Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 240501
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1201 AM EST Sat Jan 24 2015
...Updated Aviation Discussion...
Issued at 940 PM EST Fri Jan 23 2015
The widespread heavier snow band is continuing its weakening trend,
but smaller pockets within that band are spiking back up, like one
in Nelson county and another moving through Northern Barren and Hart
counties. Will trim part of the Winter Weather Advisory, the part
where the threat for heavier snow has ended. Will replace with a
Traveler`s Advisory for slick roads, as wet and partially
snow-covered roads could re-freeze with temperatures dropping into
the upper 20s overnight. Will also issue this advisory into the
areas that were not in the previous Winter Wx advisory but received
1-3" of snow tonight. Updated products coming out.
Issued at 750 PM EST Fri Jan 23 2015
Main snow band showing signs of losing its grip these past few
scans, with highest dBZ dropping. Past several runs of the HRRR
insist on this trend continuing, while also not showing much in the
way of further snows the rest of the night either. Given moisture in
the time height sections sticking around till a little after 06Z,
will keep in the chance for some light snows for a few more hours
before ending the threat from west to east.
With the snow rates coming down, the roads should be able to catch
up and start melting quicker than the accums on grassy areas. Just
had a report that the roads in NE Jefferson county now were wet, as
well New Circle road in Lexington. The snow rate is what got the
roads slick despite the warmer temps. Decided against expanding the
advisory northward based off the lesser impact on traffic, as rush
hour has ended, and the chance for roads to improve with the slower
Issued at 525 PM EST Fri Jan 23 2015
Though the amounts of snow likely will amount to less than our
advisory criteria in many locations, the lack of familiarity with
driving in winter situations this winter and this snow coming down
along the Parkways during the evening rush hour likely will cause
slick spots on area roadways. One thing this band is setting us up
for is for additional lighter snows to have a better chance to
accumulate this evening, creating more slick spots for travel. Thus
decided to issue the advisory for points along and south of a
Hartford to E-town to Lexington line. Updated products will be out
Issued at 450 PM EST Fri Jan 23 2015
A thin band of moderate snow has formed from Morgantown to Danville.
It is progressing northward fast enough that accumulations likely
are at less than half an inch. Area webcams show the roads are
handling this snow well, again thanks to warm ground temperatures.
Untreated roads may see some coverage because of the harder snow
rate, but those snows should melt soon after the end of the precip.
.SHORT TERM (Now through Saturday Night)...
Issued at 335 PM EST Fri Jan 23 2015
...Minor Snow/Sleet Accumulations Expected Tonight...
Model Discussion/QPF Analysis:
Model trends this afternoon have been farther north with the precip
shield which has reached the Ohio River as of 330pm and looks to
spread some light precip as far north as southern IN. The
NAM/WRF/RAP data also suggests that precip will hang around a little
bit longer than previously forecast tonight. Enhanced forcing from
the left exit region of an upper level jet as well as some negative
EPV/frontogenesis should help precipitation to be become banded with
some moderate to briefly heavy precipitation expected at times this
evening. Precipitation should continue through 4Z before it starts
to exit the area. All precipitation should be east of the area by
around 9 or 10Z.
Thermal profiles suggest that we will continue to see a mix of
rain/sleet/snow through the evening hours. A transition to
snow/sleet is then expected from roughly 23-3Z with most areas going
to a pure snow by 3Z. Some light snow accumulations are expected
near the Ohio River and south with the best accumulations still
expected to be along and east of a Bowling Green to Elizabethtown to
Frankfort line. A couple different scenarios could play out this
evening and they are all dependent on sfc temps, precip rate, and
The MAIN reason why an advisory will NOT be issued with the 4pm
forecast package is that road temps and air temps are above freezing
and are expected to remain there or hover near freezing through 5-7Z
during the time that the best snow bands may occur. Thus, expect
that a light slushy accumulation would likely occur this evening
after rush hour with some grassy areas receiving a light
accumulation possibly during rush hour. Still little to no rush
hour impacts are anticipated despite the wintry precip falling.
