Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 051925
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
325 PM EDT Tue May 5 2015

.SHORT TERM (Now through Wednesday Night)...
Issued at 320 PM EDT Tue May 5 2015

Upper ridging continues to keep the region warm and relatively dry.
We do have some clouds that have formed underneath a subsidence
inversion at around 8 kft, and expect to see most of those die off
as the sun sets tonight. The strength of the upper ridge will weaken
a little during the day Wednesday, as the feature developing off the
southeast U.S. coast nudges closer to us. The limiting factors for
storm coverage are available moisture and a trigger/focusing
mechanism, but would not be surprised to see a storm or two develop
Wednesday afternoon east of the I-65 corridor.

The ridge aloft will continue to bring above normal temperatures to
the region, with highs maybe a little warmer than today. Lows will
continue above normal as well. Drier conditions this afternoon could
allow us to cool rather quickly with sunset, enough to allow for
some patches of fog toward daybreak.

.LONG TERM (Thursday through Tuesday)...
Issued at 309 PM EDT Tue May 5 2015

The synoptic pattern at the start of the long term period will
feature a large trough across the western CONUS, with a Rex block
situated across the eastern seaboard.  This regime will place the
Ohio Valley within ridging aloft through much of the period, leading
to seasonably warm conditions with only small chances for
precipitation until next week.

For Thursday, a weak PV anomaly will eject northward from the Gulf
of Mexico.  Guidance has been going back and forth on whether this
weak large-scale ascent will be enough to foster thunderstorm
development Thursday afternoon, mainly east of I-65.  The trend of
the 12Z data has been drier, with the GFS continuing to be the
wettest solution.  Think most locations will end up dry (less than
10 percent coverage), but to keep some forecast consistency and
given there is at least a some forcing mechanism, will leave in
slight chances of t`storms east of I-65 Thursday afternoon.  The
next shift may be able to remove pops on Thursday if the drier trend
continues.

Otherwise, the ridging will win out through at least Saturday,
bringing dry and warm conditions.  In fact, given 850mb temperatures
will be rising slowly each day, have upped temperatures late this
week into the weekend.  Readings have overachieved almost daily the
past few days and see no reason why they won`t continue to do so
late this week, especially as soils continue to dry out.  New
forecast temperatures now approach 90 degrees in the typically warm
spots (Louisville metro being one) both Friday and Saturday, with
mid/upper 80s elsewhere.  Luckily dewpoints will only be in the
upper 50s and low 60s, so the airmass won`t be overly oppressive,
but it will certainly feel like a taste of summer outside.

With this forecast package, have also delayed the better
precipitation chances associated with the incoming trough/surface
front.  Rex blocks are typically stubborn, and guidance tends to
break them down too fast.  The GFS in particular is notorious for
breaking down ridges too fast and allowing widespread convection
within ridge axes.  Therefore, have largely favored the GEM/ECMWF
solutions.  This bring some slight chances of precipitation into the
northwest portions of the CWA Saturday into Sunday, with the better
chances of precipitation associated with the passing system not
coming until Monday into Tuesday.  Will cap pops at 50% with the
expected fropa given this system could very well slow down even more
leading to a longer period of drier weather than currently
forecast.

&&

.AVIATION (18Z TAF Update)...
Updated at 120 PM EDT Tue May 5 2015

VFR still expected this period with ridging aloft. We do have a pool
of moisture causing some scattered to broken clouds, but with high
bases. Winds will become more variable overnight and into Wednesday
as a surface high pressure edges a little closer to the region. With
that high, we may be able to see some light fog at the BWG/LEX
terminals Wednesday morning, but confidence is too low to put in
this set of TAFs.

&&

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

$$

Short Term........RJS
Long Term.........KJD
Aviation..........RJS





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