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068
FXUS63 KIND 251900
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
300 PM EDT Wed Sep 25 2024

.KEY MESSAGES...

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- Partly to Mostly Cloudy Tonight and Thursday

- Seasonable temperatures for much of this week with highs in the
  70s and lows mostly in the mid 50s to mid 60s

- Potential widespread beneficial rain Friday through Saturday from
  the combination of a cutoff upper low and the remnants of Helene

- Gusty winds over 40mph possible Friday from the remnants of Helene
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&&

.SHORT TERM (This evening through Thursday)...
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Issued at 300 PM EDT Wed Sep 25 2024

Synopsis:

Surface analysis early this afternoon shows high pressure centered
over the plains, nudging eastward toward the Ohio Valley. Low
pressure was found over Lake Huron with an associated cold front
stretching south through OH and eastern KY and eastern TN. Radar was
quiet across central Indiana. Looking aloft, a highly amplified
pattern was in place, with a large ridge over the western CONUS and
a large upper trough stretching from the Great Lakes to the lower
Mississippi valley. Models hinted at a cut off upper low over
southern IL. All of this was resulting in cyclonic flow in place
aloft over our region. GOES16 shows clear skies west of Indiana,
however, abundant morning stratocu was burning off across Central
Indiana leading to just some CU development and mid and high cloud
streaming across Indiana due to the upper trough and low, pulling
moisture northward.

Tonight -

Two weather features will control our weather tonight. The upper low
over southern IL is expected to become more cut off from the upper
trough and linger over western KY. This will continue to keep
cyclonic flow in place aloft across the area tonight and into
Thursday. Mid levels suggest the arrival of wrap around mid level
moisture reaching Indiana overnight, particularly across the
southern parts of the forecast area, including Vincennes, Bedford
and Seymour. Northern extend of this moisture arrival appears a bit
more limited.

Our second weather feature will be the surface high pressure in
place over the plains. This feature will be building eastward into
Central Indiana, allowing drier surface air, dew points in the 50s,
to build across the forecast area. Forecast soundings through
tonight fail to show saturation. Thus with overall weak forcing in
play, generally partly to mostly cloudy skies are expected. Expect
the loss of any diurnal CU this evening, followed by the arrival of
mid and high clouds due to the upper low overnight, particularly
across the southern area. Given the clouds across the area and the
lower dew point temps, lows overnight should reach the middle to
upper 50s.

Thursday -

Little overall change is expected on Thursday. The upper low is
expected to remain across western KY and western TN, while surface
high pressure pushes to the Great Lakes. This will set up easterly
lower level flow across central Indiana, with cyclonic flow aloft.
Meanwhile Hurricane Helena will be pushing toward Florida, toward an
eventual merge with the previously mentioned upper low. That
transition looks to occur on Friday. Back to Thursday, the upper low
and surface high pressure will again result in mid and high cloud
steaming across central Indiana, especially south, within that
cyclonic flow aloft, while the lower levels remain rather dry due to
the easterly flow and high pressure. Forecast soundings for Thursday
do suggest some afternoon CU will be possible. Thus once again, more
partly to mostly cloudy weather. As there will be little change in
the air mass, highs in the middle 70s, near persistence will be
expected.
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&&

.LONG TERM (Thursday night through Wednesday)...
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Issued at 300 PM EDT Wed Sep 25 2024

The main focus in the long term period is the Friday through
Saturday timeframe where the remnants of Hurricane Helene move into
the Ohio and Tennessee Valleys, spreading rain and wind to portions
of Central Indiana.

The start of the period features a large upper low over the Ozarks
with Hurricane Helene nearing the Big Bend of Florida. Guidance
continues to be in fairly good agreement with the hurricane tracking
northward through Georgia, then retrograding westward into
Kentucky/Tennessee, then slowly meandering eastward through the
weekend. Some uncertainty still remains regarding the northward
extend of the track and precipitation shield associated with Helene.
There likely will a south-north rainfall gradient across Indiana
Friday through Saturday with the highest rainfall amounts further
south toward the Ohio River. Latest ensemble guidance keeps the
greatest chance of an inch of more of rainfall south of the I-70
corridor with potential rainfall amounts quickly diminishing north
of there.

In addition to the rain will be widespread gusty winds across the
entire region Friday as the center of the transitioning
extratropical Helene approach from the southeast. Tightening surface
pressure gradient and a 40-50kt low level jet overhead may result in
strong winds at the surface, with gusts over 40 mph possible early
Friday morning through Friday evening. The wind threat will be
watched closely over the next few days as headlines may be needed.

Keeping 20-40 Pops through the weekend as the remnants of Helene
remain in the area. Latest guidance keeps the upper low in the area
through at least Sunday resulting in small waves of energy rotating
into the region sparking off scattered showers. With such a moist
column, extensive cloud cover should limit afternoon temperatures to
the 70s and also not promote large diurnal temperature swings. So,
look for overnight lows mostly in the 60s through at least the
weekend.
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&&

.AVIATION (18Z TAF Issuance)...
Issued at 1155 AM EDT Wed Sep 25 2024

Impacts:

- MVFR ceilings possible through 22Z. VFR Cigs thereafter.

Discussion:

An upper level low pressure area over eastern MO will push toward
southern Indiana during this period. This will keep a southerly flow
of moisture aloft streaming across the TAF sites through much of the
forecast period. GOES16 shows some lingering lower level clouds over
LAF/IND and BMG, but these should begin to mix out this afternoon as
surface high pressure of the plains builds across the area, beneath
the upper level low.

Thus expect continued MVFR Cigs for a few hours this afternoon at a
few of the TAF sites with gradual improvement late this afternoon.
Higher clouds will then persist overnight amid VFR conditions.


&&

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

$$

SHORT TERM...Puma
LONG TERM...CM
AVIATION...Puma