Area Forecast Discussion
Issued by NWS Jackson, KY-- Remove Highlighting --
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FXUS63 KJKL 212132
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
432 PM EST Sat Jan 21 2017
.SHORT TERM...(This evening through Sunday night)
Issued at 432 PM EST SAT JAN 21 2017
A large and deep low pressure system will track east across
Kentucky during the period, bringing wet weather and possibly
Models have had trouble honing in on the details of what`s going
to happen. Although runs from 24 hours ago seemed to back off on
heavy rain threats, recent runs from last night and today have
again pointed to a heavy rainfall potential, especially near the
Virginia border. An ESF statement is issued for this. The matter
was chatted about with MRX, and the decision was made to hold off
on any flood watch until there was more certainty.
In terms of synoptics and forecast details- the surface low is
being largely driven by a powerful upper level system moving east
out of the southwest CONUS. There is actually not much
baroclinicity present considering how strong the surface system
will be. A warm front being drawn north by the system should reach
KY before being overtaken an occlusion and the low itself moving
eastward. A band of overrunning precip along/north of the front
is expected to move north over KY on Sunday. A relative lull
should arrive from south to north once this passes by. Models
show weak instability, largely after the deep moisture has passed
by. Can`t rule out some thunder during this time, but have kept
it at only a slight chance.
On Sunday night, deep moisture returns under the upper low and
comma head. This is when models contain the heaviest precip.
Forecast soundings are nearly moist adiabatic but mostly stable.
This coincides with persistent strong upward vertical motion. if
models persist and show better convergence on a wet solution, a
flood watch may still be needed.
.LONG TERM...(Monday through Saturday)
Issued at 330 PM EST SAT JAN 21 2017
The extended forecast period begins on Monday with a deep closed
upper low tracking northeast through the spine of the Appalachians.
As this feature tracks northeast, blocking over the New England and
Canadian Maritime region will hinder the exit of the back edge
precip moving through eastern Kentucky. This slow exit followed with
the approach of the colder air in behind on Monday night into
Tuesday may lead to a brief mix of rain and snow on top of Black
Mountain. In addition to this, models have been coming into more
agreement of a prolonged heavy rainfall event coming to an end
Monday evening into Monday night across eastern Kentucky. Some
lingering minor flood problems may be possible, if not just some
rivers running full. Both the Euro and GFS seem to have come to an
agreement on this with the Euro being slightly wetter. Will keep
this mention in the HWO.
Heading into the midweek time frame, a brief period of ridging moves
into the OH valley with a period of drying as southwest flow
increases ahead of the next incoming cold front. High temps on
Wednesday will climb into the upper 50s to low 60s with SW 10 to 20
knot winds bringing in an unseasonably warm airmass. In fact,
models are suggesting an overall drying trend to the approaching
front with the bulk of the moisture to the north over the Midwest
and into Ohio. Little if any precip is expected with this feature.
Passage of the front on Wednesday night will bring in a colder
airmass to the region by Thursday with a possible prolonged upslope
event taking shape for Thursday and Friday. At this point the
pattern brings in a longwave trough across the eastern CONUS into
the weekend. The northwest flow then brings a series of disturbances
in an upslope scenario. At this point, while the models hint at
temps being warm enough for rainfall during the day and snow showers
overnight, an upslope event with the correct wind component would
mean some convection and snowfall at warmer temps. For now, went
with a general snowfall at 34 degrees and below due to the
uncertainties in the models but this may need reevaluated. The
general trend is cooler towards the end of the extended but models
have backed off from the depth of the cold air. Due to this, will
leave any mention of snow out of the HWO as none is expected to be
impactful at this point.
.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
ISSUED AT 1255 PM EST SAT JAN 21 2017
VFR conditions are expected to prevail until late tonight, with
mainly mid/high level ceilings. A bit of light rain will affect
far southeast KY this afternoon, and possibly near/north of I-64,
but it should not offer up much in the way of restrictions. The
next round of more significant weather will not arrive until late
tonight. Showers and lower ceilings are expected to spread into
the JKL forecast area from the southwest before dawn on Sunday.
The worst conditions should be in the far west and southwest, with
at least MVFR if not IFR occurring on Sunday morning. Further
east, drying downslope flow will work to erode the lowest clouds,
and the eastern tip of the state should remain VFR. However, there
still could be some showers even in the far east before the end
of the period. A few thunderstorms can`t be ruled out in the
southern part of the area by mid day on Sunday.