Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 070532
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1232 AM EST Sat Dec 7 2013
...Updated Aviation Discussion...
Issued at 1230 PM EST Dec 6 2013
Canceled the remaining Winter Weather Advisory for the southern
Bluegrass and Lake Cumberland Regions. Light freezing drizzle or
snow flurries will continue across these areas until just past
midnight, but now significant accumulations are expected. Skies
will slowly clear towards dawn across southern Indiana, expanding
southwards across northern Kentucky during the morning hours.
.SHORT TERM (Now through Saturday Night)...
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
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
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 (Sunday 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.
.AVIATION (06Z TAF Update)...
Updated at 1220 AM EST Sat Dec 7 2013
Very light freezing drizzle or snow flurries may continue through
08z at LEX and BWG. However, any light precipitation or light fog will
not reduce visibilities below 5SM.
Low end MVFR ceilings currently just above 1k feet will slowly rise
and scatter out at SDF and LEX around the 10 to 12z time frame.
These rises will take place a couple of hours later at BWG.
After 12z, VFR conditions expected at all TAF sites with partly
cloudy to clear skies expected through the daytime hours.
North winds around 10 mph will continue through late afternoon
Saturday, after which they will back to the northeast and range from
5 to 10 mph through early Sunday morning.
Cloud cover will increase from south to north late Saturday evening
and Sunday morning.
Mixed wintry precipitation is likely early Sunday morning right
after the ending of this set of TAFs.