Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 040300

Area Forecast Discussion
National Weather Service Indianapolis IN
1000 PM EST Sat Dec 3 2016

The Near Term Section has been updated below.


Issued at 205 PM EST Sat Dec 3 2016

High pressure over Indiana will quickly move east exiting the
region but bringing generally quiet weather tonight. A quick
moving upper level weather disturbance will sweep into the Ohio
Valley on Sunday...ahead of a weak cold front. This may bring a
mix of precipitation initially to central Indiana on Sunday
morning...before changing over to all rain during the afternoon.

Another high pressure system will arrive on Sunday night and
Monday...brining a return to dry weather to start the work week. weather is expected in the week ahead as a pair
of weather systems will push across Indiana during the
week...brining chances for rain and Monday night and Tuesday and
some snow on Wednesday night into Thursday.


.NEAR TERM /Rest of Tonight/...

Issued at 1000 PM EST Sat Dec 3 2016

Radar mosaic and observations show an area of showers and some virga
moving into southwestern Kentucky and southern Illinois. The
northward advancement of anything reaching the ground has been very
slow and hi res models seem to have a pretty good handle on this.
Current runs of the RAP and HRRR don`t bring anything into the area
until 10-11z and then bring echoes slowly into the southwestern
counties. Forecast soundings continue to show some potential for a
rain snow mix at or shortly after onset. This matches nicely with
going forecast and thus will make no appreciable changes at this
time. Previous discussion follows...

Forecast soundings tonight and time height sections continue to
shows a top down type saturation occurring through the night as
the high pressure system departs and the trough and short wave to
the west approach. Thus will keep skies cloudy tonight...and stick
close to a blend on temps.

Forcing associated with the advancing wave may arrive in the
western parts of the forecast area by daybreak. This may result
light precip amounts near 12Z...thus some low chance pops may be
needed...although confidence in a pre 12Z measurement is low.


.SHORT TERM /Sunday through Tuesday/...

Issued at 205 PM EST Sat Dec 3 2016

Active weather is in store for Sunday as both the GFS and NAM
suggest a moderate negatively titled short wave to push into
Illinois and Indiana through the course of the day. Excellent
dynamics aloft appear in place ahead of this system. Additionally
the 295K isentropic surface shows good lift through the day with a
surge of Specific humidities to over 3 g/kg. Forecast soundings
and time height sections also show deep saturation. Thus hopefully
superblend will allow a near 100 pop. Forecast soundings show
lower levels starting the day below or near freezing...thus some
mix in precipitaion type will be possible with the onset as temps
warm through the day due to daytime heating and broad warm air
advection. Given the expected precipitation through the
day...will trend highs cooler than the MAVMOS.

GFS and NAM suggest the upper wave quickly departs on Sunday
evening...and isentropic forcing is shut off. Mid levels show good
subsidence arriving through the night as High pressure is
expected to build at the surface. Cannot rule out a stray
lingering shower across the eastern parts of the forecast area
around 00z-02z as the forcing departs...but for the most
part...precip will be ending and will trend pops toward dry.

High pressure is then expected to settle across the region on
Monday. Forecast soundings remain quite dry with an inversion
aloft and unreachable convective temps. Thus will trend toward a
partly cloudy sky and a blend on Highs.

Next up...the GFS and NAM once again suggest a strong low
pressure system and associated upper wave to sweep out of the
southern plains and push in to the ohio valley on late Monday
night into Tuesday. A similar set-up appears once again within the
forecast soundings...with a top down type saturation. Once again
the 295k Isentropic surface shows excellent lift with specific
humidities over 5 g/kg. Thus again will ramping pops higher than
guidance on Monday Night and Tuesday as these features arrive.
Fortunately the column appears a bit warmer with this second
system...thus precip type should remain all rain.


.LONG TERM /Tuesday night through Saturday night/...

Issued at 205 PM EST Sat Dec 3 2016

Conditions will become dry early in the extended as a system
traversing the Southeast moves farther east. The dry weather will
be short-lived though as a more potent system tracks through
Ontario. As moisture is drawn into this system, precipitation
chances will begin increasing across Central Indiana on Wednesday
night. A cold blast of air accompanying this system could result
in some of the first snow accumulations of the season across the
forecast area from Wednesday night into Thursday. Models continue
to differ on moisture amounts though with the GFS a bit drier than
the Euro. So, this will continue to be monitored over the next
several days for timing and snowfall totals.


.AVIATION /Discussion for 040300z TAF issuance/...

Issued at 905 PM EST Sat Dec 3 2016

Updated current conditions at KIND, and extended time of MVFR
ceilings at KLAF through 4z. Previous discussion follows...

MVFR ceiling at KLAF should rise to VFR over the next hour or two
and then all sites should be VFR through the overnight. Sunday
morning expect to see MVFR ceilings first move in from the west
and then conditions to deteriorate further within a few hours as
saturation occurs through the column and rain commences. There is
some chance of a wintry mix at onset, but the probability of
occurrence and potential amount of time of a mix before a
changeover to rain is low enough to leave out at this time. Began
the precip in the TAFs with VCSH, and this would likely be the
period where mixing could occur. After that strong forcing moves
in and ceilings should drop below IFR along with visibilities
around 1 1/2SM at their worst. Light and variable winds overnight
will remain fairly light Sunday at around 5 kts but will be mainly
out of the  southwest during the day.




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