Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 210553
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
1253 AM EST Tue Feb 21 2017

.UPDATE...
Issued at 1032 PM EST MON FEB 20 2017

Temperatures are now into the mid 40s in the colder eastern
valleys. This is in line with updated forecast from earlier. This
will put our final lows somewhere down into the mid 30s tonight
for those valley locations. Elsewhere to the west, winds may stay
a bit more mixed tonight, keeping temperatures from completely
falling off, like in the east. Thus, a bit milder overnight for
most areas in the west. No changes warranted at this time.

UPDATE Issued at 705 PM EST MON FEB 20 2017

Temperatures have already started their steep descend into the
low to mid 50s this evening in the eastern valleys. With the
degree of dry air mixed down tonight, should not take much for
temperatures in the deeper valleys to again reach into the 30s
tonight. With his said, have lowered the eastern valleys well
below current forecast values in the 40s. We will likely see at
least some mid 30s by tomorrow morning. Given the colder
temperatures forecast, also beefed up the fog a bit, again mainly
for valley locations. Fog shouldn`t be as bad or as widespread as
last night, so no plans to highlight the fog in the HWO. Just some
thin cirrus drifting over the area overnight and this shouldn`t
have much impact on the overall expected weather.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 430 PM EST MON FEB 20 2017

21z sfc analysis shows high pressure shifting off to the
northeast with deep low pressure taking shape over the Norther
Plains. The pressure gradient between these is tightening up to
the west. Here in eastern Kentucky, the winds are starting to
respond to the passage of the high by turning to the southeast
and south - but still rather light. Ample sunshine through high
clouds helped to propel temperatures into the upper 60s and lower
70s. Dewpoints decreased a bit during the middle part of the day
with a range from the upper 30s to mid 40s for most places.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict a strong ridge moving
from Kentucky east to the Southeast Coast tonight while a full
latitude trough splits apart with its southern extent closing off
over the western Gulf Coast. To the north of this developing low,
the northern portion will cross into the Great Lakes while some
energy runs out ahead of its trough axis and passes over Kentucky
into Tuesday morning. The main axis - though weakening aloft -
will make it into the state later in the day and slowly pass that
night along with some small height falls - more substantial in
the ECMWF. Given the general model agreement will favor a blended
solution for the larger scale while leaning toward the HRRR in the
near term along with the ECMWF for weather details from Tuesday
through Tuesday night.

Sensible weather will feature a rather warm evening with a
moderate ridge to valley temperature split developing under
variable amounts of high clouds and an inversion. Good drying and
mostly sunny skies today should limit the fog formation tonight to
just the valleys ahead of thicker clouds moving in towards dawn.
For Tuesday showers will push in from the southwest by mid
afternoon with plenty of clouds and mild conditions continuing.
The best rain chances will be later that night as a sfc low
passes by to the south coupled with the weak energy aloft. This
will make for another warm night with some places probably seeing
soaking rains - depending on the interaction of the departing 300
mb jet north of the state and any divergence aloft that it
generates over our area. For the most part the blended model
solution looked decent, though the NAM seems to cut off the
western extent of pcpn shield quicker than the ECMWF and GFS on
Tuesday night but this seems to fast so have not backed off on
the blended solution here.

Again used the CONSShort and ShortBlend as the starting point for
the grids through the short term portion of the forecast. Did
make adjustments to temperatures tonight to account for a decent
ridge to valley difference but readings should be similar Tuesday
night with the rain. As for PoPs, did adjust them for late Tuesday
into the night - translating the higher PoPs across the CWA more
cleanly.

.LONG TERM...(Wednesday through Monday)
Issued at 330 PM EST MON FEB 20 2017

The extended forecast period begins on Monday with a deep closed
upper low tracking northeast through the spine of the Appalachians.
As this feature tracks northeast, blocking over the New England and
Canadian Maritime region will hinder the exit of the back edge
precip moving through eastern Kentucky. This slow exit followed with
the approach of the colder air in behind on Monday night into
Tuesday may lead to a brief mix of rain and snow on top of Black
Mountain. In addition to this, models have been coming into more
agreement of a prolonged heavy rainfall event coming to an end
Monday evening into Monday night across eastern Kentucky. Some
lingering minor flood problems may be possible, if not just some
rivers running full. Both the Euro and GFS seem to have come to an
agreement on this with the Euro being slightly wetter. Will keep
this mention in the HWO.

Heading into the midweek time frame, a brief period of ridging moves
into the OH valley with a period of drying as southwest flow
increases ahead of the next incoming cold front. High temps on
Wednesday will climb into the upper 50s to low 60s with SW 10 to 20
knot winds bringing in an unseasonably warm airmass. In fact,
models are suggesting an overall drying trend to the approaching
front with the bulk of the moisture to the north over the Midwest
and into Ohio. Little if any precip is expected with this feature.

Passage of the front on Wednesday night will bring in a colder
airmass to the region by Thursday with a possible prolonged upslope
event taking shape for Thursday and Friday. At this point the
pattern brings in a longwave trough across the eastern CONUS into
the weekend. The northwest flow then brings a series of disturbances
in an upslope scenario. At this point, while the models hint at
temps being warm enough for rainfall during the day and snow showers
overnight, an upslope event with the correct wind component would
mean some convection and snowfall at warmer temps. For now, went
with a general snowfall at 34 degrees and below due to the
uncertainties in the models but this may need reevaluated. The
general trend is cooler towards the end of the extended but models
have backed off from the depth of the cold air. Due to this, will
leave any mention of snow out of the HWO as none is expected to be
impactful at this point.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 1253 AM EST TUE FEB 21 2017

VFR conditions will continue through Tuesday afternoon and likely
through the evening. Cloud bases will lower through the day, but
any MVFR ceilings should hold off until late in the evening toward
06Z Wednesday. Rain showers will increase in coverage this evening
and tonight through 12Z Wednesday as south to southeast winds
generally range between 5 and 10 knots. Pilots flying toward
LEX/SDF/CVG should be cautious of the potential for some 30-35
knot southwesterly wind shear within the lowest 2000 feet late
tonight into early Tuesday morning.

&&

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

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...SHALLENBERGER
AVIATION...GUSEMAN



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