FXUS63 KIND 310501
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
101 AM EDT Thu Oct 31 2024

.KEY MESSAGES...

- A warm and breezy night ahead. Lows in the lower to middle 60s.

- Widespread rain, isolated thunderstorms, windy and warm on
  Halloween.

- Rain ending by late afternoon and early evening on Thursday
  afternoon; Turning cooler.

- Cooler and Dry early weekend and more rain chances and warmer late
  weekend into next week.

&&

.FORECAST UPDATE...
Issued at 934 PM EDT Wed Oct 30 2024

Going forecast is in excellent shape this evening.

Breezy conditions and anomalously warm low temperatures are expected
overnight.  Gusts will be more sporadic than during the daytime as
mixing decreases, but full decoupling of the boundary layer will be
prevented by the continued strong pressure gradient and relatively
strong flow just off the surface.

This continued mixing and low level warm advection, along with
increasing cloud cover, will keep temperatures up overnight - with
lows in the mid 60s - above normal highs for the time of year, much
less lows.

Latest high resolution guidance brings the main pre-frontal band of
precipitation into the area as early as 10-11Z in the northwest,
which fits well with current grids.

&&

.SHORT TERM (This evening through Thursday)...
Issued at 238 PM EDT Wed Oct 30 2024

Synopsis:

Surface analysis early this afternoon shows a strong pressure
gradient in place over Central Indiana. This was allowing for a
moderate southerly flow of warm air across our forecast area. This
was due to a strong area of high pressure found over NC and a cold
front a trough of low pressure stretching from Lake Superior to
western IA  and Central KS. Aloft, water vapor imagery showed a deep
trough over the western CONUS and strong ridging in place over the
eastern third of the CONUS. GOES16 shows high clouds streaming
within the SW flow aloft over Indiana, mainly focused over IL/MO/WI.
Temperatures remained quite warm, mainly in the lower 60s this
morning. Dew points were unseasonably moist for this time of year,
in the mid to upper 50s. Radar shows light showers over far western
IL, while convection and thunderstorms were developing along the
front over KS and NB.

Tonight

Quiet, breezy and warm weather is expected tonight. The strong
ridging aloft is expected to depart to the east coast tonight, but
it will take almost the entirety of the period to do so.  Meanwhile
the upper trough over the Rockies will push toward the Central
Plains. During the overnight hours, little in the way of forcing is
expected to pass across Central Indiana, however the southwest flow
aloft will continue along with a continued flow of warm air. A
strong LLJ, around 50 knots, is expected to advance into the area
late overnight. This along with the strong surface pressure gradient
will continue to allow for good mixing, and allow for a breezy warm
night. Forecast soundings through much of the night remain dry for
most of Central Indiana. Points in the west, near the Wabash, do
shows hints of saturation as the cold front and LLJ arrive toward
12Z. Thus a dry evening will be expected and small chances for rain
will be included across the western parts of the forecast area after
09Z.

Given the expected increasing cloud cover and continued mixing of
warm air, unseasonably warm low temperatures will be expected in the
lower 60s.

Halloween (Thursday)

Get ready for a spooky weather day as the atmospheric ghouls stir!
Models reveal that a menacing upper trough is lurking over the
Plains, set to glide across the Great Lakes like a ghostly
apparition. This ominous system will drive a cold front across the
plains toward Indiana in the morning, creeping ominously into our
state by the afternoon.

A wisp of eerie mid-level moisture is expected to accompany the cold
front, arriving in the west during the morning and gradually
haunting Central Indiana throughout the day. By the witching hour of
21Z to 00Z, this moisture will have drifted southeast, with the best
rain producing moisture lurking near the Ohio River.

Forecast soundings reveal a saturated atmosphere enveloping
Indianapolis around 18Z, but as the clock strikes 21Z, subsidence
will creep in, drying the air out by 00Z. With these trends, expect
a late afternoon filled with fleeting rain showers, fading into dry
conditions as the darkness descends.

The forecast reveals a peak precipitable water value of 1.62 inches
(a rare and potent brew for this time of year) boosting our
confidence for rain as these atmospheric forces pass. Near 100
percent chances of precipitation mean the ghosts of rain are likely
to haunt us. However, while a rumble of thunder might echo in the
distance, widespread storms seem unlikely.

Given the encroaching clouds and the spectral showers, anticipate
high temperatures in the upper 60s. A fitting backdrop for this
Halloween haunt. As night falls, temperatures will drop to the lower
60s. This combined with a ghostly breeze howling at 10-20 mph may
result in chills, making it feel even colder. So, don your raincoats
during the day and afternoon and get your costumes ready by the
evening and keep an eye out for those creeping clouds.

