Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 270613
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
213 AM EDT Sat May 27 2017

.UPDATE...
Issued at 214 AM EDT SAT MAY 27 2017

MCS has passed by to our north, missing most of our area. Thus,
dry conditions have continued overnight. We will have some slight
moistening of hte low levels towards daybreak, and this could
yield a few light showers during the early morning hours today.
This will also keep quite a bit of cloud cover around through the
morning hours. Cigs may try to break up later today, then
attention turns to potential severe threat. Still lots of
questions as to where a east/west oriented boundary sets up as it
could serve as an initiation point for convection later this
afternoon. 00z NAM sounding over KJKL had nearly 2200J/KG of
MLCAPE with LI`s near -8C. This is pretty decent for this area.
Combine this with the modest unidirection shear, and you have a
decent setup for some severe storms. Damaging winds and hail look
to be the primary threat at this point.

UPDATE Issued at 1021 PM EDT FRI MAY 26 2017

Updated the forecast this hour to adjust the hourly trends for
temperatures and dew points. Some of the more sheltered valleys in
the east have dropped off a bit. Have adjusted the temps for this.
As well, adjusted the pops as some showers may cross the area
later tonight as the MCS tracks by to the north. Any thunder
should hold off till after dawn. By 15Z tomorrow, convection
should refire over the area south of the boundary as it begins to
slide south through the morning hours. Adjusted pops to address
this change. Strong convection should still hold off till later in
the day after max heating. A new zfp has been sent out with this
update.

UPDATE Issued at 720 PM EDT FRI MAY 26 2017

Issued an update to adjust for the hourly trends over the area.
Temperatures in the far eastern valleys appear to decouple later
tonight before the extensive cloud cover and showers move in.
Adjusted for these updates.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 400 PM EDT FRI MAY 26 2017

The latest surface map features a modest ridge of high pressure
aligned from the Ohio Valley down through Florida. Broad low
pressure is located across Missouri and Oklahoma, with a warm
front aligned to the east into central Indiana. Aloft, the flow is
fairly zonal across the southern half of the CONUS. Further
north, a short wave trough is pulling away from southern New
England, with another deeper trough aligned from south central
Canada down into California.

Eastern Kentucky has enjoyed a welcomed dry day, with dew points
down into the mid 50s, and temperatures in the mid to upper 70s.
Unfortunately, this tranquility will be short-lived, as a return
to stormy conditions across the area is anticipated into the
Holiday Weekend.

Tonight, an MCV, currently located in northern Illinois, will
track east. Organized convection will track east and southeast,
with most of the model guidance showing activity mainly staying
just north of our area. Will allow for some slight to chance POPs
after midnight; however, given a stout cap in place, will keep out
the mention of thunder. Temperatures will drop off into the low
to mid 60s for most, although there may be a few sheltered valleys
that dip into the upper 50s, given the early clearing and drier
dew points in place.

On Saturday, the leftover convection to our north will likely
bring a surface boundary closer to the I-64 corridor. Another
instability axis may also develop closer to the TN/KY border. The
model guidance is erratic with timing and placement of the
convection for tomorrow afternoon. As such, have stuck with mainly
a persistence forecast, keeping chance POPs, peaking in the
afternoon. Model soundings remain supportive of a few storms
possibly approaching severe limits.

Saturday night, a short wave trough will be moving into the Ohio
Valley, with organized convection likely approaching the area
after midnight. There is still some uncertainty on the timing and
to some degree the placement of the MCS. Have continued with
likely POPs across the western half of the area, with somewhat of
a weakening trend to the complex towards dawn as it heads further
east into our area, as is more typical with these types of systems
as they move further away from the main forcing. The greatest
threat with this complex will be damaging wind gusts and also
isolated flash flooding given the recent wet conditions.

.LONG TERM...(Sunday through Friday)
Issued at 416 PM EDT FRI MAY 26 2017

A low pressure system will be traveling NE across the Mid-
Mississippi Valley Sunday morning, with KY in the warm sector (warm
front to our north and cold front approaching from the west with
strong southerly flow). Models are all still pointing at a MCS
initiating in this unstable atmosphere to our west Saturday/Saturday
 night and traveling eastward into our region. However still a large
amount of uncertainty to start out the period on Sunday morning as a
MCS is expected to be somewhere in the area. Models are still very
inconclusive as to where the MCS will actually be located, or if it
will even be impacting our CWA at all. The CAMs are not much help,
with the ARW pegging all convection to our south Sunday morning, the
Hi-res NMM is much slower and much farther north over central
Kentucky by 12Z, and the NAM12 has a line spreading across our CWA
during this time frame.

As such, ended up sticking more with the model blend during the day
Sunday given the high uncertainty. This keeps chance to likely pops
across the CWA into the afternoon as well, at which point the
unstable atmosphere is likely to produce more convection across the
region just ahead of the cold front. Based on latest forecast
soundings, instability is quite impressive, as are lapse rates, with
large hail and high wind gusts still looking to be the primary
threat. CAPE values are ranging from 3,500 j/kg to 4,000 j/kg Sunday
afternoon, with LI`s between -9 and -11, with good drying aloft to
help aid in hail growth.

The cold front is expected to pass eastward across our CWA Sunday
night into Monday morning, with best pops and convection expected
over the far SE portion of the state just ahead of the frontal
passage. Rain should move out of far eastern KY during the day
Monday with a drier airmass moving in behind, allowing skies to
clear out and temperatures to rise to near 80 under westerly flow.
Dry weather will persist into the day Tuesday as well.

SW return flow will return for Wednesday with some precip expected
to make it back into the CWA. Based on the latest GFS20 soundings, a
strong cap will be in place Wednesday morning, so did not include
thunder until the afternoon. Instability then increases nicely
through the afternoon. Models are in good agreement that pops will
remain in place, at least over our southern CWA to round out the
forecast period.

Temperatures will be fairly stead through the period, generally in
the upper 70s to around 80 during the afternoon. Sunday night will
remain relatively warm with the clouds and ongoing rain ahead of the
cold front, with lows in the low to mid 60s. After that point, lows
will generally be in the mid and upper 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 214 AM EDT SAT MAY 27 2017

VFR conditions will be replaced with a period of MVFR conditions
towards daybreak through the remainder of the Saturday morning
hours as the low levels moisten up overnight. A few showers may
accompany the lower cigs. Cloud heights will return to VFR by
early afternoon. The threat for showers and storms will develop as
we head through the afternoon and evening hours on Saturday, but
still some question on how much coverage we will see with this
activity. Thus, have gone mainly VCTS in the TAFS, but more
prevailing in the south, where there might be a slightly better
chance for thunderstorms. Strong winds will be seen around the
thunderstorms that do develop today. Activity will wind down by
late evening with a lull expected overnight Saturday night.

&&

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

$$

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


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