000
FXUS63 KLMK 062351
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
651 PM EST Fri Dec 6 2013

...Forecast Update...
Precipitation is starting to become more scattered in portions
of the area this evening. The heavier bands are now along and south
of the Ohio River, with lighter snow across southern Indiana.
The transition line from freezing rain/sleet to snow appears to run
approximately along a line from Butler county to Clark county in KY
and will continue to sink to the southeast. Just made some minor
updates to the grids based on current radar and temperature trends.

.SHORT TERM (Now through Saturday)...
Issued at 410 PM EST Fri Dec 6 2013

...IMPACTFUL WINTER EVENT ONGOING...

First of all, have extended the Winter Storm Warning into the
Bowling Green and Lexington areas for wintry weather during the rush
hours this evening.  Mixed precip has already been reported near
these metros and anticipate it will only get worse as we near rush
hour.

Also, have extended the Winter Weather Advisory down through all of
south central Kentucky since the latest model soundings indicate some
light wintry precip before midnight which could cause light
accumulations of ice/snow...and then a prolonged period of on and
off freezing drizzle after midnight which could make travel
hazardous.

Both the Winter Storm Warning and Winter Weather Advisory have been
extended through 12Z tomorrow morning because of the after midnight
freezing drizzle possibility and due to plummeting temps which will
cause any wet surfaces to refreeze overnight.  This may cause
additional travel hazards.

Dual pol CC`s are doing an awesome job nailing the freezing line.
As of 21Z, the freezing line was just south of the Ohio River with
all snow north (southern Indiana and extreme central Kentucky), a
narrow band of sleet/freezing rain south of the Louisville metro and
nearing the Bowling Green/Lexington metro areas, and then rain or
rain with periods of freezing rain mixing in south of that.
Basically, the freezing line will continue to slowly move southeast
through the rest of central KY this evening.  While some ice
accumulation will still be possible over portions of central KY.
The main concern will be a prolong period of light to moderate snow
with bursts of heavy snow at times.  The latest high-res models
still indicate the highest snow accums over southern Indiana and
extreme north central KY.  Frontogenesis and some elevated
instability will likely cause heavier bands in the warning area this
evening.  A few models indicate a band could set up from Louisville
and into the northern Bluegrass region.  If so, snow accums may be
higher than currently forecast there.  For the latest forecast
snow/ice amounts...please see weather.gov/louisville.  The main
accumulating snow should be done by midnight.

After midnight sounding profiles indicate that we will lose ice
crystals aloft but a thick lower lever moisture layer will remain in
place.  This will likely result in freezing drizzle as temperatures
plummet into the lower teens and upper 20s.

Saturday conditions will dry out and skies will clear but temps will
stay below freezing for much of the area (in the 20s to around 30).
The Cumberland area may reach the mid 30s for highs.

.LONG TERM (Saturday Night through Friday)...
Issued at 340 PM EST Fri Dec 6 2013

...WINTRY WEATHER EXPECTED LATE SATURDAY NIGHT AND SUNDAY
ACROSS THE REGION...

...Saturday night through Monday...

Round two of wintry weather will push north into the region late
Saturday night.  Initially, it appears a band of frontogenetically
forced precipitation will fall across south-central KY.  Thermal
profiles within this band vary from model-to-model, thus not highly
confident in exactly what it will fall as.  At this time, it appears
the northern edge will likely be sleet/snow, changing over to
freezing rain on the southern side.  What is certain is this initial
batch of precipitation will fall in cold air at the surface, so
there will be impacts, just need to pin down whether those impacts
will be more sleet/snow or more ice, and how much of each.  The good
news is that after this initial batch of precipitation moves
through, surface temperatures will begin to rebound as a weak
surface low pushes through the state.  The exact track of this
surface low and resultant surface temperatures will likely depend on
whatever snow pack we get from the ongoing storm, which will be
better known in the next forecast cycle.  However, at this time it
appears as if most of KY will rise above freezing, which will mean
areas that receive frozen precip Sunday morning/early afternoon will
transition to plain rain as the surface low approaches by Sunday
evening, easing any impacts.  Portions of southern IN will remain in
the coolest air the longest, but QPF amounts look quite low which
means amounts of any frozen precip will stay generally light.

All in all, the best significant freezing rain potential (up to 0.25
inches of ice) will be along and southeast of a line from Bowling
Green up to Frankfurt.  Travel impacts across southern/central KY
will be early Sunday morning, pushing northeast toward
Lexington/Frankfurt by mid-morning.  As stated above, these impacts
will likely diminish by late Sunday afternoon/evening as
temperatures ooze above freezing.

By Sunday evening, most should see rainfall, expect perhaps
southern IN where a light wintry mix may be falling.  Forecast
soundings show the loss of ice crystals aloft, which could mean the
event may end as some freezing drizzle on Sunday night.  Will not
get quite this detailed in the grids at this time, but certainly
something to monitor in the coming shifts as slick roads could
redevelop Sunday night due to the freezing drizzle and temps falling
back into the upper 20s and lower 30s.

&&

.HYDROLOGY...

Issued at 315 PM EDT Fri Dec 6 2013

A winter storm was moving through the region dumping a large amount
of rain and mixed precipitation. Locations in southern Kentucky
collected over 2 inches overnight with up to an additional inch of
liquid expected. However...as the night goes on...much of the
precipitation will be freezing or frozen. This precipitation
will cause rises on river and streams but no flooding of large
rivers in expected.

The second system Saturday night through Sunday could drop an
additional inch of precipitation over southeast Kentucky and lighter
amounts elsewhere. Again, the precipitation will be a mixture of
frozen and freezing types and will runoff slower than pure rain.
This next shot could trigger some minor flooding on parts of the
Green and Salt basins. If so, flooding will extend into next week.
&&

.AVIATION (00Z TAF Update)...
Updated at 620 PM EST Fri Dec 6 2013

IFR snow continues at SDF, while the changeover looms very close to
BWG and LEX, with IFR to barely MVFR ceilings. Main challenge is in
handling the winter precip overnight. Will initialize SDF with all
snow, but will watch obs right up until issuance time at BWG and LEX
but the best bet is some kind of mix.

The steady precip will continue through mid to late evening, with
primarily IFR conditions especially at SDF. Could go into LIFR in
any mesoscale banding, and will handle that with a TEMPO. As the ice
in the clouds is lost, precip will taper off to freezing drizzle
just before midnight, and will continue the FZDZ and IFR ceilings
for much of the overnight.

Precip potential will wind down and ceilings will lift to MVFR just
before daybreak, before finally scattering out mid-morning. Should
be VFR for the rest of the day, with any mid-level ceiling coming
back in close enough to the end of the SDF planning period that we
will not include it. Beyond the valid TAF period, mixed
precipitation will be in play again by daybreak Sunday.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...WINTER STORM WARNING until 7 AM EST /6 AM CST/ Saturday FOR
     KYZ023>043-045-053-061>063-070>072.

     WINTER WEATHER ADVISORY until 7 AM EST /6 AM CST/ Saturday FOR
     KYZ046>049-054>057-064>067-073>078-081-082.

IN...WINTER STORM WARNING until 7 AM EST /6 AM CST/ Saturday FOR
     INZ076>079-083-084-089>092.

&&

$$

Update.........EER
Short Term.....AMS
Long Term......KJD
Hydrology......CMC
Aviation.......RAS