Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 231751
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
151 PM EDT Fri Jun 23 2017

.UPDATE...
Issued at 1052 AM EDT FRI JUN 23 2017

Forgot a zero in my 1050 AM discussion. Storm relative helicity
should be 400 not 40.

UPDATE Issued at 1050 AM EDT FRI JUN 23 2017

We continue to monitor the evolving weather situation regarding
the interaction of the remains of Tropical Storm Cindy and the
approaching cold front. The 12Z NAM has shifted the heaviest
swath of rain northwest with the 2 inch and above amounts confined
to the extreme northern part of the forecast area, mainly over
Fleming County. However even at this short time frame would not
focus on the details but on the overall trend. Regardless showers
and thunderstorms this afternoon and evening will be efficient
rainfall producers with precipitable water in the 2 to 2.5 inch
range. Flash flood threat remains in place, with the biggest
threat over the northwest one-third of the forecast area.

The severe weather threat continues to be of concern. Parameters
point towards the possibility of a few tornadoes this afternoon
into the evening. The latest short range guidance soundings
indicate surface to 1km storm relative helicity approaching or
even exceeding 400 m2/s2 late this afternoon and evening as the
remains of Cindy approach. Some rotating storms will definitely be
possible and with lifting condensation levels low, any rotating
storms may be capable of producing a brief tornado. How much
instability will be realized is still in question, but satellite
indicates there should be enough breaks and enough insolation to
at least increase the low level lapse rates, though mid level
lapse rates do not look too impressive. Main severe thunderstorm
threats continue to be isolated wind damage and a few brief
tornadoes. Overall forecast is on track but will continue to
update NDFD for latest observational trends.

UPDATE Issued at 759 AM EDT FRI JUN 23 2017

Ongoing forecast was in decent shape, and the only change was to
blend early morning obs into the forecast.

&&

.SHORT TERM...(Today through Saturday)
Issued at 531 AM EDT FRI JUN 23 2017

The remains of Tropical Storm Cindy were very obvious in radar
and satellite imagery over AR early this morning. Meanwhile, a
cold front over northern MO and northern IL was moving southeast.
Models are in general agreement on the evolution of these features
during the period. Interaction with the prevailing westerlies will
continue to carry the tropical remnants east northeast ahead of
the cold front, with a track expected to be through KY. Low to mid
level wind fields will strengthen as the low approaches, and
continue to transport very moist air into the area, with
precipitable water expected to reach 2-2.5". A significant lull in
the precip is expected through much of the day, allowing warming
and destabilization. This would aid convective development as the
system arrives in the afternoon and evening. Both heavy rain and
severe weather are threats.

In term of rainfall, the deep tropical atmosphere will support
very efficient precip production. Models agree on the heaviest
amounts to be in our northwest counties. This is also where the
heaviest rain has already fallen. A flash flood watch was already
issued area wide, but the greatest threat looks like it will be in
our northwest counties. That being the case, confidence is not
all that high that we will see problems in our southeast counties.
However, with the watch already out, the onus is to prove that
hydro problems won`t occur there. Certainly don`t want to have
flips in the watch situation, so will leave it run in the
southeast.

In terms of severe weather, low level shear looks significant,
both in terms of speed and direction. The more questionable factor
seems to be the degree of surface based instability which will be
present. At most, it should be rather weak for this time of year.
However, with the degree of shear, any surface based instability
would be a concern. Dragging down environmental winds and adding
on a bit due to convection could be enough for damage. Also, the
low condensation heights along with the high storm relative
helicity in the soundings are supportive of brief tornadoes. Due
to the warm atmosphere and lack of strong instability, hail is not
a concern.

The tropical remnants pull out to the east this evening, wind
fields weaken, and the severe threat drops off. It will be a
little while longer until the cold front passes, and some
additional showers or thunderstorms could fire until it passes
late tonight and early Saturday. However, mid level drying is
expected when the tropical system departs, which will also allow
the heavy rain threat to diminish during the night. Much drier air
will arrive at the ground behind the front on Saturday.

.LONG TERM...(Saturday night through Thursday)
Issued at 358 AM EDT FRI JUN 23 2017

A period of drying is on the horizon and near record cool
temperatures possible early next week. That said, in the wake of
a cold front we will see falling heights and a building Canadian
surface high pressure. The models are in fair agreement on this
Canadian surface high pressure and matter of fact really strong
agreement in the GFS ensemble members. Also several reinforcing
waves will bring single digit 850MB temperatures into the region
for the first part of next week. These temperatures will be
significantly anomalous, with 500mb to 850mb temperatures expected
to be 3 plus standard deviations below normal for this time of
year.

At the surface, the coolest day may be Wednesday morning depending
on how cloud cover shakes out on Tuesday morning, but temperatures
in the low to mid 50s and some valleys could drop into the upper
40s. These kinds of temperatures will be close to record
temperatures for both days with JKL current record for Tuesday is
54 degrees and 53 degrees on Wednesday. However, our records at
JKL may be a little weaker compared to LOZ, where LOZ records
showing 48 degrees Tuesday and 50 degrees on Wednesday which may
be more difficult outside of valley locations. Temperatures by
Wednesday do warm, as the high pressure moves off toward the VA/NC
coast line and we see increased return flow. By Thursday, the
models show a little less agreement, but a wave could generate
some showers by the afternoon. Past this the CPC would suggest
more chances of precip becomes possible as we begin July.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 150 PM EDT FRI JUN 23 2017

Conditions will deteriorate late this afternoon and into the
evening as tropical depression Cindy and an approaching cold
front interact to bring showers and thunderstorms to the forecast
area. Early this afternoon the center of the tropical depression
was moving from northwest TN into southwest KY, while a cold front
extended from MI though northwest Indiana, central IL and on into
northeast OK. The low pressure system will continue to move ENE
while the the cold front sags southwest. Showers and thunderstorms
will become more widespread as the low pressure system and front
move closer.

Even ahead of the showers and thunderstorms MVFR ceilings will
prevail across the area, although many areas will lift to VFR for
a time this afternoon. Once the rain moves in ceilings will
gradually lower with some areas becoming IFR. Once the rain exits
tonight there will likely be a period of fog and low ceilings. The
cold front will be southeast of the area by Saturday morning and
conditions will improve quickly with VFR conditions expected
across most of the area by late morning.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch through Saturday morning for KYZ044-050>052-
058>060-068-069-079-080-083>088-104-106>120.

&&

$$

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



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