Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 061705
Area Forecast Discussion
National Weather Service Louisville KY
1205 PM EST Tue Dec 6 2016
...Updated Aviation Discussion...
Issued at 945 AM EST Tue Dec 6 2016
Deformation band of precipitation headed now bringing heavier
precipitation along and west of the I-65 corridor. This band is
headed east northeast across the region. It should clear our I-75
counties by mid afternoon after dumping an additional half inch to
inch of rain. If it were one month later, this band likely would be
an efficient snow producer! Did a zone update to cover trends in the
radar as well as other parameters. Did lower highs a little for some
places, most noticably for Lexington, where do not believe it will
be able to make it into the 50s today. Lake Cumberland should be
close enough to the surface low track to allow lower 50s though.
One other addition...put in some drizzle on the back edge of the
precip. We`ll lose mid/upper level moisture, but there could be a
couple of hours where the low levels hang on enough for drizzle.
Issued at 320 AM EST Tue Dec 6 2016
Added brief, isolated mention of sleet across northern Kentucky and
southern Indiana as several reports via social media have come in
the past hour or so. The latest RAP and HRRR sounding for the area
does show a good dry layer between 700 and 900 mb and likely dynamic
cooling under the highest radar reflectivities is helping to bring
down some sleet pellets with the rain. This shouldn`t be anything
more than `conversational` and very brief - once the air mass
saturates there will be a +4 to +7C warm nose that should keep all
precipitation as a cold rain. Thanks to the local broadcast
meteorologists for relaying reports early this morning.
.Short Term (Now through Wednesday)...
Issued at 249 AM EST Tue Dec 6 2016
...Widespread Rain For This Morning`s Commute...
Latest water vapor imagery with 500 mb heights showed a shortwave
trough over northern Louisiana and western Mississippi with a plume
of Gulf moisture lifting through Tennessee and southern Kentucky.
At the surface, high pressure was centered over central PA. Locally,
readings were in the low to mid 40s.
As expected, shortly after midnight steady rain blossomed across
central Kentucky and southern Indiana thanks to the approach of the
aforementioned shortwave trough aiding in upper level divergence
along with increasing 850 mb moisture transport. Regional radar
shows this rain extending across TN, northern MS and AL and much of
Plan on a rainy morning commute as this shield of rain lifts through
central Kentucky and southern Indiana with the steadiest rain likely
to persist through early afternoon. As the shortwave kicks off to
the mid-Atlantic, rain will end southwest to northeast mid to late
afternoon. Overall, total rainfall amounts will be between 0.5 and
0.75 inches, with some local 1 inch amounts possible. Highs today
will top out in the 40s for most, with parts of south-central KY
around the Lake Cumberland region reaching the low 50s.
West to northwest winds this evening and tonight will bring in drier
and cooler air, and plan on temperatures to bottom out in the low to
mid 30s. Clouds will begin to scatter out toward Wednesday morning,
especially along/west of I-65.
.Long Term (Wednesday Night through Monday)...
Issued at 251 AM EST Tue Dec 6 2016
...Unseasonably Cold Later This Week...
Main highlights in the long term are the unseasonable cold later
this week with the next chance of precipitation coming late in the
weekend and early next week.
The well advertised upper level trough will drop southward into the
region Wednesday night and Thursday morning. This feature will push
a strong cold front through southern Indiana and central Kentucky.
With the NAM being the exception, the 06.00z guidance continued the
trend of a dry cold front passage with very little moisture to work
with as it passes. As a result, nudged down precipitation chances
further to the 10 to 15 percent range. The main story will be the
sharply colder temperatures for Thursday as highs will reach only
the low 30s across southern Indiana to mid 30s near the TN border.
Combined with northwest to west winds 15 to 20 mph, and it will feel
more like the teens during the afternoon and evening hours.
Canadian high pressure builds south across the mid-Mississippi River
Valley Thursday night and Friday. Lows will drop down into the teens
and low 20s with highs Friday only in the upper 20s to low 30s.
Some moderation in temperatures is expected Saturday and Sunday as
the high pushes to the east and southerly return flow sets up.
Timing the next system remains uncertain with a few models bringing
in precipitation as early as Sunday morning while others hold off
until late Sunday or early Monday. Either way, the air mass looks to
be warm enough to support just a brief rain/snow mix to all rain as
even warmer air is brought up ahead of a cold front.
.Aviation...(18Z TAF Issuance)
Issued at 1204 PM EST Tue Dec 6 2016
IFR conditions are expected to continue across the region this
afternoon and into tonight. Rain band continues to push on off to
the east. The back edge of the rain band will clear KSDF and KBWG by
06/18Z and should clear the KLEX area by 06/20-21Z. After the rain
ends, low-level moisture will be plentiful and some residual drizzle
will persist for several hours. Overall trend in the data is to
keep lower ceilings in the forecast than previously thought. For
now, plan on keeping ceilings under IFR for the afternoon and
evening hours and then letting ceilings slowly rise overnight. VFR
conditions probably will not occur until around 07/12Z. Winds have
shift to the northwest at KSDF and KBWG and will remain that way
through the TAF period with speeds of 5-10kts. Winds at KLEX will
start out of the south and then shift the southwest around 06/18-19Z
and then to the northwest by 06/19-20Z.