Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 220003
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
703 PM EST Tue Feb 21 2017

.UPDATE...
Issued at 703 PM EST TUE FEB 21 2017

Showers are starting to expand from central Kentucky up across
northern Kentucky, impacting our forecast areas north of I-64 with
some light rain. Meanwhile, showers working across the Cumberland
Plateau are hitting a wall as they try to push deeper into eastern
Kentucky as the low level dry air remains in place, limiting the
push of showers into the area. As the night wears on, we should
slowly erode some of the dry air from above, but they may be a
tough battle as downsloping southeast low level flow also
strengthens. Thus, while it looks like we should see rain
continuing to expand across the area, most of it will be on the
light side, given the low level dry air. Areas that may do best
with the rainfall would include our southwestern zones, farther
away from the effects of this downsloping and areas north of I-64.
It does appear rainfall is still a good bet despite the hostile
environment in the low layers. Thus, no changes to the rain
chances except to slow them down through the evening hours as it
takes awhile to saturate low enough to see more than sprinkles.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 355 PM EST TUE FEB 21 2017

20z sfc analysis shows a low pressure area moving out of the
Southern Plains and into the Deep South. This is attempting to
push its pcpn shield into the area from the southwest but so far
has been hindered by dry air at the sfc and still high ceiling
levels. Sun shine through the earlier high thin clouds allowed
temperatures to soar into the lower and middle 70s for much of the
area this afternoon setting a record at JKL (75 degrees) and at
least matching one at LOZ - 70 degrees. Dewpoints are starting to
moisten up from the southwest with values across the CWA ranging
from the lower 50s at EKQ in Wayne County to the upper 30s in the
far east. Combined with temps in the 70s this is yielding RH
values down in the mid to upper 20 percent range in the far east.
Winds, meanwhile, are mostly light from the south at 10 mph or
less, though a few places with more sunshine did see some gusts
as high as 20 mph for a time.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict a deep closed low
breaking out of the pattern and sinking south to the Central Gulf
Coast tonight while near zonal flow continues over Kentucky. The
southern low then will progress into the eastern Gulf of Mexico on
Wednesday while weak packets of energy make their way over
Kentucky along with some weak height falls. The flow locally then
turns more southwesterly as heights bottom out and start to climb
again Wednesday night along with weak energy passing over head.
Given the agreement will favor a general model blend for the broad
picture and the HRRR/NAM12 for wx details through at least the
near term portion of the forecast.

Sensible weather will feature showers moving into the area from
the southwest as cigs lower in the face of a moistening column.
The northern edge of the pcpn shield from the low passing to the
south will then slowly cross Kentucky tonight with some places
picking up soaking rains on account of enhanced lift from a minor
300 mb jet streak passing to the northeast late tonight into
Wednesday morning. Plenty of low level moisture will then be in
place over this part of Kentucky into Thursday morning even as the
accumulating rains gradually move out of the southeast during the
day Wednesday. Showers may redevelop late Wednesday night over the
northwest as more energy moves through aloft and a warm front
starts to take shape from a developing deep sfc low well to the
west.

Started with the CONSShort and ShortBlend for the short term grids.
Did not make too many adjustments of note to temperatures tonight
and Wednesday night owing to the moist environment expected to be
in place both nights. As for PoPs, did again adjust them for
later tonight into Wednesday morning - translating the highest
PoPs across the CWA more cleanly - with a significant nod to the
NAM12.

.LONG TERM...(Thursday through Tuesday)
Issued at 230 PM EST TUE FEB 21 2017

The extended period begins on Thursday with the highlighted feature
of the extended bearing down on eastern Kentucky. In the upper
levels, a strong closed low ejects from the Front Range into the
central Plains and east as it intensifies. Extending east along a
stationary boundary, low level flow out of the south increases
heading into Thursday afternoon and Thursday night as a warm front
develops and lifts north. With the weak wave passing through before
the front truly develops, would expect medium to low chance pops
for thursday afternoon into Thursday night. Model soundings
indicate substantial instability with the southerly flow and
increased gradient so will be dealing with some thunder chances
during the Thursday and Thursday night period.

By Friday, the surface low shifts from the central Plains northeast
into the western Great Lakes as it warps up and matures. Convection
develops out in the Midwest and in central Kentucky Friday afternoon
into Friday evening. Due to timing, the CAPE values of 800 to 1000
J/KG in eastern Kentucky will be on the wane heading into Friday
night with the loss of daylight so for now, will keep the severe
chances in central Kentucky. Due to the shear with this front a
strong storm or two still seems possible. The line of showers and
thunderstorms pushes through by midday Saturday. Models have
remained consistent on the post frontal trough staying north and the
cold air being slower to advect in behind the front for any change
over to snow. Will continue to keep snow out of the forecast for
this post front CAA.

With the current pattern in place, this cold air doesn`t stay
entrenched very long as after lows on Sunday morning in the upper
20s, already rebound into the upper 40s to near 50 for highs. With
the upper level pattern remaining quite progressive and flattening,
a weak wave will track across the north OH Valley by Monday morning
into Monday afternoon. Due to the timing of arrival in the morning,
temps will be cold enough for the rain to mix with or become all
snow, especially in the higher elevations before changing to all
rain Monday afternoon. Overall through the extended, temperatures
remain abnormally warm and even the cold air push on Saturday and
Sunday doesn`t seem to have a good residence time with a rather
progressive pattern remaining.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 703 PM EST TUE FEB 21 2017

Difficult aviation forecast tonight across eastern Kentucky. While
most hi-res model output wants to crater ceilings later tonight.
The flow will remain out of the southeast and is generally
downsloping for eastern Kentucky. This will produce a hostile
environment for low level cloud development. Thus, opting to go
more optimistic with the TAFS. The flow only strengthens through
the night, so at best, perhaps we see some brief periods of MVFR
cigs at some of the TAF sites. Best shot at more persistent MVFR
conditions would be KSME, farther away from the downsloping winds,
but even here will experience some disruptions. Thus, low
confidence forecast with very few models picking up on this
southeast flow impacting the cloud bases. However, situations like
this in the past have resulted in more VFR ceilings across most of
the area. Regardless, some very light rain will be seen overnight.

&&

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

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...SHALLENBERGER
AVIATION...KAS


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