FXUS63 KJKL 140554 AAA
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
1254 AM EST Thu Dec 14 2017
Issued at 1254 AM EST THU DEC 14 2017
A surface cold front is closing in on our area, currently aligned
from near KFGX to just west of KBWG. Southwest to west winds of 10
to 20 mph, with gusts of 30 to 35 mph continue to howl. The
strongest winds remain just west of our area; however, a few gusts
to around 35 mph will be possible near and around frontal passage.
Have freshened up hourly temperatures, which continue to run mild
in the low to mid 40s out ahead of the front. The models typically
struggle with this leading edge air mass, and have tried to blend
into the existing curve through the rest of the night. Will stick
with the current lows; although, the low temperatures will likely
be achieved closer to the mid-morning hours. A few post-frontal
flurries still look possible as well.
UPDATE Issued at 915 PM EST WED DEC 13 2017
Increasing and lowering cloud cover continues to invade eastern
Kentucky on the southern fringes of a clipper system pushing
through the Great Lakes and mid-upper Ohio Valley. Gusty southwest
winds will veer westerly and then northwesterly later tonight with
the approach of an associated cold front. A dry near-surface layer
combined with the bulk of any upper support riding north of the
Bluegrass should keep any precipitation, other than a few
negligible snow flurries, north and east of eastern Kentucky
through the night and Thursday morning.
Have let the Red Flag Warning expire as relative humidity values
have increased above 25 percent. Still seeing some sustained
southwest winds of 15-20 mph at times with gusts of up to 30 mph,
so any ongoing fires should be watched closely for erratic
behavior through the night.
.SHORT TERM...(This evening through Thursday night)
Issued at 404 PM EST WED DEC 13 2017
A potent clipper type system was moving southeast across the
Midwest today, headed for the upper Ohio Valley by late tonight.
It is bringing an increasing pressure gradient and warm air
advection to Kentucky this afternoon. An increase in mid level
moisture was resulting in radar returns moving over the area, but
very dry low levels were resulting in virga. Despite the
combination of wind and dry air, verification for the RFW has been
hard to find. Much of the area has seen RH below 25%, but the 20
ft winds above 15 mph have been much more limited so far, and not
coincident with the lowest RH. There is still time for winds to
pick up more by early evening, and the RFW will be left to ride.
If conditions do not materialize, it's possible it could be lifted
During the night, the clipper system's cold front will pass
through. With a return to cold air advection, the low levels will
moisten in the upslope flow once again, and low clouds should
develop. If the top of the convective moist layer can reach cold
enough levels, we could see some flurries, but forecast soundings
look marginal for this. Have included a chance in all but our far
southwest counties for late tonight into Thursday morning.
The system quickly departs to the east on Thursday and a weak
surface ridge will build in from the west. Cold air advection will
ease and become more neutral, and the moisture in forecast
soundings become very shallow. We should see low clouds start to
break up, but whether or not the whole area sees it by the end of
the day is uncertain. High clouds will start to thicken during the
day, which would limit sunshine even where low clouds do scatter
.LONG TERM...(Friday through Wednesday)
Issued at 411 PM EST WED DEC 13 2017
The extended portion of the forecast begins on Friday with an
amplified upper level pattern in place with a stout ridge in the
western CONUS transitioning to a trough in the east. On Friday, a
decent short wave passes through the OH Valley but current model
trends keep the majority of the lift and moisture to the north of
the CWA so Friday will remain dry in addition to Saturday as a
weak ridge quickly passes through the area. The upper level
pattern transitions to a more progressive through the weekend
before the next system develops with a stronger shortwave diving
to the south and developing over the lower MS Valley area. This
combined with another wave passing to the north. This set up will
bring a much needed surge of moisture northward with precip
developing into eastern Kentucky by Sunday morning and lasting
into Monday evening.
