Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 041708 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1208 PM EST Sun Dec 4 2016

.UPDATE...
Issued at 1208 PM EST SUN DEC 4 2016

Just sent out and updated zone forecast text product. The update
was mainly to remove any remaining morning wording from the text
product. Also ingested the latest obs into the hourly grids a
couple of times to establish new trends. Overall the forecast is
staying on track. We are currently experiencing a lull in the
precipitation across the area. However, more widespread rain
showers should form to our west in association with an approaching
cold front. These showers are expected to move across eastern
Kentucky later this afternoon and this evening, before tapering
off to drizzle overnight.

UPDATE Issued at 700 AM EST SUN DEC 4 2016

Light rain is continuing to move across the southern CWA, and is
showing signs of weakening and falling apart as of the last 15
mins or so. Pops should line up fairly well as ongoing rain starts
to lose strength and becomes more scattered in nature over the
next couple of hours, with a likely resurgance just after noon,
and a secondary wave coming into the northern portion of the CWA
later this afternoon. As such, left POPs the same from the 4pm
package issuance. Highest elevations continue to warm, so all
precip should be falling as rain at this point. Remainder of the
forecast seems to be on track, but did load in the latest
observations to make sure the near term forecasts for temps, dew
points, and winds reflected the ongoing conditions. All changes
have been published and sent to NDFD/web.

&&

.SHORT TERM...(Today through Monday)
Issued at 408 AM EST SUN DEC 4 2016

Light precip has encompassed our southern CWA and is continuing to
slowly work its way north as it overcomes a layer of llvl dry air.
Temperatures across the CWA are above freezing so far this morning,
so all precip should be falling as rain, even if some wet bulbing is
occurring. However, can`t rule out some of the higher
elevations(generally above 2k ft) still seeing some snowflakes mix
in as temperatures will be a tad bit cooler here at onset, and they
could possibly tap into colder air aloft as well. Overall, continued
to slow down pops through this morning based on the latest radar and
hi-res model trends. It also looks like there may be more of a break
into the afternoon, with a defined southern extent of rain pushing
eastward of the state, and a secondary northern extent moving in
after 21Z. Kept chance pops in otherwise during this time and into
the overnight. Between about 6Z and 10Z (starting in the east), dry
air really begins to pull in aloft as the upper level forcing starts
pushing east of the region and allows cooler drier flow into the
region. This will limit saturation to the lower levels, supporting
more of a drizzle event, before the dry air continues to quickly cut
off remaining precip potential by dawn Monday. Lows Monday morning
should remain just above normal, generally in the upper 30s across
the CWA.

Low level clouds will likely persist throughout the day Monday as
winds near the surface will be from a more NE to E direction
compared to the Wrly flow in the mid and upper levels, keeping
lingering moisture trapped near the surface for much of the day.

A strong upper level low located across TX during the day Monday
will begin to track northeastward as we head into the extended
portion of the forecast. As this occurs, expect another strong pull
of Gulf moisture into the Ohio Valley region, with a surface low
pressure system rotating across Louisiana. This will result in high
clouds building into the region once more from south to north
throughout the day Monday and will help boost temps to just above
seasonable normals in the afternoon despite cloud cover. While
precip chances should generally hold off until after 0Z Tuesday,
there is still a small potential that some pops could overcome mid
level dry air between 18Z Monday and 0Z Tuesday, mainly along the TN
border. As such, did include slight chance to low-end chance pops
here for this time frame.

.LONG TERM...(Monday night through Saturday)
Issued at 518 AM EST SUN DEC 4 2016

Models solutions are in reasonably good agreement with the
general mid/upper level pattern through the extended but
continue to differ significantly with details in the strength and
timing of several features embedded within an overall progressive
flow. This results in even larger differences in sensible weather
later in the forecast.

