Special Weather Statement, NWS Louisville, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1001 AM EDT MON MAR 18 2013

.Forecast Update...
Issued at 1000 AM EDT Mon Mar 18 2013

Just a quick update to mention that a severe thunderstorm watch box
was issued a little after 9 for the border counties in our
southeast. Line coming out of Nashville is producing some damage.
The threat for damage should quickly leave our area as the line
progresses eastward, so likely will be clearing the watch over the
next couple of hours for our region. Based on mesonet data, the best
chance for surface-based storms looks to be over Clinton, where
temperatures are in the lower 60s. We may get some hail out of
storms just north and west of Clinton.

Issued at 825 AM EDT Mon Mar 18 2013

Updated the forecast for trends in obs and winds. Overall bumped
highs down a category, which may not be enough for my northwest
forecast area. Still watching the line of storms over western
Tennessee, to see how much of that will get into our southern
forecast area. Most of our area has been worked over, but more
unstable air will get advected in to our border counties with
Tennessee, which could allow some stronger wind gusts down there.
Likely will be issuing updates frequently through the morning to
match obs.

&&

.Short Term (Now through Tuesday)...
Issued at 305 AM EDT Mon Mar 18 2013

Surface warm front is now starting to make some northward progress
early this morning.  The front is currently located from near
Dyersburg, Tennessee eastward through Nashville down towards
Chattanooga.  All of the available guidance suggests that this front
should start to surge northward/northeastward over the next several
hours as the low-level jet axis pushes on off to the east.  Much of
our area remains dry this morning.  However, with the cold front
just off to the west, showers and thunderstorms across western
Kentucky will move eastward through the remainder of the overnight
hours.  So, we expect precipitation coverage to expand quite a bit
in areas west of I-65.  Further east, isolated to scattered showers
will be possible within the warm air advection scheme and increasing
isentropic lift.  Temperatures have been very slowly creeping upward
with southern Indiana and the northern half of Kentucky in the upper
30s...while southern Kentucky is generally in the lower 40s.  With
the warm front surging northward, we should see temperatures across
the south start to spike up in the next couple of hours with
readings warming to the lower 50s in the south and lower-middle 40s
in the north.

For today, the multi-model short term consensus is in agreement with
the surface cold front pushing eastward into the region later this
morning.  Widespread shower and scattered thunderstorms will
accompany the front as it pushes through our forecast area.  Out
ahead of this front, we should see dewpoints pool into the mid-upper
50s.  This combined with some diurnal heating will lead to surface
based instability developing...especially across our southeastern
third of the forecast area.  As this destabilization occurs, the
wind field will strengthen quite a bit.  Forecast soundings suggest
show a weakly veering wind field with height developing but speed
shear is plentiful.  This should support organized storm
development...mainly across south-central KY.  Given the shear and
instability forecast, it appears that small scale lines of
convection with short bowing segments will probably be the most
likely convective mode supporting a damaging wind threat across
southern/southeastern Kentucky.  Convection should push east of the
area later this afternoon as the cold front clears the area.
Temperatures will feature a gradient across the region with highs in
the lower-middle 50s in the northwest with readings generally along
and southeast of the Ohio River warming into the upper 50s to the
lower 60s.  The warmest readings would be down in the Lake
Cumberland region where mid-upper 60s will be possible.

As the cold front pushes east of the area this evening,
precipitation will end from west to east and winds will shift from
the southwest to the northwest and remain gusty as the pressure
gradient will remain rather tight in the post frontal airmass.
Low-level moisture will remain in place so cloud cover will be
likely this evening with clearing commencing from west to east
overnight.  Lows will drop into the upper 20s across southern
Indiana tonight with lower 30s expected across Kentucky.

High pressure will build into the region for Tuesday with mostly
sunny conditions expected.  Temperatures will remain below normal
with highs in the upper 40s across southern Indiana and the northern
half of Kentucky.  In areas south of the BG/WK parkways, lower 50s
still look attainable Tuesday afternoon.

.Long Term (Tuesday Night through Sunday)...
Issued at 310 AM EDT Mon Mar 18 2013

The long term will start out with northwesterly flow aloft and a
quick moving shortwave traveling through this flow. Most of the
models indicate the area could see some precipitation from the wave
late Tuesday night through Wednesday morning. The soundings show the
column moistening, with deep enough moisture for ice crystals. Will
therefore include a slight chance for snow showers across the region
during this time period. There may be some very light accumulations
with this snow, but these would be short lived as temperatures will
rise into the 40s by Wednesday afternoon.

Surface high pressure ridging in from the northwest will keep things
dry Wednesday night through Thursday. Temperatures Wednesday night
will be quite cold, dropping into the lower to mid 20s. Thursday
will see highs in the upper 30s to lower 40s.

Thursday night into the weekend a broad low pressure system will
develop over Texas and slowly shift east. The ECMWF continues to
keep this system suppressed well to the south while the GFS tries to
bring it further to the north and then develop a stronger system
across the central CONUS later in the weekend. Will continue to lean
more towards the ECMWF with this forecast and keep pops on the lower
end and more suppressed to the south Friday through the weekend.
Temperatures will remain well below climatological normals for this
time of year with highs in the mid to upper 40s and lows in the
lower 30s. With lows dropping into the lower 30s, any precipitation
overnight could result in a rain/snow mix or all snow at times.
However, the forecast remains rather uncertain for this weekend, so
it is likely to change as the models get a better handle on the
situation.

&&

.Aviation (12Z TAF Issuance)...
Issued at 648 AM EDT Mon Mar 18 2013

Large area of showers with embedded thunderstorms will continue to
move across the region this morning.  With the cold front still west
of the area, another round of showers and storms is expected later
this morning and into the afternoon hours as the actual front sweeps
through the region.  Ceilings through the period will generally be
in the low end of the MVFR range and may drop occasionally into the
high end of the IFR range at times.  Surface winds will generally be
out of the southeast but veer to the southwest over the next few
hours.  Sustained winds of 10-15kts with gusts up to 20-25kts will
be possible.  The winds will shift to the west and northwest after
the front clears the area this afternoon.  Conditions should start
to improve from west to east late this afternoon after the cold
front passes through.  The latest data suggests that a period of
MVFR ceilings will be likely in the post frontal airmass with
conditions improving late tonight as drier air pushes in from the
northwest.

&&

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

Updates..........RJS
Short Term.......MJ
Long Term........EER
Aviation.........MJ

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