Concerning the top down of Sunday morning. At this point, surface
temps will be border line for any sleet or freezing rain
development. It appears with surface temps warming up ahead for
this event, will keep a snow and rain mix in the morning hours and
warming quickly into the late morning hours. Thus, will not expect
any accumulation as well. With the drier pattern taking over again
and the main storm track remaining to the north, the last two days
of the extended will likely be dry at this point. This is
especially the case with the outlooks and climatology. The last
half of the extended looks to be at or just above normal as well.
.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 1254 AM EST THU DEC 14 2017
A cold front will move through eastern Kentucky between 06 and
10z. Gusty southwest to west southwest winds of 10 to 15 kts,
with gusts of 15 to 25 kts at times, will shift to the west
northwest through 10z. Northwest winds will then diminish to 5 to
10 kts after 14z. Clouds will gradually lower to MVFR from
northwest to southeast between 08 and 14z, before scattering out
thereafter. Low level clouds will break up by late this
afternoon, with at least some mid-level clouds hanging around
through the rest of the period. A few snow flurries may also be
seen through 15z, but these should not cause any significant
FXUS63 KLMK 140527
Area Forecast Discussion
National Weather Service Louisville KY
1227 AM EST Thu Dec 14 2017
...Updated Aviation Discussion...
Issued at 1152 PM EST Wed Dec 13 2017
The latest observations from the KY mesonet have shown a couple of
sites gusting to 39 mph across the region with Owen county just to
the north of the forecast area gusting to 44 mph. The latest runs of
the RAP and HRRR show these higher wind gusts will last for the next
few hours at least across the area with some stronger gusts
possible. The area of strongest gusts should weaken and move east of
the region around 09-10Z. Given all this, have decided to issue a
short Wind Advisory as the stronger gusts do look to continue for a
Issued at 530 PM EST Wed Dec 13 2017
Have cancelled the Wind Advisory early this evening as winds are no
longer a threat to gust over 40 mph. The loss of daytime heating
combined with transient upper sky cover has limited mixing up into
the 40-45 knot 925 mb jet. Did replace the Wind Advisory and ongoing
SPS with a new SPS highlighting gusty winds a bit deeper into the
evening. A look at upstream obs behind the secondary cold front that
will move through shows some gusts in the 30 to 40 mph range. Don't
expect any new Wind Advisories to be hoisted, but will have to
monitor gusts with this secondary feature later this evening. Will
update the remaining products to remove Wind Advisory wording
.Short Term...(This evening through Thursday night)
Issued at 300 PM EST Wed Dec 13 2017
Fast moving clipper system will continue to move through the
southern Great Lakes this afternoon and will drag a cold front
through the region this evening. Winds have been a bit slower to
pick up today. However, we've had gusts at or near 35 MPH out west
of the I-65 corridor. The gradient is still tightening up, so a few
gusts to 40 MPH still look likely this afternoon, west of I-65. A
few gusts to 35 MPH still look likely in areas east of I-65 this
evening. Therefore, we plan on leaving the Wind Advisory in place
through 700 PM EST. Temperatures this afternoon have exhibited a
gradient across the state. Readings were in the lower 50s over far
western KY, near 40 in the I-65 corridor, and in the upper 30s over
eastern KY. Not expecting much change in the temperature field this
afternoon, but readings should fall into the upper 30s this evening.
For tonight, the front to the west will pass through the region.
There is not a whole lot of moisture to work with, so mainly we will
see just an increase in cloudiness as the boundary moves through.
Some of the high resolution models still show some sprinkles or
drizzle behind the front, mainly north of the I-64 corridor. We
plan on keeping a mention of sprinkles this evening an a few
flurries into the overnight hours as the column cools down. Lows
tonight look to cool into the upper 20s in the north with lows
around 30 in the south.
For Thursday and Thursday night, weak high pressure will build into
the region resulting in dry weather. Highs Thursday look to warm
into the 30-35 degree range across our northeastern sections with 35-
40 across much of central and southwestern KY. A chilly night is
expected Thursday night with lows dropping into the upper teens to
the lower 20s.
