Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 191849

Area Forecast Discussion
National Weather Service Indianapolis IN
249 PM EDT Wed Jul 19 2017

The SYNOPSIS...NEAR TERM and SHORT TERM Sections have been updated below.


Issued at 231 PM EDT Wed Jul 19 2017

Still too early to call for Heat Advisory as heat and humidity build
slowly east towards central Indiana. Convection may impact highest
heat indices expected Friday and Saturday and is discussed below.

Still, the hottest and most humid air of the year so far will expand
into central Indiana Thursday into Saturday. Peak heat indices
will be above 100 and possibly reach Heat Advisory criteria in
some areas Friday and Saturday.

Current and future rounds of convective complexes in the Upper
Midwest in coming days will drop southeast across the Great Lakes
north of a stationary boundary. Central Indiana will be on the
edge of these storm clusters but may tangle with them as early as

An upper low currently off the Pacific Northwest today will
traverse southern Canada into the Upper Great Lakes this weekend.
This will sweep a cold front across our area late Sunday bringing
cooler, less humid and sunny weather for Monday into Wednesday.


.NEAR TERM /Tonight/...

Issued at 231 PM EDT Wed Jul 19 2017

Remaining isolated convection this afternoon will dissipate soon
with no additional convection expected to develop at peak heating
as upper ridging and weak subsidence overtake the area.

Upper Midwest convection dropping southeast not likely to impact
our area before daybreak though it may get close.

Like last night, mostly clear skies and humid near surface
conditions suggests areas of fog are likely once again after
midnight lasting into dawn.

Current min temps in the lower half of 70s appear reasonable and
will be used.


.SHORT TERM /Thursday through Saturday/...

Issued at 231 PM EDT Wed Jul 19 2017

Forecast challenges focus on heat advisory potential and whether
thunderstorms impact that potential.

Synoptically, the growing heat ridge centered over the High Plains
will slowly expand into the Tennessee Valley by the weekend. With
592-594dm heights and 850mb temps in lower 20s celsius over
central Indiana, the hottest temperatures of the season in the
lower to middle 90s appears reasonable and followed.

Dewpoints...forecast into the lower 70s Thursday looks good though
this may have to be adjusted upward a degree or so. Middle 70
dewpoints Friday and Saturday appear reasonable as pooling of max
dewpoints in central Indiana south of convection to the north is
likely. Would not be surprised with 78F-79F dewpoints in a few
spots for a few hours Friday or Saturday.

Heat out in 98-103 Thursday with dewpoints only
into lower 70s. Again higher dewpoints Thursday could push heat
indices to 105 in WC and SW counties and bears watching.

Forecast heat indices above 105 in southwest and south central
counties Friday and Saturday remain a concern and any Heat
Advisory issuance will be held off until at least Thursday. Reason
for this is that active convection spilling southeast across the
Great Lakes Friday and Saturday should impact at least locations
east of I-65. It is not uncommon for such storm clusters, with
good cold pool development, to drop further south than expected.
This could result in clouds or rain impacting those areas forecast
to reach mid 90s Friday and Saturday. Hopefully another couple model
runs will depict southern extent of clouds/rain and whether it
would impact potential heat advisory needs for SW/SC counties

Convection...models have been pretty consistent in developing
storm clusters in the Upper Midwest and tracking them into the
Great Lakes, but with each new cluster each day dropping the
surface boundary they ride along further south. Strong ridging
Thursday along with very warm mid level temperatures should
prevent convection in central Indiana Thursday everywhere except
far northern counties. Thursday nights convective cluster looks to
drop a bit further south and impact more of the north half of
central Indiana Friday. Same story Saturday and Sunday with the
boundary even further south each time affecting more of central
Indiana. Eventual cold front Sunday night will begin the drying
and cooling process though enhanced cloud cover and precipitation
should keep Sunday max temps below 90 except along the east fork
white river.


.LONG TERM /Saturday night through Wednesday/...

Issued at 214 PM EDT Wed Jul 19 2017

A look at the GFS Ensembles show the basic idea of the main band
of westerlies remaining over the northern third of the U.S. The
European model also went this direction so we have some basic
consistency in the models so far. Both models bring a threat of
showers/thunderstorms with a cold front Saturday night and Sunday
morning as the mid/upper level ridge retrogrades back west into
the Plains. But, then high pressure moves southeast into the Great
Lakes region. The blend brings a slower clearing than expected
compared to the other models and feel it is going to be faster.
Monday into Tuesday look like pretty nice days bringing
temperatures closer to normal which is the mid 80s for highs and
upper 50s for lows to start the new work week.

While basically northwest flow aloft comes back into the picture by
midweek, looks like another chance of precipitation for the area.
The GFS still has high pressure centered over the region on
Tuesday, but Euro brings what looks like a MCS into the mid
Mississippi Valley by Wednesday morning. Not very sure about this
at this time.

Confidence: Medium through the weekend and early week.
            Low Tuesday afternoon and Wednesday.


.AVIATION /Discussion for 191800z TAFs/...

Issued at 1257 PM EDT Wed Jul 19 2017

Remnant shower mid clouds near 8000 ft across the southwest half
of Indiana and TAF sites continues to track southeast and will
gradually dissipate and exit the area this afternoon.

Destabilization as afternoon heating wears on could result in
isolated storms forming but odds are too low and coverage to low
to include as mention at TAF sites.

Any afternoon cumulus that does form will dissipate early evening
and remaining cloud cover will be cirrus blow-off from Minnesota
convection as it tracks into Wisconsin tonight.

Still carrying 3SM fog at KLAF and KBMG where it occurred last
night in humid airmass, clear sky, near calm wind scenario. Any
fog which does form will dissipate by 201200z-201300z.

Winds to remain light and mainly west through 201400z after which
a bit steadier SW wind near 10 knots develops.




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