Area Forecast Discussion
Issued by NWS Jackson, KY

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085
FXUS63 KJKL 212230 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
630 PM EDT Fri Apr 21 2017

.UPDATE...
Issued at 630 PM EDT FRI APR 21 2017

Convection is currently aligned along the Cumberland Valley,
close to the surface boundary near the TN/KY border. Some of the
embedded thunderstorms are slow-moving, and will have to watch
for locally heavy rainfall in places. Further west, an area of
showers and storms are moving in from the southwest, associated
with a short wave trough in the mid-levels. The HRRR seems to
have a decent handle on this feature and its timing. As such, have
beefed up the POPs a bit into this evening from southwest to
northeast. A lot of the thunderstorms will likely remain confined
to along and south of Highway 80 and the Hal Rogers Parkway, where
better instability will remain. Updates have been sent.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 311 PM EDT FRI APR 21 2017

Slow moving frontal boundary lies across Southeast Kentucky,
through Tennessee to Northern Mississippi. Showers and a few
thunderstorms are showing a diminishing trend early this
afternoon as a short wave travels east. This drier trend should be
short lived as more ripples of short wave energy interact with
moisture along the boundary. Locations in the southern portion of
the area should see widespread showers and thunderstorms by this
evening. Locations farther to the north should experience
widespread precip by around midnight when the front will be
lifting northward in response to a potent wave of low pressure to
the southwest. Thunder chances are expected to be limited to the
early evening hours until instability wanes with loss of daytime
heating.

For Saturday, the front should be located near the TN/KY border.
1005 mb low pressure is expected to be tracking through TN.
Numerous to widespread showers and thunderstorms are forecast to
develop and persist through the day and into Saturday night. High
precipitable water lifting over the slow moving frontal surface
parallel to the mid level flow will result in a few rounds of
heavy rain, possibly leading to localized high water problems.
Elected to hold off on a flood watch due to model uncertainty with
respect to rainfall amounts and locations of heaviest amounts.
Rainfall should decrease in coverage and intensity over western
counties late Saturday night when the low is forecast to be over
East Tennessee, though far Eastern Kentucky could stay under
showers for the bulk of the period.

While all locations can expect below normal temperatures, highs
Saturday will vary with respect to the frontal position, with
upper 60s in the far south contrasting with upper 50s central and lower
50 far north.

.LONG TERM...(Sunday through Friday)
Issued at 305 PM EDT FRI APR 21 2017

An upper level low will drop southeast across the Tennessee Valley
and across the southeastern United States Sunday into Monday. This
will keep a lingering chance of showers across the area through much
of the day on Sunday before tapering off heading into Sunday night.
Highs on Sunday will generally be in the lower 60s. Weak high
pressure will then build into the area Monday into Tuesday leading
to dry conditions and a bit of a warming trend. Highs on Monday will
be in the upper 60s to around 70, increasing to the mid 70s for
Tuesday.

An upper level trough axis will weaken as it moves from the central
United States into the the Great Lakes region Wednesday through
Thursday. This will help a weakening cold front drop down toward the
area through mid week but there is quite a bit of model variation
with the timing and placement of the front. Will therefore just
allow for some lower chance pops to overspread the area Wednesday
afternoon into Wednesday night. Highs on Wednesday will warm into
the lower 80s across most of the area.

Mid and upper level ridging will then build into the area Thursday
into Friday. This will lead to dry conditions and unseasonably warm
temperatures with highs both days in the mid 80s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 305 PM EDT FRI APR 21 2017

Less than ideal conditions for aviation will result from a slow
moving frontal boundary and potent wave of low pressure,
interacting in an environment containing much above normal
moisture.

For the early part of the TAF period, MVFR conditions associated
with shower and thunderstorm activity will affect mainly southern
sites that are closer to the current position of the front. MVFR
should impact all sites by late tonight when a large swath of
precipitation is forecast to develop ahead of the advancing wave
of low pressure. Showers and thunderstorms should then persist on
Saturday as moisture and forcing linger around this slow moving
weather system. Kept ceilings in the MVFR range, but IFR may be
necessary if the boundary layer achieves saturation.

Winds are forecast to be from the north to northeast, with speeds
staying under 10 knots.

&&

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

$$

UPDATE...Geogerian
SHORT TERM...Coniglio
LONG TERM...Lott
AVIATION...Coniglio



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