Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 090719
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
219 AM EST Fri Dec 9 2016

.UPDATE...
The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated below.

&&

.SYNOPSIS...
Issued at 219 AM EST Fri Dec 9 2016

Although a few flurries will be possible this morning...Polar
High pressure over the central plains will continue to build
across Indiana today through Saturday...bringing mainly dry
weather and below normal temperatures.

The HIgh will drift east of Indiana by Sunday and a warm front
associated with a deepening low pressure system over the plains
states will push toward Indiana. Cold air will be in place to
start the day on Sunday...as as precipitation arrives in the
area...freezing rain or a mix of precipitation will be possible
before warmer air arrives and the precipitation changes to all
rain.

Another pair of quick moving cold fronts will push across Indiana
early next week...providing more polar air to Central Indiana for
the middle of next week.


&&

.NEAR TERM /Today/...

Issued at 219 AM EST Fri Dec 9 2016

Surface analysis early this morning shows cold high pressure in
place over the Plains states. Cold NW flow was in place across
Indiana. Water Vapor was showing a weak short wave pushing across
the region. Radar trends continue to show light snow
showers/flurries pushing across the forecast area. Temps were in
the teens and lower 20s.

GFS and NAM suggest the short wave responsible for the ongoing
snow flurries and showers will depart the area after 12Z-15Z...and
will keep a mention of low chance pops in the grids for this
during the morning hours. After that Forecast sounding and time
heights keep mostly cloud skies in place amid a partially
cyclonic flow as high pressure to the west build across the ohio
Valley late tonight. Thus clouds and ongoing cold air advection
should lead to high temps today cooler than MAVMOS.

&&

.SHORT TERM /Tonight through Sunday Night/...

Issued at 219 AM EST Fri Dec 9 2016

Quiet weather to set up tonight and Saturday before a more active
period arrives on Late Saturday night through Sunday Night.

Tonight and Saturday...GFS and NAM suggest surface high pressure
to build across Indiana and the Ohio Valley...reaching the middle
Atlantic states Saturday Night. Time height sections and forecast
soundings during that period reveal a generally dry
column...however....with a quick upper flow in place...a few
passing short waves will result in a passing high clouds. Will use
a blend on tonight`s lows and Saturday Highs.

Active Weather sets the stage on Saturday Night through Sunday
night as the GFS and NAm depict a quick moving wave pushing into
the central Plains by Sunday afternoon...before arriving in
Central Indiana on Sunday Night. Models suggest mid cloud arriving
on Saturday night and Early Sunday as Warm air advection begins
with Warmer...southerly flow in place on the backside of the
departing High pressure. Meanwhile...stronger low pressure and an
approaching warm front will arrive in the area on Late sunday
morning. For Now...will try and hold off on any precip mention
until late sunday morning...as forecast soundings show dry air in
the lowest levels...and any precip may just end up as virga.
Superblend might force me into low pops...but confidence there is
low.

Forecast soundings suggest strong warm air advection within the
column on Sunday afternoon into Sunday evening. Excellent lift is
seen by Sunday afternoon as seen on the GFS 290K Isentropic
Surface as specific humidities over 4 g/kg arrive within the area.
However...initially lowest levels look to start the day below
freezing. Top down methodology suggest not enough melting for
freezing rain initially...thus precip could start as
sleet...before the column warms toward freezing rain in the late
afternoon...before finally warming to rain by Sunday evening. Will
try and trend pops toward categorical both on Sunday afternoon and
Sunday evening as this forcing is expected to persist. Will stick
cloud on Sunday to slowly rising temperatures given the ongoing
warm air advection.

Cold front is expected to pass on Sunday night as the low pushes
through the great lakes. THis should cut off the
moisture...however low level clouds and perhaps the typical
flurry will not be able to be ruled out given the cyclonic flow.
Will trend lows below mexmos given the cold air advection.

&&

.LONG TERM /Sunday Night through Thursday/...
Issued at 255 PM EST Thu Dec 8 2016

The period begins with a weak warm front lifting north across the
area. An upper trough begins to amplify over the western great
plains...particularly South Dakota and Nebraska. The GFS is stronger
and more amplified with this feature...leading to a stronger surface
low passing across Illinois and Indiana Sunday night/Monday morning.
This allows for more warm air into the forecast area on the front
end and a quicker return of cold air after the low passes. It also
allows for higher QPF across the area. Mid/long range models have
not been in good agreement as it pertains to this portion of the
forecast lately. Thus...confidence not high in timing...depth and
strength of the cold air in advance of and behind the passage of the
surface low...affecting precipitation type. Model initialization
went with a blend...which seems reasonable.

Tuesday night sees the passage of a strong cold front with model
differences in the amount of precipitation Tuesday and Tuesday
night...but both the GFS and ECMWF signal the coldest air of the
season pushing in behind the front...with temps at 850mb in the
teens Wednesday afternoon/evening as an example.

&&

.AVIATION (Discussion for the 09/06Z TAFs)...
Issued at 1140 PM EST Thu Dec 8 2016

MVFR ceilings will likely persist through the night. VFR conditions
may return Friday afternoon.

Widespread stratus in cyclonic flow aloft will persist overnight
into Friday. Scattered flurries and occasional snow showers may
briefly reduce visibility but this should be minimal.

Winds will remain northwesterly through the period, generally around
8-12KT.


&&

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

$$

SYNOPSIS...PUMA
NEAR TERM...PUMA
SHORT TERM...PUMA
LONG TERM...MRD
AVIATION...NIELD


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