Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 230558

National Weather Service Jackson KY
158 AM EDT Tue May 23 2017

Issued at 158 AM EDT TUE MAY 23 2017

IR SAT continues to show high clouds streaming into the region as
an upper level wave moves NE across the TN Valley. Given the
drier air in the lower levels anything on radar is likely virga
at best at this point. However, does look like much the initial
precip will be high based, with KCHA reporting -RA with 9 KFT
cloud bases. Right now will leave POPs as is and evaluate more for
the upcoming forecast package. Otherwise updated grids with
latest obs and trends.

UPDATE Issued at 1110 PM EDT MON MAY 22 2017

Hourly grids were freshened up based on recent observations, which
led to no substantial changes at this time.

UPDATE Issued at 835 PM EDT MON MAY 22 2017

The region remains under the influence of a broad trough that
encompasses much of the Conus east of the Rockies. Within this
trough, a shortwave was moving from the Lower MS Valley and into
the Southeastern Conus. This shortwave is expected to track into
the Southern Appalachians tonight and then northeast of the area
during the day on Tuesday. This system is still expected to bring
a threat of isolated to scattered rain showers late tonight and
on Tuesday mainly across the southeast parts of the area. A
thunderstorm cannot be ruled out on Tuesday as well. As for
tonight and tomorrow, the inherited forecast looks on track with
only slight adjustments to hourly temperatures and dewpoints.


.SHORT TERM...(This evening through Tuesday night)
Issued at 430 PM EDT MON MAY 22 2017

19z sfc analysis shows high pressure in place over Kentucky,
though it was not effective enough to keep the high clouds at
bay. These, along with light north winds, have helped to keep
temperatures contained in the 60s through the afternoon for most
places. Readings did hit the low 70s in the far south but only
mid to upper 60s, so far, elsewhere. Meanwhile dewpoints are
running in the mid 40s to lower 50s.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict a deep and broad trough
over the mid section of the nation amplifying and dipping
southeast into the mid Mississippi Valley during the next 36 to 48
hours. This will place eastern Kentucky in broad southwest flow
with plenty of energy breaking free to ride over the JKL CWA from
Tuesday afternoon into Wednesday. Toward the end of the period
the GFS solution starts to separate from the ECMWF with the core
of its trough digging a bit closer to Kentucky. Will favor a
general blend through the period with a lean toward the higher
resolution HRRR and NAM12 models through the first part.

Sensible weather will feature a quiet night with some ridge to
valley distinctions opening up after sunset but mitigating late in
the night due to increasing clouds from the south. These clouds
will be the vanguard of a sfc low moving into the southern
Appalachians tomorrow with a few showers possibly sneaking past
the border and into our CWA by dawn. The shower chances will
continue in the far east Tuesday with a few thunderstorms possible
by mid afternoon in these areas. A better chance of showers and
storms then develops to our southwest - pushing in later Tuesday
night - likely washing over the bulk of the CWA by sun-up

Again used the CONSShort and ShortBlend as the grids` starting
point with some adjustments to lows tonight owing to a ridge to
valley split developing early but mixing out in the east late. As
for PoPs, did tighten them up along our southern and eastern
border late tonight into Tuesday.

.LONG TERM...(Wednesday through Monday)
Issued at 347 PM EDT MON MAY 22 2017

Models are in good agreement with mid and upper level features
through DY5 Friday, then increasingly diverge in solutions from
there. Amplified and somewhat progressive flow will dominate the
pattern through the extended. Upper level low and associated deep
long wave trough will track slowly across the eastern half of the
CONUS through week`s end. Short wave ridging will then transit the
region before a second upper level low or trough drops out of Canada
and into the Midwest and/or Great Lakes region. Most of the
differences showing up after DY5 center around the evolution and
timing of the second main storm system. The 0Z ECMWF is fastest with
this system and the 6Z GFS the slowest. The 0Z Canadian appears to
split the difference. The 12Z Canadian is showing better run to run
continuity than the 12Z GFS and even trends closer to the ECMWF. The
GFS suggests some phasing of the Canadian low with energy moving out
of the Pacific, causing a futher deepening and digging of the system
across the plains and into the Great Lake, a much slower and
stronger solution overall. As a result confidence is quite low for
the last 48 hours of the period.

With respect to sensible weather, unsettled weather with periods of
showers and thunderstorms will tend to keep daily highs near to or
below normal levels for this time of the year and overnight lows
above normal. Good forcing coupled with some instability will
probably bring the threat of some thunder to the area on Wednesday.
In addition, lowering freezing levels may allow for some of the
showers/storms to contain small hail/graupel at times.

A short lived window of dry weather can be expected across eastern
Kentucky Friday, as the aforementioned transient short wave ridge
moves across the Ohio and Tennessee Valleys. The threat of rain
returns to the area Friday night and lingers through the weekend.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)

The TAF period will be met with VFR and this is expected to be the
prevailing through the period. We are watching an upper level
wave to our south that is bringing mostly high clouds into the
region this early morning hour. This nearby wave could induce
showers and perhaps a few isolated thunderstorms for Tuesday into
Tuesday evening. The better forcing should be in the TN Valley
and therefore keep best POPs nearer the VA border with a sharp
cutoff to the NW. Did add some VCSH and -SHRA to most of the sites
given this nearby disturbance, but confidence remains low on how
much activity in fact makes it into the region given the low level
flow. Winds are expected to remains light through the period.




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