&&

.LONG TERM (Thursday night through Wednesday)...
Issued at 238 PM EDT Wed Oct 30 2024

A low-amplitude shortwave trough will be departing Thursday night
and will temporarily nudge a cooler and drier continental air mass
into Indiana. Sensible weather on Friday will be reminiscent of what
we experienced this past weekend, and could actually be the coolest
temperatures that we have experienced since the 16th. Medium-range
deterministic and ensemble guidance agree on the retrograding and
amplifying nature of the eastern mean ridge as stronger westerlies
aloft shift poleward and western trough amplifies and moves slowly
eastward. Deep/rich moisture is only relegated to near or just south
of the Ohio River given the character and path of aforementioned
departing shortwave trough, and should readily flow northward late
Saturday into Sunday in response to the approaching west trough.

There is a QPF signal in most models late Saturday night into Sunday
that appears to be tied to broad weak isentropic ascent within an
anomalously moist environment, and subtle lead shortwave
perturbation. The ascent per deterministic model isentropic charts
is most concentrated during a period of frontogenetical forcing
along the advancing warm front, and may tapper off later on Sunday.
But, the timing varies among the ensemble members. More members than
not show the more concentrated ascent and probable warm advection-
driven rain band to be early, while a smaller percentage of members
lag. We will refine the timing but for now it appears slightly
higher probabilities are needed early in the day with low-mid range
probabilities late in the day into the evening. This latter period
may actually be a lull in precipitation if the broader weak
isentropic ascent weakens further and/or the aforementioned
shortwave perturbation is less influential this far east. This will
potentially have some impact on temperatures, but a blended approach
will suffice for now until we can better refine precipitation timing.

Sunday night into Monday, well be on the eastern periphery of a
pronounced deep anomalous (>+3 sigma) moisture river with
subtropical connections. While the stronger forcing for ascent will
still be to our west, another shortwave perturbation augmented by,
or originating from, Plains convection late Sunday will result in
precipitation chances increasing again. Given the spread in the
ensembles and sensitivity of compact convectively-induced impulses,
we will not attempt to refine timing further at the moment and
continue with a fairly broad mid-range probabilities Sunday night
through Monday night. Throughout this period there is little to no
conditional instability and thunder should be limited.

Tuesday, there is noteworthy spread in the ensembles seen in
spaghetti plots and clustering techniques. There seems to be a
general convergence on ejecting and deamplifying shortwave trough
bringing a period of stronger forcing into the established deep
subtropical moisture ribbon. This would likely bring the best chance
of precipitation of the long term period to Indiana during a roughly
6-9-hour period sometime on Tuesday. Specific timing and magnitude
of the precipitation is in question given the ensemble spread. There
is about a 1.00 inch spread among the 25th-75th percentile multi-
model ensemble, and a mean of around 0.50-0.75 inches.
Instability/thunder should again be limited by the misalignment of
colder midlevel temperatures with the warmer/moist lower
troposphere.

The general synoptic pattern looks similar post-wave into Wednesday
with temperatures returning to near climatology for early November,
but not likely below given the amplitude and track of the shortwave
trough and tendency for anomalous midlevel heights/ridging to
quickly build back in. The Day 8-14 day period generally shows a
warmer than typical pattern with at least normal if not above normal
precipitation chances. But, confidence is not particularly high
since some medium-range models show a transition to a less
progressive (and less predictable) pattern with weakening
subtropical jet and closed low over the Southwest or southern
Plains. There are some variations with a potential eastern trough
near/northeast of our region as well.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 100 AM EDT Thu Oct 31 2024

Impacts:

- LLWS through 12Z
- Southerly wind gusts up to 35kts, more frequent gusts to 30kts
after 12Z
- Wind shift from south to west between 15Z and 18Z.
- MVFR cigs/vsbys expected with showers from 12Z to 18Z, brief TSRA
possible

Discussion:

LLWS will persist through the remainder of the overnight hours,
ending as surface gusts increase after daybreak.  Showers with
embedded thunderstorms expected after 12Z with best chance for TSRA
at HUF and BMG.  Brief wind gusts to 35kts possible with more
frequent gusts to 30kts with a gradual wind shift from the south to
west between 15Z and 18Z. Vsbys will stay VFR outside of any showers
with MVFR cigs persisting for a few hours after the end of
precipitation.

&&

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

$$

UPDATE...Nield
SHORT TERM...Puma
LONG TERM...BRB
AVIATION...White