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Area forecast discussion 
National Weather Service Jackson Kentucky
502 am EDT Sat Jul 26 2014

Short term...(today through sunday)
issued at 502 am EDT Sat Jul 26 2014

A strong shortwave currently sitting over southern Saskatchewan is
still on track to bring some very unsettled weather to Kentucky during the
short term period. A surge of southerly winds and warm air advection
will be the main focus for a warm front pushes through
the region during the afternoon. This will drive temperatures to
near the 90 degree mark...with humidity values making a rise as
well. Meanwhile...the associated cold front...spanning from the
upper Great Lakes region to Kansas this afternoon...will push
eastward by the evening as the shortwave and surface low move into
southern Manitoba. As it nears the Ohio River valley region...expect
clouds to increase from north to south...and showers and
thunderstorms to begin affecting the region from the same direction
during the overnight hours. Despite a near-surface inversion...low
level wind shear is quite good...there is good speed sheer in the
middle and upper levels...lapse rates rise into the 6.0 to 6.5 c/km
range...and precipitable water values exceed 1.8 to 2.0 inches for a 6 hour period
in some locations. Based on this...still supporting the idea that
any storms that develop overnight will hold a threat for heavy
rainfall as well as damaging winds as the storms collapse.

By 15z...things start to get a little more interesting. Low level
wind shear is quite impressive...with wind speeds reaching in excess
of 50 knots by 12k feet. Daytime heating will break the low level
inversion early on...with temperatures expected to surge back into the middle
and upper 80s by afternoon. A strong low level well as the
upper level jet position themselves from west to east across the
Ohio River valley region...with the best activity expected to form
along this axis. A few things to note...between 12 and 18z
Sunday...the latest European model (ecmwf) is pointing at the best qvector
convergence setting up closer to the actual low pressure
center...over the upper Great Lakes and expanding into northern
Indiana and Ohio. The upper level jet/S horizontal position also
supports that storms will set up and move in the same
direction...from west to east...rather than from north to south. The
6z nam12 storm relative motion is also from the west-northwest. While forecast
soundings show a prime environment for mesoscale convective system/S to form...the overall
best forcing still seems to be to our north closer to the low
pressure system and along the northern half of the jet maximas.
Agree with Storm Prediction Center/S thinking that the best mesoscale convective system/S will develop
here...with strong outflows pushing outwards...including southward
into the Ohio River valley and eastern Kentucky region. Along these
outflows is where we can expect the best severe potential in the
afternoon for eastern Kentucky.

By 18z...and continuing into Sunday evening...forecast soundings
show an impressive signature for severe potential...with continued
strong winds in the middle levels and resulting good speed
sheer...moist low levels...but very dry middle and upper levels. All of
this is indicative of good damaging downdraft well as
a large hail threat. The concern however is the loss of low level
directional sheer...especially in the lowest 2k feet...and therefore
the lack of high helicity values in this level. As noted
above...think the best severe mesoscale convective system storms at this point will be
driven by the low level wind sheer created by the outflow boundaries from
larger mesoscale convective system/S to our north...and fading mesoscale convective system/S over our area. Given
the fast motion of these storms...would not be opposed to the idea
of a line of storms developing along an outflow boundary...with
embedded super cells and a few isolated spin up tornadoes possible
within the organized line. But that is not to say that some isolated
to scattered individual cells could not develop as well in
addition...with the main threat being damaging winds and large hail.
The storm system shear...moisture profile...and Li/S would
definitely support this potential as well. Perhaps the biggest thing
to question is where the boundary will set up. Given the parameters
and uncertainty...all storm modes...including
qlcs/S...supercells...and Bow echos are possible. Will continue to
monitor the situation as things progress...and fine tune the
forecast as more information is made available.

Long term...(sunday night through friday)
issued at 415 am EDT Sat Jul 26 2014

The models are in good agreement with an amplified pattern to
continue through the period. Troughing will dominate across the
eastern half of the Continental U.S....with ridging out west.

A strong short wave trough and surface cold front will cross the Ohio
Valley Sunday night...with strong to severe convection likely ongoing
across eastern Kentucky in the evening. Once this has cleared
out...much cooler air will invade from the northwest...with highs
retreating to the 70s. The cyclonic flow lingering across the area
will allow for at least a small chance of convection during peak
heating on Monday and Tuesday.

Dry weather will ensue for Wednesday and for most locations
Thursday...besides a stray shower or storm popping up along the
southeast terrain. An upper level low then looks to evolve across
the Mississippi Valley through next weekend...with diurnally driven
convection becoming more of a threat once again. Temperatures will
modify somewhat...but will still average below normal.


Aviation...(for the 06z tafs through 06z Saturday night)
issued at 205 am EDT Sat Jul 26 2014

A mass of middle/upper level clouds to our north will continue to spread
southward into the region...remaining scattered to broken in nature. Although
kloz is seeing some light br at the moment...expect this incoming
cloud cover to hamper any further br development across the taf
sites. Otherwise...VFR conditions should prevail through the day
tomorrow with the middle/upper level clouds expected to continue.
Clouds will then thicken and lower slightly by late in the taf
period as a cold front nears the region. Winds throughout the period
will remain light and predominately out of the west-southwest.


Jkl watches/warnings/advisories...


Short term...jmw
long term...geogerian

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