Area Forecast Discussion
Issued by NWS Indianapolis, IN

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647
FXUS63 KIND 190621
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
221 AM EDT Wed Jul 19 2017

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

&&

.SYNOPSIS...
Issued at 156 AM EDT Wed Jul 19 2017

Strong high pressure in place across the Ohio Valley will keep
warm and humid air in place across Indiana the next several days.

A few upper level disturbances are expected to push toward Indiana
each day through Friday. This in combination with the very warm
and humid air mass in place may result in some isolated
thunderstorms each day. Otherwise hot and humid weather through
Friday will continue to expected which will be some of the warmest
weather of the summer so far.

Cooler temperatures will arrive by early next week as well as the
heat is shoved off to the south and west.

&&

.NEAR TERM /Today/...

Issued at 156 AM EDT Wed Jul 19 2017

Surface analysis early this morning shows Broad High pressure in
place across Appalachia...extending far west into the middle
Mississippi River valley. A few isolated showers were found across
Central Illinois...drifting southeast with a diminishing trend.
Very high dew points were in place across Central Indiana...in the
middle to upper 60s.

GFS and NAM suggest an upper short wave over Illinois drifting
southeast across southern Indiana today...around stronger High
pressure in place aloft over the Central Plains. Forecast
soundings suggest a favorable column for convection today with
CAPE this afternoon over 2500 J/KG and convective temperatures in
the middle 80s. No cap appears present this afternoon once
convective temps are achieved. HRRR suggests isolated/scattered
convection development this afternoon which seems reasonable. Thus
will include low chance pops this afternoon for some pop-up
showers/storms. Given the little change in air mass will trend
highs at or above the forecast builder blend.

&&

.SHORT TERM /Tonight through Friday Night/...

Issued at 156 AM EDT Wed Jul 19 2017

Models keep generally the same pattern across the area through
Friday Night. Strong High pressure appears to remain in place
aloft over the Central Plains. This allows several ridge riding
short waves to push across the northern plains and stream toward
Indiana and the Great Lakes. The GFS and NAM suggest the first
wave arriving late tonight...reaching NW Indiana near 12Z
Thursday. Model precipitation fields suggest MCS type
precipitation...but suggest rapid decay upon arrival in Indiana
near 12Z. Confidence is low for this given the favorable warm and
moist air mass in place. Thus will continue to keep some pops in
the forecast tonight. Will continue to keep the low at or above
the forecast builder blend given the warm air advection.

The GFS suggests yet another short wave pushing through by Friday
evening while the NAM show a subtle weak wave passing Friday
morning and again on Friday Night. Confidence in these wave is low
given their weak nature. However forecast soundings continue to
suggest a favorable column for daily convection with plenty of
CAPE available on Thursday and Friday. Convective temperatures on
Thursday and friday appear a bit more marginal...in the middle
90s. Thus given this will still need to include some low chc pops
each day until better confidence is in place. at this
point...should rain occur...best chances should be across the
northern parts of the state which will be closer to the quicker
flow aloft. Again will trend highs at or above the forecast
builder blend given the ongoing warm air advection and little
change in the air mass.

No heat advisories or watches at this point as confidence that
criteria will be met is low...particularly with uncertainty due to
possible thunderstorms. May consider an SPS.

&&


.LONG TERM /Saturday Through Tuesday/...
Issued at 221 AM EDT Wed Jul 19 2017

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

An upper trough will develop and move into the area through Monday.
Upper disturbances moving through the flow along with a surface cold
front will provide forcing for rain chances for much of the area
Saturday into Monday. Do not believe that it will rain for large
portions of any day, but uncertainties in timing of the forcing
result in more generalized PoPs each period.

High pressure then will build in Monday night and Tuesday, providing
dry conditions those days.

Saturday will be the warmest day with hot and humid conditions, then
temperatures will cool to near or below normal readings by Monday
and Tuesday as the airmass changes with the passage of the cold
front.

&&

.AVIATION /Discussion for 190600z TAF issuance/...

Issued at 1216 AM EDT Wed Jul 19 2017

Light winds and humid airmass should lead to fog development within
the next few hours. High confidence that at least some patchy fog
will form at the sites starting around 7-9z, but low confidence on
how low the visibilities will get. Will go with prevailing MVFR and
tempo IFR until around 12-13z. The western sites have seen more
subsidence and less cloud development during the day, as well as
should have more cloud debris, so will leave IFR out there and
shorten the length of time of even MVFR. Will go most pessimistic at
KBMG. After around 12-13z should see any visibility restrictions
clear and then VFR for the rest of Wednesday.

Confidence is still too low that any parts of the current convective
line over Illinois will hold together enough to reach KLAF so will
continue to leave out of the TAFs but monitor closely.


&&

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

$$

SYNOPSIS...Puma
NEAR TERM...Puma
SHORT TERM...Puma
LONG TERM...50
AVIATION...CP



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