Area Forecast Discussion
Issued by NWS Jackson, KY

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836
FXUS63 KJKL 270639 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
139 AM EST Mon Feb 27 2017

.UPDATE...
Issued at 125 AM EST MON FEB 27 2017

Hourly grids have been freshened up based on satellite and
observation trends. Decoupled valley locations that had dropped
to the upper 20s to lower 30s are experiencing rising temperatures
at this time, as mid level clouds increase from the west and
southwest. In fact, there is virga being indicated by radar
imagery, but the lowest 5000 feet remains dry as evidenced by
surface dewpoints in the teens to 20s and the 11 degree dewpoint
at the Pike Co KY Mesonet site at 2774 feet and extrapolation
northeast of 0Z BNA RAOB data. However, as dewpoints at the
surface and aloft continue to increase from southwest and west to
east and northeast, some sprinkles will be possible starting over
the next couple of hours.


UPDATE Issued at 1110 PM EST SUN FEB 26 2017

The ridge to valley temperature split continues through eastern
Kentucky late this evening. Do expect it to start mixing out over
the next few hours as thicker clouds move in from the west.
Sprinkles or light showers are still on track to arrive toward
dawn in our west. In fact, even some virga returns are starting
to show up on radar from cloud decks up around 9k feet AGL. The
dry air at the sfc will keep the pcpn from reaching the ground for
a while longer this night. Have updated the grids mainly to fine
tune the Sky/Td/T ones per the latest obs and trends. These have
been sent to the NDFD and web servers.

UPDATE Issued at 740 PM EST SUN FEB 26 2017

00z sfc analysis shows high pressure over eastern Kentucky, but
retreating quickly. This led to mostly clear skies today and into
the first part of the evening, but high clouds are on the uptick
from the west. The high was also responsible for very dry air in
place with some locals seeing humidity values near 20 percent
earlier in the afternoon. Now the temperatures are dropping and
allowing the humidity to slowly increase while dewpoints remain
rather low in the the teens for most places - though lower 20s
are found near Tennessee. Also, for fire weather concerns, the
winds were rather light and variable - continuing that way into
the night. Temperatures currently vary from the mid 40s on the
ridges to the mid 30s in the valleys. Expect that split to remain
through the evening before the clouds thicken up with a mix out
late tonight allowing the valleys to warm up towards dawn.
Additionally, the thickening clouds will build in from the west
with even some sprinkles or light rain showers developing in the
west and spreading east through the late night hours potentially
affecting our western most counties by dawn. Have updated the
grids to reflect this and also to match up the current obs and
trends. These grids have been sent to the NDFD and web servers
along with a freshened set of zones.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 300 PM EST SUN FEB 26 2017

A ridge of high pressure will keep eastern Kentucky dry through
late this evening, before an approaching area of low pressure
brings some rain back to the area late tonight. In the meantime,
we can expect middle and high level cloud cover to stream across
the area, bringing partly to mostly cloudy skies to eastern
Kentucky for the next several hours. The cloud bases should
finally begin to lower a bit towards dawn on Monday, ahead of the
approaching weather system. A lack of moisture return should allow
for no more than isolated to scattered showers tonight into early
tomorrow. A few snow showers may mix with the rain late tonight
in our far northern and northeastern counties, where some cold air
will still be in place, but these should not cause any issues.
Tonights lows will likely range from around 30 in our deep eastern
valleys, to the low to mid 30s elsewhere. The colder locations in
our north and east is where a few snow showers may form late
tonight. The rain should begin to steadily increase in coverage
tomorrow night, as the aforementioned weather system finally
begins to move into the area from the southwest. A weak trough of
low pressure passing to our west tonight will be what brings the
initial push of precipitation to the area late tonight through
tomorrow morning.

Temperatures should rebound a bit on Monday, as winds shift more
to the south and southwest and increase in intensity a bit
compared to today. This will also begin a period of moisture
advection off the Gulf of Mexico into the Tennessee and Ohio
valley regions. Highs on Monday should max out in the mid to upper
50s across the area. The warm air will remain in place Monday
night, as lows in the 40s are expected.

.LONG TERM...(Tuesday through Sunday)
Issued at 349 PM EST SUN FEB 26 2017

Increasing southwest flow will continue Tuesday, lifting a warm
front through the Ohio Valley as a surface low ejects out of the
central Plains into the Midwest. This along with developing
isentropic ascent will lead to rain showers during the morning
into at least early-mid afternoon. Portions of southeast Kentucky
may very well remain dry as winds initially maintain a downslope
component. Temperatures warming into the upper 60s to near 70 in
the warm sector will allow for at least meager enough instability
to spark isolated chances of thunder through the late morning and
afternoon.

After a relatively drier period late Tuesday afternoon into a
portion of Tuesday night, rain chances will increase in earnest as
height falls overspread eastern Kentucky downstream of an upper
trough stretching from the western shores of Hudson Bay through
the Great Plains. Concurrently, evolution of a double-barrel
surface low pattern may occur as the base of the trough moves
across the front range of the Rockies. Still some question as to
how quickly increasing thunder chances will materialize Tuesday
night as stout earlier day warm air advection creates a strong
elevated mixed layer, thus keeping any convection elevated.

Despite recent rainfall and plenty of cloud cover, surface heating
Wednesday morning/early afternoon should lead to ample enough
instability for surface-based thunderstorm development across all
of eastern Kentucky as a cold front bears down on the
Commonwealth. Impressive shear profiles, characterized by 0-6 km
values of 60-70 knots with 50 knots within a few thousand feet off
the deck, will promote damaging wind gusts as a line of storms
pushes through. Peak shower/thunderstorm activity currently looks
to take place Wednesday afternoon, further promoting strong/severe
wind potential, given enough instability can develop in order for
updrafts to survive in a highly sheared environment.

After a few storms likely linger into the evening timeframe,
cold/dry air advection will blast into eastern Kentucky Wednesday
night. Lingering rain/snow showers will be possible into early
Thursday as below normal temperatures return through late week. A
clipper system may bring some light rain/snow showers turning to
all snow showers Thursday evening/night. Having a tough time in
believing enough moisture advection will occur to see anything
measurable following the strength of the recent front, but the
best chances will be across northeast Kentucky.

Quasi-zonal flow/weak ridging then looks to take shape for the
weekend with warmer/drier conditions ensuing. Precipitation
chances may then again ramp up heading into the following week as
cyclonic flow redevelops out west.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
ISSUED AT 137 AM EST MON FEB 27 2017

Surface high pressure continues to depart to the east while return
flow and the approach of a shortwave trough from the Plains into
the MS Valley and lower OH Valley is leading to increasing
moisture from the top down. Mid level clouds will continue to
increase with cloud bases lowering toward 6Kft or perhaps lower
during the first 6 to 9 hours of the period or near 12Z or so as
the wave passes by. VFR is expected to continue although there
will be some sprinkles or perhaps light rain showers or patchy
light rain falling from these, especially across the west and
northwest starting during the first 3 to 4 hours of the period as
low level moisture increases. Once the wave passes by, cloud bases
will likely return toward 10kft or higher by the 16Z to 19Z
window with a lull in the precipitation chances. Winds will
average out of the southeast to southeast at 10KT or less.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...JP
SHORT TERM...AR
LONG TERM...GUSEMAN
AVIATION...JP



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