Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 251738

Area Forecast Discussion
National Weather Service Jackson KY
138 PM EDT MON JUL 25 2016

Issued at 1126 AM EDT MON JUL 25 2016

Heat and humidity appears to be peaking today. Moisture pooling
near the frontal boundary approaching from the north has sent
dewpoints well into the upper 70s over our northern counties, with
a few Mesonet stations approaching 80. With temperatures again
forecast to reach the low 90s for most locations, this will put
afternoon heat indices pretty solidly in the 100 to 105 degree
range. I noticed several locations had heat indices briefly peak
above 105 late yesterday afternoon. With increased cloud cover and
at least scattered showers and thunderstorms expected to develop
this afternoon, think most stations will stay below the 105 heat
advisory criteria today. Did issue an SPS though since we will be

Otherwise, forecast database looked good aside from a few upward
adjustments to dewpoints per current obs.

UPDATE Issued at 752 AM EDT MON JUL 25 2016

Isolated showers beginning to develop near the Bluegrass region
back into central Kentucky. Will likely see these continue to
develop and strengthen along an outflow boundary stemming from
storms overnight across Indiana.


.SHORT TERM...(Today through Tuesday)
Issued at 359 AM EDT MON JUL 25 2016

Upper trough swinging through Ontario toward Hudson Bay is currently
pushing a frontal boundary through the eastern Great Lakes extending
back through the central Plains and Missouri Valley. A broken line
of showers and thunderstorms spans much of this region with plenty
of moisture and instability to work with downstream. When this
arrives locally will be dependent upon how quickly this activity
progresses south and east without a significant meridional
component to the mean layer flow this far south into eastern
Kentucky. Upper ridging across the mid-Atlantic will also delay
any of this preexisting convection in making headway through the
Commonwealth by way of deep layer subsidence. An outflow boundary
across southern Indiana may be the initial instigator of showers
and storms later this morning across the Bluegrass region.

Regardless if this initial round of storms fires this morning,
many more will be in the forecast this afternoon and evening as
moisture pooling along and ahead of the approaching boundary
increases precipitable water values to near 2 inches. The
continued presence of this sultry airmass combined with additional
sources of lift will lead to a greater coverage of storms compared
to that over the weekend. Storm motions this afternoon of near or
below 10 mph combined with abundant moisture will promote the
primary threat being heavy rainfall and potential flooding.
Additionally, precipitation loading will promote the potential for
gusty downburst winds as weak shear leads to quickly collapsing
updrafts. Despite slowly lowering heights and lower thicknesses
compared to Sunday, temperatures should still climb toward the
lower 90s with heat indices once again near the 100F mark by mid

The potential for storms will continue overnight with eastern
Kentucky remaining squarely in the warm/moist sector ahead of the
frontal boundary which looks to likely stall in vicinity of the Ohio
River. Scattered to perhaps numerous storms will be in the offing
Tuesday afternoon as surface ridging across the Ohio Valley attempts
to veer winds northwesterly and produce a period of enhanced low
level convergence. Another upper wave on the heels of the previous
one across Canada will act to keep quasi-zonal/cyclonic flow in
place thus promoting passing pieces of energy capable of setting off
storms in a warm/moist airmass. Deep layer shear may increase
slightly to on the order of 20-25 knots Tuesday afternoon, but
continued capping near 600 mb should once again prevent cores from
developing substantially before downdrafts become dominant. Given
greater cloud cover and more moist conditions along with lower
heights aloft, high temperatures should finally top out a little
more seasonable in the mid-upper 80s.

.LONG TERM...(Tuesday night through Sunday)
Issued at 359 AM EDT MON JUL 25 2016

Upper level ridging encompassing much of the southern half of the
conus will continue to break down throughout the extended portion of
the forecast, with two separated areas of high pressure over the four corner states, and one just off the
southeast Atlantic coast. This will put the weak point across the
Ohio River valley, which is where the epicenter for falling heights
will be. An upper level low is expected to traverse James Bay in
Canada to start the period, which will bring deamplified troughing
to points south, including Kentucky. Multiple shortwaves will move
through this trough axis, deepening the trough through the week.

The first shortwave will be moving through the region as of 0z
Tuesday, with multiple smaller waves expected through midweek.
Models then show a stronger shortwave taking shape across the upper
midwest Wednesday, digging the trough farther and continuing to
lower heights across the upper Mississippi River valley and portions
of the Ohio River valley. Latest model runs show a weak blocking
pattern setting up, with the centers of low pressure centered to the
southwest and the southeast of the trough, resulting in
amplification but little movement through the first part of the
weekend. Eastward progression finally takes control for Sunday,
continuing into Monday, though at this point models start to diverge
somewhat on their solutions.

At the surface, a weak cold front will be moving into the state from
the northwest to start the period. With the overall deamplified
flow, the front will become elongated from west to east across the
state, transitioning into a quasi-stationary boundary. This frontal
boundary will then fluctuate slightly northward and southward
throughout the rest of the week. As the blocking pattern breaks down
late in the period, the frontal zone will finally make a push back
southward across the state Monday, before finally exiting to our
south by Tuesday.

With this frontal zone in place, in addition to continued warm and
muggy conditions, expect chances for showers and thunderstorms to
occur each day. Peak coverage and intensity will likely be diurnally
driven, during the afternoon/early evening. The main concern at this
time will be storm motion. Though there will be some improvement
going into the weekend, overall mean steering flow will be weak.
Meanwhile lift and instability will be enough to spawn some
potentially strong storms. In other words, expect pulsy slow moving
storms with heavy rain potential, and the possibility of training
storms as well...all of which could lead to urban and flash flooding
concerns. Will continue to highlight these concerns in the HWO as
of now.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)

Scattered thunderstorms continue to erupt in a sultry airmass.
These will likely remain rather hit and miss and will maintain no
more than a VCTS mention in the TAFs for now. Expect these storms
to exhibit a diurnal trend and diminish in coverage slowly after
sunset, although there will be a small threat for a shower or
storm anytime through the night and into tomorrow morning due to a
frontal boundary sagging southward toward our area. Fog is another
concern but it should remain patchy and is likely to only affect
TAF sites that are hit directly by a thunderstorm this afternoon.
With that in mind, will go with VFR TAFs for now through 18z
Tuesday and let later shifts fine tune.


.JKL Watches/Warnings/Advisories...


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