Severe Thunderstorm Warning 140, NWS Indianapolis, IN

Area Forecast Discussion...UPDATED
National Weather Service Indianapolis IN
941 PM EDT Mon Jul 29 2024

.KEY MESSAGES...

- Thunderstorms, possibly Severe, expected late this afternoon and
this evening.

- Thunderstorms may produce very heavy rain

- Morning fog possible

- Dry and Hot on Tuesday

- Daily storm chances continue through Friday, severe weather and
  localized flooding concerns possible each day.

- Heat indices near or above 100 degrees possible Tuesday through
  Thursday afternoons.

- Drier conditions with temperatures nearer normal this weekend.

&&

.MESOSCALE UPDATE...
Issued at 941 PM EDT Mon Jul 29 2024

Convection is most concentrated near and ahead of a midlevel
perturbation seen in 7.4 micron water vapor satellite imagery
crossing central Indiana. Enhanced warm advection at the leading
edge of EML plume is where a supercell evolved earlier with
persistent deep rotation and deviant motion. VWP-derived hodographs
show enough low level elongation and curvature for additional
supercells, with the most likely candidates being the current
cluster in Hamilton County moving into Madison County, which has
exhibited weak rotation. There appears to be enough low level
buoyancy for an isolated tornado threat with any additional
sustained and rightward-deviant supercells that can evolve.

Otherwise sustained multi-cells will be carried eastward by the mean
cloud bearing wind at around 25-30 mph and could pose a marginal
severe threat into the first part of the night. The greatest severe
threat will be if a larger cluster can develop a stronger cold pool
and forward propagate producing a greater wind threat. Several
convective allowing models show this process but with different
spatial placement. Given latest trends, this seems most likely to
evolve from the deeper convection now over central Illinois, and
would result in the greatest potential for organized severe
thunderstorms to be across our southwest counties roughly along and
south of a Terre Haute to Seymour line. The threat further north is
still present but should be more isolated and marginal.

An equally if not greater threat will be heavy rainfall and
flooding. Deep moist warm cloud layer will enhance precipitation
efficiency, and any location that experiences multiple rounds of
convection and/or training convection may experience flooding. There
may be an enhanced corridor of training at the western flank of any
cold pool system that can form, and this may be most likely just
southwest of our area. Will monitor closely for corridors of
enhanced flash flood potential overnight.

&&

.SHORT TERM (This evening through Tuesday)...
Issued at 214 PM EDT Mon Jul 29 2024

Synopsis -

Radar this afternoon shows new thunderstorm development along a
boundary in east Central IL that was laid out earlier today by prior
convection. The earlier MCS complex has continued to decay, pushing
southeast of Central Indiana. Cloud cover across Central Indiana has
limited heating through early afternoon, but satellite trends
suggest subsidence and decreasing cloudiness.  The surface analysis
early this afternoon shows high pressure in place across the
Carolinas and low pressure in place over western Kansas. This was
resulting in warmer southwest flow spilling into the Ohio Valley.
Aloft, a negatively tilted upper trough was in place from MN to
eastern KY, with the trough axis mainly east of Central Indiana.
Still, water vapor shows plentiful moisture within the trough over
Central Indiana. Dew Points remain very moist in the lower to middle
70s.

This Afternoon and Tonight -

SPC mesoanalysis pages shows CIN across central Indiana has
dissipated and CAPE of 1500-2000 J/KG present. IND ACARS soundings
showing plenty of CAPE aloft also, but just a lower level inversion
in place at the moment. This is expected to change as the clouds
continue to dissipate and lead to heating into the middle 80s. This
should trigger convection by late this afternoon and evening. HRRR
and several DESI members suggest strong thunderstorm development
late this afternoon and evening. A favorable column will remain
present along with warm air advection and the cyclonic flow aloft.
Thus many elements are in place tonight for continued showers and
storm development. Tornadoes cannot be ruled out given the very high
dew points that will result in low LCL's.  Best area for development
will be along and south of I-70, particularly within a IND-HUF-BMG
triangle area. Very high pwats will result in efficient rain
production. Torrential rains will be possible resulting in Flooding
and this will remain a threat.

Overnight, models suggest that convection will continue to diminish
storms as they exit southeast. Remnant lower level moisture along
with clearing skies and light winds will allow for the development of
patchy fog overnight. No strong change in air mass is expected, and
dew point depressions are expected to fall to 1-2F or less. Thus a
least patchy fog will be expected. Look for overnight lows in the
upper 60s in rural locations and lower 70s.

