Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 060845
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
345 AM EST Fri Dec 6 2013
.SHORT TERM (Now through Saturday)...
Issued at 330 AM EST Fri Dec 6 2013
...IMPACTFUL WINTER EVENT ONGOING...
Southwest feed of moisture is pumping in plenty of moisture and
working with Arctic air filtering into the region to create a messy
winter precip forecast this morning. Freezing rain line running
roughly from Russellville in Logan county to Etown/Louisville to
Frankfort. Had a band of heavier returns across our northern row of
counties, where sleet is coming down. SPC mesoanalysis earlier
showed a band of 850-700 mb frontogenesis where this band formed,
but that band has spread out now.
Timing for cold air continues to run a bit faster than previously
forecast, so have had to shift freezing rain timing south. Given
timing for precip coming in, that would also mean higher snow totals
over the north, where the deeper cold air will allow for a quicker
transition to snow during the day today. Bumped up the totals across
our northern counties to 6-10 inches, with areas right along the
Ohio River now getting between 2 and 6 inches.
Current headlines still look good. The northern part of the winter
storm warning looks solid for reaching the heavy snow criteria,
whereas the southern part looks like the combination of freezing
rain, sleet, and snow will be the main threat. The advisory area
looks in line for around an inch of snow and/or a tenth to a quarter
inch of freezing rain.
Moisture tap runs out aloft starts to run out this evening.
Soundings show we may have a period of freezing drizzle, as the top
of the saturated layer gets warmer than -10C. Given temperatures
falling quickly, this freezing drizzle combined with already wet
roadways and temperatures well into the 20s will make for continued
dangerous travel conditions overnight.
Highs Saturday will struggle to get into the lower 20s, if that
high, over southern Indiana in the snowpack. Down south, the
freezing mark will be the hard point to reach. The cold temperatures
will set the stage for the next system to come in, read on below.
.LONG TERM (Saturday Night through Thursday)...
Issued at 320 AM EST Fri Dec 6 2013
...SIGNIFICANT WINTRY WEATHER EXPECTED LATE SATURDAY NIGHT AND
SUNDAY ACROSS THE REGION...
...Saturday night through Monday...
Ding, ding! Round two of wintry weather will commence late Saturday
night and through the day Sunday, as our next mid-level southern
stream wave heads northeastward. Precip may begin across southern
Kentucky around midnight, but models seem to rush it in after
midnight. Precipitation types are still a difficult forecast, which
depends on the final snow/sleet/ice totals from this first round of
wintry precip today.
Currently believe surface temperatures will be cold and the depth of
the cold airmass will be sufficiently deep to support mostly snow at
the precipitation onset. The snow could be particularly heavy early
Sunday across portions of southern Indiana and central Kentucky. As
the wave continues to move northeast, warmer air aloft would
eventually overspread the cold lower layer and result in a change
over to perhaps sleet for a very brief period, but freezing rain
would quickly take over and progress northward. Still too difficult
to pin down the snow and freezing rain amounts, but they could
accumulate rapidly before warmer surface air arrives.
Speaking of that, warmer air will work in at the surface across
southern Kentucky in the afternoon, changing freezing rain over to
rain. This too will continue northward into the evening as the wave
shifts northeast. In fact, the warmest temperatures Sunday may very
well occur in the evening as the warmer surface air gets in here. As
the wave departs, colder air rushes back in and will lead to any
leftover precipitation changing back over to snow before ending.
Highs Sunday look to warm to around the freezing mark in areas north
of the Ohio River late in the day, with mid to upper 30s across much
of Kentucky. Lows Sunday night will cool back into the lower 30s.
Highs on Monday are really tough because they will be so dependent
on snow/ice cover. Right now will go with highs in the lower 30s
across the northwest to lower 40s across the southeast.
Monday Night through Thursday...
Will keep a slight chance of light snow over far eastern and
southeastern counties Monday evening as broad shortwave aloft moves
through. Otherwise, weather during this period calms down as flow
aloft becomes less amplified with no noticeable weather systems to
track across our area. This period looks dry, even with a shortwave
trough diving through the Great Lakes Thursday. Any precip
associated with that trough appears to stay north of the area.
Temperatures will be the big story. It will be quite cold with highs
in the 20s across the north and 30s across the south Tuesday through
Thursday, with lows generally in the single digits across the north
and teens across the southern CWA. As mentioned in the previous
forecast, whatever snow cover exists in our north will affect these
Issued at 315 PM EDT Thu Dec 5 2013
A prolonged period of precipitation will continue into the weekend.
The first system has already dumped up to an inch and another 1 to 2
inches are expected before the precipitation ends Friday night. The
northern portions will see much of this precipitation change over to
freezing or frozen forms. Thus, rises will occur on rivers and
streams but no flooding on major rivers is expected. However,
localized flooding could still occur tonight into Friday.
The second system Saturday night through Sunday could drop an
additional 1 to 2 inches of precipitation is expected over southeast
Kentucky. 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, Licking,
and Salt basins. If so, flooding will extend into next week.
.AVIATION (06Z TAF Update)...
Updated at 105 AM EST Fri Dec 6 2013
High impact weather event set to affect all TAFs over the next 24-36
hours, bringing a wintry mix of precipitation and at least IFR
KSDF: Light rain showers/drizzle now should transition to freezing
rain mixed with some sleet very soon as the colder air arrives at
the surface. This agrees with some of the latest AMDAR soundings and
upstream observations. Surface temperatures will be hovering right
around freezing from about 08-15Z Friday, so anything liquid that
falls will have the potential to accumulate on elevated/exposed
surfaces, specifically aircraft wings. Latest guidance has come in
cooler aloft closer to dawn, with precip changing to all snow for
the afternoon. Will lose ice crystals aloft this evening, with light
sleet likely toward the end of the TAF period. Ceilings will drop to
IFR and staying there throughout much of the TAF period. Visibility
will also be reduced with the snowfall. Winds will be out of the
north at 9-14 knots.
KLEX: Showers will continue through much of the overnight hours.
The cold air will work in around daybreak, which will change the
precipitation over to sleet and freezing rain. This will transition
to snow and sleet into the evening. Will lose ice crystals aloft
this evening, with light sleet likely toward the end of the TAF
period. Ceilings will stay IFR throughout the TAF period. Winds will
be out of the north at 9-14 knots.
KBWG: Rain will continue for several more hours before freezing
temperatures reach the site, where precip will fall as sleet or
freezing rain. Some light accumulations of snow are possible Friday
evening before things taper off to just some light snow, sleet or
freezing drizzle. Ceilings will stay IFR throughout the TAF period.
Winds throughout the period will be northerly at 9-14 knots.
KY...WINTER STORM WARNING until 1 AM EST /Midnight CST/ Saturday FOR
WINTER WEATHER ADVISORY from 8 AM EST /7 AM CST/ this morning to
1 AM EST /Midnight CST/ Saturday FOR KYZ039>043-045>049-
IN...WINTER STORM WARNING until 1 AM EST /Midnight CST/ Saturday FOR