Area Forecast Discussion
Issued by NWS Jackson, KY

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722
FXUS63 KJKL 042135
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
435 PM EST Sun Dec 4 2016

.SHORT TERM...(This evening through Monday night)
Issued at 300 PM EST SUN DEC 4 2016

Active pattern on tap in the short term. The initial weather maker
for eastern Kentucky will be an area of low pressure aloft, that
is expected to move across the region this afternoon through the
overnight period. Scattered to at times numerous light rain
showers will move across eastern Kentucky through early this
evening. The rain should finally begin to taper off after 4Z
tonight, as the upper low moves off to our east. Eastern Kentucky
should be precipitation free by around 11Z Monday. Rainfall
amounts with this first system should be very light across eastern
KY tonight, generally a tenth of an inch or less. After several
hours of quiet weather, another area of low pressure is forecast
to approach the region from the southwest Monday afternoon and
evening. Rain showers associated with this second weather system
should have overspread the entire area by around 6Z Tuesday. This
second weather system will provide a more robust shot of rain. We
could see rainfall amounts Monday night into early Tuesday morning
rain from around 0.4 inches in our far north, to between 0.5 and
0.8 inches in our far south.

Temperatures should be running at or slightly below normal during
the day on Monday, with highs ranging from the mid 40s in our
northern areas to around 50 in our southern areas. Tonights lows
should bottom out with above normal values in the mid to upper
30s, due to the influence of cloud cover and precipitation.
Tomorrow nights lows look to be even warmer, as winds shift from
the east to south and increase in strength and cloud cover and
precipitation also increase in coverage. Monday nights lows are
expected to fall into the low to mid 40s, with a non diurnal
hourly temperature pattern also expected due to cloud cover and
wind influences.

.LONG TERM...(Tuesday through Sunday)
Issued at 434 PM EST SUN DEC 4 2016

There are three potential systems to deal with, and the unusual
situation where the greatest uncertainty is in the middle of the
forecast period.

System number one will be here as the period begins. Surface low
pressure is expected to be over middle TN at 12z Tuesday, with an
affiliated shortwave aloft just a bit further to the southwest.
The low should be tracking northeast along the western edge of the
Appalachians during the day while coastal development occurs over
the Carolinas. Rain is expected, mainly Tuesday morning. It looks
as if cold air advection will bring a nondiurnal temperature,
with temperatures starting to drop off Tuesday afternoon. The
coastal low will take over as the main low while the system is
pulling out Tuesday night, and surface ridging will build in just
to our north and bring quiet weather lasting into Wednesday.

The effects of the model controversy come Wednesday night into
Thursday for our area. It involves a shortwave moving east from
the central Rockies Tuesday night into Wednesday, and its
interaction with an upper low over southern Canada. The ECMWF
holds a substantial portion of this upper low over southwest
Ontario Wednesday, while the GFS allows it to take off to the
east and leaves a weaker portion behind. The aforementioned
shortwave phases with whatever of the upper low is left behind.
This results in the ECMWF having a stronger system than the GFS.
The ECMWF has weakened with its related surface system and is
slightly more progressive with it when compared to earlier runs,
which is a trend toward the GFS. The stronger and slower system
of the ECMWF would briefly pull in milder air and result in rain.
the GFS would have much less precip, but would allow for snow or a
mix. At this point, have continued to use a blend. The resulting
forecast has high chance pops Wednesday night into Thursday,
mainly in the form of rain, but does mention snow.

Better agreement comes to finish the period. Cold air advection
and northwest flow brings scattered snow showers Thursday night,
followed by the coldest air of the season so far strong high
pressure drops into the central CONUS from Canada and then heads
east.

Both the GFS and ECMWF show warm air advection and isentropic lift
bringing a potential for precip on Sunday, with borderline temperatures
allowing for rain or snow.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
ISSUED AT 1227 PM EST SUN DEC 4 2016

Look for VFR conditions through around 21Z today as we see a lull
from the rain for a few hours. Conditions are expected to
deteriorate to MVFR as low clouds and rain showers move back into
the area from the west between 22 and 23Z today. CIGS should
fluctuate between 2.5 and 3K. Conditions will worsen slightly
between 0 and 1Z, as an approaching cold front brings more
widespread showers and lower level cloud cover to eastern
Kentucky. That MVFR conditions should persist between 0 and 3Z
this evening. After that, we can expected a period of IFR CIGS as
rain showers and even lower level cloud cover invade the area.
These conditions should last until roughly 12Z tomorrow, before
things gradually improve through out the morning. MVFR conditions
should once again be in place as the rain departs and cloud levels
rise a bit from 12Z onward.

&&

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

$$

SHORT TERM...AR
LONG TERM...HAL
AVIATION...AR



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