Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 100238
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
938 PM EST Mon Dec 9 2013
...Updated Aviation Discussion...
Issued at 925 PM EST Mon Dec 9 2013
Latest models, including the 18Z GFS, 00Z NAM, and the 21Z SREF are
all trending a bit farther south with both of the expected snow
bands overnight. That said, adjustments to the going forecast are
Advisory already flying along the Cumberland Escarpment will
continue, as new NAM QPF is still fairly robust. Even with just a
10:1 snow ratio there should still be little difficulty getting an
inch of snow across most of the counties included in the advisory.
Southern Indiana remains tricky, as it looks there there will be a
quick glancing blow across our northernmost counties just before
daybreak, and snow ratios will be greater up there due to colder
temps. Will probably see 1 inch along and north of a line from
Jasper to Salem to Madison, but the gradient to the south will be
quite sharp. Not enough confidence in covering the majority of any
of those counties to raise an advisory, but will freshen the SPS and
beef up the wording for local 1+ inch amounts. The main mitigating
factor is that most of the snow will fall before the morning
In between, we aren`t looking for anything more than a deck duster
north of I-64 in Kentucky, and a dry forecast west of I-65 in
.SHORT TERM (Now through Sunday)...
Issued at 325 PM EST Mon Dec 9 2013
Light snow and drizzle from early this morning pushed east and/or
dissipated by this afternoon. There have been a few breaks in the
clouds but skies have remained mostly cloudy through the day.
Temperatures have struggled today, with readings in the upper 20s
across southern Indiana to middle 30s across the Lake Cumberland
An upper-level jet to our northwest will intensify as it approaches
tonight. Models continue to indicate two bands of snow. The first
will generally parallel the Ohio River as it stretches southwest to
northeast across southern Illinois and southern Indiana. This band
of snow should produce accumulations ranging between a dusting along
the Ohio River to just under one inch across our far northern
counties in southern Indiana. The other band of snow will stretch
southwest to northeast across the Lake Cumberland region. This area
could experience an inch or slightly better, mainly across our
forecast border. For this reason, have issued a Winter Weather
Advisory from midnight EST/11 PM CST tonight to 10 AM EST/9 AM CST
Tuesday. Both areas of snow should have a fairly sharp accumulation
gradient, with the highest totals begin just out side our CWA.
Skies should clear quickly behind this system, with a breezy
west-southwest wind on tap. Temperatures in the upper 20s over the
north and mid 30s in the south can be expected, with wind chill
values in the teens and 20s. Tuesday night lows will drop into the
lower teens across the north to around 20 degrees in the far south.
.LONG TERM (Sunday night through Friday)...
Issued at 257 PM EST Mon Dec 9 2013
The synoptic pattern at the start of the long term period will
feature split flow aloft, with this flow becoming confluent across
the Ohio Valley. Subsidence beneath this confluent flow aloft will
keep the Ohio Valley rather tranquil through the remainder of the
week, before another system affects the region this weekend.
An area of high pressure, originating more from the southern stream
will shift east of the Ohio Valley on Wednesday. This will bring
W/WSW surface flow to the region, aiding in warming temperatures up
a bit. With full sunshine, areas with no snowpack should rise into
the upper 30s and 40s. The areas still with a healthy snowpack will
struggle a bit more as the insolation goes into melting, likely
warming into the low to mid 30s.
A dry cold front will push through the region Wednesday night into
Thursday. Another area of high pressure will build in behind it,
but this high will be of Arctic origin, bringing renewed cold
temperatures to the region. The surface high will settle over the
region by early Thursday morning, with generally clear skies and
light winds. This will set the stage for a very chilly night, as
lows quickly fall off into the teens, with single digits likely over
the snowpack in southern IN.
After another cold but quiet day Thursday, the sprawling high will
shift east on Friday allowing southerly flow to usher in warmer
temperatures. Highs on Friday will likely into the upper 30s, with
40s likely across southern KY.
Eyes will then turn to the west Friday night into the upcoming
weekend as the next system approaches from the southwest. This
system will be tied to an upper-level low (which can be seen on WV
imagery this afternoon just off the West Coast), which will attempt
to phase with the northern stream somewhere near the Mississippi
River Valley. Despite decent agreement in much of the 12Z guidance
suite, suspect models will waffle a bit as they typically due in
these phasing systems. Either way, precipitation looks like a
pretty good bet across the Ohio Valley once again for the upcoming
weekend. What exactly this precipitation falls as remains a bit
uncertain. Forecast soundings showing much of the precipitation
starting with surface temperatures just above freezing. However, if
the precipitation is heavy enough initially to cool to wet bulb
temperatures, the precipitation could fall as some snow. Will
continue to carry rain/snow with the onset of precipitation, but at
this time it does look as if everyone will get above freezing by
Saturday afternoon, changing all precipitation over to plain rain.
Will need to watch this system carefully as a southward jog may
cause wintry precipitation to become more of a player.
.AVIATION (00Z TAF Update)...
Updated at 615 PM EST Mon Dec 9 2013
MVFR stratus will scatter out and/or lift early this evening as we
get into the gap between two systems. Overnight the gap will close
as an upper jet streak zips across Indiana, and pulls southern
stream moisture back northward into mainly eastern Kentucky.
Ceilings will drop back below fuel-alternate thresholds after
midnight at BWG and LEX, which will be closer to that southern
stream moisture, while SDF remains at the high end of MVFR. Expect
any significant snow to remain north of SDF, and south of BWG/LEX.
However, will include a tempo in the pre-dawn hours for snow
showers, but no worse than MVFR visibilities, just as a heads-up.
Upper shortwave scoots across the Ohio Valley around midday, giving
way to clearing skies as west winds pick up to around 10 kt.
KY...WINTER WEATHER ADVISORY until 10 AM EST /9 AM CST/ Tuesday FOR