Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 240646 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
146 AM EST Sat Feb 24 2018

.UPDATE...
Issued at 145 AM EST SAT FEB 24 2018

Showers are starting to fill in as scheduled, as a low level jet
noses in from the southwest, and a surface boundary bisects our
area. Merely freshened up the hourly temperatures through the
night. Updates have been sent.

UPDATE Issued at 1121 PM EST FRI FEB 23 2018

Late evening update to lower temps in the eastern valleys as we
were meeting or just below advertised mins. Only dropped them a
few degrees as incoming cloud cover should retard any serious
drops through the remainder of the night. Still can not rule out a
period of heavier rainfall through the morning hours Saturday
due to aforementioned jet coupling and corresponding enhanced
lift over portions of our area. But models are still undecided on
exact amounts and location of potential heavier band. Thus was
hesitant to make significant changes at this time. Averaging model
QPF and it would appear there could be a half to three quarter
inch swath of rainfall across some portion of our area through
Saturday morning. For now passed on concerns to oncoming shift for
reevaluation.

UPDATE Issued at 833 PM EST FRI FEB 23 2018

Short wave disturbance will push across the area late tonight into
early Saturday morning. Nose of an H850 LLJ, between 40 and 55
kts depending on what model you look at, will provide some
convergence in the lower levels across a good part of our area
towards sunrise. Area will also be near the right rear quadrant
of a relatively weak but definite upper level jet streak. It
appears that these two features may go through a short period of
coupling, perhaps providing a bit more enhancement to our initial
QPF forecasts across the south. At present there is some
disagreement between the higher resolution convective allowing
and synoptic models in the details of exactly where the core of
more intense precipitation will occur. The 12Z ECMWF and 18Z GFS
both show a relative max across our southwest of between three
quarters and an inch of rainfall. The 18Z NAM is lighter, a bit
slower, and further northwest with the heaviest rainfall. The HRRR
has been waffling with the track of more intense rainfall. Will
be watching trends in the HRRR/RAP and compare to the initial few
hours of the 0Z run as they become available before deciding
whether to increase QPF across our south with the late evening
update.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 450 PM EST FRI FEB 23 2018

Record warmth occurred again today as a warm front lifted
northward and sunshine broke through the clouds. It created enough
instability for scattered showers to percolate this afternoon,
along with a few isolated, sporadic lightning strikes. A few
showers were ongoing at forecast issuance, but have been on the
decline.

Models depict the frontal boundary slowly sinking back south into
our area this evening, with more showers developing. However,
there is disagreement on the rainfall amounts and the axis of the
precip. That being the case, confidence in forecast specifics is
low for this evening, and nothing more than broadbrushed chance
POPs were used. Both models show deep layer RH increasing
overnight, and a greater potential for showers. MOS POPS are quite
high for tonight as well. Taking this into account, have hit the
POPs hardest toward dawn. Showers should last into the day on
Saturday. The frontal boundary is expected to lift northward again
on Saturday, and forecast soundings also show weak instability
developing during the day. A slight chance of thunder is included
in the forecast for Saturday. Barring training, rainfall amounts
do not look overly impressive tonight and Saturday. If training
occurs and localized amounts are heavier than forecast, some water
problems can`t be ruled out. With a flood watch already in place,
will leave run. However, the heaviest rain will probably occur on
Saturday night.

On Saturday night, a strong low pressure system tracking through
the Midwest will bring a definitive cold frontal passage and a
band of showers, and possibly thunderstorms. Brisk low level flow
from the southwest will develop ahead of the front. If enough
instability can develop to mix down environmental winds, severe
weather can`t be ruled out. However the better chance is further
west. The front and its showers will be progressive, so that once
it passes overnight and early Sunday morning, our hydro concerns
will end for a while.

.LONG TERM...(Sunday through Friday)
Issued at 323 PM EST FRI FEB 23 2018

A cold front will exit southeast Kentucky on Sunday, and rain
chances will decrease as the day continues. While the 12Z GFS pushes
the front far enough southeast Sunday night that rain chances would
come to an end, the 12Z ECMWF shows another wave moving northeast
along the front and thus keeping at least a slight chance of showers
in the far southeast into Monday. Our standard blended model
approach actually takes this into account and our forecast will push
rain chances back north Sunday night, with slight rain chances
lingering into Monday afternoon in the far southeast. Forecast rain
amounts Sunday morning will mostly be less than 0.25 inch. Any rain
from Sunday afternoon into Monday will be on the light side with
amounts of 0.10 or less.

Weak upper level ridging then builds into the area and a surface
high slides across the OH valley, before moving to the east coast
Tuesday night. This results in dry weather for Tuesday. Rain chances
return by Wednesday as short wave energy moves northeast from a
western U.S. trough. Rain chances then continue until another cold
front moves through the area on Thursday. Dry weather will then
return Friday, though a few showers may linger in the east to start
the day.

Temperatures will remain above normal with only a very slight
cool down with the frontal passage on Sunday. Temperatures return
to close to normal values with the passage of the late week cold
front.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
ISSUED AT 145 AM EST SAT FEB 24 2018

A low level jet will bring widespread showers to the area through
Saturday morning. Have left out the mention of low level wind
shear, as it appears marginal between 09 and 13z. Expect
ceilings/visibilities to drop down to MVFR/IFR at times. Showers
will become more scattered in nature in the afternoon, as a warm
front lifts north of the area. Surface winds will be variable at
around 5 kts through Saturday morning, before becoming southwest
at around 10 kts, with gusts of 15 to 20 kts at times during the
afternoon and into the evening hours.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Sunday morning for KYZ044-050>052.

&&

$$

UPDATE...GEOGERIAN
SHORT TERM...HAL
LONG TERM...SBH
AVIATION...GEOGERIAN



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