Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 192353
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
653 PM EST Sun Feb 19 2017

.UPDATE...
Issued at 653 PM EST SUN FEB 19 2017

Narrow band of clouds continue to hold on just north of the I-64
corridor. While the erosion of the clouds has slowed some with
sunset, the subsidence building into the region should help to
gradually erode the remainder of the clouds as the night goes on.
Something to note is that we have a nice boundary showing up on
JKL radar this evening associated with the differential
temperature boundary from the cooler/cloudy areas in the north
today to the areas that cleared out to the south. This boundary
appears to be sagging southward towards our office. Behind the
boundary, valley locations have already reached the upper 40s. We
should see a sharp fall continue with temperatures in the valleys
this evening. MOS guidance is supporting some mid 30s and based
on current conditions, this doesn`t seem that unrealistic. Thus,
will drop the valley locations a bit colder tonight. Regardless,
temperatures will fall well under cross over temperatures, setting
up a good night of radiational fog. Current forecast has this
covered well. Also tweaked sky cover down overnight. Outside of
the clouds in the north early on, probably only dealing with some
high clouds moving in late tonight.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 335 PM EST SUN FEB 19 2017

19z sfc analysis shows high pressure moving over Kentucky. While
rather weak it has mustered enough strength to start the clearing
process through the southern two thirds of the CWA. With the
returning sunshine temperatures have rebounded into the lower 60s
in the south but still are in the low 50s under the clouds for
locations north of Interstate 64. Dewpoints, meanwhile, have held
rather steady in the mid and upper 40s along with light and
variable winds. Look for the ceilings continue to erode into the
early evening with most places seeing clear skies through sunset.

The models are in good agreement aloft through the short term
portion of the forecast. They all depict a strong ridge passing
over Kentucky and the Deep South tonight through Monday in advance
of a full latitude trough crossing thr Rockies. This trough starts
to split apart later Monday night with the southern portion
closing off as it exits into the western Gulf. Meanwhile, the
northern portion pushes quickly into the Great Lakes stretching
the energy with this trough. Some of that energy will look to ride
over eastern Kentucky early Tuesday ahead of the main trough axis.
Given the decent agreement among the models have favored a
general blend with a significant lean toward the higher
resolution HRRR and NAM12 in the near term.

Sensible weather will feature mostly clear skies to start the
night leading to good radiational cooling. With the fairly high
low level moisture in place we will likely see fog develop rather
early in the night in the valleys and spread through much of the
CWA - becoming dense late - particularly in the valleys. Have hit
this in the grids (and TAFs) and will highlight it in the
forthcoming HWO. Later shifts will need to monitor cloud cover and
vsby changes tonight for a possible SPS or Dense Fog NPW. The fog
will burn off quickly Monday morning with a very warm day on tap
ahead of the slowly approaching cold front. For Monday night, the
front starts to move into the state, but likely remain too far
west through dawn for any significant rain chances. Will also
apply some patchy fog to the valleys early Tuesday under
increasing and thickening high clouds.

Used the CONSShort and ShortBlend as the starting point for the
grids through the short term portion of the forecast. Did make
some adjustments to temperatures each night to account for a small
ridge to valley difference tonight and a bit larger one tomorrow
night. As for PoPs, kept them as initialized with no impact
expected before 12z Tuesday.

.LONG TERM...(Tuesday through Sunday)
Issued at 330 PM EST SUN FEB 19 2017

The extended portion of the forecast will begin on Tuesday with an
active and progressive pattern setting up. At this time, the main
features of concern will be a wave tracking across the northern
CONUS as well as another low tracking over the lower MS Valley
undercutting the upper level ridge along the Front Range. During this
time, eastern Kentucky falls in between the bulk of the forcing of
these two features leading to a bit less QPF over the area,
especially as it seems this boundary passing through the area begins
to shear out by Wednesday morning. The super blend seems to hint at
some lingering moisture behind this feature but with the new 12z
Euro showing no indication, will leave pops out on Wednesday.

By Thursday, a vigorous low ejects from the Front Range and into the
central Plains as strong southerly flow develops just east of the MS
River. Model profile indicate some good instability developing with
the formation of the warm front on Thursday and into Thursday night.
Therefore have introduced some thunder into the forecast during this
period. By Friday morning, the warm front has lifted north of the
area putting eastern Kentucky firmly in the warm sector. In fact,
expect highs to reach into the lower 70s across the area. For this
period, some of the best baroclinicity develops that has not been
seen for a few weeks. Model profiles indicate a renewal of some good
instability with the developed cold front. Have indicated some
thunder for late Friday and into Friday night as well. While severe
convection is still a low chance for eastern Kentucky, it is worth
noting that SPC has highlighted a slight severe chance in central
Kentucky for the Friday period.

After passage of the most significant cold front not seen in a few
weeks, temps on Saturday morning and into the day on Saturday will
either be slowly rising or steady through the day. At this point,
the bulk of the CAA is slow to enter the area with much of the
moisture exited by the time the colder air filters into the area.
While now apparent at this time, a post front would chance this
chance but it seems the profile dries and clears out after passage,
which also means for some of the coldest low temps of the
extended.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
ISSUED AT 653 PM EST SUN FEB 19 2017

Some MVFR cigs will hold on north near I-64 over the next hour or
two, before slowly eroding. Attention will then turn to fog
formation as we have fairly high cross over temperatures. This
will allow for an earlier onset of fog than normal late this
evening. This will allow the fog to become dense in the valleys
overnight. The fog may try to creep onto some of the ridges around
daybreak Monday, but confidence is somewhat low on this
potential. Fog will burn off Monday morning with VFR conditions
returning by 14z.

&&

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

$$

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



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