Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 141031
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
531 AM EST Thu Dec 14 2017

.UPDATE...
The AVIATION Section has been updated below.

&&

.SYNOPSIS...
Issued at 241 AM EST Thu Dec 14 2017

Continued northwest flow aloft through the end of the week will keep
chilly temperatures across the area. Other than a few light snow
showers over northeast portions of central INdiana Friday...dry
weather is expected into Saturday. Upper ridging will expand into
the area over the weekend with warmer temperatures and by Sunday...a
chance for precipitation as an upper level wave tracks through the
Ohio Valley. HIgh pressure will return with dry weather and
seasonable temperatures by late Monday and continue through the
middle of next week.

&&

.NEAR TERM /Today/...
Issued at 241 AM EST Thu Dec 14 2017

Low pressure tracking rapidly away from the region early this
morning. The surface pressure gradient was beginning to relax as a
result with gusts starting to diminish. Low clouds lingered with a
trailing surface trough dropping south through the forecast area.
07Z temperatures ranged from the upper 20s to mid 30s.

Quieter day expected for the region as high pressure tracks across
the Ohio Valley. An issue to focus on this morning remains the
potential for a few flurries on the southern edge of the developing
lake effect band to make it into the northern Wabash Valley for a
few hours. Radar trends early this morning showing the evolution of
the band coming almost due south along the west shore of Lake
Michigan. The band is expected to extend south from Lake County into
northwest Indiana and while the core of the band will remain north
of our forecast area...potential exists for flurries to drift into
northwest counties through about 14-15Z before the boundary layer
flow veers and weakens.

Winds will continue to diminish through the remainder of the predawn
hours with gusts diminishing prior to daybreak. The low stratus
lingering in the wake of the surface low should begin to break up by
daybreak as well with the surface trough departing off to the
southeast. With that being said...the presence of cold advection
will keep clouds around periodically through the day with sunshine
at times as well.

Temps...colder temperatures are expected today with northerly flow
and cold advection. Low level thermals were matched well by an
overall model blend as highs should range from the upper 20s
northeast to the mid 30s southwest.

&&

.SHORT TERM /Tonight through Saturday Night/...
Issued at 241 AM EST Thu Dec 14 2017

Forecast challenges are largely focused on temperatures through the
period as predominantly benign weather is expected.

The upper level pattern across the country over the last 10 days or
so highlighted by the western ridge and eastern trough will finally
relax over the weekend as energy dives into a developing upper low
moving ashore over southern California and Baja Mexico by Saturday.
The southeast ridge will flex its muscle so to speak in response
with solid mid level height rises over the region by late Saturday.
This will result in southerly flow developing with a warming trend
for Saturday ahead of an approaching system poised to impact the
Ohio Valley on Sunday.

Prior to that transition taking place however...central Indiana and
the entire region will remain under the influence of the eastern
trough with yet one more wave aloft tracking through the Great Lakes
Friday before shifting off to the east as a deep upper low carves
out the trough over New England. Model trends remain further north
with the Friday system as a surface low rotates through the upper
Great Lakes before kicking east into Quebec on Saturday. Forcing
aloft remains displaced off to the north of the region with growing
confidence that this system has little if any impact on central
Indiana. Could see light snow showers and/or flurries graze
northeast counties during the day Friday as the upper wave passes
by...otherwise expect just an increase in clouds for much of the
day.

Low level flow will back to southerly by early Saturday as surface
high pressure tracks into the southeast states. Model soundings and
RH progs indicate more substantial drying and subsidence present on
Saturday with mostly clear skies developing for the Ohio Valley. The
approach of a weak frontal boundary Saturday night will encourage a
surge of moisture advection out of the Southern Plains and Gulf of
Mexico. Clouds will increase in response late Saturday night but any
precipitation will hold off until after daybreak Sunday.

Temps...undercut guidance temperatures tonight as cold advection
persists. Trended closer to cooler MET guidance for Friday with
greater cloud coverage likely stunting temperature rises. The
arrival of warm advection...increased sunshine and southerly flow on
Saturday should ensure temperatures closer to the higher MAVMOS with
the entire area rising into the 40s. Utilized a model blend for lows
Friday and Saturday nights.

&&

.LONG TERM /Sunday through Wednesday/...
Issued at 222 AM EST Thu Dec 14 2017

Ensembles in good agreement with a fairly zonal and progressive
upper patter during this period.

Appears the best threat for precipitation during this period will
be from Sunday into early Monday as an upper disturbance passes
through the area. Will keep PoPs in the forecast at these times to
cover this feature. Appears most of the precipitation will be in
the form of rain, with some potential for mixed precipitation at
the beginning and end of the event, Sunday morning and Monday
morning.

Some of the ensembles suggest a mixed precipitation threat around
Monday night and Tuesday morning with a possible upper wave
passing through the Great Lakes, but confidence is low in this
feature at this time.

&&

.AVIATION /Discussion for the 141200Z TAFS/...
Issued at 530 AM EST Thu Dec 14 2017

Lingering MVFR ceilings 020-030 expected to scatter out from the
north across the terminal by the midday hours, although moisture
plume off of Lake Michigan may keep some cloud cover near that
level into the afternoon hours.

Surface winds 340-010 degrees at 9-13 kts this morning will
gradually diminish to 6 kts or less by mid to afternoon.

&&

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

$$

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


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