Area Forecast Discussion
Issued by NWS Louisville, KY
FXUS63 KLMK 181050
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
650 AM EDT Mon Aug 18 2014
...Updated Aviation Discussion...
.SHORT TERM (Now through Tuesday)...
Issued at 302 AM EDT Mon Aug 18 2014
Low pressure centered over Louisville before dawn this morning will
move off to the east, reaching West Virginia this afternoon. In our
position behind this system both at the surface and aloft, we should
see much less shower activity this morning than we did yesterday.
Low level moisture will remain in place, however, resulting in
An upper wave over the Red River Valley this morning will arrive in
the Tennessee Valley this afternoon. Most shower and thunderstorm
activity associated with this feature will remain to our south, but
we could still see isolated to scattered convection in the LMK CWA
Tonight atmospheric moisture will decrease and there aren`t any
obvious triggers moving in, so most of us should have a dry night.
On Tuesday, a slightly negatively tilted low will move from
Wisconsin to Michigan with a cold front dropping back into the mid
Mississippi Valley. Meanwhile, a 500mb vort will advance from the
mid Missouri Valley to KY/TN (though there does appear to be some
convective feedback contamination in some of the models with this
feature, decreasing confidence in the forecast). We should become
moderately unstable with only weak capping by afternoon as these
features approach from the west. With plenty of moisture available,
scattered thunderstorms should be able to develop. Some models`
soundings suggest that the more robust afternoon storms will be
capable of producing gusty winds.
Guidance temperatures have been too warm recently, and were *much*
too warm yesterday. So, will continue to shade the forecast cooler
than guidance, though not as much below guidance today as yesterday
since we should be less rainy today. As a result we`ll shoot for
lower 80s most places today, though wouldn`t be surprised to see a
few locations in the Blue Grass not make it out of the 70s. Tonight
will be muggy with lows around 70. Tuesday we`ll warm up on
southwesterly breezes, into the middle and upper 80s.
.LONG TERM (Tuesday Night through Sunday)...
Issued at 335 AM EDT Mon Aug 18 2014
The top two weather stories for the upcoming long-term period are
the unsettled pattern enveloping the forecast area, followed by an
H590+ ridge taking over the SE CONUS and extending well into
southern Canada via the Great Lakes.
Starting off tomorrow night through late Wednesday, a low pressure
system traversing across the Great Lakes will allow for tentacles of
vort maxes to rotate through the Ohio Valley. Additional forcing
from an upper jet nosing down from the Dakotas on Wednesday, along
with a low-level jet ramping up simultaneously, will assist in
convective development. Diurnal heating, plenty of surface-based
instability, good low- and mid-level lapse rates, and a moist
airmass in place look to come together on Wednesday to produce an
active convective day. Tack on 30+ knots of 0-6km shear, thanks to
the aforementioned jets, and the ingredients appear to come together
to produce some organized thunderstorm activity. However, persistent
cloud cover and the potential for ongoing morning activity could
limit storm strength/intensity. Stay tuned to future updates.
For Thursday through the early part of next weekend, the driving
mechanism for rain chances will be shortwaves riding along the
periphery of the building ridge over LA/MS/AR. Unlike the 00Z runs
on the 17th of the GFS and ECMWF, the 18/00Z runs show a much more
amplified ridge building in, whereas the latest run of the GEM
maintains it`s flatter appearance. Since the models seemingly don`t
have the best handle on this feature just yet, couldn`t entirely
rule out precip chances on Saturday but the trend is drier. By
Sunday, the ridge is depicted to have taken over. Have kept in
slight chance PoPs for Sunday as models hint at a fropa but for
now, confidence is low with this feature.
Confidence is high, however, with much warmer temperatures headed
our way later this week. Ensemble guidance points to excellent
chances for a warm airmass to settle in by week`s end. Upper 80s to
low 90s should be the rule for highs each day with possibly mid 90s
in the south and west by the weekend, closer to the well-advertised
ridge. Heat indices will need to be watched as the time approaches
as dewpoints also look to linger near the 70 degree mark. Lows
should be a few degrees above normal, ranging from around 70 degrees
to the mid 70s.
.AVIATION (12Z TAF Update)...
Issued at 650 AM EDT Mon Aug 18 2014
Ceilings will be a challenge for aviators and forecasters alike
during this TAF period.
At 10Z low pressure was centered near LEX. This low will continue to
move to the east today, however low level moisture will linger
behind it. Ceilings will begin the TAF period near the LIFR/IFR
boundary, and are then expected to diurnally lift into MVFR by late
morning and VFR for the afternoon hours. Cloud base heights may
then sink a bit back toward MVFR category tonight.
Scattered light rain showers will be possible just about any time
during this forecast period, but the airports should be prevailing
Winds should stay under 10 knots and will prevail from the west and
southwest, especially once the low moves a bit further off to the