IND issues Area Forecast Discussion (AFD) at Jul 31, 7:20 PM EDT800
FXUS63 KIND 312320
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
720 PM EDT Wed Jul 31 2024
.KEY MESSAGES...
- Uncertainty remains high on thunderstorm coverage and timing
through tomorrow night
- Heavy rain/flooding and some severe storm potential exists
- Heat indices near or above 100 degrees possible Thursday
afternoon
- Drier conditions this weekend into early next week with a
warming from near normal to above normal once again
&&
.MESOSCALE UPDATE...
Issued at 452 PM EDT Wed Jul 31 2024
The bow echo accompanied by a rear inflow jet has moved south and
east of Jennings county. This prompted an earlier severe
thunderstorm warning as the line moved into better shear balance and
low level lapse rates increased as a 60+ knot base velocity
signature popped up along the northern edge of the line. However,
the activity has moved off to the east which will result in the
cancellation of the Severe Thunderstorm Watch. Areas near and north
of I-70 have been worked over and should not longer be a big concern
tonight but would not completely ruled out additional isolated to
scattered convection, in warm advection, south of the I-70 corridor,
where the atmosphere is much more unstable with LAPS data indicating
SB CAPEs to 2500 J/kg. HRRR reflectivity progs are going along with
this potential scenario.
&&
.SHORT TERM (This evening through Thursday)...
Issued at 251 PM EDT Wed Jul 31 2024
The most intense convection today has reformed south of residual
cold pool in reservoir of stronger instability across roughly the
southern third of central Indiana. This convection should continue
to overturn the low-level thermodynamic environment and perpetuate
further southward expansion of effective cold pool, limiting further
thunderstorm development into the evening. Midlevel overcast will
be present in the wake of remnant MCS.
With complicating factors of today's convection and weak flow to
replenish the low-level moisture, convective development late
tonight is in question. As is potential MCS maintenance tomorrow
morning. We think modest west-southwesterly 850-mb flow helping
advect deeper moisture in and increasing large scale ascent from the
approaching trough should be enough for some isolated convection
later tonight, though spatial details on this development remain
uncertain. This modest moisture advection may help maintain any MCS
that evolves from convection upstream as well, though this may
preferentially propagate further south than most CAMs currently
anticipate along residual cold pool periphery. At least the more
intense part.
Tonight/tomorrow's scenario will continue to influence the mesoscale
environment which will drive convective coverage and intensity late
tomorrow. However, forcing for ascent with the trough and
strengthening warm advection coupled with diabatic surface heating
should lead to an uptick in convection late tomorrow somewhere
across the area. Modest effective shear and sufficient instability
will support some severe threat, with damaging winds being the
primary concern, especially if a more organized cold pool-driven
forward propagating system can evolve. Anomalous moisture will
continue to support some heavy rain/localized flooding threat,
especially if training happens.
Bottom line, mesoscale details that cannot yet be resolved will
drive the important details of the forecast, with regards to storm
timing and associated hazards. Thus, confidence is lower than
typical given the pattern and frequent forecast updates will be
needed through the short term period.
&&
.LONG TERM (Thursday night through Wednesday)...
Issued at 251 PM EDT Wed Jul 31 2024
A couple of notes based on the latest model cycles. Please see the
previous discussion below.
1. Broadening deep low over our area Friday will shunt the stronger
IVT and deepest moisture southeast by early Friday. Remnant low-
level moisture and convergent flow pattern will support extensive
clouds and numerous showers with locally heavy rainfall/flooding
potential. Organized heavy rain and flooding will decrease during
the day. Have trended temperatures down slightly with
clouds/showers.
2. With aforementioned low detached from main polar jet, we won't
see an intrusion of dry continental air, and will thus remain
moist/humid. Weak perturbations within west-northwesterly flow aloft
may be enough for periodic chances of convection through the long
term period, but it remains difficult to identify a period of
stronger forcing and greater coverage at this time.
--previous discussion--
Friday and Saturday...
An upper low will move south into the area and a surface cold front
will move through on Friday. This forcing will interact with the
still plentiful moisture to produce widespread showers and some
thunderstorms across the area. Will go at least likely category PoPs
all areas. Heavy rain and flooding will remain threats.
Clouds and rain will keep temperatures in the 80s.
As the upper system moves east on Saturday, enough forcing will
remain for chance PoPs most areas. Highs will be in the mid to upper
80s.
Sunday and beyond...
High pressure will keep the area dry Sunday into Tuesday for most
areas. The upper ridge will try to sneak back in from the southwest,
bringing some 90s back into the area, especially south.
A cold front may be able to get into the area on Wednesday,
depending on how strong the upper ridge is. This may spark a few
showers or storms. Hot temperatures will continue south ahead of the
front.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 719 PM EDT Wed Jul 31 2024
Impacts:
- Thunderstorms with MVFR and briefly worse conditions are possible
mainly after 11z Thursday
Discussion:
Isolated thunderstorms are possible this evening. Better chances for
storms will be Thursday, however coverage and timing is too
uncertain to throw in the TAFs at any one given time. A lot of the
uncertainly hinges on whether or not the atmosphere can recover
from convection earlier today. MVFR and briefly worse visibilities
and ceilings are possible in convection.
Winds away from convection will be SSW mostly 10 knots or less and
very light tonight. Higher gusts are possible in thunderstorms.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...BRB
LONG TERM...BRB/50
AVIATION...MK
Source:
IND issues Area Forecast Discussion (AFD) at Jul 31, 7:20 PM EDT---------------
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