Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 062113
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
413 PM EST Fri Dec 6 2013
.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
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 (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.
...Monday through Friday...
Light precipitation will linger behind the departing front on
Monday. Precipitation type will, as always, be a challenge. At
this point will go with a rain/snow mix in the morning transitioning
to rain in the afternoon. Areas with deep snowpack will likely
remain below freezing through the day, but the precip shield should
be to the east of those areas. Still, any slight shift in the back
edge of the precip shield would make a difference in precipitation
chances and types along and northwest of the Ohio River.
Monday night an upper trof will approach from the west and may
manage to spin up one last wave of precipitation, affecting
southeastern sections of central Kentucky. Temperatures will be
well cold enough for all snow, and the Lake Cumberland region and
Blue Grass could see an inch of accumulation. However confidence is
not great in this particular wave at this point.
Surface high pressure moving in from the Plains Tuesday and
Wednesday and then getting reinforced by high pressure dropping to
the southeast out of the prairie provinces Thursday and Friday,
combined with zonal flow aloft, will keep us dry for the remainder
of the week.
Temperatures will be a big story Monday night through Thursday.
Have gone several degrees below guidance over the expected snow pack
across southern Indiana and northern Kentucky. At this time we have
temperatures as cold as 1 degree above zero Tuesday morning and 4
above Wednesday morning in areas where there will be the deepest
snow. These numbers will be refined once we have the snow on the
ground and can make a better forecast on just how cold it will get.
Record lows for those mornings are in the single digits below zero.
The whole week will be quite chilly indeed until we get a possible
warm-up Friday with highs in the 40s as the Canadian high moves off
to the east.
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 (18Z TAF Update)...
Updated at 1231 PM EST Fri Dec 6 2013
A wintry mess will dominate the first several hours of the
forecast. Moisture streaming northeastward through central Kentucky
will continue to interact with cold air at the surface.
Precipitation type should change to snow within the first hour or
two of the forecast period at SDF and by late afternoon/early
evening at BWG and LEX. The snow will only last until mid evening
at SDF and late evening at BWG and LEX, but could be quite heavy at
times. Have accounted for this with TEMPO groups.
Deep moisture will quickly exit by mid to late evening, but low
level moisture will remain, resulting in continued low ceilings
through the night. Could see some freezing drizzle or ice pellets
from this low overcast but any precipitation should be very light.
Low clouds may finally begin to scour out by late Saturday morning
as Canadian high pressure noses in from the northwest. Of course,
this will still be something to watch since low ceilings can often
hang around longer than expected.
KY...WINTER STORM WARNING until 7 AM EST /6 AM CST/ Saturday FOR
WINTER WEATHER ADVISORY until 7 AM EST /6 AM CST/ Saturday FOR
IN...WINTER STORM WARNING until 7 AM EST /6 AM CST/ Saturday FOR