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000
FXUS63 KPAH 302055
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
255 PM CST Sat Nov 30 2013

.SHORT TERM...(This Evening through Monday Night)
ISSUED AT 254 PM CST SAT NOV 30 2013

In the very near term (i.e., this afternoon), adjustments in
temperature, dewpoint, and wind were made to account for the
combination of decent insolation (sunshine) and mechanical mixing
within the boundary layer associated with pressure changes leading
to gradient wind production.

For tonight into Sunday, weak ridging aloft in the broad west-
northwesterly zonal flow aloft should keep any precipitation
chances at bay. However, broad scale lift and ageostrophic
response within the boundary layer should lead to the development
of very late tonight to around daybreak on Sunday. There may be
some breaks during the afternoon hours, especially in Southern
Illinois.  These breaks in the cloud cover should fill in the evening
as the ridging aloft lessens and large scale lift builds across
the area. The rate and intensity of the lift will be too week to
support noticeable updrafts, but will be enough to help
significantly saturate the boundary layer.

With that in mind, a mix of either drizzle or measurable rain
drops were added to the forecast for late Sunday evening through
early Monday Morning. The preferred Canadian (GEM) numerical
guidance suggests that there will be a period of seeder-feeder
action at mid-levels as a sharply sheared mid level vorticity axis
and moderate mid-level moisture moves through the WFO PAH forecast
area. With this mechanism in place, could not limit the
precipitation chances to only trace precipitation (as in the case
of drizzle), especially in the chance PoP category. Therefore, a
chance of measurable rain was emphasized, especially on Monday.
The QPF (rainfall amounts) will still be extremely light,
generally less than one or two hundreds of an inch. There will
still be enough saturation in the boundary layer to generate some
fog at times.

Although a cold front is expected to bisect the WFO PAH forecast
area around noon time on Sunday, most of the energy with this
front will dissipated or focused vertically for cloud and
precipitation production. The front will then move slowly north of
the area Monday night into Tuesday, but will provide enough focus
to create enough moisture pooling for fog production. At this
time, it is a little too early to tell if the fog may reduce
visibilities enough to warrant an advisory over parts of the area
Monday night.

Went slightly higher with min/max temperatures through the period,
as the combination of clouds and weak southerly surface flow
should keep temperatures somewhat elevated.

.LONG TERM...(Tuesday through Saturday)
ISSUED AT 254 PM CST SAT NOV 30 2013

Forecast confidence has decreased in the extended forecast...esp
as we had into the wed through Fri time frame, as operational
model spread continues to increase with the timing/handling of a
strong system that will be tracking across the country.

After a period of h50 ridging Tue...chances for light rain will
begin to increase Wed/wed night as moist sw flow aloft develops
ahead of a highly amplified trof digging into the western states.
However...it still looks as though appreciable rainfall will likely
hold off until this trof spawns a sfc low over the srn plains Thu
and then tracks up a frontal boundary Thu night.

The latest 12z GFS now suggests this boundary will come through the
forecast area on Wed...while the 12z ECMWF does not bring it through
until Thu...about 24 hours later. The GFS then maintains a
progressive system and takes the front on to the Appalachians, while
the euro wants to hang it up in the Oh Valley for 12 hours or so
(thus is warmer and keeps significant precip in our area longer).
Our current forecast is somewhat of a compromise of these solutions,
so will try to make as little changes as possible to the timing of
cold air and possible transition period to some type of
freezing/frozen precip at the end of the event. Our confidence is
too low right now to even speculate on details.

One thing that seems more sure is that we will probably get another
shot of arctic air after this system departs toward the end of the
extended forecast period.


&&

.AVIATION...
ISSUED AT 1115 AM CST SAT NOV 30 2013

Main challenge with the 18z Saturday TAF package is 1) persistence
of gradient winds this afternoon, and 2) timing of stratus ahead
of cold front on Sunday.

Initially, the gradient winds at or below 2500 ft agl this
afternoon should aid in the introduction of periodic gusts through
sunset. Given the short duration of these wind gusts, they were
placed in a TEMPO group for this afternoon.

The moisture associated with the stratus field in Texas, southeast
OK, and southwest AR should advect into KCGI and KPAH between 06z-
09z Sunday, as general, but weak lift associated with approaching
cold front moves closer to these locations. The stratus should
hold off until daybreak at KEVV and KOWB. The timing of the
diurnally enhanced stratus field and the broad, but weak lift from
the approaching cold front may yield a little morning drizzle at
these two locations.

Although visibilities could dip below six statute miles at all TAF
sites, a visibility restriction was only added at KOWB and KEVV
due to the potential for drizzle.


&&

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

$$

SHORT TERM...Smith
LONG TERM...GM
AVIATION...Smith