287 
FXUS63 KIND 171042
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
642 AM EDT Mon Jun 17 2024

.KEY MESSAGES...

- Extended period of hot and humid conditions through next weekend

- Afternoon heat indices approaching 100 this week may be hazardous 
  to sensitive and vulnerable groups 

- Isolated to scattered storms today and tomorrow afternoon, 
additional storm chances over the weekend

&&

.SHORT TERM (Today and tonight)...
Issued at 301 AM EDT Mon Jun 17 2024

Today...

Another hot and humid day expected across the entire region as a 
tropical airmass remains in place. Temperatures have been slow to 
fall during the overnight hours and into this morning with some 
locations holding steady around the 80 degree mark, much warmer than 
what guidance has suggested for lows. Latest IND ACARs sounding 
around 0620z still shows steep low and mid level lapse rates with no 
low level or subsidence inversion present. Noticing this, once the 
sun comes back up, expect surface temperatures to heat up fast as 
deep mixing quickly begins. 

Kept max temperatures for this afternoon closer to the NBM25th 
percentile, which puts forecasted highs in the 92-95 degree range 
for most places. With an uncapped, very moist airmass and unstable 
airmass, cumulus clouds will likely develop by late morning and 
persist through the day. Weak upper level energy riding up the 
western edge of the ridge into the state will work to spark off 
isolated to scattered thunderstorms as convective temperatures are 
reached. This is the main reason for not going higher with max 
temperatures for today. A few spots that escape storms may reach 95+ 
degrees, but with increased clouds and storms around, most places 
should stay below 95 degrees. Nonetheless, temperatures in the 90s 
with such high humidity levels will result in heat indices in the 
98 to 103 degree range. 

Convective coverage is expected to remain isolated to widely 
scattered at best due to lack of appreciable forcing and very weak 
wind shear. Any storms that do develop will likely be short lived 
and slow moving. Will have to watch local mesoscale processes and 
outflow boundaries that develop as this may enhance wind shear 
locally and create an environment more suitable for storm 
development in certain locations. Heavy rain and lightning are the 
main threats with any storm. With little wind shear, storms likely 
will become top heavy and collapse relatively quickly, resulting in 
a brief strong wind gust threat as convection collapses. Overall, 
most areas will remain dry, so do not rely on storms to provide 
widespread beneficial rainfall or relief from the heat. In fact, 
areas that do see rainfall will likely be more humid this week 
resulting in higher heat indices and warmer overnight lows.

Overnight lows tonight will likely be in the 70s for most places,
with more urban areas holding steady in the upper 70s to near 80 
through the nighttime hours.

&&

.LONG TERM (Tuesday through Sunday)...
Issued at 301 AM EDT Mon Jun 17 2024

HOT AND HUMID CONDITIONS PERSIST INTO NEXT WEEKEND 

Tuesday and Wednesday... 

An extended period of hot and humid conditions persists into next 
weekend with daily highs in the 90s and heat indices approaching 100 
degrees. Anomalously strong upper ridging centered near the 
Northeast will continue to amplify resulting in increasing heights 
over the entire Eastern and NE CONUS. At the surface, high pressure 
also centered across the Northeast will promote southerly return 
flow from the Gulf across the Ohio Valley early in the period. 

For Tuesday and Wednesday, a plume of deeper moisture will move 
north into the region likely resulting in an increased cloud cover 
and a continued chance for isolated thunderstorms. Adding isolated 
storm chances to the Tuesday morning timeframe as guidance continues 
to indicate a weak upper wave and strengthening LLJ capable of 
producing some convection outside of peak heating hours. Similar to 
Monday, lack of forcing and wind shear will keep convective 
coverage isolated to widely scattered at best, but will have to 
watch local mesoscale boundaries that can enhance storm coverage and 
intensity in some spots. The combination of clouds and storms will 
keep temperatures a few degrees cooler than Monday, but still hot in 
the upper 80s to lower 90s. High humidity values will likely result 
in heat indices still in the mid 90s to near 100 degrees during the 
afternoon hours both days.

Lower confidence for high temperatures Tuesday and Wednesday (with 
models showing a wider spread in between 25th and 75th percentiles 
on temperatures) precludes any issuance of excessive heat products 
at this time. However, will still have to keep a close eye on the 
cumulative effects of the heat this week.

Thursday into Next Weekend...

Upper ridging is expected to retrograde late in the week and build 
back west which will bring even warmer 850mb temperatures towards 
central Indiana compared to earlier in the week. This could result 
in hotter temperatures Thursday/Friday with highs possibly at or 
above 95 degrees. Humidity may be slightly lower late week as 
surface high pressure also builds west helping to advect drier air 
into the mid levels, which may mix down to the surface during the 
daytime hours. Even with lower dew points, mid to upper 60s rather 
than 70s, feels like temperatures may still exceed 100 degrees.

The extended stretch of heat this early in the season 
is abnormal so make sure to stay hydrated and take frequent breaks 
in air conditioning if you are outdoors. Sensitive and vulnerable 
groups should especially take the necessary precautions to avoid the 
potentially hazardous temperatures. 

Most guidance shows upper ridging breaking down late weekend 
allowing for a system to move in from the northwest. While there is 
a good signal the ridge will break down, there is disagreement 
between models in how quickly this occurs which limits confidence on 
exact details such as precipitation chances or timing. The best 
chance for rain at this time appears to be on Sunday once a 
shortwave trough moves into the region. Increasing rain chances and 
clouds should bring some relief to the heat, but there is 
uncertainty in how much this will help. 

Longer range guidance continues to indicate a pattern supportive of 
above normal temperatures into the last week of June and early July.

&&

.AVIATION (12Z TAF Issuance)...
Issued at 642 AM EDT Mon Jun 17 2024

Impacts:

- Isolated thunderstorms Monday afternoon

Discussion: 

Mainly VFR conditions expected today. Moisture advection will bring 
a more robust cumulus field, and isolated showers and thunderstorms 
this afternoon and evening. Coverage is very limited and confidence 
is low in exactly where convection will spark. Most locations will 
stay dry but the threat is still there with such a humid and 
unstable environment. Did add VCSH to all TAF sites to account for 
the low chance and will update accordingly based on satellite and 
radar imagery later this afternoon. Mixing will again be enough for 
at least sporadic wind gusts up around 15-17 knots from 15z 
through 00z.

&&

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

$$

SHORT TERM...CM
LONG TERM...CM
AVIATION...CM