167
FXUS63 KIND 101032
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
532 AM EST Fri Jan 10 2025

.KEY MESSAGES...

- Winter Weather Advisory today through the early overnight tonight
  with snow accumulations of 2 to 4 inches

- Below normal temperatures continue through the next week along
  with a weak clipper system Sunday night

&&

.SHORT TERM (Today and Tonight)...
Issued at 258 AM EST Fri Jan 10 2025

A thick blanket of cirrostratus have overspread central Indiana
early this morning as the winter storm that has brought snow and
freezing rain from the southern Plains east now into the lower
Mississippi Valley. Lows have already been reached for the night as
temps have ticked up a few degrees from earlier readings...with 07Z
temps in the 15 to 20 degree range.

The aforementioned winter storm to our southwest will continue its
expansion towards the Ohio Valley this morning...serving as the next
salvo in the extended cold and unsettled winter regime we reside in
currently and are likely to remain in for the next 1-2 weeks. While
heavier snowfall amounts will be focused more across the Tennessee
Valley with this system...this will serve as a snowpack freshener
for the region with an extended period of steady snow beginning
later this morning and lingering through late evening.

Meteorology:

The primary surface low will remain confined to a track along the
Gulf Coast through tonight...but its interaction with a deep
meridional upper level trough and a frontal boundary extending north
into the Great Lakes. Moisture will advect poleward ahead of the
front and encompass the Ohio Valley later this morning.

Initially...a broad layer of dry air generally below 650mb will
slowly saturate from the top down but in the absence of more
substantial lift...this process will take some time with snow
holding off on expanding into the Wabash Valley until near daybreak
at the earliest and even then...it may take until late morning for
snow to become steadier and more widespread over the forecast area
as persistent southeasterly flow through the near surface layer
delays more substantial saturation.

The heaviest snow rates will come this afternoon into the early
evening as the deepest moisture aligns with an axis of stronger
isentropic lift north of a low level jet pivoting through the
Tennessee Valley. The favorable left front exit region of a strong
upper level jet will track through the Ohio Valley and further aid
in the broad area of snowfall through the afternoon. Deep moisture
and lift will extend up through the dendritic growth zone for
several hours as well and may enable brief periods of slightly
heavier snowfall rates. A dry slot will expand northeast from the
lower Mississippi Valley will expand northeast as far as Kentucky by
late day...but the presence of enhanced forcing ahead of the
approaching surface front and upper trough will maintain light to
moderate snowfall into the evening across the region.

While snow rates will gradually lighten and coverage will decrease
through the evening as the deeper isentropic lift shifts to the east
of central Indiana...anticipate snow will not completely diminish
until the trailing upper trough axis moves through the forecast area
around or shortly after midnight. Low clouds will persist through
daybreak Saturday as model soundings show low level moisture trapped
beneath an inversion for the remainder of the night.

Snowfall and Headlines:

High confidence continues in overall precipitation amounts for much
of the forecast area from 0.15 in the northern Wabash Valley to
around 0.25 inches over the southern half of the forecast area. The
cold surface temps and overall thermal profiles remain supportive of
snowfall ratios hovering near 15:1 for much of the upcoming event
resulting in overall snowfall totals of 3 to 4 inches for much of
the forecast area...with slightly lower amounts over the far
northwest counties of the forecast area. There remains potential
for a few spots to overachieve locally higher than 4 inches...most
likely across the southeast half of central Indiana where the
highest qpf values will reside.

The Winter Weather Advisory will continue but with subtle changes to
start and end times based on overall trends. Will push back the
start time this morning to 12Z based on the slower onset...and bring
the end time to the headline tonight up by a few hours to 06Z Sat.

&&

.LONG TERM (Saturday through Thursday)...
Issued at 258 AM EST Fri Jan 10 2025

The long term period will be characterized by fluctuating but still
primarily below normal temperatures, with multiple upper
level waves moving through the larger scale cyclonic flow in place
across much of the country.

One or more low probability chances for precipitation will be
possible, but with significant questions about both moisture
availability and model disagreement, the only mentioned PoPs during
the long term will come Sunday afternoon and evening.

Forecast profiles show very disjointed moisture with this late
weekend disturbance, with upper levels saturating Saturday night but
drying out by the time low levels moisten up and forcing arrives.
Will carry a mention of snow showers or freezing drizzle during this
period, given the modeled loss of cloud ice. Will need to keep an
eye on this as the weekend goes along.

Another fairly substantial cold blast is expected in the wake of
this late weekend system, with temperatures likely to fall much of
the day Monday. Several single digit nights are likely again this
week, with subzero temperatures again possible as well.

Temperatures may moderate a bit late in the week into the coming
weekend, but models suggest this will be brief, with another,
potentially even more significant Arctic airmass poised to plunge
into the CONUS at the beginning of the following week.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 532 AM EST Fri Jan 10 2025

Impacts:

- Snow developing this morning and continuing into the evening
- Widespread sub-IFR conditions developing within the snow
- MVFR conditions likely to linger after snow ends tonight

Discussion:

Clouds continue to thicken and lower early this morning with light
southerly winds. Snow will expand into the region through late
morning with ceilings and visibilities dropping quickly as snow
becomes moderate to locally heavy at times this afternoon. Expect
widespread 1SM and lower through the afternoon with ceilings
hovering between IFR and low MVFR. Winds will remain light through
late day from the south.

Snow will begin to diminish in intensity and coverage this evening
before ending early into the overnight. Model soundings show
moisture remaining trapped beneath an inversion through daybreak
Saturday with MVFR conditions expected to linger after the snow
ends. Winds will veer to W/NW by late evening into the overnight as
a frontal boundary passes through.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 1 AM EST Saturday for INZ021-
028>031-035>049-051>057-060>065-067>072.

&&

$$

SHORT TERM...Ryan
LONG TERM...Nield
AVIATION...Ryan