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000
FXUS63 KLMK 231908
AFDLMK
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
308 PM EDT THU MAY 23 2013

.Short Term (Now - Friday Night)...
Issued at 300 PM EDT Thu May 23 2013

A deep trough over the Great Lakes is currently pivoting, with the
axis on track to pass over the forecast area this evening and
tonight. At the surface, a cold front is dropping southeastward
through central Indiana. This front is forecast to exit our
southeast forecast area by about midnight tonight. Scattered showers
are developing along and ahead of the front. This will continue
across our area the rest of this afternoon and into the evening
hours. Surface-based instability is rather weak and these showers
are capped at or just above the freezing level. Could see an
isolated thunderstorm, but chances are rather low. Activity will
dissipate late this evening and clouds will slowly diminish from
northwest to southeast overnight.

Winds will become northwesterly with the frontal passage, then
northerly by daybreak Friday. Dry and much cooler air will begin to
work into the region from the northwest, with temperatures dropping
into the middle and upper 40s tonight. Despite almost unlimited sun
on Friday, temperatures will be rather cool, ranging from the middle
60s to around 70 degrees. High pressure will build directly overhead
Friday night. Clear skies and light winds will provide for quite
chilly conditions, with lows bottoming out in the upper 30s and
lower 40s. Typically cooler valleys could drop into the middle 30s.

.Long Term (Saturday through Thursday)...
Issued at 308 PM EDT Thu May 23 2013

High confidence forecast for Saturday with a 1030mb surface high
over Lake Michigan, and extending south into the Ohio Valley. Expect
plenty of sunshine and below-normal temps. Given forecast soundings,
low-level thicknesses, and typical behavior in NE low-level flow,
believe that GFS MOS temps are too warm. Have leaned more toward the
cooler NAM MOS, with highs ranging from the upper 60s over the
Bluegrass to the mid 70s near Bowling Green.

Confidence heads downhill quickly beginning on Saturday night thanks
to NW flow aloft and divergent model solutions. There is consensus
that a NW-SE oriented surface boundary will develop somewhere across
the Ohio and/or Tennessee Valleys. However, the GFS leans more
toward a warm front developing over the Ohio Valley and lifting
north by Monday night, while the ECMWF has the front to our south
initially and not lifting out of the Ohio Valley until Wed/Thu. With
a shortwave ridge axis over the Plains, there is at least a decent
chance that MCSs will develop west of the Mississippi and roll SE
along the front. Confidence is limited by the difficulty in timing
the development of these complexes, and determining whether they
will hold together as they move into what will be a less favorable
environment. Therefore we will generally advertise slight chance
POPs, only bumping up to a 30 POP west of I-65 for Monday. Temp
forecast will undercut the GFS MOS as we do not believe the warm
front will lift northward that quickly. Will stay below normal
through Monday.

Upper ridging will build from the southern Plains beginning on
Tuesday and continue through at least Thursday. Expect temps
trending back above normal for late May, and will continue diurnal
slight chance POPs. Greatest bust potential will be from southern
Indiana into the Bluegrass, where the cooler and wetter pattern
could persist an additional day or two if the warm front is slower to
lift out.

&&

.Aviation (18Z TAF Issuance)...
Issued at 130 PM EDT Thu May 23 2013

Cloud cover has filled in across the region, with cloud bases
generally above the MVFR threshold. However, bases should drop into
the MVFR category later this evening as low clouds upstream pass
across the region. Scattered showers are expected this afternoon as
another frontal boundary sweeps southeastward. Will continue VCSH in
the TAFs. West winds around 8 to 12 knots, with a few gusts up to 20
knots will continue through the afternoon. West winds will shift
more northwesterly this evening, as the cold front moves through.
Cloudy skies this evening will clear after midnight, with northerly
winds expected by daybreak Friday and continuing through the
remainder of the TAF period.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
KY...NONE.
$$


Short Term.......MJP
Long Term........RAS
Aviation.........MJP