Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 151120
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
620 AM EST Sun Jan 15 2017

.SHORT TERM...(Today through Monday)
Issued at 332 AM EST SUN JAN 15 2017

Surface analysis shows area of high pressure centered to the NW
this AM across IA/IL region and quasi stationary boundary is now
across portions of the TN Valley. Based on the upper level data,
would suspect the 925mb boundary still resides across the region
and 850mb just to our north. That said, WSR-88D radar does
indicate a line of shower/drizzle has developed across the center
of the CWA and is near where the SPC mesoanalysis shows weak
forcing at the 925mb level as mentioned above. This will progress
south through the morning and kept as a drizzle mention given some
areas are seeing light drizzle outside this line. Overall the
HRRR/CONSSHORT seemed to be handling this idea and therefore
nudged my POPs in that direction. Based on the obs this morning
would think fog is more of the patchy dense variety and therefore
kept that going through early morning before tapering through mid
morning.

The previously mentioned surface high pressure will progress east
today with winds veering around to the NE by this afternoon. The
850mb front will remain north as mentioned before, as a mid level
wave/PVA rides along the baroclinic zone. These two forcing
mechanisms combined with saturated column will lead to decent
chance of rain showers late this afternoon into this evening
mainly north of the Mountain Parkway. While this is a decent shot
of rain showers, the QPE will remain light with only a couple of
hundredths of an inch expected. POPs will wane through the
evening from west to east as better forcing pushes east. Given the
moisture in place did opt to add patchy fog in for a good portion
of the region through Monday morning.

For Monday did keep slight POPs in the north and far NE, but this
may have to be looked at further. The only fly in the ointment
here will be the aforementioned quasi stationary will likely lift
back north, and therefore could lead to slight POPs ahead of the
eastward progressing cold front. Better POPs for the cold front
will take place beyond this forecast period.

.LONG TERM...(Monday night through Saturday)
Issued at 434 AM EST SUN JAN 15 2017

Models start out in decent agreement, but soon go their separate
ways concerning wx systems and precip potential. There is agreement
that it will remain mild. It`s a question of how mild.

For specifics, a low pressure system will be passing northeast over
the middle of the CONUS Monday night. Its cold front will push
into KY, with warm air advection ahead of it. This should keep
temps nearly steady on Monday night. Showers along the front
should be arriving from the northwest on Monday night, and lasting
into Tuesday. This is when the first model differences start
showing up. The ECMWF is more pronounced and faster with an upper
level wave supporting the storm system, which allows the ECMWF to
advance the cold front well to our southeast by Wednesday morning.
Meanwhile, the GFS is weaker and slower with the upper level
system, and still has the front near the KY/VA line early
Wednesday. The NAM is in between. The result is a difference in
precip/POP for early Wednesday, and a variation in Tuesday
night/Wednesday morning low temps. The forecast is a compromise at
this point.

There is agreement for a period of dry weather from Wednesday
afternoon into Thursday, even though upper level pattern differences
continue to grow. The upper level differences affect the forecast
again beginning late Thursday. The GFS has a shortwave trough
dropping southeast out of Canada and phasing with the slower
aforementioned upper level wave, morphing into one large trough over
the northeast CONUS and Appalachians. This would bring cool temps
and stratocu. The ECMWF does not phase the two systems and
remains flatter with the flow over the northeast CONUS. Instead,
the ECMWF becomes more amplified with a trough/upper low over the
middle of the CONUS on Thursday. The resulting system pulls
moisture back north, allowing for clouds to increase from top
down on Thursday, and an area of showers moving through the JKL
forecast area from SW to NE on Thursday night and Friday. The
slower and weaker GFS takes this system by mainly to our south
late Friday and Friday night. There is a large amount of
uncertainty with this system, and have used low chance POPs
Thursday night into Friday.

Finally, by Saturday there is loose agreement for an upper level
ridge to be positioned just to our east, supporting mild and dry
conditions.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
ISSUED AT 620 AM EST SUN JAN 15 2017

Most sites are starting the period flirting or exceeding airport
minimums for CIGs, however VIS is varying more across the sites.
While no sites are seeing drizzle this hour, some portions of the
region are still seeing some drizzle. There will be improvements
as we move toward the late morning into the early afternoon where
most sites will see low MVFR CIGs. A upper level wave will
interact with upper level front to bring rain showers by late this
afternoon into this evening. Best chances will reside along and
north of the Mountain Parkway. Guidance and models soundings would
suggest we lower CIGs once again tonight and would think at least
IFR CIGs are possible. Light winds are expected with wind out of
the NE through most of the period before becoming more east to
round out the period.

&&

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

$$

SHORT TERM...DJ
LONG TERM...HAL
AVIATION...DJ



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