351
FXUS63 KIND 232333
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
633 PM EST Sat Nov 23 2024

.KEY MESSAGES...

- Cloudy through at least midday Sunday
- Warming trend this weekend
- Wintry precipitation potential mid-week with accumulating snow
  and travel impacts possible

&&

.SHORT TERM (This evening through Sunday)...
Issued at 226 PM EST Sat Nov 23 2024

Visible satellite shows western end of stratus slowly eroding over
Illinois as mixing has increased. This should continue through the
afternoon with the western edge approaching the Indiana border, but
likely slowing as mixing subsides this evening. Once the low-level
ridge axis passes tomorrow and lower tropospheric flow becomes more
anti-cyclonic, along with modest dry advection and increased mixing
by late morning Sunday, stratus may finally erode. At least across
roughly the southwest two-thirds of central Indiana.

We have adjusted temperatures downward from previous forecast the
rest of the afternoon given ~1-km thick stratus layer persisting and
limiting surface diurnal temperature swing some. Likewise, with
persistent stratus likely tonight, we have increased temperatures
from the previous forecast by a degree or two.

There may be a tendency for the ceiling to lower some late this
evening and overnight. While lower tropospheric flow won`t be quite
as cyclonic given the departing deep low, it is possible that some
brief light patchy drizzle could reform and persist through early
Sunday morning. This will be non-measurable and if it happens be
barely noticeable.

Temperatures on Sunday will be warmer as ridge axis passes and
southwesterly flow strengthens with warmer plume and mixing driving
temperatures into the 50s, with low 60s possible across the
southwest portions of the forecast area (near Vincennes). If stratus
persist longer in the northeast this would limit the diurnal
temperature climb to just the upper 40s (near Winchester and
Muncie).

&&

.LONG TERM (Sunday night through Saturday)...
Issued at 226 PM EST Sat Nov 23 2024

As an approaching midlevel shortwave trough deepens some Sunday
night into Monday, and ageostrophic flow strengthens in response,
broad ascent should develop. The moisture connection isn`t as
rich/deep as with previous systems (PWAT anomaly only ~1-sigma), but
isentropic surfaces moisten sufficiently for light rainfall amounts
on Monday. Multi-model ensemble mean has around 0.10-0.25 inch QPF
amounts.

We will still be in a fairly low-amplitude synoptic flow pattern, so
this system won`t be very effective at dislodging higher latitude
Arctic air mass. Yet, modified cP post-frontal air mass Monday night
into Tuesday will be noticeably colder. After warm advection pattern
gets tempered some by precipitation and resultant diabatic effects
Monday (still mid-upper 50s area wide), cold advection should hold
us in the upper 30s to low 40s Tuesday. Low stratus is less likely
in the wake of this system due to stronger cold/dry advection in its
wake.

High-level Pacific moisture plume coupled with midlevel
frontogenesis late Tuesday night into early Wednesday could result
in a east-west band of virga/flurries, but only a low chance of
measurable due to dry sub-cloud layer. As ascent from the approaching
shortwave trough approaches later in the day and top-down
saturation/modest moistening continues, this east-west frontogenesis
precipitation band should become more intense yielding light QPF
amounts. Dry easterly continental flow should allow evaporative
effects in the lower troposphere that would result in sufficient
temperature for snow ptype across most of the area. Ascent appears
to peak late Wednesday/evening. The ECMWF/EPS camp seems to be more
aggressive with cyclogenesis and a closed low- to mid-level
circulation with comma-head/deformation type structure. This would
keep some snow chances into Thursday. It`s worth noting that the
GFS/GEFS camp, although displaying a more open wave, is not devoid
of the deeper low scenario, with some ensemble members overlapping
with the ECMWF scenario. Details with regards to snow amounts are
unclear with the aforementioned synoptic-scale uncertainties. A
deeper low may result in more QPF (i.e., a decent number of EPS
having >1.00" amounts as far north as Indy) but concurrently could
be stronger with warm advection, meaning ptype is more in question.
Likewise, this is also a scenario where mesoscale banding could
occur, and so the ceiling for snowfall amounts somewhere across
Indiana may be quite high.

How long snow showers linger will depend on how deep
the low develops, and its influence on MSLP fields. A deeper low
with lingering cyclonic lower tropospheric flow would lead to
rain/snow shower potential into Friday. The eastern trough may
persist into the weekend with minor perturbations causing occasional
light precipitation events, though the ensemble spread grows by this
time period, so there is some uncertainty.

The Day 8-14 period looks cold with periodic waves and light
precipitation events, with a warming trend toward the end as there`s
a signal in medium-range models for eastern trough slowly departing.
So, on average, below normal temperatures and near or below normal
precipitation.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 632 PM EST Sat Nov 23 2024

Impacts:

- IFR/MVFR ceilings will continue into Sunday
- Light southwesterly flow will back to southerly by 12Z Sunday,
  with sustained winds increasing to 8-12KT in the afternoon

Discussion:

Ceilings this evening will likely continue their slight downward
trend with low-MVFR possibly dropping into high-IFR levels at all
terminals.  Improvement back to MVFR may occur after 06Z when the
staunch inversion within the 925-850 mb layer approaches an
isothermal lapse rate.  Stratus should break Sunday during morning-
midday hours...with VFR prevailing by afternoon.

Visibility reduction from BR/FG is possible tonight, mainly at KIND/
KBMG where MVFR to brief IFR will be possible.

Southwesterly winds will diminish this evening, and continue to
slowly back to southerly by daybreak.  Flow will gradually increase
Sunday morning...with winds from 170 degrees at 7-11KT by the end of
the TAF period.

&&

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

$$

SHORT TERM...BRB
LONG TERM...BRB
AVIATION...AGM