Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 222210
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
510 PM EST Wed Feb 22 2017

.UPDATE...
Issued at 510 PM EST WED FEB 22 2017

Per satellite trends, mid/upper level clouds starting to exit to
the east with low deck of clouds breaking up with southeast flow.
This will allow for some partial clearing this evening into the
overnight hours. Updated the sky cover to allow for this break up
in the sky cover. With less cloud cover, temperatures,
particularly in the valleys will likely take a more sizable
tumble this evening. Coop guidance suggest mid 40s as the bottom
for temperatures tonight and this seems reasonable with dewpoints
currently in the mid 50s over much of the region. However, will
dip lows into the upper 40s tonight and this should establish some
river valley fog. Updated forecast to put this fog mention into
the forecast. Finally, clouds look like they may try to redevelop
across central Kentucky towards dawn or early Thursday morning and
could trigger a few sprinkles. This was in line with the previous
forecast, but did slow down the arrival of the sprinkles until
closer to dawn in the Bluegrass region. With the increase in
sprinkles expected, cloud cover will also move back in, with fog
lifting as the clouds arrive in the morning. All updated grids
have been saved and sent to NDFD.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 400 PM EST WED FEB 22 2017

20z sfc analysis shows East Kentucky between a broad area of low
pressure to the northwest and another dropping into the northeast
Gulf of Mexico. The showers associated with this southern low have
just about dried up over the area with only some lingering
sprinkles around along with patches of lower clouds. These clouds
are trying to break up over Central Kentucky and in the I-75
corridor. Temperatures are responding to the returning peeks of
sunshine in the west with low and mid 60s noted while to the east
under the thicker clouds readings are in the mid to upper 50s.
Dewpoints, meanwhile, are in the low to mid 50s across the area.
Winds are generally from the south to southeast at 5 to 10 mph.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict the southern low deeply
diving west to east through southern Florida while southwest flow
will commence over Kentucky for tonight into Thursday. A
strengthening band of energy will pass through the Ohio Valley
Thursday afternoon as the southwest flow builds in the face of a
large trough moving through the northern Rockies and into the High
Plains Thursday night. The GFS is a bit faster and further east
than the ECMWF with this feature. All in all, though, a general
model blend looks reasonable through the short term given the
broad model agreement and limited differences seen for eastern
Kentucky.

Sensible weather will feature a few lingering showers in the far
east early this evening before we start to dry out overnight. Have
carried a chance of sprinkles an hour or so beyond the measurable
PoP before all pcpn comes to an end from northwest to southeast
this evening. Do expect the breaks in the clouds to fill back in
later tonight which should hamper radiational cooling and fog
formation. Have limited the latter to the valleys with a minima
of terrain based differences in temperatures overnight. For
Thursday, rather cloudy conditions will continue with moisture
left behind and the development of a warm front from a deep low
approaching from the west. Ahead of this low, sprinkles will be
possible and even a shower or thunderstorm as eastern Kentucky
will reside in the warm sector of the larger system. For Thursday
night the warm front will lift well north of the area with WAA
through the night setting up a good ridge to valley difference in
temperatures with very warm readings expected on the hilltops.
Will also allow for some patchy valley fog late at night in the
valleys.

Again started with the CONSShort and ShortBlend for the short
term grids. Did not make too many adjustments of note to
temperatures tonight owing to the moist environment but did open
up a distinct ridge to valley terrain differences in temperatures
Thursday night as WAA really kicks in ahead of the next cold
front. As for PoPs, did adjust them closer to the previous
forecast for Thursday afternoon which also matched up better with
the latest NAM12 - maintaining the slight chance values for this
time frame.

.LONG TERM...(Friday through Wednesday)
Issued at 240 PM EST WED FEB 22 2017

The long term portion of the forecast will be active, with several
systems affecting the area. Record warm temperatures will be on tap
to end the week, with a cool down in store for the weekend.
Temperatures will quickly warm again as we move into next week.

The first system to affect the area is a dynamic upper low and
associated surface low that will move out of the plains Friday and
into the Great Lakes region Friday night. The Day 3 Outlook from the
Storm Prediction Center indicates a marginal risk for severe storms
with this system with the slight and enhanced areas to our west and
northwest. Strong southwest flow ahead of the low will help to
shatter record highs at Jackson and London on Friday. Currently we
are forecasting 77 at Jackson on Friday and 76 at London. The record
highs for Friday, February 24 are 71 at Jackson and 70 at London.

Model soundings indicate the atmosphere will be capped for much of
the day Friday, and it appears there will be little or no shower
development in eastern KY on Friday. The most likely scenario for
Friday is for thunderstorm development to occur in the late
afternoon or early evening in Indiana ahead of an advancing cold
front with the storms evolving into a line and developing southwest.
There is good model agreement that the line will not move into
eastern KY until late Friday night. The best dynamics and
instability will exist to our west Friday evening and it is likely
the storms will be on a decreasing trend as they move across our
area Friday night. However, this will need to be monitored over the
next couple of days.

The cold front which will be focusing the thunderstorms is forecast
to pass to the east of KY by daybreak Saturday, and cooler air will
spread into the area for the remainder of the weekend. Temperatures
will still be above normal to begin Saturday but then near normal
temperatures should prevail for Saturday night into Sunday night.

The next system will approach the area from the plains Sunday night,
bringing more rain to start the week. However, there is considerable
model disagreement with the evolution and track of this system. The
GFS is further north and quicker to exit the system to our east,
with dry weather returning Tuesday, before the next system moves in
on Wednesday. The ECMWF is slower and further south with the early
week system, with rain chances lingering through Tuesday. The
blended approach used here favors keeping rain chances in the
forecast for Sunday night into Wednesday. In either case if
precipitation moves into the area quick enough Sunday night, there
is a remote possibility a few snow flakes could mix with the rain
late Sunday night before quickly transitioning to all rain early
Monday morning.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
ISSUED AT 510 PM EST WED FEB 22 2017

Skies will start off VFR this evening. However, partial clearing
spreading overhead will allow temperatures to quickly fall after
sunset with valley locations quickly reaching their cross over
temperatures. This will likely lead to some thick valley fog
tonight, likely impacting KSME, KSYM, KSJS, and perhaps KLOZ. This
impact will likely start after 06z with fog lifting at or around
13z. Winds will generally remain light out of the south or
southwest through the period.

&&

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

$$

UPDATE...KAS
SHORT TERM...GREIF
LONG TERM...SBH
AVIATION...KAS



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