Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 210855

National Weather Service Jackson KY
455 AM EDT Fri Apr 21 2017

.SHORT TERM...(Today through Saturday)
Issued at 455 AM EDT FRI APR 21 2017

A cold front has dropped south of the Ohio River this morning,
stretching from roughly CMH southwest to just northwest of LEX to
DYR. This boundary will continue to drift southeastward through
the morning. The GFS stalls this boundary out just south of the
Kentucky-Tennessee state line by this evening. The ECMWF and NAM
are similar but stall the boundary out slightly further north...
possibly by as little as 50-75 miles. There is good agreement
among model solutions, bringing a wave of low pressure eastward
across the TN Valley just south of the Commonwealth through the
day Saturday.

For sensible weather, and with the frontal boundary draped across
the region and more particularly across our southern zones today,
had to keep higher PoPs in place across the southern half of our
forecast area. We will probably see a lull in activity through the
morning, but expect convection to refire along the boundary
through the afternoon with the help of diurnal heating. The front
drifts slightly further south late this afternoon and evening.
Then the wave of low pressure will brings rain back into our area
by late tonight. Rain continues to affect the area through the
remainder of the short term period. Thunder will generally be
restricted to areas along and south of the frontal boundary.

There are considerable differences showing up with respect to
QPF Saturday, with the ECMWF showing some hefty amounts through
the upcoming event. Overall models have not been real consistent
with QPF totals. But with the boundary draped from west to east
across the region and the potential for some training to take
place, we may need to consider some hydro headlines with future
updates. Will pass on concerns to upcoming shifts.

.LONG TERM...(Saturday night through Thursday)
Issued at 455 AM EDT FRI APR 21 2017

The models are in good agreement aloft in the first part of the
extended. This entails a developing closed low descending into the
Tennessee Valley and through Kentucky. This low tracks slowly across
the area this weekend with the GFS reflecting the strongest and
furthest south position while ECMWF and CMC are more northerly -
closer to eastern Kentucky. By Monday morning the upper low will be
passing south and east of the area with the GFS continuing to be the
deepest and furthest south solution - though the ECMWF is similar
while the CMC weaker and more northerly. In fact, the ECMWF and GFS
move the low almost in lock step off the Southeast Coast by Tuesday
morning lending support for the GFS`s more aggressive scenario. For
this feature, will favor the more extreme and classic closed low
solution of the GFS as the ECMWF plays a bit of catch up. Heights
will rebound over Kentucky in the wake of the low while the pattern
becomes more active to the northwest of Kentucky. As it does so,
more energy will brush by the state while broad troughing develops
over the northwest quarter of the country into midweek. This mid
level trough will sharpen up heading into Thursday with an axis over
the desert southwest in the ECMWF and more northerly for the GFS.
This will evolve into a closed low for the ECMWF over the High
Plains on Thursday while the GFS`s version is much further west. The
downstream effects will relate to the strength of a burgeoning ridge
through the Southeast and deep into Kentucky. The model
disagreements during this latter period lowers confidence in the
specifics of the forecast at this time step.

Sensible weather will feature a large sfc low pushing through the
Southern Appalachians as it moves east toward the Atlantic Coast.
This will take its heaviest rains east along with it by Sunday
morning. However, plenty of wrap around lighter rains will follow
through the rest of the weekend and into Monday morning. This
lingering rain, plenty of clouds, and being on the northwest side
of spring sfc low will make for a cool end to the weekend and
slow a temp rebound on Monday. Warmer weather and more sunshine
should arrive in full force Tuesday continuing through the rest of
the upcoming week. As part of this rebound, a warm front lifts
through and becomes active on Wednesday afternoon and evening for
our northern counties with a potential for showers and
thunderstorms. By Thursday, very warm conditions will be in
control of our weather due to ridging aloft and strong high
pressure off to the east resulting in temperatures climbing well
into the 80s.

Made some low temperature adjustments for ridge to valley
distinctions during the latter half of the extended forecast as
we dry out and move out of a weak CAA pattern. As for PoPs, mainly
just enhanced them through Sunday morning as the core of the low
passes through the region.


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

An approaching cold front will bring an uptick to shower and
thunderstorm activity through the remainder of the overnight,
generally from west-northwest to east-southeast. Flight conditions
are expected to gradually deteriorate through dawn into solid MVFR
territory. May see some improvements through the middle portion of
the day as the boundary drifts further southward. Northern
terminals such as SYM, SJS, and JKL may even see a break in
activity for several hours. However, a wave of low pressure to the
southwest will ride up into the region later tonight and bring
widespread rain into the area, eventually dropping flight
conditions into IFR or lower just beyond the end of the forecast
period. Generally speaking weather late tonight into Saturday
looks less than favorable for general aviation interests. Winds
will be generally from the southwest around 10kts or less, with
some gusts to about 15kts from time to time. Of course winds could
be a bit stronger near any thunderstorms. Winds will veer out of
the northwest behind the front as it drops through the area.





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