Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 201902

Area Forecast Discussion
National Weather Service Indianapolis IN
302 PM EDT Sat May 20 2017

.UPDATE...The SYNOPSIS...NEAR TERM and SHORT TERM sections have been
updated below.



Issued at 302 PM EDT Sat May 20 2017

A cold front will slide east across central Indiana overnight and
Sunday. The front will interact with a warm, moist and unstable
airmass and result in widespread thunderstorms. The storms will be
ending from west to east overnight and Sunday morning. High pressure
will usher in seasonably dry weather through Monday. Then, an upper
low pressure area will bring more showers and thunderstorms and cool
temperatures to the area through the middle of next week. Warmer
temperatures and more showers are possible next weekend as another
frontal approaches from the west.


.NEAR TERM /Tonight/...

Issued at 302 PM EDT Sat May 20 2017

Main focus tonight will be on timing and coverage of thunderstorms.

Models in good agreement that an upper low will lift from Nebraska
to the northern Plains by 12z Sunday. In response, a surface low
will lift from southwestern Iowa northwestern Wisconsin. The
thunderstorm complex, that went through central Indiana earlier, has
now moved into northern Indiana. Satellite was showing breaks in the
cloud cover which should allow the southern Indiana front to move
northward and the atmosphere to de-stabilize once again ahead of a
cold front, that was sagging south from the surface low, across
western Missouri and the southern Plains. The front should be just
to the west of a Kokomo to Indianapolis to Bedford line by daybreak.
The front will interact with the very moist and unstable atmosphere
and should result in numerous thunderstorms. The thunderstorms will
be ending overnight west of the front and continue east of the
front. Pre-frontal precipitable water values will be near-record
around 1.70 inches at ILX and ILN. In addition, central Indiana will
be within the right rear entrance of a 105 plus knot jet streak over
western Wisconsin. All this suggests heavy rain is possible. In
addition, 30-40 knot 1000-500 bulk shear suggests a few strong or
severe storms are possible, mainly during the late afternoon and
early evening, when surface base CAPES should exceed 1000 j/kg.

Blend lows in the lower and mid 60s look good tonight with the
cooler temperatures in the wake of the cold front.


.SHORT TERM /Sunday through Tuesday/...

Issued at 302 PM EDT Sat May 20 2017

Main challenge for the short term will be timing the showers and
thunderstorms out of the area in the wake of the cold front and also
will be on timing and coverage of the return of unsettled weather
associated with an approaching upper low.

Models are in good agreement that the showers will be ending near
and west of a Kokomo to Indianapolis to Bedford line by 12z Sunday
and over with across all of central Indiana by 18z, as the front
moves into Ohio. Skies will be decreasing Sunday afternoon with
seasonable blended highs in the lower and mid 70s looking
reasonable. It will be cool Sunday night under high pressure. Some
areas may dip to the 40s. Look for slightly below normal
temperatures Monday despite a good deal of sunshine expected.

Models then in good agreement that an upper low will rotate
southeast across the western Great Lakes by late Tuesday. This will
promote more showers by Tuesday. Although areas near and west of
Tipton and Terre haute could see an overnight storm Monday night.
For now chance pops look good for most of the forecast area, but
chances look a little better northwest. With extensive cloud cover,
below normal temperatures are a good bet.


.LONG TERM (Tuesday night through Saturday)...

Issued at 150 PM EDT Sat May 20 2017

There is good confidence it will rain either Tuesday night or
Wednesday, and that Friday should be dry. Otherwise there is much
forecast uncertainty.

The American and European models disagree on the timing of
systems that would cause precipitation. The exception is they both
have Indiana covered by dry high pressure Friday. Depending on
which model ends up best, POP errors may be as high as 20 percent.

The American and European models also disagree about cool Canadian
air arriving in the Hoosier state. This makes temperature forecasts
progressively more uncertain. Errors through Wednesday night should
be 2 degrees or less. Errors late in the period could be 5 degrees.


.AVIATION (Discussion for 201818Z TAFs)...

Issued at 1259 PM EDT Sat May 20 2017

Expect numerous thunderstorms.

Thunderstorms, some causing LIFR in heavy rain, are going to
occur into the night. Late tonight or early Sunday a cold front
passage will end precipitation. The frontal passage should bring
widespread MVFR, and local IFR, ceilings.

Conditions should improve dramatically starting late in the morning,
with most clouds dissipating by early Sunday afternoon.

Winds are going to have speeds of about 10 knots as they veer from
east today to west by late Sunday. Storms could produce higher gusts.




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