Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 131734
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1234 PM EST Fri Dec 13 2013
...Updated Aviation Discussion...
Issued at 1150 AM EST Fri Dec 13 2013
In the near term, clouds will be on the increase from west to east
this afternoon...so we will go from mostly sunny conditions to
mostly cloudy by late afternoon. Temperatures have warmed into the
middle to upper 30s across KY with upper 20s to the lower 30s over
the snowpack over southern Indiana. We still expect temperatures to
warm into the lower-middle 30s across southern Indiana this
afternoon with lower 40s across northern KY with middle 40s being
possible across southern KY.
As for tonight, latest guidance continues to hold steady in the run
to run continuity. A slightly warmer trend in temperatures was
noted across KY...but overall it was fairly small. Current thinking
remains the same as yesterday and overnight. We currently have a
fairly dry atmosphere in place across the lower Ohio Valley
(reference 12Z BNA and ILN soundings). Precipitation and moisture
will work in from the west this evening and we will have to wait for
the column to moisten up from top to bottom. This will lead to
wetbulbing and initially we`re likely to see a mix of
rain/sleet/snow developing after sunset.
Depending on precipitation intensity, a change over to plain snow
looks to occur over southern Indiana with a mix of sleet/snow across
northern KY. Southern KY will see a mix of rain and snow initially,
but quickly change over to plain rain as warmer air aloft surges
into the region.
Best chances of accumulation still look to be across the snowpack
area of southern Indiana along and north of I-64 where 1 to 3 inches
of snow is expected overnight. Some of our far northern areas from
Dubois county eastward to northern Jefferson county Indiana could
see mainly 2-3 inches with some spots picking up close to 4 inches.
At this time...no changes are being made to the current advisory
.SHORT TERM (Now through Saturday Night)...
Issued at 335 AM EST Fri Dec 13 2013
...ANOTHER ROUND OF SNOW LIKELY TONIGHT FOR SOUTHERN INDIANA AND
PORTIONS OF NORTHERN KENTUCKY...
No changes to the current Winter Wx Advy are planned for this
forecast package although did debate throwing in Oldham and Henry
Counties in KY. The most challenging parts of this forecast which
will affect p-type and snow amounts are the initial thick layer of
dry air in the low levels initially and what the new temp profile
will look like once things saturate. For locations over southern
Indiana, the resultant sounding will most likely be a snow sounding
and so we have the Winter Wx Advy in effect. Suspect that where
there is snow pack right now, temp profiles will tend to stay on the
colder, snowier side with the antecedent colder air in place due to
the snowpack. For this reason, Oldham and Henry counties which
still have a decent snowpack were considered for this advy and may
very well be added later today in coordination with surrounding NWS
offices. Generally speaking though, locations south of the Ohio
River will have more of a questionable sounding closer to the
freezing mark and it`s hard to determine where that rain/snow line
may form, thus will continue the SPS for north and east central KY.
To start the day today, skies will be mostly clear with temps in the
upper teens to around 20. A warm southerly flow will allow temps to
warm into the mid 30s to mid 40s for highs this afternoon with
Think that the arrival of precip will hold off until after sunrise
although we may start to see some radar reflectivity echos
indicating virga just to our west by late afternoon or early
evening. The atmosphere should saturate enough to produce at least
light precip some time between 0-4Z. That precip will likely be in
the form of a rain/snow or snow grain mix until the air column cools
yielding snow over southern Indiana and rain over south central KY
with a mix some where over north and east central KY. Tonight
expect southern Indiana to see 1-3 inches of snow with locations
along and south of the river likely to see up to an inch of slushy
By Sat mid to late morning, we`ll see a surge of warm air as the sfc
low makes its way through central/east central KY. This will cause
a change over to all rain over most areas except maybe a line from
Jasper to Madison, Indiana which may stay all snow or have a mix of
rain/snow. Either way, temps should rise above freezing for most if
not all locations causing any morning snow accums to melt Sat. Highs
are expected to be in the mid 30s to mid 40s Sat afternoon.
As the low pressure system moves off to the northeast, cold air will
rush back into the region Sat night causing left over shallow
moisture to precipitate out as either freezing drizzle or light
snow. This light moisture on the back side will have the potential
to produce slick spots for late Sat night/Sun morning. Sun morning
lows will be in the 20s to around 30.
.LONG TERM (Sunday through Friday)...
Issued at 305 AM EST Fri Dec 13 2013
After an active first half of the weekend, most of the long term
will be rather quiet. Northwesterly flow will remain in place aloft
through Wednesday. It will then transition through Friday as a
trough moves into the plains and ridging builds over the Atlantic. A
couple of waves will move through the northwesterly flow aloft. Most
of the precipitation associated with these waves should stay north
of the forecast area. There may be a slight chance to see some
precip Monday evening across southern Indiana and north central
Kentucky. However, am not confident enough at this point to put any
mention of this in the grids. The next significant system will be at
the end of the week as a strong cold front approaches the area. This
system is just beyond the end of the forecast period at this point.
Temperatures will slowly warm through the week, though they may be
affected by the shortwaves moving across the area. This will depend
on how far south these waves dive. Temperatures will be coldest
Sunday with highs only in the upper 20s to lower 30s. By mid week
temps will rise to the upper 30s to mid 40s with temps close to 50
across south central KY by Thursday. Lows in the teens to lower 20s
early in the week will shift to lower 40s by the end of the week.
.AVIATION (18Z TAF Update)...
Updated at 1234 PM EST Fri Dec 13 2013
Surface high pressure will move on off to the east this afternoon.
This will result in a southerly flow across the area. Mid-high
level cloudiness will continue to increase from west to east this
afternoon. Ceilings are expected to remain VFR through 14/00Z.
We expect ceilings to drop into the low end of the VFR range this
evening as moisture spreads eastward out of Missouri and southern
Illinois. Initially dry air in the atmosphere will keep
precipitation from reaching the ground early this evening...but we
expect quick moistening and precipitation to develop sometime
between 14/00-03Z at KSDF and KBWG...and around 14/04Z at KLEX.
Precipitation will likely be in the form of a mix of rain and
snow...but change over to a period of snow at SDF and LEX
overnight. The exact timing of this will depend on precipitation
intensity and the depth of cold air in the lower atmosphere. For
now, plan on leaving the predominant weather as a mix of RASN for
now. Precipitation is expected to change back over to plain rain at
SDF and LEX by 14/12Z and continue through the day on Saturday.
Ceilings overnight will likely drop into the high end of the MVFR
range and then fall to IFR by 14/12Z. Winds tonight and overnight
will generally be out of the southeast at 5-10 kts.
KY...WINTER WEATHER ADVISORY from 7 PM this evening to 10 AM EST
Saturday FOR KYZ032.
IN...WINTER WEATHER ADVISORY from 7 PM EST /6 PM CST/ this evening to
10 AM EST /9 AM CST/ Saturday FOR INZ076>079-083-084-