Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 271748
AFDJKL

Area Forecast Discussion
National Weather Service Jackson KY
148 PM EDT WED JUL 27 2016

.UPDATE...
Issued at 1245 PM EDT WED JUL 27 2016

Latest radar trends show showers and thunderstorms popping up in
far northeast KY, which seems to be on par with the latest HRRR
run. Expect this trend to continue into the afternoon with
additional showers likely forming south of the area and moving
north (per latest Visible satellite imagery). So updated pops
accordingly and refreshed hourly temps. Sent updates to NDFD and
web servers.

UPDATE Issued at 942 AM EDT WED JUL 27 2016

Early morning showers have lost their gusto and are dissipating as
they move east-northeast. The HRRR model reflected this trend
well. Also updated hourly grids to reflect recent obs and sent
updated to NDFD and web servers.

UPDATE Issued at 653 AM EDT WED JUL 27 2016

A cluster of thunderstorms that developed across south central KY
and north central TN continues to work its way northeastward
during the 6am hour. While they seem to finally be losing steam,
they did put down some quick torrential rainfalls along the TN/KY
border, with several reports of flash flooding ongoing. The HRRR
model is the only model so far that has picked up on this ongoing
activity, and shows it expanding but losing strength over the next
few hours. Based on radar trends over the last 15 minutes...this
seems to be pretty well on track. Trended closer to the HRRR
through the next few hours, with isolated to scattered pops
expanding northeast through the CWA, before scattered pops take
over across all of eastern KY for the afternoon. Also updated the
sky cover to accommodate this increase in pops.

Finally, loaded in the latest observations for temps, dew points,
and winds, to make sure the near term forecast was on track with
current conditions. All changes have been published and sent to
NDFD/web.

&&

.SHORT TERM...(Today through Thursday)
Issued at 405 AM EDT WED JUL 27 2016

Clouds were starting to increase in coverage at 7z, with a few
showers starting to pop up across the central TN and moving into
south central KY. Kept low end isolated pops in across the southern
extent of the CWA to cover these isolated showers through daybreak.
Otherwise, today should be much in the same as yesterday, with the
stalled frontal boundary still located across the northern half
of the state, and a warm, very moist airmass in place. As we head
into the daylight hours, expect convection to begin popping here,
across our northern CWA, then quickly spreading across the
remainder of the CWA throughout the afternoon. Kept with scattered
pops across the CWA through the afternoon given the uncertainty of
where and when storms will actually form. This may need to be
fined tuned a bit as convection starts developing today. PWATs
continue to hover around the 2 inch mark today, so any storms that
do develop will continue to be heavy rain producers. This,
combined with very little directional shear, could lead to some
training of storms as well, so will continue to monitor for any
localized flooding concerns.

Focus then shifts to the overnight hours tonight and heading into
the day Thursday. The stationary front across the state will push
slightly north of the Ohio River late tonight, and remain just north
of the state through the day Thursday. Winds will take on a slightly
more SW heading, and increase in intensity, allowing for a deeper
pull of moist southerly air. This increase will be due to a
deepening shortwave, which is expected to move across the mid
Mississippi River Valley tonight, and then across Kentucky
Thursday and Thursday night. This wave will interact with the
stationary frontal boundary, as well as the phasing of the
southern and northern jet streams, to create a large surge of warm
deep moisture, and lift for which storms to develop. PWAT values
for tonight will be well over 2 inches, and will continue to
increase to between 2.25 inches and 2.4 inches in some places
during the day Thursday.

CAPE values and LIs remain decent from tonight through Thursday,
but overall the more long/skinny nature of the CAPE and little
wind shear continues to lend itself to heavy rain being the
primary concern with any storm. Somewhat unidirectional flow in
the mid and upper levels may lend itself to some training of
storms, which would be worst case scenario for any peoples under
these storm`s path. Flooding will likely be imminent, the
question is how isolated will it be, and where will it occur. It
may also play directly into which locations receive heavy rainfall
today. No flood watch has been posted at this time by our office
or any neighboring offices, but will pass along for the day shift
for consideration.

