Severe Thunderstorm Warning 62, NWS Louisville, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
310 PM EDT WED MAY 22 2013

.Short Term (Tonight through Thursday night)...
Issued at 310 PM EDT Wed May 22 2013

Deep moisture continues to feed north through the Ohio Valley today,
as the surface cold front extends southward from low pressure over
Wisconsin through Illinois into southeast Missouri. A series of
impulses aloft will round the base of the upper trough and swing NE
through the Ohio Valley through tonight, getting sheared out as they
move through. Extensive mid-level cloud cover has kept us stable,
but showers and a few thunderstorms have blossomed over the last
hour.

Main challenge in the first few hours is severe potential, which is
looking more and more limited due to the failure to destabilize.
Will keep with the likely POP until just before sunset, but it will
be mainly showers and a few garden-variety thunderstorms.

The surface front that will move through tonight is fairly diffuse,
so we still expect decent low-level moisture to remain in place. The
main upper trough will swing through Thursday afternoon, triggering
showers and low-topped thunderstorms. With the cold pool aloft, a
few of the stronger storms over the north and east could drop some
small hail. Will taper POPs from 50 over southeast Indiana and the
Bluegrass to 30 along the Tennessee border.

After a mild and initially muggy night tonight, Thursday will begin
a period of below-normal temps. Highs will reach the lower/mid 70s,
with unseasonably chilly Thursday night mins in the upper 40s on
Thursday night.

.Long Term (Friday - Wednesday)...
Issued at 300 PM EDT Wed May 22 2013

Distinctly cooler air with low dewpoints will build in behind the
departed cold front for Friday and continue into the weekend. Even
with clearing skies, Friday will stay quite cool, with northerly
winds and highs ranging from the middle 60s to right around 70
degrees. Temperatures will slowly moderate to low and mid 70s by
Sunday, as ridging aloft edges back over the Lower Ohio Valley.
Expect lows generally in the low to mid 40s Saturday morning.

By late Saturday, ridging will take hold across the southern Plains,
with northwest flow aloft developing across the Ohio Valley. A warm
front will move northward, with moisture beginning to pool late
Sunday along and north of this boundary. Guidance suggests a
weakening area of showers and perhaps storms approaching the
forecast area from the northwest late Saturday, but believe we will
be too dry in the lower levels for any thing to survive, other than
clouds. So, temperatures Sunday morning should be several degrees
warmer with the added cloud cover closer to dawn. For Sunday, the
warm front is forecast to stretch along a line from northern
Missouri southeastward into Kentucky, and slowly shifting north
during the remainder of the extended forecast period. However, there
remains a lot of model spread with the placement of this boundary,
which makes temperatures and rain chances difficult a forecast.

Still expect isolated to scattered convection to periodically
develop along this boundary and propagate in waves southeastward.
Using an ensemble approach, it appears convection should develop
upstream and propagate southeast into our area late Sunday into
Monday morning, and another round late Monday into Tuesday morning
before rain chances shift north with the warm front.

Heights and temps aloft increase nicely through next week, with warm
southerly surface winds expected as the warm front slides north.
High temperatures ranging from the middle 70s to around 80 degrees
Monday will give way to generally middle 80s by Wednesday.

&&

.Aviation (18Z TAF Issuance)...
Issued at 1245 PM EDT Wed May 22 2013

SW winds are well established over Kentucky, and mixing has picked
up just enough to support gusts near 20 kt at SDF. Speeds increasing
just enough at BWG and LEX, and we expect to see gusts by the valid
time of the TAFs. Mid-level clouds have been the limiting factor in
convection thus far, but we are starting to see some Cu and expect
that will continue to increase with heating.

POPs are quite high but it is still difficult to pin down when and
whether any storms will impact each terminal. At this point, will
carry VCTS from 20Z until 00Z Thursday, with prevailing VFR.
However, once storms do develop an update will likely be required to
get a better handle on actual impacts. If any storms directly affect
any of the airports, conditions will likely drop to MVFR if not IFR,
but only for a brief period.

Storms and winds will diminish this evening, but a VFR ceiling will
remain through the night. Broad frontal wind shift will give us SW
flow through the night, and then due west on Thursday with a VFR
ceiling. Upper-level impulse and associated cold pool aloft will
move ESE through the Ohio Valley on Thursday, and will likely
trigger scattered showers and even a few thunderstorms. However, the
better chances are in SDF and LEX, and will be late enough in the
day to be mainly limited to the 24-30 hour planning period in the
SDF TAF.

&&

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

Short Term.......RAS
Long Term........MJP
Aviation.........RAS

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