Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 261734

Area Forecast Discussion
National Weather Service Louisville KY
134 PM EDT TUE APR 26 2016

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1219 PM EDT Tue Apr 26 2016

Forecast is on track at this hour and will continue to monitor
destabilization progress through the afternoon. Still expecting
scattered to numerous thunderstorms to develop in the late afternoon
as 700 mb inversion erodes and low level convergence increases ahead
of the front and MCV currently over central MO. The combination of
low to mid 60s dew points pooling ahead of the frontal boundary over
central IL/IN/OH, and good surface heating should contribute to ML
CAPE values over 2000 J/KG along and west of I-65. Main storm mode
should be pulse in nature given the strong instability, but
relatively marginal deep layer shear. However, a few storms may
exhibit a line segment mode with damaging wind threat. Additionally,
will have to watch cold pool driven storms currently over central MO
to survive into our region, where a wind threat will accompany.

Issued at 837 AM EDT Tue Apr 26 2016

Picking up some light rain showers on radar over southern Indiana
associated with a weak isentropic lift component. Will introduce an
isolated shower mention across southern IN and north central KY to

Issued at 532 AM EDT Tue Apr 26 2016

In light of recent radar trends and the latest convection-allowing
model guidance, have made some updates to the going forecast for
this afternoon.  As some of the guidance has been depicting,
convection has become more widespread across portions of southern
NE/northern KS early this morning, an isentropic response to the
ejecting western trough.  There is growing consensus among the
latest hi-res data that this convection will actually induce an MCV,
which will help to enhance thunderstorm coverage across portions of
MO/western IL later this afternoon, moving into areas west of I-65
very late this afternoon and into this evening.  Until then,
thunderstorm coverage may be sparse in our area due to weak capping
and the cold front remaining off to the north.  Therefore, have
trimmed pops further for this morning.  Think the best threat for
any locally severe storms will be mainly along/west of I-65 and
north of I-64 late this afternoon and this evening where the
expected MCV will tap into the best diurnal instability.

.SHORT TERM (Now through Wednesday)...
Issued at 322 AM EDT Tue Apr 26 2016

...A Few Strong Storms Possible Late this Afternoon and Wednesday...

The synoptic pattern early this morning features a large upper-level
low continuing to spin across eastern Canada, with a potent trough
digging into the southern Plains.  In between, a flattened ridge is
located over the Great Lakes/Ohio Valley, through which a few
perturbations will travel through the period.

The latest radar mosaic continues to show a general lack of
convection to the northwest along a cold front, currently located
across north-central IL into northern IN.  Almost all available
guidance is overdoing convection currently, which does lend to some
uncertainty for convective evolution today into tonight.

Given the lack of current convection and lack of a trigger in the
near term, have lowered pops through this morning.  Without any
convection along the front to force it southward, like the idea of a
slower arrival of precipitation this afternoon/evening. Expect
scattered thunderstorms to break out generally to the north of the
LMK CWA early this afternoon, but spreading southward into the
region late this afternoon into this evening as cold pools attempt
to congeal.  Therefore, the best coverage through the day today will
remain along/north of the I-64 corridor.  Think much of southern KY
will stay dry through most of the day, but a few isolated storms are
not out of the question.  Given some sunshine expected this
morning, temperatures should climb into the 80s areawide.  This will
help push MLCAPEs into the 1500-2500+ range.  However, deep layer
kinematic fields will be rather weak, with only around 20-30 knots
of deep-layer shear expected.  Therefore, expect multicell clusters
capable of some hail, locally to quarter-size and locally damaging
winds (given enough dry air in the mid-levels to push enhance
downdraft potential).

Convection will help to force the front southward tonight, but not
for long as the western trough becomes negatively-tilted and ejects
out into the Central Plains.  In response, the front will lift back
to the north late tonight into Wednesday morning.  Isentropic lift
atop this frontal surface will lead to elevated shower/storm
development through the first part of Wednesday.  Will have to watch
how quickly we become warm-sectored on Wednesday and how quick the
elevated convection clears out.  If we can get within the warm
sector during the late afternoon hours, a few strong storms will be
once again be possible Wednesday evening into Wednesday night.
However, as of now the better diurnal destabilization concurrent with
the more favorable kinematic fields look to remain off to the west,
thus agree with SPC`s continuance of only a Marginal risk for the
western CWA.

The PV anomaly will lift north by Thursday, but the surface front
and surface low will continue to remain off to the northwest.
Therefore, additional destabilization and thunderstorm development
will be possible on Thursday, especially east of I-65 as the front
pushes through.

.LONG TERM (Wednesday Night through Monday)...
Issued at 300 AM EDT Tue Apr 25 2016

The synoptic pattern at the start of the long term period will
feature a flattened ridge across the Ohio Valley, with a strong
trough continuing to remain across the western CONUS.  This trough
will pinwheel into the central CONUS through the period, bringing
continued unsettled weather to the region this weekend into early
next week.

Thursday night into Friday will be the only dry periods of the
forecast, as the Ohio Valley becomes situated in between systems.
Highs on Friday will climb into the 70s under partly to mostly
cloudy skies.

The latest deterministic and ensemble guidance continues to suggest
another strong system ejecting into the Midwest/Ohio Valley this
weekend.  Still plenty of uncertainty in the strength and position
of the surface low and warm front Saturday morning, but overall the
chances of showers/storms will be on the increase during the day.
Higher confidence that we`ll see additional rounds of storms
Saturday night into Sunday, and likely into the first part of next
week. The environment will favor stronger to potentially severe
storms as well with a more favorable shear environment, but timing
of the waves of storms will be crucial to the quality of the
thermodynamic environment. Guidance continues to suggest that 2-4
inches of rain will be possible over the next several days,
particularly with this weekend system, so hydrologic issues could
arise especially by late this weekend/early next week.


.AVIATION (18Z TAF Update)...
Updated at 133 PM EDT Tue Apr 26 2016

VFR conditions with a steady SW surface wind will persist through
the remainder of the afternoon outside of any convective activity.
Do expect that scattered showers and t-storms could fire by late
afternoon just ahead of a frontal boundary slowly sagging toward the
Ohio River. Will mention VCTS at SDF/LEX by 5 to 7 PM.

Main concern will be with convective complex over central MO, and
its arrival around just after sunset. With unstable atmosphere ahead
of it and already well established cold pool, have high confidence
in it surviving into our region. Have best estimate of timing of
TSRA at SDF between 8 and 11 PM EDT where low MVFR or IFR
visibilities would be accompanied by gusty W winds between 35 and 40
mph. Same timing and conditions apply to BWG. Have best LEX timing
between 10 PM and 1 AM EDT where slightly less impactful weather is

Thereafter, expect variable winds and ceilings near the VFR/MVFR
threshold through the rest of the overnight. As synoptic winds
recover, look for a return to SW winds toward dawn, with chances for
showers and a few storms increasing through the morning as the front
hangs in the area.


.LMK Watches/Warnings/Advisories...


Short Term.....KJD
Long Term......KJD
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