404
FXUS63 KIND 180326
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
1126 PM EDT Fri Apr 17 2026

.KEY MESSAGES...

- Showers and thunderstorms late tonight into Saturday

- Severe storms are possible, mainly late this evening into early
  overnight across western portions of the area

- Much cooler Sunday into Monday with the potential for
  frost and near freezing temperatures early Monday morning

&&

.MESOSCALE UPDATE...
Issued at 1125 PM EDT Fri Apr 17 2026

Marginally severe QLCS currently aligned SSW to NNE over east-
central Illinois will continue its east-northeast storm motion into
the early overnight...bringing this line into Warren and Vermillion
Counties in Indiana by 1200A EDT.  Overall weakening trend is
expected to continue, with chances of damaging winds diminishing as
the line crosses the Upper/Middle portions of the Wabash River.
Tornado Watch in effect for Vigo and Clay Counties NNE to the Kokomo
area...with overall low chances of any spin-ups that will also
decrease as the line drags east into the early overnight.

Severe wind threat is greatest along and west of a line from
Rockville to Lafayette...while any tornadic activity will be favored
over next couple hours, especially where any transverse waves track
orthogonally to the NNE immediately ahead of the main line.  Any
hail is expected to be sub-severe.  Any flash flood threat would be
later in the overnight and contingent on intensity and duration of
better organized rain following the cold front during pre-dawn hours.

&&

.FORECAST UPDATE...
Issued at 1020 PM EDT Fri Apr 17 2026

Strong to severe upstream thunderstorms currently aligned over north-
central Illinois will continue their eastward progression toward
central Indiana through the late evening.  QLCS is expected to
weaken around when crossing into Indiana and reaching the CWA`s far
northwest zones around the early overnight hours...with numerous to
widespread showers and embedded, possibly strong TRWs most likely
within the 04-10Z timeframe...before a second round of numerous
showers follow across most zones through dawn.

Severe threat tonight will begin with potential isolated discrete
cells tracking SSW-NNE along/west of a line from HUF to OKK before
06Z...just ahead of the main decaying QLCS threat whose strong/
severe winds would be most likely over the Upper Wabash Valley.
Straight line winds are the prevailing threat, with noticeably
lower, non-zero chances of large hail and weak tornadoes.  Flash
flood concerns are overall low, yet on the table for any counties
that receive over 1.00 inch of rainfall from both the late
evening/early overnight cells...as well as the later overnight rains.

Winds outside of storms to continue to gust to 20-25 mph. Most
locations are progged to see 0.23-0.75 inches of rain, with heavy
amounts possible under storms over northwest counties.  Readings
will initially drop into the 60s from rain...with more staunch trend
in wee hours behind cold front...down to low 50s near Lafayette and
mid-60s for Seymour by daybreak.

&&

.DISCUSSION (This evening through Friday)...
Issued at 319 PM EDT Fri Apr 17 2026

Low pressure developing over Minnesota has brought a warm front
northward through Indiana earlier today. Despite some cloud cover,
temperatures have risen once again into the 80s across much of the
area. Mixing has been quite efficient as well, especially further
east, with dew points falling to below the NBM 10th percentile. To
the west, dew points in the 50s/low 60s have been noted. These
locations are deeper within the best northward moisture advection.

Warm moist advection continues into this evening ahead of a surface
cold front extending southward from the low. Strong forcing along
this front with large-scale lift from a deepening trough is leading
to rapid convective development to our west. Mean flow roughly
parallel with the initiating boundary will allow for quick upscale
growth into a mesoscale convective system (MCS). This system should
then progress eastward this evening.

The environment ahead of the system is characterized by deep
instability to 250mb with strong easterly shear. CAPE values between
1000-2000 J/Kg are modeled to persist into the night, but with
gradual stabilization occurring after about 00z. Additionally, shear
magnitudes decrease with eastern extent especially from the IN/OH
border eastward.

Our convective threat will be determined by how strong surface cold
pools become. A stronger cold pool should allow the MCS to propagate
further east faster than most models indicate. A faster MCS would
then have access to greater CAPE and better shear. Cold pool shear
balance would be achievable longer under such a circumstance. A
slower MCS may miss the best instability and become outflow dominant
early, sparing much of central Indiana from a severe weather threat.

In terms of hazards, strong damaging winds are the primary hazard. A
QLCS tornado threat also exists, especially across our northwest CWA
during the MCS`s mature phase and where better low-level moisture is
found. The best wind/tor threat is within N/S oriented line
segments, and within surges which come parallel with an intensifying
nocturnal low-level jet. Further south and east, the threat is
reduced due to a more stable surface layer and likely a more outflow
dominant system.

Best timing for severe weather is between 11pm through 4am, from
west to east.

THIS WEEKEND

The aforementioned cold front arrives well behind the MCS, roughly
around daybreak Saturday. High temperatures for the day occur around
or before sunrise for most. Behind the front, temperatures fall from
the mid 60s into the upper 40s/low 50s by the afternoon. Brisk
northwesterly flow and occasional rain showers should make it feel
quite miserable. Though thunder probabilities remain low, under 20
percent, enough elevated instability may be present for an isolated
weak thunderstorm...mainly across our eastern CWA.

A quick rebound is likely on Sunday though not as warm as it has
been recently. Highs to near 60 are expected on Sunday. A subtle
shortwave diving southeast may bring about an isolated shower Sunday
afternoon.

NEXT WEEK

A northwesterly flow pattern sets up next week as troughing digs in
over the Great Lakes and Northeast. A stalled front Tuesday into
Wednesday may bring some precipitation, but nothing too organized at
this point. That front lifts back northward as a warm front allowing
a warming trend to begin during the second half of the week. A
return to temperatures in the 70s or even low 80s is possible again
by Wednesday.

&&

.AVIATION (00Z TAF Issuance)...
Issued at 740 PM EDT Fri Apr 17 2026

Impacts:

- Wind gusts up to 20-25KT continuing through most of the period
- Convective SHRA/TSRA likely...mainly within 03Z-15Z
- MVFR ceilings for 4-6 hours at any terminal, crossing NW to SE
   within 11Z-19Z
- Cold fropa will veer southerly winds to mainly SW by 12Z...and
   WNW/NW at all terminals by 17Z

Discussion:

VFR conditions to prevail over central Indiana terminals for the
majority of the period into Saturday evening...with MVFR or worse
possible in convection late this evening into overnight hours...
and MVFR CIGs likely, as early as 11Z-16Z at KLAF, and as late as
14Z-19Z at KBMG.

VFR skies expected to continue through at least 03Z amid mid/high
cloud blowing off slowly approaching convection to the west of the
region.  Convective SHRA/storms to impact KLAF after 03Z, and
perhaps not KIND/KHUF until closer to 06Z...with areas of IFR/LIFR
possible under strongest cells. Showers and embedded storms to
linger into Saturday...under a passing area of MVFR CIGs through
morning to possibly midday hours.  Winds will complete their shift
to WNW/NW within 12Z-14Z at KLAF...down to within 14Z-17Z at KBMG.


&&

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

$$

MESOSCALE...AGM
UPDATE...AGM
AVIATION...AGM
DISCUSSION...Eckhoff