Thunderstorms this
afternoon and tonight.

The front will linger across the area on Monday and Tuesday. Warm
and moist southerly flow spilling into the Ohio Valley from the
Gulf of Mexico will continue through mid week also. This in
combination with a series of upper level weather disturbances
poised to push through the region will provide chances for
showers and storms through Wednesday. Temperatures are expected to
remain above seasonal normals.

Dry weather is expected to return as the work week ends.


.NEAR TERM /Today/...
Issued at 1013 AM EDT Sun Sep 17 2017

Widely scattered showers have been developing recently over east
central Indiana, associated with a weak upper level vorticity
center. Some showers are also developing over west central Indiana
back into Illinois, associated with a stronger upper air feature
over western Illinois.

Short term model guidance suggests the feature over eastern
Indiana will pass off into Ohio by early to mid afternoon, while
the remnants of the precipitation area over Illinois will move
into the western zones towards mid afternoon. Appears most of the
better dynamics will stay west of the forecast area today, but
given the presence of current activity and building instability
with heating later today, there will be a threat for widely
scattered convection throughout most of the day. Will extend the
chance PoPs for the rest of the day to cover the current and
expected activity.

Previous discussion follows.

Surface analysis shows high pressure was over New York and
Pennsylvania early this morning...providing warm southerly surface
flow to Central Indiana and the Ohio valley. A weak trough of low
pressure and an associated cool front was found from
Wisconsin...across Iowa to eastern Kansas. Dew point temps across
Central Indiana were in the middle 60s as GOES16 shows mainly
clear skies across the state. Water Vapor imagery shows a tropical
plume of moisture streaking across Texas and into Iowa and the
western Great Lakes.

Forecast soundings today show a dry column this morning...however
by late afternoon lapse rate favorable for convection are in place
along with attainable convective temperatures. CAPE appears
marginal...but still sufficient to support a few storms. Aloft the
GFS and NAM suggest a few short waves to the west surging toward
Central Indiana. Thus will continue the forecast trend of
including chances for showers/storms late this
afternoon...particularly across the western parts of the area
where dynamics will be arriving first. Given the dry ground and
little change in overall airmass will trend highs at or slightly
above persistence.


.SHORT TERM /Tonight Through Tuesday Night/...
Issued at 223 AM EDT Sun Sep 17 2017

GFS and NAM continue to suggest the slow propagation of an upper
short wave across Indiana tonight. As mentioned
earlier...favorable moisture on southerly winds remain in play.
Time height sections show good lower and mid level moisture
overnight as the surface front pushes across Indiana and begins to
stall and elongate. Instability will be limited as heating is
lost...but with the other ingredients still present...will
continue to keep at least a low chance for pops. With possible
rain but clouds and southerly flow expected will trend lows
tonight at or above the forecast builder blend.

On Monday through Tuesday Night...the GFS and NAM suggest the
surface front stalls over Central Indiana as it become more east-
west oriented. The models suggest SW flow aloft with diffluence
aloft and short waves poised to pass on Monday Night and again on
Tuesday. Forecast soundings on Monday afternoon and again on
Tuesday afternoon suggest steep lapse rates with attainable
convective temperatures. CAPE is suggested to be near 1500 j/kg on
Monday afternoon and near 2500 j/kg on Tuesday afternoon. Thus
with all these features remaining in the area...rain chances
cannot be ruled out. Will continue with pops at or slightly above
the forecast builder blend as confidence for at least some rain
has grown. With a warm and moist air mass in place will continue
to trend temperatures at or above the blend also.


.LONG TERM /Wednesday night through Sunday/...
Issued at 210 PM EDT Sun Sep 17 2017

Good confidence that the short term will see mostly or all dry
weather under the influence of surface high pressure and an upper
ridge per similar model output.

Also, good confidence that above normal temperatures will continue
per the blend. Look for highs in the mid and upper 80s and lows in
the 60s. Normal highs for early fall are in the upper 70s.


.AVIATION /Discussion for the 17/1800Z TAF Issuance/...
Issued at 1237 PM EDT Sun Sep 17 2017

An upper wave and weak cold front will interact with a warm, moist
and unstable atmosphere and result in thunderstorm chances through
the TAF period. The best chances look to be from 21z to 06z Monday
and then again after 16z Monday. Will go with VCTS at all but BMG
for the first round and VCTS all sites after 16z. SREF and
especially the GFS LAMP suggest MVFR conditions after 09z. Would
also not rule out brief MVFR or worse in thunderstorms.

Winds will be southwest less than 10 knots.




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