Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 221916
AFDIND

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

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have 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 221800z TAFs/...

Issued at 1202 PM EST Wed Feb 22 2017

Widespread LIFR and IFR stratus has been slow to lift, thin and
break. Expect with continued sunshine from above and mixing below
from surface winds now near 10kts that wholes in cloud deck will
expand as it slowly rises with surface heating reaching broken VFR
by around 2100z. Given that low level moisture remains prevalent,
and approaching surface front tonight aids in convergence,
anticipate redevelopment of an IFR cloud deck before daybreak
Thursday, or 231000z. Since winds are expected to remain above 5
knots overnight, do not expect re-occurrence of dense fog like
this morning.

&&

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

$$

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



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