Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 201801
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
201 PM EDT Sun Aug 20 2017

.UPDATE...
The LONG TERM Section has been updated below.

&&

.SYNOPSIS...
Issued at 324 AM EDT Sun Aug 20 2017

Dry weather is expected through Monday morning. Then, a strong cold
front will interact with a very warm, moist and unstable atmosphere
and result in unsettled weather over central Indiana Monday night
through Tuesday night. A few strong or severe storms are possible.
Northwestern parts of central Indiana could even see a few storms as
early as Monday afternoon.

Broad surface high pressure will build in behind the cold front and
result in dry and cooler weather.

&&

.NEAR TERM /Rest of Today/...
Issued at 949 AM EDT Sun Aug 20 2017

Looks like showers will remain just south of the forecast area this
morning so have a dry forecast. Wouldn`t be surprised to see an
isolated shower develop this afternoon south, but coverage is still
expected to be too low to mention.

Otherwise bumped up sky cover with cloud cover from a dying MCS
approaching the area. Still expect partly cloudy skies overall.

Made some minor tweaks to temperatures given the increased cloud
cover, but no significant changes were made.

Previous discussion follows...

With an area of storms about to move into Knox county, will thrown
in 20 percent pops there through 13z. After that, the cap should
strengthen, discouraging any cell from forming or at least lasting
long, despite the front being around.

Previous discussion follows...
Issued at 324 AM EDT Sun Aug 20 2017

Main concern for the near term is potential for isolated storms to
form along a stationary front that stretched from around Sullivan to
Bloomington to Greensburg. Convergence along this line, in proximity
of a 500 plus J/KG CAPES, was responsible for a few evening pop up
storms. However, models were showing upper ridging over the area
today even as the surface high moves to the Appalachians and east
coast. With an upper ridge over the area and 700 millibar
temperatures increasing to around 10 degrees Celsius, there will be
a decent cap in place and there will be very little of chance
anything developing along the front based on research with August
700 millibar temperatures over the area and thunderstorm initiation.
Still, with convective temperatures in the mid 80s, and a weak upper
wave approaching, can not completely rule out a stray pop up south
central. Still, chances will be too low to mention.

Cu development progs suggests there could be a few to scattered
diurnal fair weather cu. Otherwise, could see some cirrus blowoff
from the Iowa storm complex.

Light southerly flow and plenty of sunshine support above normal
blend highs in the upper 80s and lower 90s, around or slightly
warmer than yesterday. The heat index could reach the mid 90s over
southwestern sections during the middle and late afternoon.

&&

.SHORT TERM /Tonight through Tuesday night/...
Issued at 324 AM EDT Sun Aug 20 2017

Due to the looming eclipse, not only severe weather will be a
concern, but also the cloud cover for Monday afternoon, prior to the
bulk of the unsettled weather.

Models in good agreement that a strong cold front will dive
southeast across central Indiana Tuesday night. The front will
interact with deep moist and very warm, moist and unstable air. This
will result in scattered to numerous thunderstorms mainly Monday
night through Tuesday evening. Also, models are trending quicker
with the convection supporting moving up thunderstorm chances to
areas near and north of Interstate 70 to Monday afternoon.
Coordinated with adjacent offices and the general feel is fairly
thick upstream cirrus blowoff shield is an increasingly very real
concern regarding viewing the eclipse over central Indiana. Thus,
will raise cloud cover to near more than 40 percent with the highest
over the northwestern half of the area.

Low level jet will pump 2 inch plus precipitable water amounts over
the area overnight Monday night and Tuesday. This should bring more
widespread storms to the area with the potential for some heavy rain
in addition to the possibility of severe weather. 30 to 50 knots
deep shear in addition to 500-1500 mixed layer CAPE support the SPC
Day2 Marginal Risk northwest and Day 3 Slight Risk southeast with
damaging winds the main severe threat.

With the front expected to be southeast of the area by 06z
Wednesday, will end pops overnight Tuesday night from northwest to
southeast per the blend.

With the eclipse, high clouds and possible nearby convection, will
cut blend highs Monday, otherwise blend has a good handle on cooling
behind the front. Should see temperatures some 5 degrees or so below
normal by Tuesday night.

&&

.LONG TERM /Wednesday Night through Sunday/...
Issued at 201 PM EDT Sun Aug 20 2017

Splendid stretch of late summer weather for the extended period as
the Great Lakes and Ohio Valley reside under a broad upper trough
and strong high pressure at the surface for much of the period.
With dry low level flow from the north then east...expect days
full of plentiful sunshine and mainly clear nights with no
threats of rainfall. High temperatures will be pleasant...ranging
from the mid 70s to lower 80s Thursday through Saturday. Nights
will have a distinct autumn feel with temperatures dropping as low
as the lower and middle 50s.

Heights aloft will recover with the upper trough shifting off to
the east by Sunday. The region will remain under the influence of
a surface ridge...but low level flow will transition to southerly
on the back side of the high...resulting in temperatures warming
into the lower to possibly middle 80s on Sunday. Not entirely out
of the question that a potential for isolated convection would be
present by late weekend with moisture being advected north into
the Ohio Valley...but chances too remote at this point for
inclusion into the forecast.

&&

.AVIATION (Discussion for the 201800Z TAF Issuance)...
Issued at 1241 PM EDT Sun Aug 20 2017

VFR conditions expected through the period (outside of any
convection).

Scattered cumulus and scattered to broken cirrus will continue this
afternoon and again on Monday, although more mid cloud will be
possible Monday. The high clouds through the period should help keep
fog at bay overnight, although if they do thin out more than
expected some fog is possible.

Cannot rule out some isolated convection near the southern sites
this afternoon, but coverage would be too low to mention. More
convection is possible later tonight and Monday, especially north
where an upper system will move through. However, confidence in this
is low so did not include yet.

&&

.IND WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SYNOPSIS...MK
NEAR TERM...MK/50
SHORT TERM...MK
LONG TERM....Ryan
AVIATION...50



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