Area Forecast Discussion
Issued by NWS Indianapolis, IN

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530
FXUS63 KIND 101502
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1002 AM EST Sun Dec 10 2017

.UPDATE...
The NEAR TERM and AVIATION sections have been updated below.

&&

.SYNOPSIS...
Issued at 335 AM EST Sun Dec 10 2017

An amplified upper level pattern will continue across the country
through much of the upcoming week with ridging in the west and a
deep trough in the eastern states. This will result in temperatures
remaining largely below normal. Periodic chances for light
precipitation mainly in the form of snow will accompany upper level
waves tracking through the region. Upper level flow will relax by
next weekend bringing warmer temperatures back to the Ohio Valley.

&&

.NEAR TERM /Rest of Today/...
Issued at 1002 AM EST Sun Dec 10 2017

Upped sky cover this morning as a large area of mid cloud covers
central Indiana at the moment. However, the back edge is already
approaching the state line, so skies will become partly cloudy by
early afternoon. Additional high clouds moving in will keep it
partly cloudy for the remainder of the day.

Tweaked temperatures and wind some based on latest data, but no
significant changes made.

Previous discussion follows...

Backing flow through the boundary layer over the last few hours had
diminished the snow showers extensively and largely cut off the Lake
Michigan fetch. Skies had cleared over much of the area early this
morning as surface ridging expands in. 08Z temperatures generally
ranged from the upper teens into the mid 20s.

A much quieter day anticipated with the surface ridging over the
region for the first half of the day. A weak wave aloft over
northern Illinois early this morning will drift quickly east through
the region...bringing increased mid level clouds and perhaps a stray
flurry focused over northern portions of the forecast area. Sunshine
should return briefly midday before additional clouds arrive by late
afternoon ahead of a surface trough set to swing across the forecast
area into the evening. Southwest winds will gust ahead of the
surface trough this afternoon...then diminishing by early evening as
winds veer to northwest behind the boundary.

Temps...a warmer day expected today as high temperatures should
recover into the mid and upper 30s over most of the area. Trended
towards the cooler end of guidance.

&&

.SHORT TERM /Tonight through Tuesday Night/...
Issued at 335 AM EST Sun Dec 10 2017

Forecast challenges focus on precip chances and types with a system
poised to track through the area Monday afternoon and night.

The highly amplified upper flow pattern over the country since early
in the week will continue through the short term with a series of
waves aloft serving to reamplify the trough by midweek. This will
result in a continuation of the weather pattern experienced here in
central Indiana of late...with a brief warmup ahead of a fast moving
wave set to track through the Great Lakes late Monday and Monday
night. Behind this feature a renewed surge of colder air will follow
with a renewed threat of lake enhanced snow showers.

The aforementioned surface trough moving into the region late today
will shift quickly east this evening with surface ridging and mainly
clear skies once again briefly reestablishing. The upper wave will
dive out of the Canadian prairies late tonight and track quickly
into the area by Monday evening. A surface wave and cold front will
accompany the upper feature. Ahead of this system...moisture and
warm advection will enable clouds to return towards daybreak Monday
with perhaps a few light snow showers over northern portions of
central Indiana.

Monday should be dry across the forecast area with some sunshine
peaking through the clouds as well before thickening cloud cover
returns late day as the surface low tracks into the region. The low
and front will swing quickly through the area Monday night bringing
light precipitation that will likely start as a mix of rain and snow
before transitioning to all snow overnight as low level thermals
crash in wake of the front. Moisture profiles are not overly
impressive but presence of the stronger forcing aloft will be more
than enough to generate a few snow showers with potentially a
dusting in some locations by daybreak Tuesday.

Tuesday will see a day similar in design to Saturday as cyclonic
flow and intensifying cold advection set the stage for a chilly...
gusty day with flurries and light snow showers impacting central
Indiana. Northwest boundary layer flow will support development of
lake enhanced snow bands that will track well southeast and likely
impact far northeast portions of central Indiana. At this point...
the boundary layer flow is weaker than that experienced on Saturday
with winds in the 925 to 850mb layer oriented more in a NW to SE
direction. Model guidance is not capturing the particular impacts
well for Tuesday at this point...but presence of mid level vort
energy over the region for much of the day will likely support
flurries over most of the rest of the forecast area outside of the
lake enhanced band. Weakening and subtle backing of the boundary
layer flow by Tuesday night should shift most flurries and light
snow showers northeast of the forecast area. At this point...could
see light accums in northeast counties under an inch in the vicinity
of wherever the lake enhanced band sets up. Will continue to monitor
and fine tune as we get closer to Tuesday.

Temps...warm advection on Monday will bring a bump up in
temperatures into the 40s for most of the southwest half of the
forecast area. Temps tumble for Tuesday with much of the area
holding in the 20s. Utilized a model blend for Monday highs then
undercut guidance for Tuesday in the cold advection regime. A model
blend should work well for lows through the period...with teens once
again returning by Tuesday night.

&&

.LONG TERM /Wednesday through Saturday/...
Issued at 221 AM EST Sun Dec 10 2017

Ensembles in good agreement on the upcoming weather pattern later
this week. A deep long wave trough is expected to move off to the
east late this week, with upper flow becoming more zonal by the
end of the week.

Only item of interest during this period will be a weak
disturbance that is expected to move through the area during the
Wednesday to Thursday time frame. Will go with small chance PoPs
for light snow or light mixed precipitation from Wednesday through
Thursday night to cover this feature.

&&

.AVIATION /Discussion for the 101500Z TAF Update/...
Issued at 1002 AM EST Sun Dec 10 2017

Adjusted height of mid cloud and allowed ceilings to last a little
longer based on latest satellite imagery. May have to up winds more
with next update with gusts being noted already in central IL.

Previous discussion follows...

Scattered to broken layered cloud above 050 and unrestricted
visibility expected at the terminals today. Surface winds 210-240
degrees at 6-10 kts this morning will increase to 12-16 kts with
frequent gusts around 22 kts by midday and on into the afternoon.

&&

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

$$

SYNOPSIS...Ryan
NEAR TERM...Ryan/50
SHORT TERM...Ryan
LONG TERM....JAS
AVIATION...JAS/50



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