Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 300326 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1026 PM EST Tue Nov 29 2016

.UPDATE...
Issued at 1026 PM EST TUE NOV 29 2016

Convection continues to blossom and fill in across the TN valley.
Fortunately, most of the organized cells are having a hard time
maintaining their integrity as they make their way north. Eastern
Kentucky remains stable at the surface and the latest meso-
analysis has only meager MU CAPE values just to our south. Despite
the low level jet ramping up overnight, it is unlikely that storms
will be organized enough to take full advantage of this jet and
overcome the stable surface layer. As such, have downplayed the
severe threat for the rest of the overnight and have only
mentioned some strong wind gusts still possible. Freshened up the
hourly pops through tomorrow based on the latest higher resolution
model trends. This yielded slightly less QPF for the Bluegrass, and
perhaps a touch more across portions of the Cumberland Valley, as
some training of storms will be possible closer to dawn. Updates
have been sent.

UPDATE Issued at 722 PM EST TUE NOV 29 2016

Convection has commenced in earnest down in the deep south. Dew
points across eastern Kentucky are currently running from the low
to mid 40s across most locations. Thicker cirrus will advect in
from the southwest through this evening; however, some of the
cooler valleys have taken advantage of the drier low level air and
nearly calm winds. Temperatures have dropped into the lower 50s,
so have allowed for a few upper 40s as a possibility, before
thicker cloud cover moves in and allows for a rise later on. The
last few runs of the HRRR have held pops off until closer to 04
or 05z. Given the drier air in place, am inclined to agree with
the slower arrival and have reflected this in the pop timing.
Updates have been sent.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 437 PM EST TUE NOV 29 2016

A strong upper level low is in place across MN this afternoon, with
deep longwave troughing across much of the central conus. A strong
ridge is also in place across the southern Gulf of Mexico. The
difference between these two systems is producing strong pressure
gradients, especially across the southern Mississippi and Ohio River
valleys. Meanwhile, a strong surface low pressure feature is in
place across Minnesota as well, in conjunction with the upper level
low. This surface low has two cold fronts protruding southeastward.
The first of these cold fronts is now east of the region, having
impacted us last night, however the secondary cold front is gaining
strength as it pushes eastward toward the Ohio River Valley
overnight. Strong southerly flow is in place, with winds expected to
continue increasing as the cold front nears.

Moisture will also be on the increase ahead of the front this
evening and through the overnight. Given the latest sounding
profiles, this increase in moisture and WAA is still strong support
for elevated instability just ahead of the front, with elevated
thunderstorms possible generally between 3 and 6z across our western
CWA. Some of the heavier rain showers could result in the mixing
down of strong winds aloft, so damaging winds cannot be ruled out.
Surface based instability will begin increasing after midnight as a
meso-low quickly pushes eastward ahead of the front and into the
region as well. This will result in higher winds transferring to the
surface, and a good potential for scattered thunderstorms across the
area. Latest forecasts soundings show highest winds transferring to
the surface between 6 and 12Z, so it won`t be hard for high to
damaging wind gusts to occur. The largest threat, as outlined by SPC
in their slight risk area, will be along I75 and points westward in
our CWA. However, this does not rule out the isolated potential for
damaging winds elsewhere either.

Also based on the sounding profiles, the storms will likely pass
over as a QLCS, in line form. Given this type of profile, with the
very strong winds, and impressive low level sheer, an isolated spin
up tornado cannot be ruled out along the front of the line.

The actual cold front will continue eastward across the CWA through
just after 18Z, before it exits to our east. Rain, chances for
thunderstorms, and potentially gusty winds will continue through the
day Wednesday, though the damaging wind threat and tornado threat
will diminish as a low level inversion sets up. Still the potential
that some gusty winds could make it to the surface in the heaviest
showers and thunderstorms. In better news, this system will bring
with it a good shot of Gulf moisture and soaking rains. Almost the
entire CWA is expected to see an inch of rain or more from tonight
through tomorrow evening, with some locations across the southwest
possibly topping 1.5 inches. This will hopefully help with
any ongoing drought concerns, as well as any ongoing wildfires.

