812
FXUS63 KIND 091900
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
300 PM EDT Thu May 9 2024

.KEY MESSAGES...

- Light showers possible Tonight
- Decreasing clouds and cooler on Friday
- Passing showers Saturday...before several rounds of showers/few
non-severe t-storms, next Monday and onward
- Slightly below normal to seasonable temperatures Thursday through
Saturday...to slightly above readings next week

&&

.SHORT TERM (This evening through Friday)...
Issued at 259 PM EDT Thu May 9 2024

Synopsis:

Surface analysis early this afternoon shows low pressure just west
of Indianapolis. The broad low was providing cyclonic circulation
across the region. A warm front extended east from the low, to
southern OH and WV. This low also had a cold front associated with
it, stretching west across Central Illinois to southern IA. Aloft,
an active pattern remained in place. A large, broad, upper trough
was in place from Quebec across the upper Midwest and continued to
another upper low near UT and NV. Ahead of this trough across
Indiana, a quick flowing westerly flow was in place. Water vapor
showed moisture in place over MI and northern IN, ahead of the upper
trough, while subsidence was in place over IL and central and
southern Indiana.  Radar this afternoon shows some scattered light
showers across Central Indiana, beneath the stratocu deck. A few
showers and thunderstorms were found across northern Indiana and
Michiana. These showers were ahead of the mid and upper trough.
Abundant cloud cover was still found across Central Indiana, but
some clearing and heating was found over Knox county, pushing
northeast. Plenty of moisture remained available as dew points
remained in the lower 60s across our area.

Tonight...

The surface low over Central Indiana is expected to quickly push to
Ohio this evening and then reach the middle Atlantic states
overnight. This will allow for the development of a northerly
surface flow of cooler air overnight. Meanwhile aloft, the
previously mentioned surface trough will be sagging across Central
Indiana trough the evening. Ongoing heating, combined with the
cyclonic flow and approaching upper trough is expected to continue
to develop scattered light rain showers across Central Indiana late
this afternoon and early evening. SW central Indiana will need to be
watched for possible thunderstorm activity. Clearing arriving in
Knox county is allowing for additional heating that could trigger
additional afternoon and early evening thunderstorms. HRRR suggests
that as this cloud shield continues to lift northeast thunderstorms
develop in combination with the arrival of the surface cool front.
Will try to keep the Thunder mention at those southern locations,
however a stray rumble of embedded within a shower will also be
possible.

Overnight, the upper trough will exit to the south and any
associated forcing will be lost. Cold air advection will be in play
as falling thicknesses are noted. This results in the formation of a
stratus deck overnight, with a trapping inversion found aloft as
seen within the forecast soundings. Thus overall, scattered late
afternoon and evening showers are expected to continue with light
rain amounts. Best thunder chances will be across far southern
Central Indiana in association with any clearing and extra heating
that occurs. Then expect cloudy and cooler conditions overnight as
cold air advection is in play. Expect lows in the upper 40s and
lower 50s.

Friday...

Models suggest the previous upper trough will quickly depart on
Friday, allowing northwest flow along with moderate ridging to build
across Indiana through the day. Surface high pressure over the
plains is suggested to build a ridge axis across Indiana through the
day, originating from the southern plains. Forecast soundings start
the day with saturation within the lower levels due to the passed
system, cold air advection and the trapped lower level moisture.
However as the ridging builds, the lower levels are shown to mix out
as the inversion aloft rises. This will allow for decreasing
cloudiness in the morning followed by some high CU development
during the afternoon. Cool northerly winds but with some afternoon
sunshine will allow highs in the upper 60s to be reached.

&&

.LONG TERM (Friday night through Thursday)...
Issued at 259 PM EDT Thu May 9 2024

Friday night through Sunday...

Northwesterly flow aloft will promote at least weak ridging this
weekend...on either side of a passing northern-stream, plunging
short wave in the late Friday night-Saturday timeframe.  This
quickly-passing feature should shake out some widely scattered rain
showers from pre-dawn to afternoon hours on Saturday...with perhaps
a rumble of late day thunder and moderate rainfall rates in isolated
convection over eastern zones.

Ample sun should otherwise prevail through the weekend. Seasonably
low humidity will be the backdrop to slightly below normal maximum
temperatures Saturday in mainly the 65-70F range, under the passing
lower heights and west-northwest gusts as high as 20-30 mph...to
more seasonably mild conditions Sunday in the 70s as lighter breezes
return from the west-southwest.

Monday through Thursday...

A rather typical late spring pattern will prevail over much of the
next workweek...as lower heights retracted to Canada allow a small
yet progressive short wave to cross the central US to the Ohio
Valley.  Solid ribbon of Atlantic and eastern Gulf of Mexico
moisture is expected to boost precipitable water values to 1.25-1.50
inches over much of the Midwest.  The overall disturbed pattern
should promote a few rounds of showers and thunderstorms...which so
far appear will be best organized in the late Monday to Tuesday
night timeframe.  Total rainfall would likely be under an inch for
most areas, with perhaps heavier amounts across southern
counties...although ultimately this would be determined by wherever
corresponding surface low pressure and associated boundaries would
focus any heavier rains.

Severe weather is so far not expected with primarily overcast skies
likely limiting instability despite above normal dewpoints...and
vertical wind shear likely low per the overall weak nature of the
passing wave.  Temperatures trending from near to slightly above
normal...will be led by overnight lows in mainly the mid to upper
50s...courtesy of noticeable humidity amid the often southerly
breezes.  The normal max/min at Indianapolis for the long term is
73/53.

&&

.AVIATION (18Z TAF Issuance)...
Issued at 1231 PM EDT Thu May 9 2024

Impacts:

- MVFR and worse ceilings at times through much of the TAF period.

Discussion:

Low pressure over Central Indiana and an associated upper trough was
push across the Indiana during the TAF period. The low will push to
east of the TAF sites this afternoon, allowing the surface winds to
become northerly. Meanwhile the upper trough will sag southward
through the state through the overnight hours.

Daytime heating in combination with the passing low and approaching
upper trough will allow for some scattered light showers through the
afternoon and evening. Coverage and duration will be too low for a
prevailing mention, thus a longer period of VCSH was used while
these forcing features pass.

Overnight, the best forcing will be lost, leaving just cloudy skies
across Central Indiana. Forecast soundings show saturation within
the lower levels persisting through the night with the arrival of
cooler air on northerly winds. Thus MVFR should continue through
that time.

&&

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

$$

SHORT TERM...Puma
LONG TERM...AGM
AVIATION...Puma