Area Forecast Discussion
Issued by NWS Jackson, KY

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798
FXUS63 KJKL 212358 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
758 PM EDT Sat Oct 21 2017

.UPDATE...
Issued at 758 PM EDT SAT OCT 21 2017

High pressure is maintaining control tonight; however, there are
some high clouds streaming in on southwest flow aloft. Late
afternoon dew points were similar to yesterday, so think that
valley locations will drop off more, especially in the east. There
may be a touch of fog along the river valleys, but this should be
a bit less than previous mornings, given the modified air mass.
Updates have been sent.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 300 PM EDT SAT OCT 21 2017

A ridge of high pressure will bring dry and warmer than normal
weather to eastern Kentucky through early Sunday evening.
Scattered to broken high level cloud cover will stream across the
area during that time. Highs on Sunday should be similar to today,
with max readings in the upper 70s to lower 80s expected. Tonights
low will also be warmer than normal, with minimum readings ranging
from the upper 40s to the mid 50s across the area. Cloud cover
will finally begin to increase Sunday evening, as a large trough
of low pressure aloft, and its attendant surface cold front,
begin moving across the region. We should see the first rain
showers begin moving into the southwestern portion of the forecast
area late Sunday night.

.LONG TERM...(Monday through Saturday)
Issued at 413 PM EDT SAT OCT 21 2017

The period is expected to begin with a closed low over the mid MS
Valley near the confluence with the OH River while a northern
stream shortwave trough is expected to be digging into the Upper
MS Valley and toward the Great Lakes. At the same time, upper
level riding is expected to be building along the West Coast of
the Conus. At the surface, an area of low pressure is expected to
be approaching from TN Valley region. A band of Gulf Moisture is
also expected to extend into the region with PW climbing to at
least the 1.25 to 1.50 inch range across the area at the start of
the period.

The closed 500 mb low is expected to track across the Commonwealth
through Monday evening and open up as it begins to merge with the
approaching northern stream shortwave. Meanwhile, the surface low
is expected to track to the west of the area on Monday before
deepening as it moves into northwest OH as the northern stream
shortwave trough approaches the Great Lakes. The northern stream
shortwave should work into the Great Lakes and OH Valley for Monday
night into Tuesday. Another shortwave trough is expected to
rotate through the trough and into the area at midweek. Overall,
the weather should remain unsettled into midweek with periodic
chances for showers. The GFS remains colder compared to the ECMWF
at midweek, but it is conceivable that the highest elevations
such as the top of Black Mountain could experience a flurry or two
mix in at midweek.

Upper level and surface ridging should work into the area behind
the midweek system for Wednesday night through at least early on
Friday while another trough moves into the Central Conus. Models
vary in the timing and evolution of this trough and this will
ultimately determine the timing of the next chance of precipitation
into the area late in the period as well as temperatures.

As for the initial system, an initial downslope component to the
flow should cut back on QPF in the southeast part of the area
early on Monday. However, sufficient forcing and moisture should
be in place for a decent soaking rain across the entire area. Most
locations should pick up at least an inch from Monday into Monday
night. Categorical pops of 90 were carried for Monday, however
measurable rain on Monday is nearly certain.

Temperatures will be initially mild and around 5 degrees above
normal on Monday, but will drop to below normal levels at midweek.
If enough clearing occurs on Wednesday night, frost could develop
in some sheltered valleys, particularly in the southwest. Temperatures
should again moderate during the second half of the week ahead of
the next approaching system.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
ISSUED AT 758 PM EDT SAT OCT 21 2017

Mainly high clouds will be seen through the period, with perhaps a
few cumulus developing late in the day on Sunday. Some MVFR fog
will also develop between 06 and 12z, but this should be limited
to the deeper river valleys, given the low crossover temperatures.
South to southeast winds will remain less than 5 kts through late
Sunday morning, before increasing to 5 to 10 kts during the
afternoon.

&&

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

$$

UPDATE...GEOGERIAN
SHORT TERM...AR
LONG TERM...JP
AVIATION...GEOGERIAN



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