Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/10/24

Area Forecast Discussion

National Weather Service Indianapolis IN

 946 PM EDT Tue Apr 9 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms along and south of the I-70
  corridor late this afternoon and evening. Some flooding
  concerns if thunderstorms train over similar locations.

- Unsettled and wet pattern the second half of the week with
  prolonged or renewed areal flooding possible.

- A marginal severe threat exists for late Thursday morning into
  the afternoon, but uncertainty is high on location.

&&

.FORECAST UPDATE...
Issued at 946 PM EDT Tue Apr 9 2024

- Cloudy; Showers/Storms south Overnight

Surface analysis this evening shows a frontal boundary stretching
across Central Indiana, reaching from south of MIE to south of IND
to south of HUF.  Radar this evening has shown showers with some
thunderstorms along and south of the front. Spotters have reported
between 1 and 1.60 inches of rain in some locations, which may be
resulting in minor flooding, hence the ongoing Flood Advisories. On
the north side of the front, dew points were in the 40s and
northwest lower level flow was prevalent ahead of approaching high
pressure over northern IL. South of the front, dew points were in
the middle to upper 50s with lower level southerly flow.

As daytime heating diminishes and the front sags farther south, HRRR
suggest heavier rain showers should come to an end within the next 1-
4 hours. Thus have used categorical pops across southern areas for
the next few hours, but trended toward lower pops overnight as any
precipitation is expected to diminish and lessen in overall coverage.

As the surface high over IL drifts northeastward, lower level flow
will become easterly overnight across much of the forecast area.
This will help to push the frontal boundary farther south, but also
allow that boundary to act as an area of lower level convergence.

Given the current temperature trend and higher dew points,
especially south, trended overnight lows a bit colder, mainly in the
lower 50s northwest to the upper 50s southeast.

&&

.SHORT TERM (This evening through Wednesday)...
Issued at 256 PM EDT Tue Apr 9 2024

This evening and tonight...

Scattered showers and possibly a thunderstorm will develop along a
weak boundary draped across North Central Indiana this afternoon.
This same front will be the focus for multiple rounds of rainfall
and storms over the next several days as it becomes quasi-stationary
in the Ohio River Valley.

Not much cold air associated with the front, but current
observations show a strong dew point gradient through the state. The
boundary is approximately located along a line from Muncie to Lebanon
to Terre Haute with dew points dropping into the upper 30s and 40s
behind the front and a humid airmass south of it with dew points
approaching 60 degrees. Latest IND ACARs soundings this afternoon
show a near saturated 0-1km layer and increasing upper level
moisture aloft with SBCAPE around 1000 j/kg and 0-6km shear around
25-30 kts. Weak forcing along the front and significant dry mid
levels will likely limit coverage and intensity of convection. Main
area of focus for any showers or thunderstorms is along and south of
this boundary, mainly along and south of the I-70 corridor. Radar
imagery already shows a few cells developing in SW IN and moving
northeast. Expect shower activity to expand in coverage through the
late afternoon hours and spread northeastward, then diminishing
around and after 03z. Brief periods of gusty winds, a few lightning
strikes, and small hail expected in the strongest showers or storms.

Tomorrow...

Deep upper troughing developing over the Southern Plains today
begins to shift eastward by tomorrow with a continued
southwest/southerly flow regime ahead of it and into Indiana. The
aforementioned frontal boundary from Tuesday becomes quasi-stationary
over the region and stretches southwestward towards a surface low
developing in SE Texas. Upper level energy along this quasi-
stationary warm front will promote the development of widespread
rainfall along it as the surface low begins to eject northeast.
Heaviest and most widespread rainfall develops south of the boundary
from WVA to KY to AR early Wednesday then shifts northward into
South Central Indiana Wednesday afternoon. Rainfall eventually
overspreads all of Central Indiana Wednesday evening into Wednesday
night.

The airmass north of the boundary will feature saturated low levels
with light winds becoming easterly through the morning, typical of
an airmass north of a warm front of mid latitude systems. Depending
on how much rain falls Tuesday night, there may be areas of fog by
early Wednesday morning as winds become light and the boundary layer
saturates. Continued moist air advection northward over the boundary
will keep skies cloudy all day with temperatures steady in the lower
60s. Instability is fairly minimal at the moment, but would not be
surprised to see a few lightning strikes within the widespread
rainfall over the state late Wednesday afternoon. For more
information on the rainfall and flooding potential this week, refer
to the Long Term Discussion below.