Roads should remain wet for the most part with only a few slick
spots possible on bridges/overpasses during rush hour. So between
0-6Z this evening, bands of snow may form likely melt at the sfc at
onset but eventually producing up to 1 inch of slushy accumulation
of snow. Should a heavy band of snow develop and persist over a
particular area resulting in high snowfall rates and thus more
accumulation (1-2 inches) despite warm ground temps, then an advy
would be needed. It`s very tough to pinpoint where a band of
moderate to heavy snow may set up though. Therefore, rather than
plaster the entire area with an Advy, will wait and see if/when this
evening such a band of snow may setup to warrant an advy for 1-2
inch snow amounts. Perhaps the area that is most prime for this
type of banding would be E-town to Frankfort and points east. If you
plan to be traveling this evening, pay particular attention to the
latest forecasts and changing weather conditions.
Later tonight after precip has ended, temps are expected to fall
into the upper 20s which may cause slick spots on roadways Sat
morning. Will need to watch for this potential later tonight.
Sat any snow accums will melt as temps rise into the low to mid 40s
for highs. Sat night will be dry with lows in the low to mid 30s.
.LONG TERM (Sunday through Friday)...
Issued at 315 PM EST Fri Jan 23 2015
Sunday - Monday...
A clipper will dive into the Ohio Valley on Sunday, with its
associated surface low likely tracking across our northern CWA.
Ahead of this feature, precipitation will be all rain as warm
advection allows for surface temperatures ranging from the low and
mid 40s north to the low 50s south. The surface low and trough axis
quickly pass through Sunday evening, with thermal profiles falling
through the overnight. This will lead to a transition to rain/snow
and then by early Monday morning across much of the area. Southern
KY may hold onto rain/snow. At this point, deep moisture will be
diminishing and with the previously warm ground so dont expect any
accumulations. Will hold onto some lingering snow showers along the
I-75 corridor on Monday. Temperatures will struggle under the cold
advection regime through the day, and aren`t expected to make it out
of the 30s for highs.
Monday Night - Tuesday...
There continues to be some evidence of another weak clipper diving
through the highly amplifed flow Monday night into Tuesday. However,
models are struggling with the placement, and the system looks to be
pretty moisture starved. Will leave mention out for now, however
chances for light snow or rain may need to be introduced if more
confidence can be gained in placement. Lows Monday night should drop
solidly into the 20s, with highs on Tuesday again not making it out
of the 30s.
Tuesday Night - Friday...
Strong surface high pressure and upper ridging take hold through the
middle of the week, with dry conditions and gradually moderating
temperatures toward normal. Highs on Wednesday should reach into the
upper 30s and low 40s Meanwhile, Wednesday night lows will trend
milder toward the 26 to 31 range.
Another system will scoot across the Great Lakes on Thursday, with
the trailing cold front swinging through the Ohio Valley Thursday
night. Ahead of this feature, temps will again rise into the 45 to
50 range with light rain chances. Temps fall again Thursday night
behind the cold front, with cold air struggling to catch up to any
lingering low level moisture.
Dry conditions return Friday, with moderating temps under high
pressure and zonal flow aloft.
.AVIATION (06Z TAF Update)...
Issued at 1200 AM EST Sat Jan 24 2015
Wintry precip continues to affect KBWG and KLEX this hour as a band
of snowfall moves through, bringing IFR to at times LIFR conditions.
SDF has gone VFR with just some light fog/haze renaming in the
area. However, there is another deck of MVFR stratus across
southern Indiana that looks to move through. In addition, the light
fog/haze will likely continue for much of the night, before
conditions improve to VFR by the morning hours and last through the
day on Saturday.
Conditions will remain LIFR for the next few hours as snow and low
stratus affect the terminal. Will be pessimistic and leave IFR cigs
in through the early morning hours, but snow should end in the next
couple of hours. If clouds clear out sooner than expected, then
some fog may come more into play. Otherwise, conditions will
improve to VFR by the mid-morning hours as the low cigs scatter out.
The heavier snow will come to an end by TAF issuance time. Low
clouds (IFR or even high-end LIFR) will likely linger for the next
several hours, before conditions improve slightly. However, if the
clouds do break, think there will be some BR at the terminal, so
will add in a TEMPO group to cover that potential. Otherwise,
conditions will improve to VFR by the morning hours on Saturday.
KY...WINTER WEATHER ADVISORY until 5 AM EST /4 AM CST/ early this
morning FOR KYZ027-028-039>043-045>049-053>057-062>067-