Area Forecast Discussion
Issued by NWS Indianapolis, IN

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646
FXUS63 KIND 051828
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
128 PM EST Mon Dec 5 2016

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

&&

.SYNOPSIS...
Issued at 324 AM EST Mon Dec 5 2016

A brief break in the precipitation chances will occur today as high
pressure moves across. Precipitation returns tonight into Tuesday as
an upper system moves across the area. A potent cold front will
bring some snow chances mid week and then usher in much colder air.
Another system will bring more chances for rain and snow this
weekend.

&&

.NEAR TERM /Rest of Today/...

Issued at 926 AM EST Mon Dec 5 2016

UPDATE...
Current forecast is on track, so no changes. Widespread clouds
continue to linger across all of Central Indiana, and will
continue to do so into the afternoon hours. Best chances for some
partial clearing will still come late in the day. Current temps
across the area are generally in the low to mid 30s. Daytime highs
are still projected to top off in the low to mid 40s. Updated
grids have been sent.

PREVIOUS DISCUSSION...
The clearing line across Illinois that was moving toward the area
is no longer making good progress east. An inversion will continue
to develop across the area this morning, trapping these clouds. Thus
will go pessimistic with cloud cover this morning.

Forecast soundings show that some breaks in the clouds will develop
this afternoon as the center of high pressure moves off to the east.
Will go cautiously optimistic and allow for partly cloudy skies by
late afternoon.

Some short term models are showing fog developing early this
morning. However, they`re already overdoing fog coverage right now.
With the clouds sticking around, do not believe fog will become
significant.

With the cloud cover, went below (and in some cases well below) MOS
for highs, closer to a raw model blend.

&&

.SHORT TERM.../Tonight through Wednesday night/
Issued at 324 AM EST Mon Dec 5 2016

Models are close enough that the SuperBlend initialization
was accepted for most items.

Clouds will quickly increase tonight ahead of an approaching upper
system. However, it now looks like forcing and moisture with this
system is a little slower than previously thought, so went dry most
areas this evening. During the overnight, isentropic lift ramps up
and moisture increases, so went likely PoPs far south by late
tonight with chance PoPs elsewhere.

While there could be some mixed rain/snow at precipitation onset,
feel that temperatures will rise enough that rain will be the main
type by the end of the night.

Forcing continues across the area Tuesday morning, with the best
forcing across southeast areas closer to the upper system. Kept the
blend`s likely or higher PoPs southeast half and chance PoPs
elsewhere. Forcing quickly exits, allowing most areas to be dry
Tuesday afternoon.

Colder air flows into the area for the remainder of the short term.
A weak upper system will bring some forcing Wednesday night. Models
aren`t very bullish with forcing or QPF (with the exception of the
Canadian). However feel that with the cold advection and the upper
wave, chance category PoPs are still warranted.

&&

.LONG TERM /Thursday night through Monday/...

Issued at 125 PM EST Mon Dec 5 2016

ECMWF depicts a bit of more settled pattern during this run than
its previous run. Models vary a bit on timing of late weekend
weather system and GFS has come in colder and wetter than previous
run. Confidence is low on precipitation outcome given this
variability but upcoming runs hopefully will better align with
each other.

Flow aloft depicts short wave trough embedded in eastern Canadian
low rotating across the Great Lakes Friday with snow showers in
vicinity of the Great Lakes. More zonal flow with embedded weak
wave passes across the Great Lakes on Saturday Night, moistening
the atmosphere, but for moment, generating no precipitation.

Onward in time, Canadian is a bit more progressive with arrival
of more substantial wave Saturday night while GFS exhibits fairly
strong over running Saturday Night. ECMWF, later still, shows
over running by Sunday. Upshot of all this will be precipitation
can be expected Sunday, but timing, the amount of warm-up before
precip onset, and precipitation type are still all in question.
For now, expectation is for a start-up as snow by or before
daybreak Sunday and transition to snow/rain mix Sunday afternoon
as warm air continues to infiltrate. Latest GFS,being colder,and
now with a bit more moisture, develops several inches of snow
before transitioning to mix though ensembles range from slight
snows in the north only, to widespread 2"-4" across most of the
forecast area. Again, this far out in time, several adjustments
can be expected.

As for temperatures...coldest of the season to start Friday
morning with gradual moderation through the forecast period,
but overall, temperatures will remain below normal this period.


&&

.AVIATION /Discussion for the 051800Z Tafs/...

Issued at 1144 AM EST Mon Dec 5 2016

MVFR Cigs are expected to improve to VFR this afternoon. A return
to MVFR to IFR Conditions are expected late tonight...after
061000z.

Satellite shows extensive cloud cover across the region...however
with mixing and heating...the lower level clouds are expected to
become MVFR to VFR. Clouds approaching from the southwest ahead of
an approaching low pressure system will also provide VFR CIGS
through the evening hours...time heights and forecast soundings
confirm...showing saturation aloft.

Strong isentropic lift and a saturated column looks to arrive on
Tuesday morning as low pressure moves across Kentucky.
Thus a return to MVFR/IFR is expected near 12Z Tuesday as these
features pass.


&&

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

$$

SYNOPSIS...50
NEAR TERM...50/TDUD
SHORT TERM...50
LONG TERM....TUCEK
AVIATION...JP



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