Tuesday -

The very warm and humid air mass is expected to remain in place on
Tuesday. Models suggest ridging building aloft as warm air advection
continues. 850MB temps are suggested to reach near 24C through the
afternoon as a thermal ridge is expected to build across Indiana
from the plains. Little in the way of forcing aloft will be present.
Forecast soundings suggest a capped column with a mid level
inversion in place due to the warm air advection aloft. An isolated
afternoon storm cannot be rules out across southwest central Indiana
where the cap may be a bit weaker. Small pops might be used here.
Thus after morning fog burns off, look for a partly to mostly sunny
day along with hot weather. Look for highs in the lower to middle
90s.

&&

.LONG TERM (Tuesday night through Monday)...
Issued at 214 PM EDT Mon Jul 29 2024

Much of the long term will remain rather unsettled as
central Indiana is positioned down stream on an amplified ridge, with
a succession of upper level waves moving over northern portions of
the CONUS. Also of not will be the presence of a quasi-stationary
boundary that will be the focal point for continued convective
initiation each day through Friday. As we enter the weekend, the
troughing to our NW looks to become more prominent, pushing central
Indiana into a potentially cooler and drier northwest flow for the
coming weekend.

The mesoscale environment will largely be synonymous with a typical
high CAPE/Low Shear pattern, outside of increases to shear in the
evening and overnight associated with nocturnal LLJs. Those type of
patterns typically lead to robust convection on the periphery of the
moisture tongue and along any instability gradient. This general
area should be broadly over the Ohio Valley each of Wednesday
through Friday, but there is still some uncertainty on the specific
locations. Given the high probability of steep low level lapse
rates, and high low level moisture, linear complexes are the most
likely mode, with high winds and isolated tornadoes possible within
any organized structure. Also of concern will be trailing boundaries
along the moisture axis leading to training thunderstorms and
flooding. This will become an even greater concern late week if
these MCCs develop over similar areas.

The amplifying pattern late week into the weekend, with central
Indiana between the ridge axis well to the west and trough axis to
the east, along with southward push of a cooler and drier Canadian
high pressure center, will bring temperatures and humidity back down
nearer seasonal normals, with highs in the mid to upper 80s and
dewpoints back into the 60s.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 649 PM EDT Mon Jul 29 2024

Impacts:

- Thunderstorms increasing this evening

- Some fog with IFR or worse possible late tonight

Discussion:

Some MVFR stratus is possible in the near term, but is not expected
to be consistent. Thunderstorm coverage may be somewhat limited, but
probability is high enough for a window of TEMPO thunder this
evening. Afterwards, cloud cover is the caveat to fog formation but
moist ground and light winds and perhaps some cloud breaks could
allow for some fog. Potentially locally dense. Amendments for storm
timing and fog magnitude will be needed through the evening and
tonight.

&&

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

MESOSCALE...BRB
SHORT TERM...Puma
LONG TERM...Updike
AVIATION...BRB

Hazardous Weather Outlook
National Weather Service Indianapolis IN
320 PM EDT Mon Jul 29 2024

INZ031-038-040>042-049-301930-
Howard-Tipton-Madison-Delaware-Randolph-Henry-
320 PM EDT Mon Jul 29 2024

This hazardous weather outlook is for central Indiana.

.DAY ONE...Through Tonight.

Thunderstorms are expected at times this evening and tonight. Heavy
rain and localized flooding are possible with any storm along with
lightning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Daily storm chances will continue through Friday, and some of these
storms may be severe. Damaging winds, lightning, and isolated
flooding will be the primary threats.

Potential for heat indices in excess of 100 degrees mid-week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening.

&&

More information, along with other weather, hydrological and climate
information can be found at http://weather.gov/ind

INZ021-028>030-035>037-039-043>048-051>057-060>065-067>072-301930-
Carroll-Warren-Tippecanoe-Clinton-Fountain-Montgomery-Boone-Hamilton-
Vermillion-Parke-Putnam-Hendricks-Marion-Hancock-Vigo-Clay-Owen-
Morgan-Johnson-Shelby-Rush-Sullivan-Greene-Monroe-Brown-Bartholomew-
Decatur-Knox-Daviess-Martin-Lawrence-Jackson-Jennings-
320 PM EDT Mon Jul 29 2024

This hazardous weather outlook is for central Indiana.

.DAY ONE...Through Tonight.

Thunderstorms are expected at times through tonight, with highest
chances between 7PM and 11PM EDT this evening.

Severe storms are possible this evening. Damaging winds are the
primary severe threat, but all modes of severe weather are possible.
Heavy rain and localized flooding are possible with any storm along
with lightning.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday.

Daily storm chances will continue through Friday, and some of these
storms may be severe. Damaging winds, lightning, and isolated
flooding will be the primary threats.

Potential for heat indices in excess of 100 degrees mid-week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation may be needed this evening. Storm motion will be
out of the WNW initially, shifting towards NW as the storms become
an organized line.

&&

More information, along with other weather, hydrological and climate
information can be found at http://weather.gov/ind

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