Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 221925
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
325 PM EDT Fri Aug 22 2014
.SHORT TERM (Now through Saturday Night)...
Issued at 317 PM EDT Fri Aug 22 2014
...The Heat & Humidity to Continue Through The Weekend...
The Ohio Valley remains locked in a very warm, moist, and unstable
airmass, producing heat indices in the upper 90s to near 100
degrees and widespread cloudiness. So far this afternoon, precip has
remained at bay, although as of this writing, a few cells began to
appear on radar in eastern KY and near the KY/TN border, just
outside of the forecast area.
Throughout the short-term period, slight to chance PoPs are in every
period as the forecast area lies on the periphery of a surface high
over the SE CONUS. Aloft, ridging will be building in overhead with
the axis setting up across the region and into the Great Lakes by
late tomorrow. As this ridge becomes more amplified, the 500mb
heights will be on a slight decline and will be opening the door for
vort maxes to rotate around the edge of its center. The first
noticeable one is depicted to traverse through tonight right across
the forecast area with another one Saturday night, according to the
12Z GFS. While these could help focus convection, there will still
be other factors for storms such as PWATs exceeding 2 inches, plenty
of CAPE, and steep lapse rates to work with. The high-res and other
deterministic models are having a difficult time capturing the
details and agreeing with one another, adding another layer of
uncertainty into framing the specifics and leading to a more
broad-brushed approach to the PoP forecast. One other point is that
the wind profiles look to be rather weak over the next 36 hours,
negating much in the way of a severe threat and keeping convection
unorganized, outside of those aforementioned vort maxes.
Back to the temperatures and heat indices, lows tonight and
tomorrow night will mimic those of this morning, generally in the
low to mid 70s with dewpoints to match throughout the entire
short-term period. Highs tomorrow should range from the upper 80s in
the Bluegrass to potentially the mid 90s in the SW portions of the
forecast area, although those highs will likely be dependent on
cloud cover and possible precip. Despite the actual temps flirting
on either side of the 90 degree mark and cloud cover working against
the high temp forecast, heat indices should still have no problem
reaching the upper 90s to possibly lower 100s on Saturday,
warranting a continuation of the Heat Advisory at this time. Stay
cool and hydrated!
.LONG TERM (Sunday through Friday)...
Issued at 301 PM EDT Fri Aug 22 2014
The big southeastern U.S. upper ridge is still in the picture
through at least Tuesday, and is expected to flatten as an upper
trof comes in from the northwest and moves through the region
Hot and humid weather is still on tap as we sit under this dome of
high pressure aloft and low level moisture sweeps up from the Gulf
of Mexico. How hot we get is up for some debate, as atmospheric
cross-sections suggest that we may have a fair amount of cloudiness.
Also, scattered convection, especially in the afternoon and evening
when we would otherwise be hottest, will continue to be in the
forecast. As a result, confidence in the need for the heat advisory
is less today than it was yesterday. Having said that, though,
it`ll certainly be a very muggy and uncomfortable weekend and it`s
much too early to throw in the towel just yet. Plus, it will raise
awareness for the many outdoor activities going on this weekend.
The scattered convection in the forecast should mostly be of the
usual summertime thunderstorm type. A few storms could dump locally
very heavy rain and put out some gusty winds...especially Sunday.
The best chance for the greatest heat will be in the Bowling
Green/Mammoth Cave region where lower 90s will be possible
Sun-Wed..while the Blue Grass peaks in the upper 80s to around 90.
All areas will be in the 80s Thu-Fri.
.AVIATION (18Z TAF Update)...
Issued at 126 PM EDT Fri Aug 22 2014
Categories will predominately flop between VFR and MVFR through this
evening with the lower ceilings due to a warm, moist, unstable
airmass producing this cloudiness. Could continue to see this back
and forth between the two categories through the remainder of the
TAF period. Additionally, chances for thunderstorms begin to creep
in overnight and into tomorrow as surface high pressure loses its
grip over the Ohio Valley, shifting more toward the south and
leaving the three terminals on its periphery. However, with BWG
closer to the high than LEX or SDF, the latter two locations could
have a better chance for convection within the area over the next 24
hours as compared to BWG. There is quite a bit of uncertainty at
this point as to if storms will directly impact the terminal areas
or as to the timing, given the unorganized nature of any convection
that fires up. Best timing currently looks to be this evening
through tonight across southern IN/northern KY/eastern KY, with
additional opportunities again on Saturday. Will modify/amend future
TAFs to include TS mention, if and when warranted.
Wind fields will be relatively light throughout much of the period,
with gradient winds maxing out at around 10 knots or so this
afternoon. Otherwise, winds will be lighter through tomorrow and
primarily out of the west.
KY...HEAT ADVISORY until 7 PM EDT /6 PM CDT/ Monday FOR KYZ023>031-
IN...HEAT ADVISORY until 7 PM EDT /6 PM CDT/ Monday FOR INZ076>078-