Area Forecast Discussion
Issued by NWS Indianapolis, IN

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805
FXUS63 KIND 230708
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
208 AM EST Thu Feb 23 2017

.UPDATE...
The LONG TERM Section has been updated below.

&&

.SYNOPSIS...
Issued at 212 PM EST Wed Feb 22 2017

A frontal system is expected to drop into the area Thursday, before
pushing back to the north late Thursday night and Friday. A strong
cold front will move through Friday evening. Another frontal system
may affect the area by the early to middle parts of next week.

&&

.NEAR TERM /Rest of Tonight/...
Issued at 942 PM EST Wed Feb 22 2017

Satellite loops indicate clouds have been clearing west to east
across central Indiana.  This trend will continue a few more
hours and then stratus should increase overnight.

Main change with this update will be to lower temperatures a
degree or two over western sections with the clearing and
temperatures in some locations are approaching overnight lows.

Will leave in patchy fog late tonight...but threat appears lower
tonight with a stronger pressure gradient.   SREF indicates best
threat will occur in our west and winds will diminish there towards
morning.   Except for the changes above...rest of the near term
period seems to be on track.

&&

.SHORT TERM /Thursday through Saturday/...
Issued at 212 PM EST Wed Feb 22 2017

Models suggest frontal system off to the northwest will sag into the
northern or central zones on Thursday, before lifting back to the
north late Thursday night in response to developing low pressure in
the Plains. Not a lot of forcing expected locally with this feature,
given the low level jet will be focused farther to the northwest.
However, the models suggest some instability will be around. Will go
with chance PoPs for showers/thunderstorms over mainly the northern
and central zones for Thursday afternoon and night.

Models suggest upper trough currently over the West Coast will push
east into the Midwest by Friday night and Saturday, with an
associated cold front expected to pass through the area late Friday
afternoon or Friday evening. Synoptically speaking, pattern looks
quite favorable for severe convection, given the strength and
alignment of the low and mid level jets, and an impressive EML
over the surface frontal zone. Will go with high PoPs for Friday
afternoon and evening to cover this feature.

Will keep some chance PoPs in the forecast for late Friday night and
Saturday as well to cover the passage of the upper trough axis.
Thicknesses may be low enough for mixed precipitation, especially
over the northern zones, at that time.

Progged low level thicknesses suggest the GFS MOS temperature
guidance for Thursday and Thursday night look too cool. Will raise
the guidance by several degrees in those periods. The guidance highs
on Friday may be too cool as well, but with questions regarding
amount of low cloud cover on Friday, will stay close to guidance for
now.

&&

.LONG TERM /Sunday through Wednesday/...

Issued at 209 AM EST Thu Feb 23 2017

ECMWF suggests high pressure across the area on Sunday along with
a mainly zonal flow in place aloft and no forcing. Thus cool and
mainly dry weather will be expected. By Late Monday...ECMWF
suggests a warm front returning to the Ohio Valley as the surface
high is well east of Indiana...again little forcing appears in
place...however moisture returns and will carry pops at that time.
Disagree with forecast builder here. Timing is off...forcing is
limited. It/s blend appears poor.

A better chance for precip appears to return on Tuesday night and
into Wednesday as the ECMWF shows SW flow developing aloft as a
strong trough deepens across the western plains states. Several
embedded shortwaves look to push toward Indiana within the flow
aloft Late Tuesday night and into Wednesday as Indiana finds
itself within the warm sector as a strong low moves through the
Great Lakes. An accompanying cold front is then dragged across
Central Indiana on Wednesday. These are all good ingredients for
precip...thus feel best chances will be on Tuesday night and into
Wednesday.

Strong High pressure then looks to build across the region on
Wednesday night into Thursday in the wake of the front.

&&

.AVIATION /Discussion for 230600Z TAF Issuance/...
Issued at 1145 PM EST Wed Feb 22 2017

Flying conditions lowering to MVFR Ceilings and fog towards daybreak
with pockets of IFR.   Then improving some Thursday afternoon.

Low pressure will move east across the northern great lakes and
a trailing cold front over the upper midwest will move to the
northern portions of central Indiana by late Thursday afternoon
and then become stationary.

Main aviation impacts will be VFR be areas of stratus developing
late tonight and early Thursday morning.  Model soundings indicate
widespread IFR appears less likely.   On Thursday...areas of MVFR
ceilings may temporarily improve to VFR Thursday afternoon and
then lower again Thursday night. Could see an isolated thundershower
north portions late Thursday afternoon and evening...but chances are
too low to mention in TAF.

Winds will be from the south or southwest around 5 to 8 knots through
the period.  Marginal low level wind shear may occur overnight...but
it should remain just below criteria.


&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...JAS
NEAR TERM...JH
SHORT TERM...JAS
LONG TERM....Puma
AVIATION...JH



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