759
FXUS63 KIND 211134
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
634 AM EST Sat Dec 21 2024

.KEY MESSAGES...

- Isolated light snow near Lafayette through 6 AM EST.

- Slow warming trend late weekend through upcoming week.

- Trending towards slightly below normal temperatures for the second
and third weeks of January.

&&

.SHORT TERM (Today and tonight)...
Issued at 217 AM EST Sat Dec 21 2024

Early This Morning...
Isallobaric gradient remains oriented along a north/south setup,
which is touching the marine environment from Lake Michigan. Given
the resonance time of parcels is still optimal this is allowing the
relatively warmer lake surface and minimal turning in the near
surface boundary layer and is allowing a steady lake effect snow
band to drift south. The caveat at the moment is that pressure rises
are beginning to advect east towards Central Indiana and is
beginning to decrease the precip footprint. Expect some lingering
flurries and snow showers across portions of Central Indiana through
pre-dawn hours, then stronger diffluent flow in the mid-lvls will
continue to advect east and should inhibit moisture form the favored
dendritic growth zone.

Satellite imagery is still showing a robust stratus shield over the
region but is equally starting to decrease in coverage and drift
east. Expect stratus clouds to likely linger into daybreak and
perhaps mid-day due to the lack of stronger advection from the west
and minimal mixing to further erode the moist layer.

Mid-Morning through Afternoon...Heights will continue to rise mid-
morning and continue to help erode the lingering stratus shield.
With anti-cyclonic flow overhead inhibiting the potential for strong
ascending parcels, expect mixing to be minimal through midday and
likely produce a light wind if any wind from the west/northwest.
Temps should slowly warm into the lower to perhaps middle 30s in the
far south.

Tonight...The upper level pattern influence for the Ohio Valley will
continue to see the shortwave weakening and translate eastward
reaching the western periphery of the region by tonight. A broader
negatively tilted trough will be slowly digging south across the
Great Lakes and Northeast. This should result in more influence to
the Ohio Valley and Central Indiana by Sunday morning.

&&

.LONG TERM (Sunday through Friday)...
Issued at 217 AM EST Sat Dec 21 2024

Sunday through Friday... The extended period will feature a
dynamic weather pattern for the Ohio Valley. Initial period of
benign weather will give way to increased chances for
precipitation and fluctuating temperatures as a series of weather
systems traverse the region. The overall feature will be a
progressive mid-latitude cyclonic activity, that will have a
series of shortwave troughs embedded within a broader and
potentially amplified upper level trough over the eastern CONUS.

Sunday...500mb analysis leans towards a progressive pattern. The
aforementioned shortwave trough from Sat will pivot east, allowing
the boundary layer anti-cyclonic feature to equally lift northeast
and allowing the flow to turn southerly to southwesterly by midday
Sun. This will result in perhaps some upper level clouds, but the
bigger story will be on rising temperatures. Guidance is starting to
suggest the aggressive thermal ridge could be flirting with the Ohio
Valley by Sun afternoon and usher in temps back to the upper 30s and
could even see a few locations south of interstate 74 reaching the
low 40s by late Sun afternoon. The main player will be clouds
shielding any of the sun and limiting the rate of surface parcels
realizing the potential.

Monday... Relatively zonal flow pattern will still be present across
much of the CONUS, with a quasi-weak ridge axis over the Ohio
Valley. This will translate to the weak height gradients and
generally quiet conditions at the surface despite a weak mid-lvl
shortwave trying to flirt with the Western Great Lakes and perhaps
some mid-lvl clouds from ascending parcels coming into Central
Indiana late Mon. There is some agreement that light precip could
accompany the boundary midday Mon. But confidence has backed of
slightly due to the height at which the moisture is present and
could result in less of a footprint for precip.

Tuesday...Progressive pattern starts to take hold, with a more
evident shortwave trough ejecting out of the northern Plains into
the Great Lakes late Tue. This will translate into height falls
across the downstream areas of the Ohio Valley and increasing mid-
lvl moisture from ascending parcels and warm air advection.

Wednesday...Slightly more amplified trough axis over the eastern
CONUS. The phasing will result in stronger dynamic forcing with
robust positive vorticity advection over the Ohio Valley. This will
allow strong upward momentum, and increased chances for larger
precip footprint mid-week.

Thursday...Amplified trough axis will drift eastward, with a
secondary shortwave trough potentially rotating through the base of
the trough. This will likely lead to additional unsettled weather
into the later periods of the week into weekend.

Weeks 2 Through 4 Period:

While the period will begin mild...the long wave pattern is expected
to shift toward the new year as a building western ridge allows a
deep trough to develop across the central and eastern CONUS by early
January with several potential short waves crossing the region
through mid month.

The period from Christmas to the beginning of the new year looks
very mild but also likely to be wet with an above normal
precipitation signal lined up through the Ohio valley. With warm
temperatures this precipitation should be mostly in the form of rain
with even a possibility of thunder at times.

As pattern begins to shift near New Years, timing of colder air
infiltration with pcpn signals will need to be watched for
possibility of snow as this transition develops. Once cold air
becomes established...there is uncertainty with regards to pcpn
signals. Below normal precipitation is favored in the GFS and EC
weekly anomalies, and favored by CPC, but CFS looks rather active
with several short waves and potential storm systems crossing the
central CONUS. This could bring rain or snow depending on storm
tracks and timing which cannot be resolved by any means at these
projection times. Overall temperatures during this period should be
near or below normal.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 634 AM EST Sat Dec 21 2024

Impacts:

- Isolated MVFR CIGs through 15Z then all airfields should be VFR
  through remainder of TAF period.

- Winds 330-350 degrees with speeds around 4-7kts slowly diminishing
  then winds turn northeasterly to southerly Sun morning.

Discussion:

Stratus deck that has been producing MVFR CIGs has steadily moved
east of Central Indiana, with just some spotty locations having MVFR
CIGs. Based on current satellite imagery some mid-lvl clouds are
arriving from the west but is slowly shrinking in size due to the
abundant dry air already pushing into CEntral Indiana. With high
pressure nudging across the area, winds will also continue to be
light generally from the north around 5kts. Then high pressure
pushes east late tonight and winds will start to turn northeasterly
and eventually southerly by midday Sun.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

SHORT TERM...Beach
LONG TERM...Beach/Lashley
AVIATION...Beach