Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 301429

Area Forecast Discussion
National Weather Service Indianapolis IN
1026 AM EDT TUE AUG 30 2016

The AVIATION Section has been updated below.


Issued at 239 AM EDT Tue Aug 30 2016

One more day of warm and humid weather is in store today as high
pressure over the Ohio Valley continues to keep a tropical air
mass in place over Indiana. This will result in some scattered
showers and Thunderstorms this afternoon.

A Cold front will approach central Indiana tonight from the upper
midwest...passing across the area on Wednesday. Showers and Storms
are expected along and ahead of the front...bringing more rain for
Tonight And Wednesday.

Cooler and less humid high pressure will build across the region
on Wednesday Night and Thursday. This cool air mass will linger across
the Ohio Valley through the Holiday Weekend providing dry weather with
slowly moderating high temperatures.


.NEAR TERM /Today/...

Issued at 239 AM EDT Tue Aug 30 2016

Water Vapor imagery shows a plume of tropical moisture across
Texas streaming north across the central Plains to the Western
Great Lakes early this morning. Surface analysis shows broad high
in place across the eastern Great Lakes with NE flow streaming in
to Indiana. Dew points remained quite the lower 70s.

Main forecast Challenge today will be pops. Early this morning
models are suggesting a weak protective ridge remains in place
aloft...steering any forcing well northwest in to Wisconsin and
Minnesota. GFS and Nam suggests this upper ridge begins to break
down this afternoon as NW flow begins to take shape aloft.
Meanwhile forecast soundings this afternoon show convective temps
in the middle 80s...steep lapse rates...pwats over 1.75 inches and
CAPE generally over 2500 j/kg. Isentropic Surface fail to show
impressive lift today...but do show the very moist air mass in
place. Thus the main forcing features today will be the breakdown
of the ridging in combination with Daytime heating providing
instability. Thus will trend pops high than mavmos...particularly
across the western parts of the forecast area where ridge
breakdown should occur first. Given the little change in the the
air mass...will trend highs warmer than mavmos also...closer
toward recent persistence.


.SHORT TERM /Tonight through Thursday night/...

Issued at 239 AM EDT Tue Aug 30 2016

Very Changeable weather is in store during this period. GFS and
NAm both bring a upper short wave across Central Indiana within
the NW flow aloft tonight. Good dynamics accompany this feature as
forecast soundings reveal deep saturation overnight and time
heights also show excellent VV. Good lower level Q vector
Convergence also is in place tonight and again on Wednesday
associated with actual FROPA. Thus will trend pops highs than
mavmos tonight and again on Wednesday as these features pass.
Given expected clouds and rain...will trend lows warmer and HIghs

On Wednesday Night Forecast soundings show rapid drying amid
strong subsidence as seen within the mid levels. A linger showers
or storm cannot be ruled out early in the period across the far
souther area due to progression of the mid
evening on Wednesday Night a new...dry air mass will have arrived.
Will trend toward becoming mostly the strong High
begins to build across the region.

Highly amplified high pressure ridge will then build across the
region on Thursday and Thursday Night. Excellent Drying and
subsidence along with northerly surface flow will be in place.
Forecast soundings show a dry column with unreachable convective
temperatures. THus will trend toward mostly clear nights and
mostly sunny days. With Strong Cold air advection in place
Wednesday night through THursday night will trend lows cooler than


.LONG TERM /Friday through Monday/...

Issued at 241 AM EDT Tue Aug 30 2016

Upper ridging moving through and surface high pressure locally
will keep dry weather in the forecast as temperatures slowly warm
through the long term. Highs Friday should be in the mid to upper
70s but by Sunday middle 80s are back in the forecast. Much drier
airmass with dewpoints in the 50s and subsidence will keep any
chances for precip away. Dew points will climb back into the 60s
on Sunday and Monday but should remain sub-70 through the period.
These lower dewpoints will allow low temperatures to drop into the
50s both Friday and Saturday nights.


.AVIATION /Discussion for 301200z TAF issuance/...

Issued at 1026 AM EDT Tue Aug 30 2016

Changed from prob30 to VCTS after 21z do to TAF rules and raised
ceiling to 3.5K feet.

Previous discussion follows...

Issued at 720 AM EDT Tue Aug 30 2016

Patchy fog at the outlying sites should burn off by 13z and leave
VFR conditions at the sites. A line of thunderstorms moving
southeast from northern Illinois is weakening but could hold
together enough to impact KLAF before it falls apart and included
a tempo group for this. With the best forcing across the north
from midmorning on included a VCTS at KLAF for much of the day.
At the other sites best chances for convection will be during the
afternoon/evening initially and included a Prob30 during that time
as uncertainty on coverage and timing is still pretty high.
Brought in showers and VCTS to the sites early tomorrow morning
just ahead of the cold front.


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