.Long Term...(Friday through Wednesday)
Issued at 328 PM EST Wed Dec 13 2017
Friday through Wednesday...
We'll see another upper level wave cross through the Great Lakes on
Friday. This feature continues to have a weak surface reflection
and much of the precipitation looks to stay well to our north. The
pressure gradient is not all that tight with this system, so much
less windy conditions are expected. Highs on Friday will remain
cool with highs in the mid-upper 30s in the north with highs in the
upper 30s to near 40 across the south. Lows Friday night look to
cool into the mid-upper 20s.
We still expect to see the southeastern US ridge rise a bit over the
weekend as we will see sharp height falls develop in the lee of the
Rockies. Saturday looks to be dry and a little milder at this point
with highs in the upper 40s in the north the lower 50s in the south.
Saturday night still looks to be mostly dry, but can't rule out a
shower across the far southwest. Lows will range from 32-36.
By Sunday, the upper trough in the lee of the Rockies will head east
and surface cyclogenesis will take place over the southern Red River
Valley. We'll see clouds rapidly increase Saturday night with rain
showers overspreading the area from the southwest to the northeast
during the day on Sunday. Have bumped up PoPs a bit for Sunday
given the latest data. Highs will remain mild with readings in the
upper 40s to around 50. Lows Sunday night will cool into the mid
30s. A secondary trough axis will move through the region on Monday
brining additional rain showers to the region. Highs look to be in
the upper 40s with lows cooling back into the mid 30s Monday night.
By Tuesday we'll see a long wave trough axis centered just to our
east and it is forecast to push slowly eastward by Wednesday. This
should result in dry weather for our area. Highs on Tuesday look to
remain in the upper 40s to around 50s with lows in the lower 30s.
Highs Wednesday look to be a bit cooler with readings generally in
the upper 30s to the lower 40s and overnight lows dropping back into
the upper 20s.
Beyond Wednesday and into Christmas Week...
Overall, not much change from our analysis from yesterday. The
latest data continues to point to a potentially active period of
weather as we head into the Christmas Holiday period. It appears
that we'll see a weather system impact the region in the
Thursday/Friday time frame (12/21-22). The current dynamical models
do agree with bringing the system into the region in that time
frame, but differ greatly from Saturday (12/23) onward. In general,
the GFS and its ensembles push the system off to the east and allow
a much colder airmass to move in from the west. The current Euro
solutions stall the boundary out and allow another system to push
into the region around the 12/23-24 time frame.
The GFS and its ensembles now show a much better support of its MJO
forecast which take the MJO from phase 6 through phase 7 and then 8
which would result in a cold regime for much of the eastern half of
the US. While that would bring plenty of cold to the region, it
could result in the main storm track being shifted east and possibly
southeast of our region. There may be a little bit of the
progressive GFS bias in that solution however. On the other hand,
the Euro extended panels do not push the cold as far east and keep
the storm track a bit further west which could result in a period of
active weather for the Ohio Valley during the holiday period. Most
likely, a general solution in-between the Euro and GFS is probably
what will happen. So our latest thinking is that active weather
looks very likely in the holiday period, but specifics on the
thermal pattern still leave a lot of questions. However, there is
plenty of time to let the details get worked out over the next week.
.Aviation...(06Z TAF Issuance)
Issued at 1225 AM EST Thu Dec 14 2017
A sfc low moving through the Midwest continues to cause gusty winds
which will be the main TAF concern. SDF/LEX look to see the highest
gusts between 28-35 kts through 9-10Z. Also cigs may drop to high
end MVFR in that time period as well. HNB is already at MVFR and
will continue through around 9Z. Winds will shift at all TAF sites
from W to NW over the next 1-3 hrs. As sunrise approaches and the
low pressure moves further away, winds will decrease becoming light
northerly by this evening.
