Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 240350

Area Forecast Discussion
National Weather Service Indianapolis IN
1150 PM EDT Wed Aug 23 2017


The Aviation section has been updated below.


Issued at 130 PM EDT Wed Aug 23 2017

Dry and pleasant weather is expected through the weekend. Strong
high pressure over the plains states is expected to slowly
progress eastward through the Great Lakes and Indiana through
Sunday. This will result in dry weather along with below normal

The next best chance for rain will be on Monday and Tuesday as a
Low pressure system sweeps toward Central Indiana from the Western
Great Lakes.


.NEAR TERM /Tonight/...
Issued at 130 PM EDT Wed Aug 23 2017

Surface analysis early this afternoon shows strong high pressure
over Missouri/Kansas/Nebraska/Iowa. GOES16 shows only a few CU
across the southern parts of Central Indiana...while the rest of
the state was mostly clear. Cool and dry NW surface flow was in
place with dew points in the lower 50s. Water vapor imagery shows
ridging in place across the Rockies...with lee side NW flow in
place across the upper midwest spilling into the Ohio Valley.
Water Vapor shows the related subsidence across Iowa...Illinois
and Indiana.

Confidence is high for dry weather tonight. The strong high to
the northwest is expected to continue to dominate the weather
pattern tonight...providing NW winds and continued subsidence.
Forecast soundings show a dry column as do the time heights. Thus
again...mostly clear should work just fine.

GFS and NAM suggest ongoing cold air advection continues tonight.
Thus will trend lows at or below the forecast builder blends
except within the urban heat island of Indianapolis.


.SHORT TERM /Thursday through Saturday/...
Issued at 130 PM EDT Wed Aug 23 2017

Confidence remains high for dry weather during this period.

GFS and NAM keep the slow moving ridge to the west through friday
before beginning to flatten out the ridge and allowing just cool
and dry NW flow to develop. Models agree a weak short wave will
push across Indiana on Thursday within the lee side flow...but
with limited moisture and subsidence in place...this should not
result in anything but a few additional clouds. Forecast
soundings suggest attainable convective temps with a good mid
level inversion in place. Thus partly cloudy should work fine.
Again given the N-NW flow and ongoing cold air advection...will
trend highs at or below the forecast builder blend.

Models suggest the previously mentioned short wave will depart on
Thursday night and much of the rest of the overall weather pattern
remains in place. This will lead to more subsidence and dry
weather through Saturday. Forecast soundings through Saturday
remain dry with only a few CU expected on Friday when convective
temperatures still may be reached. By Friday night and
Saturday...the surface high will have drifted toward the eastern
Great Lakes and this will result in lower level flow across
Indiana becoming easterly. surges of warm air
anticipated. Thus mostly clear nights and mostly sunny days will
be expected with the continued below normal temperatures.


.LONG TERM (Saturday night through Wednesday)...
Issued at 155 PM EDT Wed Aug 23 2017

There is good confidence Saturday night will be dry and mild.
Sunday into Wednesday there is low forecast confidence.

The reason for the low confidence is significantly different model
solutions about how the remains of tropical system Harvey will
affect Indiana. Tropical systems are inherently very difficult to
forecast. It`s possible we won`t be confident about what will happen
early next week for several days.

Use of consensus will reduce errors. Even so POPs issued today for
Sunday through Wednesday may ultimately need adjustment by more than
20 percent. Temperature forecasts for Monday through Wednesday could
be off by 5 degrees.


.AVIATION /Discussion for the 24/06Z TAFs/...
Issued at 1150 PM EDT Wed Aug 23 2017

VFR through the period.

Surface high pressure will be in control through the period, but a
weak upper wave will skirt the area to the north tomorrow, likely
resulting in scattered to broken stratocumulus development based
around 5kft. Winds through the period will generally be light and
variable. No significant obstructions to visibility anticipated,
although light MVFR fog briefly around daybreak cannot be completely
ruled out at the outlying sites.





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