&&

.LONG TERM (Wednesday night through Tuesday)...
Issued at 256 PM EDT Tue Apr 9 2024

The long term looks to be fairly active as the subtropical jet lifts
northward over the Ohio Valley. This accompanied by a deep west
coast trough will lead to consistent rain showers over the next
few days. The largest feature will likely arrive Thursday as cold
air helps set up a stronger baroclinic zone for deep cyclogenesis.

As the low develops upstream of the deep upper level trough Tuesday
night into Wednesday, a warm frontal region should begin to develop
between the low level southerly flow and a developing cold conveyor
belt aloft. This should lead to greater shower coverage into central
Indiana Wednesday night, along with isolated elevated thunderstorms.
Severe risks should remain marginal with the bulk of the shear still
over the Mississippi Valley Wednesday night, but pockets of high
rain rates and even pea sized hail cannot be ruled out.

The low will arrive Thursday, with rain showers and thunderstorms
continuing throughout the day. Shear will be strong near the low
with 50-80kt 850-500mb southerly winds and an east of south near
surface wind in the warm sector. Instability will also be modest in
the warm sector on Thursday including near 7.5 C/km mid level lapse
rates. It total, this should lead to scattered severe convection in
the warm sector, but the current question is where will the warm
sector reside? Ensemble guidance is still widely varied on low
placement for Thursday, and the corresponding warm sector.
Deterministic models are mostly placing the warm sector over Ohio/E
KY, but latest trends are depicting a slight westward shift and
deeper/stronger surface low. This is creating some uncertainty on if
any severe weather will happen in Indiana on Thursday. Using
probabilistics, the greatest threat for severe weather will be over
OH, but this could shift westward into Indiana overtime if trends
continue. Timing has been more consistent with highest likelihood of
any thunderstorms between the late morning and mid afternoon.

Even though any severe thunderstorms look to be confined to Thursday.
Areal flooding concerns are possible for Wednesday night through
Thursday. Current QPF ranges from 1-3 inches through this 24 hour
period, and prior day rain totals could create a more saturated
surface and greater likelihood for areal flooding, and river/stream
flooding.

Temperatures Wednesday night through Thursday are expected to remain
above seasonal normals, although there could be larger gradients if
cloud cover and rainfall become thick/consistent. As the low passes
Thursday night, a brief cooldown into the 50s for highs is possible
on Friday before warm conditions return for the weekend. 6-14 day
forecast guidance suggests ridging will build this weekend into next
week and remain through the end of next week. Although briefly
cooler conditions are possible, the current expectation is for warm
temperatures through much of the next 14 days.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 727 PM EDT Tue Apr 9 2024

Impacts:

- VFR and MVFR conditions this evening and much of the overnight
period.

- MVFR to IFR conditions with rain or thunderstorms are expected
after 18Z on Wednesday.

Discussion:

A boundary was draped across Central Indiana early this evening.
This boundary stretched from MIE-IND to just south of HUF. Dew
points on the south side of this boundary were in the upper 50s to
near 60, providing moisture rich lower levels. To the north, at LAF
and HUF, dew points were in the 40s, with dew points in the 40s and
dry westerly winds ahead of high pressure over IL.

Radar this evening shows an area of showers and thunderstorms, along
and south of this boundary, pushing east within the flow aloft. HRRR
suggests these showers will continue to impact IND and BMG for the
next few hours before diminishing and pushing east. Have used VCSH
for this at the moment. As high pressure over IL builds eastward
overnight and early on Wednesday, lower level flow is expected to
become easterly. With the boundary south of the TAF sites on
Wednesday morning, MVFR to IFR clouds are expected to develop on the
north side of the boundary, particularly at BMG and HUF.

More showers and storms are expected to arrive on Wednesday
afternoon as an upper disturbance arrives providing forcing aloft
with the lower level boundary remaining in place near the surface.
Forecast soundings at that point show a saturated column at most TAF
sites with precipitation expected and MVFR or worse cigs.


&&

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

$$

UPDATE...Puma
SHORT TERM...CM
LONG TERM...Updike
AVIATION...Puma