IN...Wind Advisory until 4 AM EST early this morning for INZ078-079-
KY...Wind Advisory until 4 AM EST early this morning for KYZ030>043-
FXUS63 KPAH 140550
Area Forecast Discussion
National Weather Service Paducah KY
1150 PM CST Wed Dec 13 2017
Updated aviation section for 06z taf issuance
.SHORT TERM...(Tonight through Friday night)
Issued at 300 PM CST Wed Dec 13 2017
Latest short term guidance is not as robust with the winds late
this afternoon, so the 4 PM expiration of the Wind Advisory should
be ok. A few spots exceeded 40 mph, but much of the area has
fallen just short. The mixing apparently was not quite
deep or strong enough to tap the stronger winds over a broad area
and that is likely what held temperatures below forecast levels.
On the bright side this helped keep the fire danger in check.
The clipper system will pass safely by to our northeast keeping
any precipitation well out of our region. The associated cold
front is not very sharp, but winds will continue to veer to
northwest through the evening while gradually diminishing.
Behind this disturbance the flow aloft will gradually become zonal
Thursday, as surface high pressure settles over the region. A
broader and weaker upper-level trough will move through the region
Thursday night and Friday, but there will be no moisture for it to
work with, so our area will remain dry.
There is quite a bit of uncertainty in the cloud forecast tonight
through Thursday night, so temperatures will be tricky. Did not
stray from the consensus of guidance through the period. It will
feel quite a bit cooler Thursday, but that is as much due to
cloud cover as cold advection. With surface high pressure
lingering over the region Friday it will remain below normal, but
sunshine should allow for some warming relative to Thursday.
.LONG TERM...(Saturday through Wednesday)
Issued at 300 PM CST Wed Dec 13 2017
The latest runs of the medium range models were in decent agreement
depicting the rain event for the PAH forecast area late in the
weekend, perhaps differing by a few hours with the onset (early Sun)
and cessation of the pcpn (Sunday evening). Where they differed more
was with what may happen after that, because of different
positioning/evolution in the solutions of a second shortwave trof
swinging through the southwestern CONUS and eventually into our
The models now all show a northern Mexico cut-off low pressure
system will eject northeastward early in the weekend and open,
producing the brief Sun rain event for us. The ECMWF, while not
phasing the two shortwaves anymore, does have the second shortwave
much farther north (Four Corners), and yet another upper low over
the eastern Pacific. The position of the Four Corners low in the
ECMWF solution will enable it to move through the PAH forecast area
on Mon, potentially resulting in showers. However, the current model
consensus suggests that Mon will be dry under west-southwesterly
The GFS and CMC solutions were quite similar with the position of
the second shortwave as it moves eastward and opens Mon/Mon night,
with the exception of the deeper moisture and more coherent trof
depicted by the GFS. This had enough of an effect on the
initialization blend to have a limited chance of rain, mainly Tue
morning. This was left in the forecast for now, though the GFS has
been quite changeable.
Otherwise, as ridging aloft builds over the western CONUS by Day 7,
expect increasingly anti-cyclonic flow aloft across the nation's
midsection and a ridge of high surface pressure in our vicinity.
This pattern change will be conducive to somewhat milder
temps/dewpoints/RHs in the extended forecast.
Issued at 1150 PM CST Wed Dec 13 2017
A large area of low clouds has been dropping southward across
Missouri/Illinois/Indiana this evening. Bases are mainly vfr across
Missouri and western IL. However, mvfr cigs are prevalent across
Indiana and ern Illinois. The computer models have not been very
adept at picking up this cloudiness. The 06z forecast is more
pessimistic than the previous one, based on satellite and surface
obs. Cigs around 3k feet are forecast at all sites through the day
Thursday, with mvfr conditions at times in sw Indiana/nw Kentucky.
Low clouds should clear out around sunset.
Winds will be northwest around 10 kt, becoming north at 5 to 10 kt
on Thursday morning.