227
FXUS63 KIND 242345
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
645 PM EST Sun Nov 24 2024

.KEY MESSAGES...

- Periodic light rain possible Monday.

- Marginal temperatures for rain/snow Wednesday and Thursday;
  limited accumulation and travel impact currently expected

- Much colder Friday into the weekend.

- Light snow possible next Saturday.

&&

.SHORT TERM (This evening through Monday)...
Issued at 229 PM EST Sun Nov 24 2024

We`re now on the windward side of low-mid level ridge axis, and so
the low stratus has ended. Some alto-stratus and cirrus is present,
but satellite trends shows this is mostly relegated to our north
where strong westerlies aloft are.

A warm/moist advection pattern will strengthen preceding the next
midlevel shortwave trough that is expected to pass through Monday
evening. There is an good IVT signal and slightly anomalous
precipitable water values, although this is tempered somewhat by
relatively dry mid-upper levels. Low-level moisture is rich and
ceilings are expected to be quite low tomorrow morning. Thus, a more
substantial/heavier precipitation is not expected, but this may
manifest as drizzle with occasional heavier showers.

As deeper moisture and ascent become increasingly aligned later in
the day, eastern portions of Indiana may see the highest amounts,
where HREF mean exceedance probabilities for >0.10" are highest.
Many areas further west may not even reach 0.10" total by Monday
evening.

Some of the high-res models are cooler with temperatures tomorrow
despite the warm advection pattern, due to thick stratus, low
ceilings and potential for persistent drizzle. We have lowered
temperatures some.

&&

.LONG TERM (Monday night through Sunday)...
Issued at 229 PM EST Sun Nov 24 2024

On Tuesday, the low-amplitude synoptic flow pattern will be
ineffective at displacing cold Arctic air mass in Canada, and so the
post-frontal environment will be colder and and drier, but barely
anomalous. Temperatures should be a little below climatology in the
low-mid 40s. Will watch trends, but an extended period of wake
stratus looks less likely than the previous two systems. If PBL
moisture ends up slightly greater below strong subsidence inversion,
it may linger longer than currently expected.

Previous indications of phasing and a resultant deeper more intense
low mid-week are now less than ECMWF-EPS weighted clusters,
including its AI counterpart. More multi-model ensemble members show
the suppressed scenario than not. It seems increasingly likely that
the heaviest precipitation amounts will be focused to our south late
Wednesday into Thursday. We have trended precipitation probabilities
and amounts downward for this period.

Current thinking is the initial northern stream shortwave
perturbation approaching the Great Lakes on Wednesday will interact
with an east-west oriented baroclinic zone and result in a band of
light precipitation/virga across roughly the northern half of
Indiana. For central Indiana, dry sub-cloud layer may preclude
measurable amounts, and wet bulb temperatures look marginal for
rain/snow. The ECMWF-EPS lags this wave and phases it somewhat with
the much faster southern stream wave (relative to GFS-GEFS camp).
The GFS-GEFS is about 18 hours slower with the southern stream wave
and has most of the QPF south of our forecast area. If precipitation
does end up confined further south, most/all of it would be rain. If
we trend toward a more phased scenario like ECMWF shows, snow and
some accumulation with travel impacts would still be possible, but
even then the more amplified scenario may be preceded by stronger
warm advection and at least initially favor more rain than snow.

Friday we have removed rain/snow showers, as this was contingent on
a broader/deeper closed low exiting and moisture/cyclonic flow on
its western periphery. We will be considerably colder with a trend
toward a more amplified upper flow pattern and eastern troughing
helping dislodge higher latitude cold air southward. We will likely
be around 10 degrees below normal for late November Friday into the
weekend.

Saturday we have increased precipitation chances as most model
ensembles point toward a low-end precipitation event. Thermal
profiles will support snow. Amounts seem meager at this time given
northwesterly flow and limited moisture.

We then enter a colder northwesterly flow pattern with persistent
eastern troughing for much of the Day 8-14 day period. Periodic
light precipitation/snow may occur, but this pattern supports below
normal precipitation during that period.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 645 PM EST Sun Nov 24 2024

Impacts:

- Sub-VFR ceilings return tonight
- Non-convective low-level wind shear tonight
- IFR or lower ceilings Monday and rain/drizzle possible through
early afternoon

Discussion:

The next system will be preceded by moisture advection and lowering
ceilings. IFR/MVFR ceilings should start during the pre-dawn hours
with moderate confidence on onset timing indicated in the TAF.
Moderate confidence on ceilings lowering to IFR or below. Moderate
confidence in IFR or lower ceilings persisting at least into
afternoon. Delayed the timing of the lowering ceilings for the 00z
TAF issuance as upstream obs and satellite imagery show largely high
clouds and VFR conditions. Latest guidance keeps conditions mostly
VFR through the first half of the overnight period.

Periods of light rain may manifest more as drizzle through the
morning, with light amounts and intensity, and minimal visibility
restrictions expected.

The accompanying low-level jet may be just strong enough for
minimally meeting non-convective low level wind shear thresholds.
There are some indications that surface wind speeds may remain high
enough for thresholds not to be met, but have included for the first
part of the night, until the core of the low level jet shifts
southeast.

&&

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

$$

SHORT TERM...BRB
LONG TERM...BRB
AVIATION...CM