Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 071849
Area Forecast Discussion
National Weather Service Louisville KY
249 PM EDT WED OCT 7 2015
.SHORT TERM (Now through Thursday Night)...
Issued at 245 PM EDT Wed Oct 7 2015
Weak ridging aloft and sfc high pressure will continue to dominate
the region through Thursday. This will result in dry conditions and
temperatures slightly above normal. Expect low temps to bottom out
in the 50s tonight with some light patchy fog developing toward
morning. High temps on Thurs will range from 81-86 degrees.
Thurs night a cold front and upper trough will approach the Ohio
Valley bringing showers and a slight chance of elevated t-storms
mainly after midnight to portions of southern Indiana and northern
Kentucky. All locations will at least see increased cloud cover
Thurs night. Clouds/precip and a bubble of warm air right ahead of
the front should limit lows to the lower 60s.
.LONG TERM (Friday through Wednesday)...
Issued at 230 PM EDT Wed Oct 7 2015
The synoptic pattern at the start of the long term period will
feature split flow aloft with a cutoff low across the the Desert
Southwest/northwestern Mexico and generally zonal flow across the
Ohio Valley. A PV anomaly diving southeast through the northern
stream will help carve out more of a trough across the Ohio Valley
Friday into the upcoming weekend, before the pattern returns to a
more zonal/slight northwest flow regime early next week.
The main focus of the long term period will be Friday into Friday
night as the aforementioned PV anomaly dives southeast into the
region. The ascent with this system is rather deep with a
convergent surface front, positive mid-level vorticity advection,
and the right entrance region of a 90-knot jet streak all combining
to create lift over the Ohio Valley. Therefore, will go with high-
end likely to categorical pops with this system. Guidance continues
to suggest 500-1000 J/kg of MLCAPE will build ahead of the front.
While likely overdone a bit, the hi-res NAM solution does show
decent coverage of thunderstorms in the eastern CWA Friday afternoon
and evening. Even though MLCAPE will not be impressive, the rather
deep ascent aided by the digging trough may help to make up for the
lack of MLCAPE a bit. Therefore, have bumped thunderstorm wording
up to chance (instead of slight chance) in the eastern CWA where the
frontal passage will coincide more favorably with peak heating. A
strong storm is possible given the marginal deep-layer shear around
30 knots, but the weak mid-level lapse rates and lack of mid-level
dry air should help to temper the hail and wind threat, respectively.
The remainder of the long term looks mainly dry. There could be a
few showers with the passage of a sharp trough and associated cold
front Monday night into Tuesday, but moisture seems rather limited
so will continue with a dry forecast. Temperatures will be cooler
behind the first front on Saturday (highs in the low to mid 60s),
but will warm back into the 70s Sunday through the beginning of next
.AVIATION (18Z TAF Update)...
Issued at 120 PM EDT Wed Oct 7 2015
Weak upper level ridging and sfc high pressure will continue this
TAF period. Overall think that we`ll see the same fog concerns as
this morning tomorrow morning. MOS guidance generally agrees with
this thinking with mainly light br forming late tonight into
tomorrow morning under almost clear skies, nearly calm winds, anda
good inversion. Thus, went ahead and took BWG down to IFR minimum
although they may need a flight restriction lower than that. Took
SDF/LEX down to MVFR toward morning. All TAF sites should improve
to VFR by 13-15Z tomorrow. Winds will become more southerly
tomorrow ahead of a cold front which will approach the area just
beyond this TAF period.