IND issues Area Forecast Discussion (AFD) at Jun 20, 8:46 PM EDT ...PROLONGED HEAT AND HUMIDITY EXPECTED INTO LATE NEXT WEEK...889
FXUS63 KIND 210046
AFDIND
Area Forecast Discussion
National Weather Service Indianapolis IN
846 PM EDT Fri Jun 20 2025
.KEY MESSAGES...
- Heat Advisory in effect Saturday through Tuesday
- Hottest conditions of the season thus far this weekend into next
week, with heat index values peaking near 105 degrees
- Hot/humid conditions expected through next Thursday, although
scattered showers/t-storms may bring partial relief late next week
&&
.FORECAST UPDATE...
Issued at 844 PM EDT Fri Jun 20 2025
The forecast remains on track with only minor adjustments needed.
Expect quiet weather through the overnight period as surface high
pressure is centered near the region. Latest satellite imagery
shows only a few passing high clouds. Despite surface high
pressure near the region, a low pressure system moving across the
Plains should help keep southerly winds slightly elevated tonight.
This will limit diurnal cooling slightly. Look for lows to
generally range from the upper 60s to low 70s.
&&
.SHORT TERM (This evening through Saturday)...
Issued at 322 PM EDT Fri Jun 20 2025
Seasonable conditions ongoing today across Central Indiana for the
official for day of summer; however the season's first significant
heat wave arrives tomorrow and persists into next week.
Latest satellite imagery and surface analysis shows surface high
pressure over the southeastern CONUS with lower pressure over the
northern plains resulting in strong warm and moist air advection
into the region. Upper trough is currently centered just west of
Indiana with a northwesterly flow pattern aloft. A weak wave within
the upper flow is clearly evident on satellite imagery over Iowa and
Illinois. A strong theta-e and instability gradient exists from Des
Moines down to Western Kentucky, so expect any convection with the
upstream wave to follow that gradient, remaining west of the IL/IN
border. ACARs soundings show a very dry airmass through the column
for Indiana as high pressure remains the dominant weather influence
locally, keeping an environment around that is not very conducive
for convective development; therefore keeping the forecast dry for
the rest of today and tomorrow.
Ridging builds overhead tomorrow with 500mb heights increasing to
594dm, indicating a very warm airmass through the column. Surface
high pressure strengthens as well across the southeast with a low
level jet continuing to pump in a warm and very moist airmass into
the region. This is a classic set up for a summer-time heat wave for
the Great Lakes and Ohio Valley, setting the stage for an extended
period of highs at or above 90 and heat indices near and above 100
degrees each afternoon. With how wet conditions have been recently
and tropical air streaming in from the Gulf, the most humid airmass
of the summer is also expected as dew points reach oppressive levels
in the low to mid 70s. Expect highs reaching the lower 90s tomorrow
with heat index values as high as 100-105 degrees. Currently not too
concerned with record high temperatures this weekend into next week
as higher humidity values typically lead to a relatively slower rate
of increase than for a drier environment. Records for this time of
year range from the upper 90s to low 100s...forecast highs this
weekend should remain in the lower 90s, despite humidity making it
feel much hotter. Slight relief tomorrow afternoon may come in the
form of breezy conditions as deep low level mixing will allow for
wind gusts of 20-25 mph throughout Central Indiana.
&&
.LONG TERM (Saturday night through Friday)...
Issued at 322 PM EDT Fri Jun 20 2025
...PROLONGED HEAT AND HUMIDITY EXPECTED INTO LATE NEXT WEEK...
Saturday Night through Tuesday...
Strong upper subtropical ridge to build over all of southeastern
North America through the late weekend...with stacked mid-level cut-
off heights centered over central/southern Appalachians...and H850
20 degree Celsius isotherm extending across Indiana by Sunday
evening. Broad surface ridge of high pressure casually aligned from
Gulf coast to the Mid-atlantic will direct southwesterly flow into
the local region. Slight retrograde of this ridge westward will
slacken gradient over the CWA...with daytime gusts slowly decreasing
from at times moderate breezes Sunday, to mainly light winds on
Tuesday. Nonetheless advection of moisture will boost dewpoints
into the low 70s, which will combine with afternoon heat to produce
maximum heat index values around or slightly above 100 degrees.
High minimum temperatures and corresponding minimum heat index
values, both in the mid-70s will pose the potentially greater health
risk, however, especially given consecutive days likely held within
a heat index around 75F or higher across much of the region. Air
quality may also become an issue into the long term, especially as
surface winds diminish into the midweek. Expect high temperatures
Sunday through Tuesday in the low to mid-90s each day.
Wednesday through Friday...
Heat and humidity to continue through the remainder of the workweek,
although subtle drop of heights and H850 temperatures should
translate to at least a modest retreat of heat at the surface. Small
increases in chances for mainly afternoon RW-/TRW-...or at least
what will hopefully be SCT associated cumulus...should promote
afternoon highs closer to 90F, if not only upper 80s by the end of
the workweek. Widely scattered ordinary and generally short-lived
convective cells are expected amid the uncapped and rather moist
profile that should be sporting precipitable water values nearing
2.00 inches by the end of the period. Too early to assess coverage
of any possible stronger winds/downpours, although at the moment
severe weather appears less likely given the no/low shear in the
column.
Record high temperatures are not expected (neither max nor min)
given the higher threshold for records that begins around the late
June timeframe. Nonetheless the oppressively high humidity that
will promote widespread lows near 75F on several consecutive
mornings... may lead to dangerous conditions, especially where air-
conditioning is inaccessible.
Indianapolis has only observed seven consecutive days at 90F+ three
times in the last 9 years...the last occurrence being the final week
of August 2024. The normal max/min at Indianapolis next week is
84/65.
&&
.AVIATION (00Z TAF Issuance)...
Issued at 702 PM EDT Fri Jun 20 2025
Impacts:
- Wind gusts around 18-25 kts after 15z Saturday
Discussion:
Surface high pressure across the region will provide VFR conditions
through the period. Winds direction will predominately be from 180-
220 degrees during the period. Winds speeds should remain around 10
kts or less tonight before increasing on Saturday. Sustained speeds
around 11-16 kts and 18-25 kt gusts are expected after 15z Saturday,
persisting through around sunset.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM Saturday to 8 PM EDT Tuesday for INZ021-
028>031-035>049-051>057-060>065-067>072.
&&
$$
UPDATE...Melo
SHORT TERM...CM
LONG TERM...AGM
AVIATION...Melo
Source:
IND issues Area Forecast Discussion (AFD) at Jun 20, 8:46 PM EDT ...PROLONGED HEAT AND HUMIDITY EXPECTED INTO LATE NEXT WEEK...---------------
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