Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 272023

Area Forecast Discussion
National Weather Service Indianapolis IN
300 PM EDT Thu Apr 27 2017

.UPDATE...The AVIATION section has been updated below.


Issued at 300 PM EDT Thu Apr 27 2017

A southern Plains systems will strentghen and lift north over the
lower Great Lakes over the weekend and early next week. This system,
along copious amounts of Gulf moisture, will result in several
rounds of thunderstorms this weekend and into early next week.
Meanwhile, another system will trigger more storms for the middle to
late week next week.


.NEAR TERM /Tonight/...
Issued at 300 PM EDT Thu Apr 27 2017

Sky cover and temperatures will be the main focus for tonight.

A cold front will be well east and south of central Indiana tonight
as high pressure sets up over the Ohio Valley. In addition, an upper
trough will pivot northeast away from the area. Model time sections
were also showing some thinning of low level moisture. This should
allow for some breaks in the clouds.

With some breaks but winds shifting back to the south, should only
see temperatures bottom out in the upper 40s to lower 50s.


.SHORT TERM /Friday through Sunday/...
Issued at 300 PM EDT Thu Apr 27 2017

The main focus for the short term will be on heavy rain and severe
weather potential this weekend.

Models in general agreement that the cold front, that just passed
through this morning, will return northward as a warm front and move
through central Indiana Saturday and Saturday night as an associated
surface low deepens and lifts northeast from the southern Plains to
the Ozarks. A cold front will extend from this low to the Gulf. The
12z GFS was a bit faster than the 00z ECMWF, but both were within
the envolope of ensemble possibilities. On the otherhand, the 12z
NAM looked too fast.

Models were showing strong isentropic lift and moisture transport
ahead of this system with precipitable water amounts from 1.5 to
near 2 inches at times, which exceeds the maximum moving average for
this time of year at ILN and ILX, seen on the Storm Prediction
Center sounding climatology page. In addition, model instability
progs were showing increasing instability starting Friday afternoon,
mainly near and south of Interstate 70, where SPC has a Slight Risk
for severe weather. Far southwest parts of the forecast area are
even in an Enhanced Risk. With strong moisture transport,
instability, a plus 120 knot upper level jet over the lower Great
Lakes and convergence on the nose of a plus 45 knot low level jet,
heavy rain and training is also a good bet. Should see thunderstorms
increase from southwest to northeast on Friday as a low level jet
moves in. Coverage should increase Friday night as upward vertical
motion fields increase ahead of the approaching warm front in
continued isentropic lift on the 305k level. Highest QPF should be
near and south of Interstate 70, closer to the warm front, per model

With the high precipitable water values and good lift, heavy rain
will continue to be a threat, especially by Sunday afternoon as the
system gets closer. Model QPF may be on the low side for this event.
Best chance of pops and highest liklihood of heavy rain and flooding
for the rest of the weekend looks to be near and north of Interstate
70 to the north of the warm front. Future Flash Flood Watches may be
neccessary. Meanwhile, chances will increase again over the
southeastern counties by Sunday afternoon as a cold front gets
closer.  Per model blend, thunderstorms chances will be mostly
likely to categorical, except only chance pops on Friday.

Model blend seems to have a good handle on temperatures based on
cloud cover and warm air advection. There should be a decent
gradient in place with afternoon high temperatures mostly in the 60s
near and north of 70 and lows in the 70s south of 70 through
Saturday. Temperatures will be warmer on Sunday as the warm front
moves north of the area. Blend highs in the mid 70s north to lower
80s south look reasonable.


.LONG TERM /Sunday Night Through Thursday/...
Issued at 211 PM EDT Thu Apr 27 2017

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

A cold front Sunday night will usher in a cool and unsettled week
for central Indiana. There could be some heavy rain Sunday night. An
upper system will remain close enough for some PoPs across the area
Monday and for some areas Tuesday.

Meanwhile, another upper low will develop mid week. Models differ in
timing and location, so see no reason to change from the model
initialization at this point. This results in low PoPs most areas
Wednesday and Thursday.

Temperatures will remain below normal through the period.


.AVIATION /Discussion for the 27/2100Z IND TAF Update/...
Issued at 423 PM EDT Thu Apr 27 2017

No changes needed to the TAF.

Previous discussion follows...
Issued at 1215 PM EDT Thu Apr 27 2017

Good confidence that MVFR and possibly brief IFR ceilings will
persist this afternoon based on latest satellite and ob trends as
well as models. Then, moderate confidence that MVFR conditions will
improve to VFR 21z-23z.

Winds will shift southwest to south after 04z. Wind speeds will drop
from near 15 knots to less than 10 knots. Finally, winds will back
to southeast near 10 knots after 14z.





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