Severe Thunderstorm Warning 167, NWS Louisville, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
243 PM EDT Sun Jun 21 2015

.SHORT TERM (Now through Monday Night)...
Updated at 244 PM EDT Sun Jun 21 2015

...Strong to Severe Storms Possible Late This Afternoon into This
Evening...

The synoptic pattern early this afternoon features an expansive
ridge building in across the southern CONUS, whose reach extends up
into portions of southern KY.  Further north, an active northern
stream continues to send generally subtle PV anomalies through the
flow, each of which continue to set off clusters of convection.

The forecast for late this afternoon into this evening remains a
rather difficult one, as there are many subtle features to contend
with.  Have fairly high confidence that any thunderstorm activity
late this afternoon will be focused across central and southern KY.
KLVX showed a nice boundary push through earlier this afternoon, and
SPC mesoanalysis shows strong moisture convergence along it.  The
latest satellite loop confirms this, as a line of cumulus has now
formed along the boundary.  Along and south of this boundary is
where the best coverage of storms will be this afternoon.

Forecast soundings still suggest there will be a cap to contend with
across central/southern KY which may help limit updraft intensity to
some extent.  However, MLCAPEs in this area have risen to 3000-4000
J/kg according to the latest mesoanalysis data (though this may be a
bit overdone).  This strong instability coupled with 20 to 30 knots
of effective shear may lead to some loose storm organization.  The
high DCAPE environment suggest localized damaging wind gusts will be
the main threat, although some quarter-sized hail will be possible
as well given the strong instability in place.

That activity should sag south by early this evening, as attention
then shifts to the current convection ongoing over MO.  The CAMs are
really struggling with what will happen with this activity through
the rest of the afternoon into this evening, as some want to keep it
mainly elevated and fade it this evening, while others develop it
into a severe linear MCS and plow it southeast into our region
tonight around/after 00Z.  The area downstream of this activity over
IL has been slow to destabilize given a thick cirrus shield in place
through much of the day, but that cirrus has now mostly dissipated.
Dprog/dt of the typically reliable HRRR shows a very inconsistent
solution, so confidence is low.  Will go with a rather conservative
approach to pops and keep them around 40 percent for the potential
of this activity getting in here later tonight.  If it does develop
a cold pool and begin to bow out, then it could bring some severe
wind gusts into portions of southern IN and KY later this evening,
mainly west of I-65.  Once this moves through, the rest of the
overnight period will be mainly dry as upper-level ridging builds
overhead.

The ridge will really take hold Monday into Monday night, bringing
mostly dry and hot conditions.  Can't completely rule out a stray
storm Monday afternoon, but forcing mechanisms are lacking and the
mid-level cap will be strong.  Therefore, will go with a dry
forecast. Highs will be in the low to mid 90s, with heat indices in
excess of 100 degrees at times.  Overnight lows on Monday will be
quite muggy out ahead of another system slated to push through on
Tuesday, with readings only dropping into the mid and upper 70s.

.LONG TERM (Tuesday through Sunday)...
Issued at 220 PM EDT Sun Jun 21 2015

Models have not changed much in their overall pattern, with a ridge
near but centered just southwest of the region early on and then
transition to a more dominant western ridge by the end of the work
week, with troughing over us.  That should mean hot days at first
and a little cooler by the end of the work week, but with rain
chances pretty much every day.

&&

.AVIATION (18Z TAF Update)...
Updated at 113 PM EDT Sun Jun 21 2015

Generally VFR conditions are expected through the TAF period,
although restrictions may prevail in thunderstorms this afternoon
and evening.  The latest satellite and environment trends support
the idea that storms will initiate mainly south of KLEX and KSDF,
with little coverage expected around KSDF and KLEX.  Therefore, have
removed VCTS mention at those sites, but added it into KBWG where
coverage is expected to be a bit better.  Winds outside of storms
will be out of the WSW with gusts of 15-20 knots at times.

Confidence decreases a bit tonight, as convection across MO may
congeal and make a run at all sites overnight.  However, it has
really struggled so far this morning and only a few guidance members
have it getting into the terminals later tonight, so will leave out
for now.  Could be some light fog at KBWG and/or KLEX, but there
once again may be some mid/upper level clouds from convection to
limit any BR development, so will leave out for now.

Despite the overnight early morning thunderstorm chances, tomorrow
should be mainly dry as upper-level ridging builds in.  VFR
conditions are expected with winds out of the WSW at 10-15 knots
with gusts to 20 knots.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

Short Term........KJD
Long Term.........RJS
Aviation..........KJD

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