Rain chances will finally taper off through tomorrow evening as the
cold front continues to exit east of the region and high pressure
starts to take hold. By this point the upper level low and the
surface low pressure system will be moving across the Great Lakes
region, with northerly flow on the back side makings its way into
the Ohio River Valley. This will result in much cooler overnight
temps compared to tonight, much closer to seasonal norms.

.LONG TERM...(Thursday through Tuesday)
Issued at 438 PM EST TUE NOV 29 2016

The period is expected to begin with an area of broad troughing
across much of the CONUS and southern Canada with ridges over the
Atlantic and Eastern Pacific. At the sfc, a slow pressure system is
expected to be tracking through Quebec and the Northeastern CONUS
with the trailing cold front moving off the eastern seaboard at that
time with sfc high pressure nosing into the area. A mid level low
over the Great Lakes with associated shortwave trough south into
the Lower OH Valley is also expected early in the period.

Thu through Friday, the closed low is expected to meander into
Eastern Canada while a shortwave initially over the Norther Rockies
moves south to the Four Corners region and closes off. The 12Z model
runs seem to be in better agreement in handling this with a slower
and generally less consolidate system. Height rises are expected
over the OH Valley especially on Friday with sfc high pressure
settling across the area.

Late Friday through Sunday, a series of northern stream shortwaves
are expected to move from the Rockies/Northern Plains east to the
Great Lakes and OH Valley with the strongest of these nearing the
Mid Valley and Lower OH Valley late Saturday night. This pattern
would lead to a sfc wave moving across the southern states with
inverted trough north into the area on Sunday with chances for
mainly light precipitation. At the same time, the closed low is
expected to dig further south into Northern Mexico from the Four
Corners and then track across Northern Mexico. During this period,
lowered pops compared to the Superblend for Saturday into Saturday
night as it was biased up by the 0Z ECMWF run and did not reflect
the model consensus with the upper air pattern/closed low with the
12Z runs and past few GFS runs.

High pressure is then expected to bring a lull in precip chances for
late Sunday or Sunday night into most of Monday. However, rain
chances should return with the potential for another wetter system
with more Gulf of Mexico moisture possibly getting involved as the
closed weakens, opens up, and interacts with a trough moving across
the Canadian Maritimes and Western CONUS. At the surface, a low
pressure system should develop over TX or the Western Gulf of Mexico
region and track toward the Lower OH Valley Monday into Tuesday.

As for sensible weather, plenty of moisture is expected to remain
near 850 mb and below to start the period with potential for
diurnally driven cu and or lingering stratocu. This and cold 850 mb
temperatures should lead to below normal highs Thu into Friday, but
diurnal ranges will be a bit limited. Clouds should thicken and
lower late Saturday night into Sunday with light preciptation
possible. Depending on how quickly the lower levels saturate a rain
and snow mix might be possible early on Sunday. However, the better
chance of preciptation with this system will hold off until during
the day on Sunday when the atmosphere will have moderated further
and precipitation should fall as rain. As already noted, Sunday
night and Monday should be mainly dry although there will be some
passing mid and high clouds from time to time. Monday night into
Tuesday rain chances will return with the surface low moving into
the Lower OH Valley region.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 722 PM EST TUE NOV 29 2016

An area of low pressure will track towards the area overnight into
Wednesday morning, bringing widespread rainfall and scattered
thunderstorms. Ceilings will gradually lower from southwest to
northeast through 06z, with precipitation breaking out west of
I-75 first. Have held onto VFR for all sites, with deteriorating
conditions expected between 06 and 12z. Ceilings and visibilities
will fall to MVFR, and even IFR at times, within heavier showers
or thunderstorms. South to southeast winds will average at 5 to 10
kts; however a strong low level jet will allow for ample wind
shear from approximately 05z through 14z. Precipitation will
diminish from west to east Wednesday afternoon, with improving
conditions towards the end of the period. South winds will also
shift to the southwest during the day on Wednesday, and could
become gusty at times in the afternoon.

&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...JMW
LONG TERM...JP
AVIATION...GEOGERIAN



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