153 
FXUS63 KPAH 181139
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
539 AM CST Mon Nov 18 2013

.UPDATE...
ISSUED AT 539 AM CST MON NOV 18 2013

The AVIATION section has been updated for the 12Z TAF issuance.

&&

.SHORT TERM...(Today through Wednesday) 
ISSUED AT 346 AM CST MON NOV 18 2013

Surface high pressure will dominate the region through Wednesday.
The 00Z models are in agreement in continuing to build the high 
into the area today, and then settling it over the area tonight.
The high will then shift gradually east Tuesday into Wednesday.
Aloft, a weak ridge of high pressure will pass eastward across the
region tonight and Tuesday, resulting in weak southwest flow
Tuesday night. Overall the flow aloft will be very flat/nearly
zonal through the period. Southwest flow aloft will begin to
increase Wednesday afternoon. 

Skies will be clear through tonight and then a modest increase in
high clouds will begin mainly in the west Tuesday into Tuesday
night. As the flow aloft becomes southwest and a minor disturbance
approaches, mid clouds will spread eastward across the area on
Wednesday.

Guidance is having a hard time keeping up with the dry air which
is very noticeable over southeast Missouri early this morning.
KPOF has a dewpoint in the lower 20s, and the MET and MAV guidance
are about 10 degrees too high. Relied on the LAMP guidance, which
seems to have the best handle on the situation to achieve a decent
trend through the morning. 00Z NAM and GFS soundings definitely
support dewpoints at or below 32F throughout the area this
afternoon. Sounding data show no significant increase in the low-
level moisture until Wednesday, as southeast winds pick up, and
even then mainly in southeast Missouri and southern Illinois. 

These low dewpoints will result in relative humidity dropping
into the 30s, at least, today and possibly Tuesday, as well, even
though temperatures will be a notch cooler Tuesday afternoon.
Hopefully, fuels are relatively wet with yesterday's rains,
because the low RH and decent northwest winds mixing to the ground
this afternoon could result in near red flag atmospheric
conditions, especially in the northeast half of the area.

With the dry air in place, decided to lean toward the warm side of
guidance for highs today, and the low side of guidance for lows
tonight. Consensus guidance is cooler than the existing forecast
by a few degrees for highs on Tuesday with the surface high
overhead. Still figure with the dry air that we may warm up more
than guidance believes, so did not alter the forecast much at
all. 

The pressure gradient looks like it should support a southeast
wind throughout the area Tuesday night, so the dry air may not
have as great an impact on lows. Still leaned a little bit toward
the cooler side of guidance. Clouds may hold temperatures down
some over southeast Missouri and southern Illinois Wednesday, but
the warm side of guidance seems reasonable over the southeast half
of the area.

.LONG TERM...(Wednesday Night through Sunday)
ISSUED AT 346 AM CST MON NOV 18 2013

The preferred guidance suite (GFS Ensemble, Canadian, deterministic 
GFS) all appear to begin the extended part of the forecast with 
nearly identical solutions. With time, the Canadian numerical model 
is more aggressive with the deepening of the Northern Baja closed 
low and the extent of the cold air southward from High Pressure from 
Central Provinces. 

Although the closed low the west coast moves very little through 
next Sunday, vorticity is ejected in the resultant zonal flow in the 
southern stream. This is similar in the aforementioned guidance 
through next Saturday evening. The subtle, but key difference is the 
southeastward extent of the High Pressure center in the Midwest and 
the attendant cold air advection, aided by a Great Lakes upper low.

Even as the Baja California closed low is eventually ejected into 
the Central Plains by next Monday, distinct ridging takes place, 
holding back the decent warm air advection and moisture return to 
the local area.

The main challenge with this extended forecast package is the 
transitional phase of a low amplitude northern U.S. progressive 
trough to the formation of the closed low.  It is at this time 
period that a subtle inverted surface trough develops northeast from 
Texas. The subsequent moisture convergence and warm air advection 
associated with the upper trough forces a weak baroclinic zone, 
supported by a model vorticity in the nearly zonal flow.  

There is the possibility that enough lift through the moisture 
bearing layer to indicated the potential for isolated thunderstorms 
working up from Arkansas this Thursday. Given the uncertainty and 
marginal coverage, elected to keep any differential PoP mention of 
thunderstorms out of the forecast at this time. On the flip side, 
there is the potential for mixed precipitation Friday night. In this 
case, low level temperatures are sufficiently warm to warrant an all 
liquid solution for that time period. Basically, the extremes for 
precipitation type and intensity of precipitation have been muted. 

With the GFS/GEM guidance, leaned toward a colder and drier 
temperature/dewpoint solutions for the extended period.

&&

.AVIATION...
ISSUED AT 539 AM CST MON NOV 18 2013

Winds have become light or calm across the region early this
morning, but the surface high will still be building across the
region through the day. Northwest winds 10-13kts with gusts 16-21kts
will mix down by 16Z. The strongest winds will be in the
northeast. The surface high will settle over the region tonight,
so north winds will become light if not calm. By morning the light
winds should be from the northeast. Latest guidance indicates that
a few cu will be possible at KEVV and KOWB through the middle part
of the day.

&&

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

$$

UPDATE...DRS
SHORT TERM...DRS
LONG TERM...Smith
AVIATION...DRS