Area Forecast Discussion
Issued by NWS Indianapolis, IN

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FXUS63 KIND 192036

Area Forecast Discussion
National Weather Service Indianapolis IN
436 PM EDT Fri May 19 2017

The AVIATION Section has been updated below.


Issued at 205 PM EDT Fri May 19 2017

A low pressure system will lift northeast from Colorado to
northwestern Ontario by late Sunday. As it does, a cold front will
sweep east across central Indiana Saturday night and Sunday. Warm,
moist and unstable air will interact with a stationary front and
later the cold front and result in scattered to numerous
thunderstorms through the weekend. After a brief dry period early
next week, an upper low will drop southeast across the lower Great
Lakes and Ohio Valley and result in cooler and wet weather for the
middle of next week.


.NEAR TERM /Tonight/...
Issued at 205 PM EDT Fri May 19 2017

Models agree that an upper low over eastern Colorado will move
northeast to south central Nebraska by 12z Saturday. In the
meantime, this upper low will spin up a wave along a cold front.
This surface low will move to near extreme northwestern Missouri
Saturday morning. Also, a quasi-stationary front is expected to
remain near south central Indiana providing a decent surface
temperature gradient across the forecast area.

This afternoon, strong to severe storms were devloping and moving
over the eastern half of Indiana ahead of an upper disturbance.
Golfball size hail was reported in Spencer from the storm that was
currently moving toward Bloomington. Behind this area, a lull is
expected in the activity. That said, with warm, moist and unstable
in place and a stationary front nearby, thunderstorms are certainly
a possibility tonight. However, models were not showing any
significant short waves oer upper jet dynamics, and a modest low
level jet does not move across west central Indiana until after 12z.
So, will go with small chance pops tonight. Plenty of instability
around to include thunder and with 30 to 40 knot bulk shear, a few
severe storms can not be ruled out, mainly during the evening per
the DAY1 SPC Outlook.

Northeasterb sections of central Indiana could drop into the 50s
overnight with light northeast winds there to the north of the quasi-
stationary front. The location of this front will have a big impact
on temperatures and it is difficult to know exactly where it will
settle overnight.


.SHORT TERM /Saturday through Monday/...
Issued at 205 PM EDT Fri May 19 2017

Timing and coverage of thunderstorms will be the main focus for the
short term.

The 00z ECMWF and Ensemble Means and 12z GFS were pretty close in
moving the upper low to northwestern Ontario late Sunday. The ECWMF
is just slightly faster. They also agree, a broad weak surface low
will be over the Great Lakes and an associated cold front will move
to west central Indiana 12z Sunday and into western Ohio at 18z
Sunday. With good agreement, a blend of model features should do.

The warm front is expected to lift northeast across central Indiana
on Saturday, allowing the area to destablize with model CAPES to
2000 J/kg during the afternoon. In addition, a modest 30 knot low
level jet will be moving in from the west and a 100 knot upper level
jet will be moving into the Mississippi Valley. As the latter
feature gets closer, along with a cold front, thunderstorm activity
should become more widespread by Saturday afternoon and night and
into Sunday morning. Model precipitabloe water values 1.60 inches or
more are near the max moving curve of climatological soundings from
Wilmington and Lincoln. Thus, could see some heavy rain. In
addition, 30-40 knot bulk shear combined with the instability
supports a severe weather threat including supercells and bows,
especially during the afternoon and early evening. Instability dies
off overnight, but still will be enough for below severe limit
thunderstorms. Damaging winds and large hail will be the main
threats, although a tornado or two can not be ruled out with the
warm front in the area per the DAY2 SPC Outlook which has all of
central Indiana under a Slight Risk for severe weather.

The storms will be ending from west to east early Sunday and into
the afternoon, as high pressure builds in. The break will be short-
lived, however with an upper low bringing more convection to the
area for the long term.

Blended temperatures look reasonable with most areas expected to see
the lower 80s on Saturday in the warm sector. Then, temperatures
will return to near normal by Sunday in the wake of the cold front
with highs in the lower and mid 70s Sunday and Monday. Overnight
lows in the lower and mid 60s Saturday night will drop to the lower
50s Sunday night.


.LONG TERM (Monday night through Friday)...

Issued at 150 PM EDT Fri May 19 2017

Confidence in this forecast is rather high.

For the next several days, the weather will be dominated by large,
powerful systems.  These are relatively easy to forecast. Models
have reached similar solutions.

All this suggests the consensus from Region can be used with possible
temperature errors of 1-3 degrees, and possible POP errors of around
10 percent.


.AVIATION /Discussion for the 192100Z KIND TAF Update/...
Issued at 435 PM EDT Fri May 19 2017

Potential for scattered convection in the vicinity of the KIND
terminal will continue for a couple more hours as a frontal system
off to the northwest passes through.

Surface winds variable due to the proximity of the frontal zone
and earlier convective outflows, but winds should become 260-280
degrees over the next hour or so, then veer around to a more
northerly direction early this evening.

Potential exists for lower ceilings in the post frontal zone to
advect into the KIND area later this evening. Will revisit this on
the next routine issuance.

Previous discussion follows.

Expect rapid changes in flight conditions.

VFR should mostly prevail. However there will be an almost continual
risk of thunderstorms caused by warm humid air and a nearly
stationary front over Indiana.  Storms could produce brief LIFR in
heavy rain as well as gusty winds.

Timing is uncertain. VCTS will be used in the TAFs to denote periods
of higher risk. Expect TAF amendments for storms in TEMPO groups as
forecast confidence allows.

Winds of less than 10 knots will gradually veer from northeast to
southeast. Higher gusts are possible near storms.




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