Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 080806

Area Forecast Discussion
National Weather Service Indianapolis IN
306 AM EST Fri Dec 8 2023

.Key Messages...

- Mild and breezy through Saturday.

- Gusts generally 20-25+ MPH through Friday, increasing to 30-35 MPH
Friday night and Saturday.

- Rain at times Friday night through Sunday, particularly Saturday.
A few snowflakes possible east Sunday.

- Turning colder and dry next week.


.Short Term...(Today and tonight)
Issued at 305 AM EST Fri Dec 8 2023

Surface analysis early this morning shows deep low pressure in place
over eastern North Dakota. A secondary low was found over the TX/OK
panhandle and a weak trough connected these two systems.  Strong
High pressure was found along the GA/FL coastline. This was
resulting in a moderate pressure gradient across MO/IL and Indiana.
GOES16 shows high cirrus exiting Indiana this morning, but some low
cloud was found ahead of the trough over IA/IL and MO. Water vapor
imagery showed an active flow aloft. Strong ridging was in place
over Indiana, Ohio and the Great Lakes. Upstream, a moderate trough
was found over the Dakotas, associated with the deep surface low. A
quick flow aloft was found across the southwestern states. Dry air
and subsidence was shown over MO and IA. Winds across Central
Indiana this morning were from the south at about 10-20 mph,
resulting in good mixing and preventing sharp temperature falls.


Models today show the ridging aloft over Indiana will push to the
east coast today, while the trough over the Dakotas and Rockies will
become deeper, producing a more amplified pattern. This results in a
strong southwest flow aloft over Indiana today, but little in the
way of forcing dynamics appears present. BUFKIT soundings show dry
air aloft along with subsidence as this was being depicted upstream
within the water vapor imagery. Meanwhile within the lower levels,
warm air advection was in play on southerly winds. Here BUFKIT
soundings show saturation arriving within the lower levels this
afternoon. Thus we will trend toward increasing clouds today.
Meanwhile the story today will be gusty winds. The strong pressure
gradient in place today should allow for wind gusts, particularly
this morning to reach 25 to 35 mph per BUFKIT momentum transfer.
These winds will be notable today.

Regarding temperatures, winds overnight have not allowed
temperatures to fall too much as we are in the upper 40s to near 50
at many locations. Thus with the warmer than expected start along
with the dry southwest wind expected through the day, high
temperatures should overperform. Look for highs in the upper 50s.
Lower 60s will be possible at locations in southwest Central
Indiana. This is about 15-20 degrees above our seasonal normals.


The southwest flow is expected to persist aloft overnight. Meanwhile
upstream the deepening trough over the plains is expected to begin
to advance eastward. Models suggest some upper forcing begging to
push toward Indiana, although the best forcing remains well to the
west with the main trough. The GFS 295K isentropic surface shows
moderate lift arriving overnight, and persisting through 12Z.
Specific humidities look quite high, around 7 g/kg. Meanwhile
forecast soundings suggest deepening saturation within the lower
levels, but dry air remains aloft. HRRR shows scattered to isolated
showers across Indiana ahead of the main forcing after 06Z. Thus
there is high confidence for some spotty light showers tonight,
mainly late, but low confidence on any given location. Best forcing
appears to be pulled north from northern IL toward Michigan and the
Great Lakes. Nonetheless, pops will be needed tonight for light rain
as all the discussed dynamics pass. Will use highest pops across the
NW parts of Central Indiana, including locations like LAF, trending
to lesser pops across the south.

It should be a warm night for December. Winds will remain southerly
all night and the moderate pressure gradient looks to remain in
play. This will keep mixing in place, and along with cloud cover
temperatures should not fall much. Look for lows in the lower 50s.


.Long Term...(Saturday through Thursday)
Issued at 305 AM EST Fri Dec 8 2023

Expect a large upper trough with embedded waves to track through the
region over the weekend with a few chances for precipitation. Strong
SSW flow ahead of the main trough will advect anomalous moisture
into the region with dewpoints in the 50s. This combined with a cold
front moving in at the start of the period should support widespread
showers saturday morning. Rainfall amounts during the first half of
the day should be light as the embedded upper shortwave and stronger
forcing  associated with the front remain displaced northwest of
central Indiana. SSW Wind gusts up to 30-35 mph will be possible
early in the day due to a strong pressure gradient. These winds
should then diminish rather quickly later in the day once the
gradient relaxes. The strong warm-moist flow will lead to well-above
average temperatures in the low 60s for portions of the area. Highs
across northwest portions of the area will likely not reach the 60s
as the cold front should pass through early Saturday morning.

By Saturday evening, guidance shows strong PVA overruning the
aforementioned front likely still lingering over parts of the area
with the main upper trough axis still near the Iowa/Illinois border.
This will likely support additional rain chances during the evening
and overnight hours, mainly across southeastern counties. It is
worth noting, some guidance is slower with the front lingering
across far southeast portions of central Indiana late in the day
while others push the boundary further east and out of the forecast
area. If the slower solutions were to verify, stronger overall
forcing would support heavier rainfall amounts around half an inch
to one inch. Further north and west, QPF amounts should be around
0.25 inches or less.

As the system moves out on Sunday, lingering low-level moisture may
support light drizzle or possibly flurries at times during the day.
Clouds and cold air advection will keep highs in the 30s.
Thereafter, quiet weather conditions are expected for the remainder
of the period as strong high pressure builds across the region. Look
for temperatures to warm up through the week and possibly return to
the 50s by late next week.


.Aviation...(06Z TAF Issuance)
Issued at 1240 AM EST Fri Dec 8 2023


- Low level wind shear overnight
- Wind gusts up to 30kts Today
- MVFR ceilings arriving this afternoon


Indiana will be caught between a strong area of low pressure over
the Dakotas and a strong area of high pressure off the Carolina
coast during this TAF period. This will result in strong pressure
gradient in place across Indiana today and gusty winds.

Overnight, LLWS due to speed will be in play as 40-50 knt winds will
be in place about 2000kt above the surface. As heating and mixing
begins on Friday, winds surface winds will begin to increase and the
speed shear will no longer be expected although surface winds will
be gusting to near 30 knts along with 40-50 knt winds aloft.

Strong warm air advection is suggested in this pattern. Forecast
soundings show a layer of warm air advection clouds arriving by mid
afternoon. These are expected to be MVFR cigs. Time heights also
show saturation arriving within the lower levels amid this warm air
advection pattern.

After 00Z...HRRR shows isolated showers developing across Central
Indiana as some forcing arrives in the area ahead of the approaching
large trough. For now, we have used VCSH to account for these
possible showers/storms.




Short Term...Puma
Long Term...Melo
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