Scientific Forecaster Discussion
fxus63 klmk 130545
Area forecast discussion
National Weather Service Louisville Kentucky
1245 am EST Fri Dec 13 2019
updated at 934 PM EST Thu Dec 12 2019
Widespread clouds over the Tennessee Valley this evening will swell
northward into the Ohio Valley overnight behind weakening high
pressure over the East Coast and Appalachians. Temperatures should
reach their nadir around or shortly after midnight and then steady
out or possibly rise a degree or two as the blanket of clouds moves
in. Some very light rain may develop east of Interstate 65 as a weak
upper wave progresses from the lower Mississippi Valley to the
Short term...(this evening through friday)
issued at 250 PM EST Thu Dec 12 2019
Weak warm advection pattern setting up over the Ohio Valley, with
one disturbance over the Great Lakes generating plenty of cirrus
over Illinois and Indiana, but a southern-stream wave over the Red
River valley still starved for moisture. Main challenge for tonight
into Friday morning will be how much Gulf moisture the southern
system can draw northward into Kentucky.
At this point that moisture, and therefore our precip chances, looks
fairly limited. Could still tap the Gulf early enough to get some
light rain into south-central Kentucky toward morning, possibly
spreading as far north as the Bluegrass region as it moves east.
However this only supports slight chance pops, and temperatures
leveling off after midnight should be just warm enough to keep it
all rain. We'll stay dry in southern Indiana and north-central
Kentucky, but there is some bust potential in the temp forecast as a
brief window of clear skies this evening could allow a quicker drop
Another stronger wave will dig into the lower Mississippi Valley on
Friday, and that should back the mid-level flow enough to produce
more widespread rain later in the day. Confidence is moderate at
best as quantitative precipitation forecast still looks fairly low for central Kentucky. Will just
barely bump into likely pops around Lake Cumberland, tapering down
to slight chance over southern Indiana.
Long term...(friday night through thursday)
issued at 245 PM EST Thu Dec 12 2019
..wintry mix potential could impact Monday morning rush hour...
..Outside shot at severe weather Monday afternoon...
The long term will have a couple of periods with precipitation
chances...Friday night thru Saturday evening and then Sunday late
afternoon through Monday night. The latter is the more interesting
as it may come with a blend of wintry precip and then perhaps some
Before that though, our first system does have some temperature
profiles to watch, though at this point it still looks like we
should stay on the rain side. The hi-res NAM hints that any of the
heavier convective cells could briefly mix down some snow pellets
Saturday afternoon. This forecast package will lean away from that
chance in favor of most other models...though I will carry a
rain/snow mix north of I-64 Saturday morning. Not expecting any
accumulations with that mix at this time.
Drier air will rush in behind this system and should keep Saturday
overnight and most of Sunday dry. The next system will begin
strengthening a warm frontal boundary across our region later in the
day, which looks to lead to some layered lift precipitation.
Question Marks still remain as to the placement of this feature, but
the trend is for the precip to be more over our southern Indiana
counties. That far north should also be starting as either all snow
or a rain/snow mix. Warm preceding ground temperatures should make
for a less impactful snow, but as with all of these wintry
scenarios, any heavier snow rates could overcome that and will be
something to watch.
A low-level jet moving into the region Sunday night should help
bring warmer air quickly into the region and Transfer US back to all
rain Monday morning. The 12z GFS has come in line with what the 00z
ensembles were showing...a surface low coming up the Ohio River
instead of the earlier deterministic warmer solution of a low
farther north. This placement will be key and something to watch
over the next few days...both for winter and cool-season severe
reasons. A more northern solution with the shear in place could make
for some severe weather Monday afternoon. A little more southern
solution would bring more of a wintry mix or snow to our southern in
and northern Kentucky counties...impacting the morning commute Monday.
This forecast package will lean toward the surface low tracking just
south of the Ohio River. That would mean a rain/snow mix at onset
north of a Tell City, in to Georgetown, Kentucky line Sunday afternoon. By
late afternoon that line should push a little farther north before
dropping back south with evening. It could get to the pkwys in south
central Kentucky by daybreak Monday...again with wintry mix potential in
our vicinity. Warmer air should overtake the precip and turn it into
rain by lunchtime. Then we will watch for any storms that develop in
the afternoon. Again, confidence in the exact track of this system
is relatively low, so this is our "most likely" forecast for this
Beyond the associated front coming through, we could see some
backside cold precip linger into Tuesday, especially east of I-65.
Wednesday and Thursday look dry...with perhaps a warmup to near
normal by Thursday.
Aviation...(06z taf issuance)
issued at 1240 am EST Fri Dec 13 2019
Current sattellite along with current taf site reports showing overcast
conditions and lowering ceiling from sdf to bwg with the exception of
hnb where it remains sky clear along with locations west of I-65. Cigs
will continue to lower for Kentucky/in through the early morning. Ceilings
will continue to drop to IFR as more moisture moves in by 16z with
lower visibilities due to drizzle. By mid afternoon moisture depth
will change the precip type over to all rain into the evening.
Models increasingly showing the possibility of field mins for Lex
and sdf due to fog with visible around 1/2 mile and ceiling around 300 ft by