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000
FXUS63 KPAH 031154
AFDPAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
554 AM CST Tue Dec 3 2013

.UPDATE...
ISSUED AT 554 AM CST TUE DEC 3 2013

Revised aviation discussion for 12Z TAFs.

&&

.SHORT TERM...(Today through Wednesday night)
ISSUED AT 350 AM CST TUE DEC 3 2013

Main near term concern is the dense fog developing or already in
progress across portions of the forecast area. Latest observations
indicate widespread dense fog across much of southeast Missouri,
with sporadic sites across the remainder of the region reporting
dense fog as well. Will expand the Dense Fog Advisory eastward to
encompass all of southeast Missouri and far western portions of
southern Illinois and western Kentucky bordering the Mississippi
River. Guidance indicates the extent of the widespread fog should be
confined in that location, and will handle the rest of the area with
a mention in the Hazardous Weather Outlook and Graphical Nowcast.

Once the fog burns off later this morning, conditions through the
remainder of the day should be uneventful as the upper flow
pattern transitions from west northwest to west southwest. This
will continue to result in a gradual increase in low level
moisture and a slow rise in temperatures over the next few days.

Models still want to develop light precipitation across the region
tonight and especially Wednesday as deep southerly flow develops
and low level winds strengthen. While the chance for sporadic
light showers cannot be completely ruled out, conditions should
largely remain dry through Wednesday. I eliminated any mention of
thunder through the near term as both the NAM and GFS model
forecast soundings indicate a strong 900-850mb capping inversion
with very dry air above the inversion. It is also for this reason
that we prefer to keep precipitation probabilities rather small
through Wednesday.

A cold front will approach late Wednesday and move across the area
Wednesday night as low pressure lifts north into southern Canada.
Developing large scale forcing for lift in response to the frontal
approach will result in a better chance for showers Wednesday
night, especially after midnight.

Modest warming of the lower tropospheric thermal profile should
translate into slightly warmer temperatures today and Wednesday.
Sharply colder air will plow southeast into the region Wednesday
night behind the cold front. However, precipitation should remain
all liquid through daybreak Thursday as temperatures are expected
to remain above the freezing mark. It will be a close call over
far western portions of southeast Missouri though...

.LONG TERM...(Thursday through Monday)
ISSUED AT 350 AM CST TUE DEC 3 2013

Winter weather impacts still likely Thursday night through Friday.
Another chance of wintry weather will come in the second 1/2 of
the weekend.

First model preference. The GFS seems to be offering a sensible
balance and will be the model of choice. First off, the NAM seems
too aggressive with low level WAA into the CWFA in response to a
H8 low over the region Thursday night into Friday, and resultant sfc
reflection over the OHX region of TN. That scenario would keep
precip liquid (freezing rain the farther NW you go). None of the
other models the past 3 days, including tonight`s runs (of the
GFS/ECMWF/GEM) have shown this setup. Meanwhile, the ECMWF and GEM
may be too aggressive with the cold air advection given climatology,
and with a respectable SW H7/H5 flow 10k/ft and up over top of the
cold air intrusion. The GFS falls in the middle of what has been
observed in the other models and will be followed closely.

Starting Thursday, only small chance PoPs in the morning, going
up quickly from SW to NE midday through the afternoon across the
area. We expect all rain, save for the extreme NW counties of SW
Illinois into the Ozark foothill region, where some sleet or initial
stages of freezing rain could develop as the thermal profile cools
and becomes more favorable there late in the day. By midnight we
should see rain changing to freezing rain or sleet over the NW 1/2
of the area with nearly all of SW Indiana into west KY remaining
rain. After midnight the transition continues to work slowly south
and east into far WRN Kentucky and part of SW Indiana. Basically
from NW to SE with time, a gradual transition to freezing rain or
sleet, maybe some snow as well toward Friday morning SRN Illinois
into SE Missouri. Generally rain SE of an Evansville Indiana to
Mayfield Kentucky line.

With respect to QPF, best precip efficiency prior to midnight
Thursday night will be NW of a KEVV to KCGI line, then south and east
of the Ohio River after midnight. So impact wise with respect to
wintry precipitation, best chance Thursday night will be over the NW
1/2 of the region and despite QPF totals tailing off after midnight
in this area.

Friday morning, will have to monitor closely areas from around KEVV
to near KPAH to the MO Bootheel and just NW of that line where good
precip efficiency will occur behind the 32F line, in the form of
either freezing rain/sleet or possibly snow by midday. Then by
afternoon, the concern for mixed wintry precip will translate east
over the rest of WRN Kentucky as CAA pushes the sub freezing line
toward the KHOP area.

Needless to say, parts of the SE 1/2 of our CWFA (minus areas east
of the KY Lakes region) Friday could see a real mess, given model
projections of 1/2" to 1" of liquid equivalent, and with the sub
freezing line pressing east through the day. The GFS at 18Z Friday
has the freezing line from KEVV to KPAH. The GEM and ECMWF are
colder at 18Z (again perhaps too cold). The NAM is close to the GFS
at the surface...but notably warmer in the boundary layer.

To sum up Thursday night and Friday, the keys will be the speed,
degree and depth of the CAA, especially Friday with the second
wave and assoc 1/2" to 1" liquid equivalents forecast for the SE 1/2
of the area in a 12 hour period. This is one of the toughest winter
weather forecasts we`ve had to deal with in some time.

Any lingering wintry precip over the ERN 1/2 of the area should
quickly depart Friday evening, with dry conditions Saturday. Saturday
night, a quick surge of moisture back north across the area means we
are looking at another wintry mix possibility. Through the day
Sunday as moisture continues to surge north, enough WAA should
transition the precip to rain SE 1/2, and a mix NW 1/2, with the
activity departing to the east Sunday night.

&&

.AVIATION...
ISSUED AT 554 AM CST TUE DEC 3 2013

A warm advection pattern will keep plenty of low level moisture
across the forecast area over the next 24 hours. The abundant
moisture has resulted in IFR/LIFR conditions in the form of low
clouds and fog at all local forecast terminals early this morning.
Conditions will likely be slow to improve through the morning. Even
by afternoon, MVFR ceilings are forecast to persist. IFR fog and low
clouds may redevelop Tuesday night, especially after midnight. South
winds 5 to 10 knots will prevail.

&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...DENSE FOG ADVISORY until 8 AM CST this morning FOR ILZ080-084-
     088-092-093.

MO...DENSE FOG ADVISORY until 8 AM CST this morning FOR MOZ076-086-
     087-100-107>112-114.

IN...NONE.
KY...DENSE FOG ADVISORY until 8 AM CST this morning FOR KYZ001>004-
     006.

&&

$$

SHORT TERM...RJP
LONG TERM...CN
AVIATION...RJP