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Area forecast discussion...updated 
National Weather Service Jackson Kentucky
210 PM EDT Thursday Aug 21 2014

issued at 140 PM EDT Thursday Aug 21 2014

With an area of scattered storms now moving east along Interstate 64
have updated the forecast to reflect the higher probability of precipitation north of the
mountain Parkway and lower temperatures there. Also added more probability of precipitation in the
higher terrain over the far southeast and lowered them elsewhere for
the next few hours. After that...outflows from the northern storms
will potentially bring convective development further south...aided
by the higher instability. In addition...made some tweaks to the
hourly temperatures and dewpoints for the rest of the afternoon given the
current observation and trends. These updated grids have been sent to the
ndfd and web servers.

Update issued at 1050 am EDT Thursday Aug 21 2014

14z surface analysis show general low pressure north of the Ohio River
with higher pressure found to the south. A stationary boundary exists
through the northern portions of the Ohio Valley and western parts of
this front...connected back to deeper low pressure over the northern
plains...has been a genesis region for recent mesoscale convective system activity. This
activity is also supported by a stream of middle level energy riding
along the northern fringe of a developing ridge to the southwest of
Kentucky. This would tend to support convection working southeast
from the upper Midwest to the central Appalachians passing by just to
our northeast. However...instability building with the recent
arrival of Summer time heat and humidity across Kentucky will be
enough to keep a threat of the storms and their outflow boundaries
sneaking into northeast portions of the County Warning Area and perhaps further to
the southwest in the afternoon. The current radar has a healthy
cluster of storms crossing from Indiana into Ohio with a growing
southern extent tracking through northern Kentucky. Expect this to
brush into northern parts of the forecast area through the next
several hours. The hrrr keeps this first wave just north of the
County Warning Area...while the 12z nam12 dips the convection deeper into east
Kentucky. For this update have split the difference between these two
scenarios and peaked probability of precipitation in the northeast through the afternoon with
some small to moderate probability of precipitation even down into the Cumberland Valley by
evening. High precipitable waters and the rains of the past several days will mean a
threat of flash flooding for places that see repeated storms...
particularly through the middle section of the County Warning Area. Storm Prediction Center has placed
eastern parts of the area...along the previously discussed storm a slight risk for severe weather...mainly damaging winds
and large hail. This appears reasonable given the high cape...low
lifted indices...and lack of a middle level cap. Accordingly this concern will
continue to be highlighted in the severe weather potential statement along with a mention of the
heat and humidity...temperatures near 90 and dewpoints in the 70s...through
the weekend. Have also fine tuned the T and dew point grids per the latest
observation...trends...and consshort guidance. These updates have been sent
to the ndfd and web servers with new severe weather potential statement and zones on their way.

Update issued at 757 am EDT Thursday Aug 21 2014

The forecast remains on track this morning. Freshened up the hourly
temperatures...dew points...and sky cover to account for the latest
trends in the observations.


Short term...(today through friday)
issued at 357 am EDT Thursday Aug 21 2014

The latest surface map features high pressure across the Gulf Coast
states...with low pressure across the plains states. A stationary
boundary extends east from the plains into the Great Lakes/Ohio
Valley region. upper level low continues to spin across
the northern Great Lakes...with an upper level ridge centered near
the northern Gulf of Mexico...and more troughing featured across
the northern rockies. Several complexes of thunderstorms have been
generating and then riding southeast on the periphery of the upper
level ridge over the past few days.

Currently...eastern Kentucky remains quiet as only a weakening
smaller complex of thunderstorms is slowly moving through southeast
Illinois and southwest Indiana. The next more organized complex is
currently moving through Minnesota.

The model guidance has been all over the place with the timing of the
more organized convection as of late. As such...have used a general
blend of the guidance and the inherited forecast. As the upper level
ridge slowly builds into the region through will
generally nudge the mesoscale convective system track further northeast...however since there
will be plenty of fuel for the storms and a weak synoptic pattern in
place...can not rule out outflow influence further southwest. Some
storms could approach severe limits...and isolated flash flooding
will also be a possibility...especially where storms can move
parallel to any established outflow boundaries. Will highlight these
threats in the severe weather potential statement. Probability of precipitation will generally peak in the afternoon hours
today and Friday...with lesser chances during the overnight hours.

Highs today will average in the 85 to 90 degree range...with around
90 degrees expected for most locations on Friday.

Long term...(friday night through wednesday)
issued at 357 am EDT Thursday Aug 21 2014

The extended portion of the forecast begins on Friday night with a
well developed middle level ridge centered over the middle west and
longwave trough entering the northwest with an exiting trough over
the northeast. The middle level ridge axis eventually shifts east over
the Ohio Valley by Monday as it weakens a bit with the approaching
trough over the northern plains and the trough over the northeast
exiting into the Atlantic. This pattern basically keeps the ridge
over eastern Kentucky through the rest of the extended.

With this pattern in place through Sunday...eastern Kentucky remains
in northwest flow with still a few mesoscale convective system/S likely poised to track
southeast into the area for this weekend. While models inherently
will have trouble tracking them...the first one should be moving
through Friday night with the next one possibly Saturday night. By
Sunday...the ridge axis really begins to set in and additional
strong convection may be less likely and may be more tied to diurnal
processes with a stationary boundary along the eastern portion of the
County Warning Area. By Monday and through Wednesday...the middle level ridge axis
moves over the area which should effectively cut off
least deep convection. Some afternoon showers and possibly a storm or
two may develop under the ridge. The solution of the all model blend
would suggest some uncertainty there with the best chance of precipitation
Friday night through Sunday. This is in good agreement with the GFS
and Euro as well. Overall the broad brush of probability of precipitation through the first 3
days of the extended seems needed due to the nature of the models
having trouble depicting the complexes moving through but did go with
some diurnal characteristics.

By the end of the extended...the models seem to hint at the ridge
moving farther east as a strong shortwave and associated cold front
seems poised to move through the MS River Valley and into the Ohio
Valley. In addition...the warm and muggy weather still looks to be
on tap through the weekend with highs around 90 through Monday and
dew points around 70. The end of the extended does show some relief
from the warm and humid weather with the approach of the
aforementioned cold front.


Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 210 PM EDT Thursday Aug 21 2014

The aviation forecast will be a challenge with the timing of mesoscale convective system
clusters and potential for fog formation through the period. Expect
the better chances for lower ceilings and visible associated with storms will
be for the northern taf sites through early evening. These locations
may have a better chance for more in the way of lower visible producing
fog. However...that will be dependent on added moisture from
convection during the rest of the day and some clearing later
tonight. For now...have brought all the sites to MVFR in br after 06z
and clearing out...back to VFR by 14z Friday. Cannot rule out
additional storms Friday afternoon...especially northeast...but
through 18z the taf sites should remain calm. Winds through the night
will be light and variable...favoring the southwest at 5 to 10 kts
during the daylight hours.


Jkl watches/warnings/advisories...


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

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