Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 130456
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1155 PM CDT Thu Oct 12 2017

.UPDATE...
Updated aviation section for 06z taf issuance

Previous update issued at 713 PM CDT Thu Oct 12 2017

Fog imagery shows the persistent low cloud cover is nearly
stationary across the area, with a light ESE trajectory seen from
the surface up through HRRR initialized 925mb data. The NAM and
RAP/HRRR continue to be the best guidance available. They suggest
our current cloud forecast is too quick with the clearing.
Satellite confirms this to some extent. Will raise lows a few
degrees east of an I-57, I-24, Highway 45 line. Our gridded
forecast for cloud cover/clearing will be based close to the
NAM/HRRR. More weight to the NAM. Left the fog mention over SEMO
counties where clearing will hold. There may be some light fog
elsewhere, especially close to the clearing line.

CN

&&

.SHORT TERM...(Tonight through Saturday night)
Issued at 205 PM CDT Thu Oct 12 2017

Main forecast challenges will be the departure of the opaque cloud
cover from the WFO PAH forecast area and the timing of the
precipitation associated with the approach of the next cold front
into the area late Saturday night (early Sunday morning).

Isentropic lift and forcing remain marginal across the area,
especially east of the surface ridge axis which extends from the
Mississippi River northeast into Southwest Indiana. Even at 1 pm
CDT, cloud thickness over parts of southern IL and parts of
Southwest Indiana remain in excess of 1500 ft.

Warm air advection tonight and Friday should continue to erode the
cloud layer from above and below as the ridge axis slowly moves
east. Given the weak advection, there may still be some
cloudiness, albeit not 100 percent coverage, across the west
Kentucky Pennyrile region and southwest Indiana, this evening.
Where skies remain clear over southeast Missouri, could see some
localized fog development overnight, even with very weak warm
advection (most significant at and above the boundary layer).

The influence of the ridge axis will likely yield to some diurnal
cumulus cloud development early on Friday, before clearing out
for the remainder of the day.

Utilized the short range ensemble guidance (SREF) to address the
timing, coverage, and intensity of rain late Saturday along and
ahead of the approaching cold front. Limited instability aloft
mitigated any differential mention of thunderstorms through
Saturday night.

.LONG TERM...(Sunday through Thursday)
Issued at 205 PM CDT Thu Oct 12 2017

The only real weather maker in the long term period will be a
frontal passage early Sunday which will bring our only chance for
rain.

Models have definitely sped up the timing of this front and
associated rainfall. At 12Z Sunday, the NAM/GFS show the actual cold
front in our far eastern counties with most of the precipitation
post frontal. The ECMWF and Canadian indicate the front a bit
further west at that time.

The speed difference between models of the aforementioned front does
not seem to have much affect on the forecast, as the best chances
for rain for our area will still come between 12Z-18Z Sunday.
Whatever precipitation is left Sunday afternoon, will be across
parts of west KY. Not sure how much thunder will be involved as most
of the instability will be tied to the front and directly behind the
front.

Will need to make changes to our going POP forecast however
in order account for the more rapid arrival and departure of the
precipitation. Will likely have to take rain chances out for Sunday
night. Temperatures on Sunday will be tricky depending on how fast
the cooler air filters into the area. We may be dealing with a non
diurnal trend. Model guidance is suggesting falling temperatures
through the morning hours so our high will likely be first thing in
the morning.

By late Sunday afternoon, a large 1028-1030mb surface high will be
situated over Kansas and Oklahoma. This sfc high will start
migrating eastward Sunday night and into Monday, really helping to
dry things out locally.

The center of this sfc high pressure system will be overhead by late
Monday night into Tuesday morning. With clear skies and calm winds,
Monday night into Tuesday morning should be our coldest, with lows
dropping into the lower to mid 40s. High pressure will dominate for
the rest of the week, which will aid in keeping any chances for
precipitation at bay. Temperatures will remain in the 70s for highs
and upper 40s to lower 50s for lows from Tuesday and beyond.

&&

.AVIATION...
Issued at 1155 PM CDT Thu Oct 12 2017

An area of MVFR cigs covered all taf sites as of late this evening.
This large patch of clouds has been slowly shrinking from the south
and east at about 5 knots. At the current rate of movement, the
clouds should clear kcgi and kpah by about sunrise. The clouds in
the kevv/kowb areas may clear out briefly overnight, then possibly
move back in early in the morning. Where skies do clear before
sunrise, fog will likely develop. Some IFR conditions are still
forecast at kcgi. All locations will become VFR by Friday afternoon.
Winds will be light, mainly from the southeast.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$

SHORT TERM...Smith
LONG TERM...CW
AVIATION...MY



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