722
FXUS63 KIND 250802
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
302 AM EST Mon Nov 25 2024

.KEY MESSAGES...

- Cloudy Skies and Periodic showers or drizzle Today.

- Cloudy and colder tonight.

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

- Much colder Friday into the weekend.

- Light snow possible on Saturday.

&&

.SHORT TERM (Today and tonight)...
Issued at 301 AM EST Mon Nov 25 2024

Synopsis:

Surface analysis early this morning shows low pressure in place over
NE MO and Western IL. A warm front extended east across northern
Indiana from this system. A cold front stretched SW from the low
across Central MO to OK.  Mainly southerly surface flow was in place
across Central Indiana within the warm sector ahead of the low.
GOES16 shows abundant cloud cover in place associated with the low,
and these clouds were invading Central Indiana. Aloft, water vapor
shows ridging in place over Indiana and Ohio, however that feature
was exiting east.  More important was an upper low found over
Saskatchewan along with a trough axis extending south across the
high plains. Pacific moisture was found within the flow aloft,
streaming across the American southwest to OK and KS before turning
northeast to Indiana and the Ohio valley on the windward side of the
departing ridge. Radar across the area and region was rather quiet

Today -

Interesting weather pattern today. Models show the low pressure
system to the west pushing to Michigan through the course of the
day. While this occurs, the associated cold front is expected to be
pushed toward and eventually across Central Indiana. Through the
course of the day, much of our area spends time within the warm
sector, and time heights and forecast soundings show shallow
saturation within the lower levels. 295K Isotropic surfaces show
weak up glide across the area through the morning hours and into the
early afternoon, with high specific humidifies. Forcing aloft is
present, albeit it appears rather weak as the upper low and trough
from the northern plains approaches. Deep moisture fails to develop.
Meanwhile the HRRR has been steady with its runs, showing scattered
to isolated very light rain showers through the day. Given these
signals, will aim for cloudy day. The low cloud decks expected to be
present will be favorable for these very light rain showers or
perhaps some drizzle.  Either way, any precipitation amounts will be
light as the weak isentropic lift appear to be the best forcing
element through morning and mid afternoon.

By late afternoon, isentropic lift appears to end, leading to lesser
chances for these very light showers. Given the warm start today,
but expected clouds and very light precipitation, highs in the
middle to upper 50s appear on the mark.

Tonight -

Dry and clearing weather is expected to arrive tonight. The upper
trough associated with the upper low moving through the Great Lakes
will be exiting east through the night. Meanwhile within the lower
levels the cold front will have pushed east of Indiana and surface
high pressure from the southern plains will be building across
Indiana. Forecast soundings and time heights suggest clearing
arriving overnight, but warm air advection and mid level ridging
does not arrive until sometime on Tuesday. Thus confidence is low
for clearing overnight and may be delayed until Tuesday. Confidence
will remain high that any precip will end as subsidence will be the
main feature in play along with cold air advection. Lows tonight
should fall to the lower 30s, but could be cooler should that
unexpected clearing occur.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 301 AM EST Mon Nov 25 2024

Cold air advection will be ongoing Tuesday after frontal passage
this afternoon. Temperatures look to dip into the 20s for a good
portion of the area. With a rather progressive flow pattern aloft,
low-amplitude ridging upstream quickly moves back into the region.
Return flow around surface high pressure should induce weak warm air
advection Tuesday night.

Further west, a series of shortwaves begin ejecting into the Plains.
Guidance shows a broad area of frontogenesis taking shape across
Illinois and Indiana, which may lead to light precipitation as early
as Wednesday morning. Model soundings show dry air below 850mb, so
much of this activity may end up as virga. At minimum, it will take
a number of hours to fully saturate the atmosphere and get
precipitation to the ground. Precipitation type could be snow north
of I-70 as wetbulb temperatures are near freezing...marginal/too
warm further south. Current guidance shows this zone setting up
across the northern portions of our CWA and into northern Indiana.
It may remain dry for most of the day further south, until increased
forcing from the approaching shortwaves helps generate another round
of precipitation.

Uncertainty still remains, however, regarding the upcoming system. A
few scenarios remain on how it might evolve. These can generally be
divided into two camps...one showing a more robust system with
central Indiana firmly in the northern precipitation shield, and a
second showing a less intense system passing quickly to our south
leaving much of the area dry. Differences in guidance stem from how
the models handle phasing of two distinct vort maxes. Where phasing
occurs, a more robust system develops and vice versa. Right now,
there seems to be an even split within guidance on which scenario
plays out. Precipitation type may be a bit tricky, as not much of a
cold conveyor exists since deep low pressure may be located across
southern Canada. Favorable thermal profiles for snow may derive
mainly from diabatic/evaporational processes. Should the system be
more subdued and further south, these effects may be limited
allowing the primary p-type to be rain. In the event of a more
robust system, increased warm advection preceding it may help offset
these effects closer to the low center. Snow/accumulating snow is
still possible, however, and impacts to Indiana therefore depend
highly on the system`s strength and track.

Ensemble guidance continues to show substantially colder weather
arriving late in the week as the upper pattern becomes more
amplified. This pattern may persist well into December as east coast
troughing and northwesterly flow are favored. Such a pattern is also
typically dry, though occasional light precipitation events may
occur.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 1221 AM EST Mon Nov 25 2024

Impacts:

- Mainly VFR Cigs overnight.
- IFR Cigs arrive after daybreak, with showers/drizzle possible.
- Non-convective low-level wind shear overnight.

Discussion:

Warm air advection ahead of approaching low pressure will lead to
VFR Cigs this overnight. HRRR suggests some isolated light rain
showers will be possible, but this should not restrict visibilities.
A moderate LLJ will result in some LLWS overnight.

As low pressure over MO pushes to Lake Michigan today, a cold front
will be dragged across Central Indiana. Forecast soundings show
saturation within the lower levels, indicative of some IFR Cigs
expected to pass with the cold front. Weak forcing and low clouds
may result in some scattered light rain showers or drizzle this
afternoon.

Southerly winds this morning will gradually shift to the northwest
in the wake of the front tonight.


&&

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

$$

SHORT TERM...Puma
LONG TERM...Eckhoff
AVIATION...Puma