Temperatures today will continue to be warm and muggy, topping out
in the upper 80s to near 90, with heat indices in the mid and
upper 90s. With the introduction of thick cloud cover and heavy
rains Thursday, temperatures will take a downward turn, with highs
only in the low 80s. It will be wet, but a welcome relief from the
heat.

.LONG TERM...(Thursday night through Tuesday)
Issued at 412 AM EDT WED JUL 27 2016

Upper troughing will remain locked in place from the northern Plains
and upper Midwest through the Appalachians and mid-Atlantic into
early this weekend, in between Great Basin to Four Corners anchored
high pressure and the stagnant summertime Bermuda high. Multiple
rounds of upper energy look to be in play, with the first and most
significant at this point, being the one mentioned in the short
term. Still some inconsistency in exactly how quickly and where this
lead wave will skirt through eastern Kentucky. GFS/ECMWF solutions
phase a southern stream impulse with the shortwave ejecting out of
the upper Midwest and lower Great Lakes, thus slowing the coupled
system`s eastward progression. The latest NAM is not as robust on
the phasing of both systems and subsequently dampens the upper
trough as it moves through the Tennessee Valley into Kentucky. There
also still remains question as to how deep and therefore exactly
where the surface low/wave will track. Nonetheless, a tropical-type
airmass characterized by precipitable water values in the 2.25 inch
range along with strong omega profiles and ample instability with
CAPE in the 1-2 kJ/kg range, suggest a dousing of rain somewhere in
vicinity of eastern Kentucky Thursday into Thursday night. Have
raised pops to categorical mention Thursday evening to account for
the overall consensus and better consistency in a slower dynamic
progression. Even without an exact morphing of the southern and
northern stream waves, lift will still be plentiful with the
combination of energy aloft and in the warm sector of a stationary
front near the Ohio River Valley. A flash flood watch seems very
likely within the next 12-24 hours for Thursday, but will let a few
of these uncertainties with respect to placement and timing refine
themselves before pulling the trigger. Additionally, depending on
how quickly storms move through Thursday, increasing deep layer
shear to near 30-35 knots into the evening could suggest a better
threat for organized updrafts and gusty downburst winds.

Friday will bring scattered storms to the eastern portion of the
Bluegrass ahead of the long-residence frontal boundary, with
coverage perhaps somewhat limited by a spout of shortwave ridging
following Thursday`s system. Additional waves of some degree look
possible both Saturday and Sunday at this time, leading to scattered
showers and storms once again, mainly confined to peak heating
during the afternoon/evening timeframe.

Late weekend into the first week of August looks to see upper
ridging expanding east across the Great Plains and into the Midwest.
Will keep isolated to scattered storms advertised at this point for
early week with uncertainty as to how far east deep layer subsidence
will build. Could get into a period of northwest flow and subsequent
mesoscale convective system development toward the region.
Nonetheless, temperatures will likely see a warming trend from more
seasonable readings in the low to mid 80s through this weekend to
mid to upper 80s with rising heights next week. Lows should
generally reside in the mid-upper 60s before approaching the 70
degree mark next week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 148 PM EDT WED JUL 27 2016

Clusters of showers and thunderstorms will continue to develop and
track mainly east across our area this afternoon and evening,
mainly along and ahead of a stalled frontal boundary. Current
thinking is that the north and eastern portions of the area will
receive the most rainfall through this evening. Tonight, did add
in the mention of fog development and vis restriction after 3Z,
though exact impacts will largely be dependent on the amount of
rain each TAF site receives through this evening. A low pressure
system will approach the area from the southwest tonight, bringing
widespread heavy rainfall and thunderstorms to the area through at
least tomorrow afternoon. These rounds of heavy rainfall will lead
to variable VIS at the TAF sites, with CIGS degrading. Winds will
generally be light and variable, though any stronger showers or
thunderstorms could produce some brief gusty conditions.

&&

.JKL Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...JVM
SHORT TERM...JMW
LONG TERM...GUSEMAN
AVIATION...JVM



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