Mid/upper level cut off low moving out of Texas early in the
period opens up into a wave as it passes through the region
Tuesday. The GFS is slightly slower and stronger with this first
disturbance compared to the more similar ECMWF and Canadian. This
system will provide a soaking rain to the area with models
spitting out about an inch of rainfall on average, mainly from
Monday night through Tuesday. Forecast soundings do hint at some
marginal, very elevated instability Monday night. Mid/upper level
lapse rates do steepen a bit between about 10k and 22k feet. In
general CAPE remains below 100 J/kg. But there is substantial
shear within this layer as well, on the order of 30 to 50 kts. So
while one could not totally rule out a faint rumble of thunder,
feel the overall threat is low enough that any mention of thunder
was left out of the forecast for now. However, will pass on to
upcoming shifts for monitoring.

Forecast gets quite tricky thereafter as a series of disturbances
rotate around a low pressure system residing along the Northern
Tier and southern Canada. A shortwave trough swings through the
region sometime towards the end of the week, most likely
Thursday, as models present a range of possibilities with respect
to the timing and strength of this trough. Details of sensible
weather are not any clearer but the GFS and Canadian continue to
advertise a more similar solution with the ECMWF a much warmer and
wetter outlier, bringing a surface low and heavier precipitation
in the form of rain across the Commonwealth. The faster GFS
solution ushers colder air into the area at a much quicker pace
and hints at the possibility of some light isold to scattered snow
shower activity. The Canadian, being a colder solution similar to
the GFS keeps our weather dry. Until models begin to show better
agreement and/or show some solid trends will continue to rely
heavily on the model/guidance blends which suggest that a wintry
mix of precipitation will be possible through that time frame
depending on the time of day/night. On a more certain note, much
colder air does eventually move into the area for Friday and next
weekend. Thus any precipitation that does fall will transition to
just snow Thursday night into Friday with the potential of some
lingering upslope snow shower activity into early Friday morning.
Wouldn`t be surprised if future forecasts extend the snow shower
activity into Friday proper or even Friday night, as this is type
of scenario is typically handled poorly by the larger scale
synoptic models. At this point do not expect anything more
significant than minor snow accumulations at best, and if that.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 709 AM EST SUN DEC 4 2016

A mid/upper level wave is currently impacting the region, with
stratiform rain across the southern TAF sites (KLOZ and KSME).
Based on latest radar trends, this rain will continue to lighten
and break up over the next couple of hours, becoming more
scattered in nature. It will likely remain along the southern tier
of the state as well, not impacting KJKL or more northern
TAF locations. A resurgence of rainfall is expected this
afternoon, generally after 21Z, encompassing the remainder of the
TAF sites. It is also during this time that mid and upper level
moisture will finally work its way down to the surface with CIGS
likely falling to MVFR (first in the south just after 16Z, pushing
northward through 21Z at KSYM). As we head into the overnight
hours, the disturbance will start to shift east of the region and
allow drier air to begin penetrating into eastern KY. Decent LLVL
moisture will remain however, so could see a transition over to
more drizzle between 3Z and 6Z, with CIGS deteriorating further to
IFR. It is possible that some sites could even drop to LIFR at
times after 6Z, with BR and visibility restrictions possible in
addition to the drizzle. These conditions will likely persist
through the remainder of the TAF period, before the drier air
finally works its way down to the surface during the day Monday.

TAF
sites through the forecast period, however surface high pressure
remains at the surface with a layer of dry air in place in the low
levels. IR SAT does show high clouds penetrating eastern KY as the
system continues to approach, and should continue to stream across
the region overnight. These clouds are expected to thicken and
lower, but based on latest trends, this may occur a bit later than
originally expected. As of the 6Z TAF issuance, VFR conditions are
expected to persist through 12Z at the southern sites KSME and
KLOZ, but will quickly deteriorate after this point to MVFR
throughout the day as moisture finally overcomes the llvl dry
layer, and rain chances set in. This will occur a couple hours
later at KJKL and KSJS and closer to 18Z at KSYM. Llvl clouds will
linger throughout the upcoming night as well, possibly lowering
further to IFR, even as precip chances begin to taper off.
Overall, winds should remain light and variable throughout the
period.

&&

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

$$

UPDATE...AR
SHORT TERM...JMW
LONG TERM...RAY
AVIATION...JMW



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