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Area forecast discussion 
National Weather Service Jackson Kentucky
1143 am EDT Wednesday Aug 20 2014

issued at 1143 am EDT Wednesday Aug 20 2014

A rather challenging forecast this morning. Tail end of frontal
zone...boundary is evident across the middle west this morning and will
play a major role in our weather over the next several days. Building
ridge of high pressure aloft and to our west will force this boundary
to the east over the next 24 hours. This boundary will become
increasingly aligned with middle and upper level flow patterns and
become stationary across the middle Ohio Valley region. Thereafter it
serves as a focus for convection and the occasional convective
complex of storms. At this time it appears at least part of our area will
feel the effects of weak impulses of energy riding over and dropping
down along the east side of the ridge axis.

Immediate question is will current upstream activity over Iowa/Illinois
manage to make it into our area. Most likely answer lies within the
synoptic pattern that is taking described as an almost
ideal mesoscale convective system generator. Models seem to have picked up on this as well...
depicting the source of moisture/energy...namely boundary layer h925
to h850 flow into these storm complexes weakening through the day due
to diurnal mixing...the increasing again at night. These complexes
once generated then ride southeast along the boundary. That being
said expect the current activity across Iowa/Illinois to weaken a bit
through the day. But confidence is low that activity will come to a
complete end. Most recent runs of the rap and hrrr support this line
of thought and regional satellite does show a definite warming trend
to cloud tops at this time. Decided to trim probability of precipitation down just a bit through the
afternoon but leaving enough to to account for isolated to scattered
convection associated with diurnal heating and activity that may fire
along any residual outflow boundaries. Previous forecast has probability of precipitation
increasing again tonight which is in line with current thoughts as
well...especially with the surface boundary shifting to the east
across our area. Also tweaked hourly temperatures and winds to bring the
grids in line with latest hourly observation. Finally freshened up zones to
remove morning fog wording.

Update issued at 800 am EDT Wednesday Aug 20 2014

Scattered to numerous showers and thunderstorms will exit southeastern
Kentucky in the next one to two hours. Once these storms clear the
area...there may be some isolated to scattered convection re-
developing across eastern Kentucky this afternoon during peak
heating. Will stay the course and continue to mention the
probability of precipitation...however some of the guidance has trended drier...and given the
subsidence following the departing wave...would not be surprised if
convection is even more isolated. Updates have been sent.


Short term...(today through thursday)
issued at 357 am EDT Wednesday Aug 20 2014

A complex of showers and thunderstorms is currently sliding east
across the Ohio Valley associated with a passing short wave trough.
The more organized portion of this complex has been confined to along
and north of the mountain Parkway. The hrrr model has not been
handling this feature well through the overnight...overplaying the
development to the south that has been weak in reality...while
underplaying where convection has been more organized and sustained.

Expect this complex to keep moving east...affecting locations along
and north of the mountain Parkway for the next few hours...before
exiting the area by 12z. There will be some subsidence following this
departing short wave for today working in from west to have
trimmed the probability of precipitation back a bit...peaking in the 20 to 30 range for most
locations during the hotter part of the day. Highs today will range
from 85 to 90 degrees.

As we head into tonight...convection will be on the downward trend
through 06z...but then looks to increase between 06 and
another short wave trough approaches from the northwest. Pop chances
will continue to increase through the day on Thursday with heating
aiding the modest forcing from the passing short wave. Have maintained
the better probability of precipitation in the northeast...and lesser values in the
southwest...further removed from the better forcing. Highs will
return to the 85 to 90 degree range in the southwest...with middle 80s
in the northeast...where more persistent cloud cover will reside.

Long term...(thursday night through tuesday)
issued at 335 am EDT Wednesday Aug 20 2014

The extended portion of the forecast begins on Thursday night with a
slowly building ridge over the central Continental U.S. And digging troughs
over the northwest and northeast. This general trend continues
through the entire extended period. During this period...quite a few
strong shortwaves travel over the building ridge in the Central
Plains and into the Ohio Valley and Great Lakes region. The first wave
of note will be the shortwave moving through at the beginning of the
extended. After this...the pattern turns into a more mesoscale convective system driven
pattern Friday through Sunday with activity centered around what the
days convection brings and is diurnally affected. Through the period
the upper ridge slowly weakens and drifts east.

Concerning the models during the extended...the GFS and Euro look to
be right on track and in good agreement. Though...the Euro looks to
cut off any convection by the end of the extended as the ridge axis
sets up right over eastern Kentucky leading to an end to all
diurnally driven convection and displacing the track of the mesoscale convective system more
to the northeast. Based on the good seems to be a
good consensus to stay close to the solution of the all blend model.
Though depending on what the 00z Euro does on the Monday and Tuesday
time frame for the ridge axis right over the area...may drop probability of precipitation
below the all model blend solution. With the solution of the all
model blend...the best chance of probability of precipitation will be during the Friday
through Sunday time frame and less during the Monday and Tuesday
time frame where the ridge will be over eastern Kentucky and have
left slight chance mainly during the afternoon on Monday and

In addition to this pattern...temperatures will be on the increase
in earnest as some of the warmest weather of the entire Summer will
begin to set in from Friday through the rest of the extended. High
temperatures will surpass 90 degrees in some areas of eastern
Kentucky and humidity will be on the increase as well.


Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 815 am EDT Wednesday Aug 20 2014

Scattered to numerous showers and thunderstorms will exit off to the
southeast in the next hour or two. IFR/LIFR fog will lift out in the next
hour...with a return to VFR conditions through the rest of the day.
Some isolated to scattered convection will threaten again this
afternoon...but coverage is expected to be limited enough to only
mention thunderstorms in the vicinity for now. Fog will likely return after 06z tonight...however
another upper level disturbance will likely approach between 06 and
12z...bringing in additional cloud cover and also renewing the
convective threat. This will likely keep the fog from becoming too


Jkl watches/warnings/advisories...none.



short term...geogerian
long term...shallenberger

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