Area Forecast Discussion
Issued by NWS Indianapolis, IN

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000
FXUS63 KIND 181719
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
119 PM EDT Tue Jul 18 2017

.UPDATE...

The Aviation section has been updated below.

&&

.SYNOPSIS...
Issued at 211 AM EDT Tue Jul 18 2017

High pressure over the southeastern states will continue to
strengthen the next several days. This will result warmer and more
humid air arriving across Central Indiana on southwesterly winds.
Temperatures are expected to get warmer each day as the work week
progresses...bringing some of the warmest and most humid weather
of the summer so far.

The next best chance for rain will be on friday through the
weekend as a few upper level weather disturbances are expected to
arrive and interact with the hot and humid air in place across
the region.

&&

.NEAR TERM /Rest of Today/...
Issued at 941 AM EDT Tue Jul 18 2017

Fog from earlier this morning was quickly burning off as surface
heating and mixing commenced. With mostly sunny skies across much
of the area...temperatures had surged into the mid and upper 70s
at 1330Z.

Overall forecast remains in very good shape...but recent trends
noted in the mesoanalysis requires making a few adjustments for
the rest of the day. The remnants of the frontal boundary that
moved into the area late Sunday still resided in a NE to SW axis
from northwest Ohio back across southeast portions of the forecast
area into central Kentucky to the west of KSDF. The boundary
remnants are hard to see in the observational data...generally
just showing as a weak convergence zone. When we delve into the
mesoanalysis data a little deeper though...moisture and weak
instability are pooling along this convergence zone and should
continue to do so into the afternoon based on CAMs and sounding
analysis. While overall forcing is generally poor underneath an
expanding upper ridge...think the presence of the above factors is
enough to warrant an inclusion of a very low pop for this
afternoon...generally east of a Bedford-Shelbyville-Winchester
line. Most areas will not see any rain...but potential to see a
few pop-up cells is certainly there.

Further to the north and west...the capping inversion is
strengthening with increasing subsidence under the surface ridge.
This will keep conditions dry and should generally limit overall
cu cloud coverage as well. With the quick rise in temperatures
this morning and based on recent performance...decided to
generally bump highs up a degree across the board. Could see highs
reach 90 in southwest counties. Heat indices will make it into the
low 90s most area based on RH progs...which will feel balmy
compared to the expected heat indices later this week.

Zone and grid updates out.

&&

.SHORT TERM /Tonight through Thursday Night/...
Issued at 211 AM EDT Tue Jul 18 2017

Little change is expected in the overall pattern tonight as High
pressure and ridging continue to remain in place across the area.
This should result in more dry weather...clear skies and muggy
conditions. Will trend the lows at or above the model blend given
expected warm air advection and urban heat island effects.

GFS and NAM suggest the ridge axis will drift SE of Indiana on
Wednesday and Wednesday night. GFS even hints at a weak ridge
riding short wave passing through the region within the flow.
Forecast soundings on Wednesday suggest a bit more moisture but
again a mid level inversion appears present...which should inhibit
deep convection. Furthermore convective temperatures suggested in
the lower 90s may be just a tad too high to be reached. Thus will
trend the dry and hot forecast again on Wednesday and Wednesday
night. Will trend highs and lows at or above the model blend.

Slightly better chance will exist for storms on Thursday...albeit
it will be small chances. GFS and NAM agree on a more organized
short wave moving across Indiana by afternoon and evening...but
there are some slight differences in the position. Forecast
soundings show attainable convective temperatures by Thursday
afternoon a loss of the previous mid level inversion that was in
place. Thus...forecast building willing...will try and include
some afternoon and evening pops with the arrival of the dynamics
aloft aided by the daytime heating withe very warm air mass in
place. Confidence for storms is low given the MOS pops. Will
continue to trend temps at or above the forecast builder blend
given the expected warm air advection.

&&

.LONG TERM /Friday Through Monday/...
Issued at 428 AM EDT Tue Jul 18 2017

Models are close enough that the model blend initialization
was accepted for most items.

The upper high will get pushed south/southwest as an upper system
digs into the northeastern USA. Early in the period, any upper waves
riding around the upper ridge could generate some convection across
mainly the northern forecast area.

However as the upper trough develops, a surface front will move in
and eventually through the area. This will bring rain chances to
most areas during the weekend into early next week.

Friday should be the warmest day of the period with the upper high
at its closest point. Readings will gradually lower during the
weekend (but still remain very warm), and then return to near normal
by Monday as the cold front moves through.

Confidence in specific PoPs for any one period are low with
uncertainties in the timing of the upper system.

&&

.AVIATION /Discussion for the 18/18Z TAFs/...
Issued at 119 PM EDT Tue Jul 18 2017

Predominantly VFR through the period. MVFR fog will likely develop
at all sites near daybreak Wednesday, with a period of IFR fog at
a few.

Warm humid airmass remains in place across the area. Some
instability is present as indicated by towering cumulus on
satellite. May see a few isolated storms develop but these are too
low probability for any explicit mention in the TAFs. Will amend
as necessary if any look to impact the sites.

This warm humid airmass will promote development of fog overnight.
BMG will likely be the lowest, with IFR at the other outlying
sites as well, and low end MVFR, perhaps patchy IFR fog at IND.
Will keep IND MVFR for now.

Winds will be light and variable much of the period, and likely
calm overnight.

&&

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

&&

$$

SYNOPSIS...Puma
NEAR TERM...Ryan
SHORT TERM...Puma
LONG TERM...50
AVIATION...NIELD



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