Area Forecast Discussion
Issued by NWS Indianapolis, IN

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616
FXUS63 KIND 210740
AFDIND

Area Forecast Discussion
National Weather Service Indianapolis IN
340 AM EDT Sun May 21 2017

.UPDATE...
Long Term Section has been updated below.

&&

.SYNOPSIS...

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 938 PM EDT Sat May 20 2017

Upper vorticity center appears to be located over western Indiana
at this time, with areas of convection ahead of this feature.
Short term model guidance suggests this feature will exit the
local area around 210500Z. Will drop PoPs into the chance category
over the western zones for the rest of the night based on current
position of vorticity center, and will keep higher PoPs over the
central and east zones until 210500Z, and cut those areas back to
chance PoPs after that time.

Low level helicity will remain enhanced over the northeastern
zones ahead of vorticity center for a few more hours, but should
diminish towards 210500Z as the vorticity centers lifts off to
the northeast.

Previous discussion follows.

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 (Wednesday through Saturday)...
Issued at 340 AM EDT Sun May 21 2017

Wednesday will be cool and wet with low pressure over Ohio and a
closed upper low over Indiana.  These low pressure systems will move
on to the east as high pressure moves east across the southern U.S.
Thursday and early Friday.  Models indicate dry weather will be the
rule late Thursday through early Friday.

After that there is more uncertainty with timing between the models.
Low pressure will move into the plains Friday and towards the upper
midwest and lower great lakes by Saturday.  The canadian model
develops a warm front across the mid Mississippi and lower Ohio
valleys and bring a strong upper disturbance towards Indiana late
Friday...while the Euro keeps the precip farther west Friday and
keeping Indiana mostly dry until Friday night.  Will go with a blend
for now and went with low rain chances over southwest sections late
Friday...slightly lower than Superblend POPS.

Went with low chance POPS Friday night and Saturday as a warm front
lifts north across our region.

Highs will be in the middle 60s Wednesday warming to the upper 70s
to around 80 by Saturday.  Lows will be in the upper 40s to near 50
Wednesday night warming to 55 to 60 by Friday night.  Stayed close
to superblend temperatures through Friday and went slightly warmer
than MOS blend some areas Friday as warm advection increases across
the region.

&&

.AVIATION /Discussion for the 210600Z TAFS/...
Issued at 1239 AM EDT Sun May 21 2017

Some lingering instability and an approaching cold front from the
west may spark off some widely scattered convection through the mid
morning hours of Sunday, but the chances of direct impacts to any
particular terminal appear fairly low at this time so just going
with VCTS during most likely time.

Should see areas of MVFR ceilings 010-015 develop overnight, with
these ceilings lingering until frontal passage by mid to late
morning Sunday.

Surface winds 160-190 degrees at 6-10 kts overnight will veer around
to 250-270 degrees at 10-14 kts by midday Sunday in the wake of
frontal passage.

&&

.IND WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SYNOPSIS...MK
NEAR TERM...MK/JAS
SHORT TERM...MK
LONG TERM....JH
AVIATION...JAS/CP



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