008 
FXUS63 KIND 150038
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
838 PM EDT Tue Sep 14 2021

.Mesoscale Update...
Issued at 837 PM EDT Tue Sep 14 2021

A broken line of convection is currently passing through western
and northern portions of central Indiana. This is expected to
continue to pass through the region after sundown. Current analysis
shows greatest surface based instability to the SW of Indianapolis
where the impacts of diurnal cooling are less apparent. Still all
of central Indiana remain above 2000 J/kg of CAPE, plenty for 
updraft development. Although surface based instability is 
greatest to the SW, lapse rates remain steeper over norther 
portions of the CWA. Even with instability, shear needs to be 
present to sustain updraft growth. With a broad trough aloft and a
strong surface low over the Great Lakes, highest levels of shear 
is over northern central Indiana, collocated with steeper lapse 
rates, where thunderstorms should be able to sustain themselves 
even after sundown. 

Severe threat looks to decrease as the night progresses given the lack 
of deep layer shear present. Still north of I-70, 30-40 kts of effective
bulk shear could be enough for an isolated organized thunderstorm to 
sustain itself for long enough to produce a severe wind gust. The 
greatest threat once again looks to be over northern portions of central 
Indiana. 

&&

.Short Term...(This evening through Wednesday night)
Issued at 333 PM EDT Tue Sep 14 2021

...A Few Strong To Severe Storms Possible This Evening...

A cold front to the NW continues to approach central Indiana as of 
late this afternoon.  A broad warm sector with temps in the mid 80s 
and sfc dewpts in the upper 60s/lower 70s has developed ahead of the 
front.  Decent low and mid level lapse rates have resulted in CAPE 
values in the 2500-3000 j/kg range this afternoon.  This moderate 
instability combined with effective bulk shear of 25-35 kts should 
result in strong to severe storms this evening.  The best timing and 
location for the strongest storms will be along and north of a Terre 
Haute to Indy to Muncie line between 22z-3z.  The main threats look 
to be strong to damaging winds and large hail. Storms should weaken 
as instability wanes by late evening and into the overnight hrs. 

Overnight expect showers/storms to continue to sink SE with the 
front with the best precipitation chances shifting from central to 
southern Indiana by the early morning hrs. For Wednesday, expect 
some showers/storms to linger in the morning across south central 
Indiana while drier/slightly cooler air filters in from the NW.  

Expect high temps in the mid 70s to lower 80s tomorrow.

&&

.Long Term...(Thursday through Tuesday)
Issued at 333 PM EDT Tue Sep 14 2021

The beginning of the long term will start out with the brief cooldown 
of near normal temperatures behind the front. The front is expected to 
stall south of the Ohio River through the latter half of the week. 
Aloft, ridging to the SE will help to keep a mostly dry forecast for 
the end of this week while heat and relatively humid conditions return 
this weekend. Temperatures will again climb above normal starting 
Friday and last into next week as southwesterly flow returns due to the 
placement of the ridging, advecting in the heat and moisture. Despite 
the SW flow, a bulk of the moisture will stay to the south of central 
Indiana for the end of the work week. A weak wave could provide enough 
lift to prompt some showers and storms Saturday into Saturday night. 
Upper ridging does look to become more dominant again Sunday into
early next week but at this point central Indiana looks to sit 
more on the periphery of the high and not where the stronger 
subsidence would lie. So going to go with the suggested PoPs 
during the afternoon hours for the end of the long term. 

&&

.Aviation...(00Z TAF Issuance)
Issued at 741 PM EDT Tue Sep 14 2021

IMPACTS:

-Scattered thunderstorms, with main threat ending at from 1z at 
KLAF...to 6z at KBMG
-Brief MVFR/IFR visibilities in/near storms, where isolated 50 kt 
gusts cannot be ruled out
-Otherwise gusty SW winds diminishing tonight, veering to N by 12z

DISCUSSION:

Generally VFR conditions will continue tonight as a broken line of 
thunderstorms crosses the region from west to east this evening. 
Most convective cells this evening will contain thunder courtesy of 
ample instability...and brief MVFR/IFR visibility is possible in 
strongest storms.  Isolated 50 kt wind gusts cannot be ruled out, 
especially through 4z.  This main threat of thunderstorms should 
pass south/east of KLAF by 1z...and through KBMG by 6z.  Following 
this threat VCSH and even a stray rumble of thunder are possible 
later tonight, although chances are generally too low to include 
either in TAFs more than a few hours after the main line passes.

The supporting cold front will then cross the region from northwest 
to southeast through the middle of the night, with MVFR visibility 
possible for a few hours pre-dawn, especially at KIND/KBMG. 
Southwesterly winds at generally 7-13 kts early this evening...will 
veer to northerly at 4-7 kts following the frontal passage. VFR 
conditions are expected during the day Wednesday.


&&

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

$$

Mesoscale...Updike
Short Term...AMS
Long Term...KH 
Aviation...AGM