Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 222252
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
553 PM EST Wed Feb 22 2017

.UPDATE...
AVIATION 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 /Tonight/...
Issued at 212 PM EST Wed Feb 22 2017

Warm/moist advection coupled with a shallow nocturnal low level
inversion suggest low clouds/fog will probably redevelop again late
tonight, although some gradient tonight favors more in the way of
low cloud and less fog than what was seen this morning. Will keep a
mention of some fog in the forecast tonight, along with a more
pessimistic sky cover, especially late.

Low level thicknesses suggest the GFS MOS lows tonight may be on the
cool side. Will raise the guidance lows about a category.

&&

.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 /Saturday Night through Wednesday/...

Issued at 125 PM EST Wed Feb 22 2017

Models vary a bit on system paths and timing this period; blended
solution accepted.

Colder weather will start this period as a high pressure ridge
moves from the Plains to the Appalachians. A weak short wave
embedded in the flow aloft coupled with slight low level warm
advection will produce a period of light snow Sunday night mixing
with and changing to rain Monday midday before departing. GFS
suggests potential for brief heavy snow Monday morning with this
wave but that appears to be an outlier for now.

Weak high pressure will slide quickly across the area Monday
night as as a more substantial system begins taking shape in the
southern Plains. This system will bring a return of warmer air,
rain, and possibly thunderstorms again, Tuesday into Wednesday.

Temperatures will begin the period near normal but trend back
above normal by Tuesday as that next system strengthens warm
southerly flow. Blend of model temperature forecasts was used.

&&

.AVIATION /Discussion for 230000Z TAF Issuance/...
Issued at 553 PM EST Wed Feb 22 2017

Flying conditions lowering to MVFR fog after midnight and
IFR Ceilings and Fog Thursday morning and then back to VFR
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.

Main aviation impacts will be VFR ceilings of 4 to 5 thousand feet
this evening...with light fog developing after midnight.  Model
soundings indicate widespread areas of IFR Stratus will develop
towards daybreak and persist until midday Thursday and then
break out Thursday afternoon. Could see an isolated thundershower
north portions Thursday afternoon...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.

&&

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

$$

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


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