000
FXUS63 KIND 130504
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
104 AM EDT Sat Apr 13 2024

.KEY MESSAGES...

- Mostly Sunny and warmer on Saturday;
- Ongoing River Flooding and standing water in low-lying areas
- Multiple rounds of showers storms next week, severe weather
  possible Tuesday and Wednesday

&&

.FORECAST UPDATE...
Issued at 649 PM EDT Fri Apr 12 2024

IND ACARS sampled 500-mb temperatures as cold as nearly -30C
earlier, and showed fairly steep low/mid-level lapse rates atop
surface diabatic heating. This resulted in isolated to scattered
convection across central Indiana. Latest observations show (1) a
trend toward flatter cumulus across the southwest half of the area
as colder air aloft drifts eastward and capping subsident layer
spreads in, (2) a more consolidated band of convection covering
roughly the northeast half of the area at the periphery of the
trough and DCVA. Thermal profile supports some charge separation and
occasional lightning in addition to enough CAPE in the hail growth
temperature range for small hail. Tapering ECAPE profile in critical
temperature layer for hail growth, and thus weak updrafts, have
limited hail size today. However, dual pol suggest some cells are
dominated by dry hail with little/no rain, and this fits the
conceptual model of the thermodynamic profile. Convection should
diminish as surface diabatic heating wanes and PBL stabilizes,
though weak surface convergence coincident with the aforementioned
band may delay its demise until late evening. We have updated
precipitation probability fields accordingly. Otherwise, as PBL
stabilizes, momentum transfer will lessen and wind gusts will
decrease this evening.

&&

.SHORT TERM (This evening through Saturday)...
Issued at 233 PM EDT Fri Apr 12 2024

Synopsis:

Surface analysis this afternoon shows deep low pressure over Ontario.
A moderate cyclonic pressure gradient remained across Central
Indiana late this afternoon, resulting in some wind gusts to around
30 mph. A strong ridge of high pressure was found over Plains
states. GOES16 shows the back edge of the cloud shield associated
with the departing low found over the Wabash valley, with clear
skies in place over IL and WI. Radar shows the morning showers have
exited central Indiana to the south and east. Isolated
showers/storms were trying to develop across the northeast parts of
the forecast area due to heating and weak instability.

The pattern aloft was high amplitude, with strong ridging in place
over the Rockies and a deep trough over the eastern Great Lakes and
Appalachia. Northwest flow was in place across across the upper
midwest, spilling into Indiana.

Tonight...

The strong ridging aloft to the west is expected to continue to
build eastward. This will allow continued subsidence across
Mississippi valley building east into Indiana overnight. The
associated surface ridge over the plains is also expected to build
across Indiana overnight. Forecast soundings and time height
sections show the arrival of a dry column. Thus as heating is lost
this evening and the low continues to depart, clouds will exit the
area this evening and wind gusts will diminish. Overall, look for
decreasing cloudiness tonight along with clearing overnight.

Weak cold air advection will be in place, so look for cooler lows
around 40 to the lower 40s.

Saturday...

A quiet weather day is in store for Saturday. Models show the strong
surface ridge in place west of Indiana and slowly moving across the
state through the day. Forecast soundings again show a very dry
column with unreachable convective temperatures. Northwest flow
aloft on the lee side of the approaching ridge will continue to
provide subsidence. Thus a sunny day is in store.

Some warm air advection is in play on Saturday afternoon as the 850
ridge axis arrives late in the day over Central Indiana. This will
allow 850mb temps to rise to 8-10C by late afternoon. Given this and
the abundant sunshine, highs in the upper 60s to near 70 will be
expected.

&&

.LONG TERM (Saturday night through Friday)...
Issued at 233 PM EDT Fri Apr 12 2024

Saturday Night Through Monday.

The brief break in the precipitation will continue Saturday night
into Sunday with high pressure building across the Central Plains
and with northwesterly flow aloft across central Indiana. A weak
shortwave will push across the Great Lakes Region Sunday morning,
but based on the current orientation of the upper level jet, not
expecting any precipitation to reach as far south as central Indiana
with impacts to Michigan and Ohio. On Monday the ridge will shift
eastwards ahead of the arrival of more impactful weather Tuesday
through the rest of the week.  Precipitation may begin as early as
Monday night along a subtle warm front towards the Ohio River, but
there remains a significant amount of uncertainty as to whether the
front will be strong enough to generate lift.

Tuesday Through Friday.

Focus then shifts on Tuesday to a strong closed low as it exits the
Rockies and tracks from Kansas into the Upper Midwest through the
daytime hours Tuesday. As a response to the approaching system, the
LLJ will begin to ramp up with a good moisture fetch from the Gulf
of Mexico extending into the Ohio Valley and bringing temperatures
to near 80 with dewpoints to near 60.  As the LLJ ramps up, model
soundings show good daytime mixing which will bring wind gusts in
excess of 40 mph and the potential for winds greater than 50 mph.
Models have a pretty good handle on the synoptics of the system when
it comes to track and strength, but details on the mesoscale
environment remains low.

That being said, highest confidence in timing for thunderstorms will
be in the evening to overnight hours Tuesday into Wednesday with the
frontal passage during the daytime hours Wednesday.  Instability
will be highest during the daytime hours Wednesday and across south
central Indiana where the frontal passage may not occur until the
evening hours.  Confidence in severe weather is low but with the
strong dynamics associated with this intense early spring low
pressure system, isolated to scattered severe weather looks probable
across portions of the Ohio Valley.  There looks to be a brief dry
period Thursday before a secondary low associated with the polar jet
moves in from the northwest bringing additional rainfall to Indiana
on Friday.  Little to no instability is expected which will keep
hazards limited to the heavy rain and associated flooding.

Total QPF between this weekend and next week may exceed 1-1.5 inches
in spots which would allow for rivers to remain in minor flood stage
through next week.  A high end scenario of 1.5-2 inches along the
White River basin would lead to moderate flooding across much of the
basin with lower chances elsewhere based on latest MMEFS ensemble
runs.

&&

.AVIATION (06Z TAF Issuance)...
Issued at 103 AM EDT Sat Apr 13 2024

Impacts:

- None

Discussion:

VFR conditions are expected through the period. An increase in mid
and high clouds will occur late in the period. Winds will become
southwest toward 00Z Sunday.

&&

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

$$

UPDATE...BRB
SHORT TERM...Puma
LONG TERM...White
AVIATION...50