Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 051012 CCA

National Weather Service Jackson KY
512 AM EST Mon Dec 5 2016

.SHORT TERM...(Today through Tuesday)
Issued at 403 AM EST MON DEC 5 2016

As the mid/upper level wave that impacted the area yesterday
continues to shift northeast of the region, more zonal flow is
taking hold with surface high pressure moving eastward across the
state. That being said, MVFR clouds continue to plague much of the
region under a pretty steep inversion that has set up. Dry air will
continue to filter in aloft and in the mid levels throughout the
day, eventually working its way down to the surface and allowing the
low cloud deck to mix out, generally after 15 to 18Z.

Attention then turns to a strong upper level low positioned over
southern TX this afternoon. At the surface, the center of low
pressure will be located just off the TX/Louisiana coast, but will
continue to push northeastward throughout the day following the
upper level low, quickly reaching Mississippi by this evening, and
TN late tonight, before traversing eastern KY and eastern TN during
the day tomorrow. This will push the center of high pressure
currently across the state to our northeast, and allow deeper
moisture to quickly begin filling into the state from the south,
reaching our southern CWA between 21Z and 0Z this afternoon/evening.
That being said, upper level winds will continue to pull moisture
into the region well ahead of this system, so even as the low clouds
begin to mix out today, high clouds will already begin building in
ahead of this system. Overall, it is not likely that we will see
much of a break in the clouds throughout the day as a result.

According to the latest forecast soundings from the NAM12, the
transition from high clouds to moisture build down and precip will
be very quick. Only slight chance pops are in the forecast along the
TN border before 0Z, but widespread rain is expected to encompass
the entire southern half of the CWA by 6Z, and and the entire
eastern portion of the state by 12Z. A steady rain is expected to
continue throughout the day Tuesday. Still not seeing enough support
for instability, even aloft, to include thunder at this time.

The upper level low is expected to decrease in strength, becoming an
open wave by the time it moves over eastern KY. As the surface low
pressure center moves across the CWA in the afternoon, drier air
will be quick to filter in behind, weakening the surface low and
cutting off best rain potential. As such, rain is likely to end just
as quickly as it started, with only low end chances expected across
far eastern KY by 0Z Tuesday.

While temperatures today will be near seasonable normals despite
cloud cover, the surge of warmer moist air into the region will
actually boost temps well into the 50s for the day tomorrow.

.LONG TERM...(Tuesday night through Sunday)
Issued at 510 AM EST MON DEC 5 2016

Models are finally showing better agreement with mid/upper level
features through the extended and have even seen some trends
towards better agreement in sensible weather elements. A broad
trough moving through the Intermountain west at the start of the
period will reach the Ohio Valley Wednesday night, passing
through during the day Thursday. The 0Z GFS and Canadian, having
been the more consistent runs, are a bit stronger with the mid
level features of this system than the 0Z ECMWF. Regardless the
boundary layer and sfc features associated with this disturbance
are quite weak. Timing is similar with all solutions now, with the
ECMWF only slightly slower. Overall trends are for lower pops and
less QPF potentials. However, this system will still usher in some
very cold air into the region, with H850 temperatures bottoming
out close to -15C. The high pressure system building in behind
this disturbance will settle down directly over the Commonwealth
Friday night, allowing temperatures to drop into the low to mid
teens by Saturday morning. Would not be surprised if morning lows
flirted with some single digits Saturday in our typically colder
valley spots.

Thereafter return flow develops rather quickly, pulling plenty of
moisture northward back through the MS valley and into the OH.
If initial indications are correct, fairly strong isentropic lift
will bring overspreading precipitation back into our area as early
as Sunday. Too early to capture details at this time, but with the
cold air in place imagine that precipitation will probably fall as
a wintry mixture at the onset early Sunday morning before
transitioning to just rain through the day.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)

Tricky TAFs for the period once again. Upper level wave is
continuing to exit northeast of the region, with surface high
pressure moving in across the state. In most situations the
lingering moisture and high pressure center would suggest fog,
however in this situation, we are still seeing thick llvl clouds
across much of the region, including well upstream of the TAF
sites. As such, redid TAFs to remove mention of fog, as this will
likely be a low stratus event, with generally MVFR CIGS expected.
Can`t rule out some IFR at times however, though it seems like the
majority of the obs upstream are within the MVFR range. Tomorrow,
low clouds will likely persist into the afternoon, before finally
starting to scour out. About this time, another system will begin
approaching from the southwest. This will allow for high clouds to
enter back into the region, and quickly build down after 0Z, with
rain chances soon to follow. Went ahead and included VCSH at most
TAF sites between 3 and 4Z, except for the far northern KSYM,
where chances will likely occur closer to the end of the forecast
period. Overall winds should remain light and variable, though
more gusty conditions may continue at KSYM through the next
several hours before finally dissipating.





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