Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 160528

Area Forecast Discussion
National Weather Service Louisville KY
128 AM EDT Sat Oct 16 2021

...Updated Aviation Discussion...

.Forecast Update...
Issued at 925 PM EDT Thu Oct 15 2021

In coordination with SPC, we elected to remain out of an earlier
severe thunderstorm watch that continues to our south. The
environment is becoming more unfavorable for severe thunderstorms.
MLCAPE values are low, so the cold front will be the forcing behind
any remaining convection. Wind shear will remain the most favorable
for the Bowling Green to Lake Cumberland areas and south over the
next few hours, but it`s still marginal with more speed shear than
directional shear.

To our west and southwest, a few decent storms have developed, but
they fail to last long as they get overtaken by outflow boundaries
from their thunderstorm cluster. The strongest storms are the ones
riding along where the storm goes from being balanced to outflow
dominant. This is where an quick spin-up is most likely due to
boundary interactions and appears may have just happened in Spencer
County, IN.


.Short Term...(This evening through Saturday)
Issued at 340 PM EDT Fri Oct 15 2021

...Severe Storm Threat This Afternoon Through Late Tonight...

Radar this afternoon shows a remaining area of rain north of I-64
and east of I-65 associated with a weakening LLJ and surface trough.
This will continue to move off to the northeast as it moves
northeast into northern KY and southern OH. Clouds associated with
this activity can be seen along and east of I-65 on visible
satellite imagery. West of I-65 across western KY/southwestern IN
clouds have been scattering out helping to destabilize the
atmosphere. SPC Mesoanalysis shows SBCAPE around 1000K/kg over
western KY and steepening lapse rates. Kentucky Mesonet is also
showing temperatures around in the upper 70s/low 80s where skies
have clears. As the deep mid/upper level trough over the central
CONUS moves eastward, 500mb winds will increase to between
50-70kts out of the southwest with effective shear around
40-50kts. Scattered convection has already started to develop
across the MS River valley where clouds were more scattered and
temperatures were in the low 80s. Between now and sunset, the main
focus for severe weather will be west of I-65, especially where
we have the better instability. Main threat will be gusty damaging
winds but given the available shear, strong rotating updrafts are
possible with more cellular convection. SPC has southwestern KY
in a 5% TOR risk.

Later this evening, the severe threat turns more linear as the
strong cold front work into the region. Instability will diminish
with the loss of daytime heating setting a high shear low CAPE
environment. Convection will form along and just ahead of the
cold front with the main threat being isolated damaging winds. The
greatest QLCS severe wind threat continues to be south across
western/central TN where instability will be the highest.

Severe threat will diminish after midnight across the eastern part
of the CWA but NW winds will increase behind the cold front. Windy
conditions and colder air arrive behind the cold front as rain
clears from west to east exiting out of the area by sunrise

It will be a cooler and drier day to start the weekend. Winds will
be around 10-15 mph and gust approaching 20 mph highs will be in the
low/mid 60s with lows in upper 40s west to low 50s to the east.

.Long Term...(Saturday night through Friday)
Issued at 243 PM EDT Fri Oct 15 2021

During the second half of the weekend and the first half of the new
work week an upper ridge will slowly make its way from the Plains to
the Appalachians, while surface high pressure spreads from the Red
River Valley to the Southeast. Pluviometers will get a break as
these features keep us dry with initially cool, then slowly
moderating, temperatures. Sunday morning in our position on the cool
side of the incoming surface high, 1000-925mb thicknesses suggest
sunrise temperatures will be 5 to 10 degrees below normal, generally
in the lower and middle 40s with sheltered rural locations dipping
into the upper 30s. NBM progs show a 10-20% chance of a few eastern
valleys touching 36 degrees. Under clear skies and with just a few
light zephyrs, can`t rule out some brief, patchy, thin frost in
those spots early Sunday morning.

After highs in the 60s on Sunday we`ll be well back into the 70s
ahead of the next system. On Thursday low pressure crossing the
Great Lakes will drag a cold front through the Ohio Valley,
accompanied by scattered showers. Looks like another high shear low
instability environment...may be enough buoyancy for a few
thunderstorms. The axis of the parent trough to Thursday`s system
will then pass overhead on Friday and may provide a few light rain


.Aviation...(06Z TAF Issuance)
Issued at 125 AM EDT Sat Oct 16 2021

IMPACTS: MVFR/IFR CIGs to begin the period. Gusty winds.

DISCUSSION: Latest surface analysis places the cold front just
upstream of LEX. Radar continues to show the main line of convection
along and just ahead of the front pushing east of LEX. Satellite and
regional observations show MVFR CIGs with patchy IFR behind the
front along with strong NW winds with gusts 15-25kt. There appears
to be an abrupt MVFR/VFR line that will push through HNB within the
first two hours of the period and spread across the other TAF sites
by sunrise. VFR conditions are expected for the rest of the period
with continued gusty NW winds, which should subside around sunset.

CONFIDENCE: Medium to high on all forecast elements.




Short Term...BTN
Long Term...13
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