Area Forecast Discussion
Issued by NWS Jackson, KY

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861
FXUS63 KJKL 242015
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
315 PM EST Fri Feb 24 2017

.UPDATE...
Issued at 140 PM EST FRI FEB 24 2017

Ample sun is helping to heat things up nicely this afternoon.
Based on hourly trends increased afternoon highs just a tad.
Winds have increased as well. From all appearances winds may peak
out at or just under Lake Wind Advisory criteria in our Blue Grass
counties. This appears less likely in our southwest but will keep
an eye on just in case. Models have generally trended a bit
slower with the cold front into the area tonight. However, based
on the HRRR timing still looks fairly decent for storms into the
area. So not expecting too much of a change form the current
forecast for the potential of severe weather tonight. Updated
zones and grids have already been issued.

UPDATE Issued at 1012 AM EST FRI FEB 24 2017

Updated temperatures with the morning update. Temps are slow out
of the gate in the east, due to a bit of valley fog and rising
faster than expected in the western valleys where gradient winds
have already mixed out the morning inversion. Also seeing a brief
jump in winds to announce the breaking of that inversion. Expect
they will die back down a bit over the next hour or so before
increasing again later this afternoon. No updates to the zones at
this time.

UPDATE Issued at 657 AM EST FRI FEB 24 2017

Mostly clear skies with a few high clouds is the story this
morning for most. Surface analysis shows surface low is
strengthening across NE MO this morning as it continues NE.
Overall forecast grids remain in good shape this morning. In terms
of the severe weather, The HRRR is aligning close to the other
CAMs at this point in terms of overall trends. Overall looking at
the newest data think the current forecast is on track and will be
looked at in subsequent updates.

&&

.SHORT TERM...(Today through Saturday)
Issued at 340 AM EST FRI FEB 24 2017

Early morning surface analysis shows an area of surface low
pressure continues to track NE out of the Central Plains into
Missouri and a warm front is now well north across the Upper Ohio
Valley region. WV imagery this morning showing plenty of upper
level moisture streaming into the region and this is leading to
scattered high clouds across eastern KY. Given these have only
been high clouds and the valleys have decoupled leading to decent
temp splits from some of the cooler valley locales. A mix of high
clouds and possible some diurnally driven CU will remain the story
through the day. LLJ will continue to move east in response to
strengthening system to our west. This will begin to mix down as
we move into the afternoon hours with gust of 25 to 30 possible
across the Bluegrass and Lake Cumberland region. The other issue
will be downsloping flow across the far east could also mix down
drier air, with RH values in the mid 30s to lower 40s possible.
This will have to be monitored today given the gusty winds, but it
will help that the gustier winds will be west of the drier
downsloped air.

All the focus shifts to strengthening system to the west as we
move into the late evening and overnight period. Models remain in
good agreement with trailing cold front approaching from the west
through the day. Initially convection will fire out ahead of the
front and track across portions of the Midwest. Some of these will
be single cell type storms, but as the system progresses east
storm mode will become more multicell/QLCS. Given the strength of
the cold front, lapse rates will remain steep through the evening
and into the overnight. Also models, specifically CAMS, are in
good agreement with the trailing cold front catching up to the
initial convection possibly providing further lift as it moves
into the region. One issue will be how much instability remains in
place at that point given the time of day and year. However, if
we are able to maintain this, the speed shear environment will be
substantial through a deep layer and low level shear is rather
impressive with some directional shear possible. This seem to be
picked up well by the SHERBE (that deals with high shear low CAPE
environments) with values near 1 or higher. Overall storm mode
will remain more QLCS in nature and therefore the tornado threat
will be very isolated. Think the better threat for tornado will
exist further north across the Ohio Valley where more boundary
interactions will take place. The main threat across eastern KY
will be damaging winds given the storm mode and strong jet, and an
outside threat of marginal hail given the airmass cooling aloft
causing freezing levels to drop to near 10 KFT. In terms of grids,
did opt to slow the progression of POPs to better align with the
CAMs and also added enhanced wording for damaging winds given the
greater threat.

Behind this front will be progressively cooler temperatures from
west to east early Saturday into Saturday afternoon. That said,
higher terrain locations could hit the freezing mark by the end
of the period. Given some wrap around moisture is possible did
keep some sprinkles and perhaps flurries across the higher
terrain into the afternoon. Given the high temperature will occur
at midnight the temp curve will be quite unorthodox, and
therefore leaned away from blended diurnally driven curve.

.LONG TERM...(Sunday through Friday)
Issued at 315 PM EST FRI FEB 24 2017

The extended portion of the forecast will be fairly active, with
alternating periods of wet and dry weather and warm and cooler
conditions. The period will likely start off dry, with slightly
above normal temperatures Sunday and Sunday night. The pattern is
then expected to shift on Monday, as a weak warm front moves through
the area, bringing persistent southerly flow and warmer air into the
region. Rain showers should begin to move into the area from the
southwest and west late Sunday night into early Monday morning. The
rain will overspread the entire area by late Monday afternoon and
early Monday evening, as an area of low pressure moves along what
will become a nearly stalled out frontal boundary. This pattern is
tentatively expected to persist through late in the day on Tuesday.
A wave of low pressure is then forecast to form along the western
end of the stalled front Tuesday night. This second area of low
pressure is then expected to push eastward on Wednesday, and will
drag another cold front across the lower Ohio valley and Tennessee
valley regions. This boundary may be just strong enough, and just
enough moisture an instability available, for a few thunderstorms to
form along and just ahead of the front, as it moves across the
region. Once the front moves past us Wednesday night, any
thunderstorms should give way to all rain showers. We may even see
enough cold air filter in behind the system to allow some snow to
mix in with whatever rain is left. The last of this precipitation
should be out of the area by late Thursday morning. Thursday and
Thursday night should be mostly dry. There is an outside chance that
a few rain and snow showers will move across the area along and
north of I64 to end the period, with due to uncertainty, this should
be taken with a grain of salt.

Temperatures in the extended on average will be above average each
day, with the warmest days being Monday, Tuesday, and Wednesday,
when the highs will be in the 50s and 60s. Closer to normal values
should be experienced on  Thursday, when the mercury is forecast to
max out lower 50s. Nightly lows should be in 30s, 40s, and 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 140 PM EST FRI FEB 24 2017

Generally high clouds out there this afternoon with a little Cu
mixed in for good measure. Southerly winds have kicked up nicely
at around 10 kts with gusts to about 20 kts. Gusts are a bit
higher to our west and up in the Blue Grass, reaching to about 30
mph. Focus shifts to tonight with a strong cold front approaching
the area as it moves eastward across the region. This system is
expected to produce some strong to severe thunderstorms across the
area with a primary risk of damaging winds. The risk for severe
weather becomes greatest as you move NW toward northern KY and
portions of the Ohio Valley. A line of convection associated with
the front appears to move into the SME area by around 04Z and exit
to the east of SJS by around 08Z. Timing is still a bit uncertain
but will likely have a more approximate timing of storms into our
terminals by next issuance. CIGS and VSBYS will drop into MVFR
range with and for a several hours behind the front. Winds will be
quite gusty again Saturday, from the west at around 10 kts
gusting to about 20 kts.

&&

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

$$

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



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