Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150559
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1159 PM CST Sun Dec 14 2014

.UPDATE:
Issued at 916 PM CST Sun Dec 14 2014

Extrapolation of leading edge of rain and scattered thunderstorms
suggests precip arriving in COU around 06z. Based on this timing,
have adjusted PoPs a bit to reflect a slower eastward progression
of the precip (especially the likely and higher PoPs) into central
and eastern sections of the CWA during the predawn hours. Update
out shortly.

Truett

&&

.SHORT TERM:  (Through Late Tonight)
Issued at 331 PM CST Sun Dec 14 2014

Rain will overspread MO late tonight as the upper level low and
associated surface low now over the OK panhandle moves northeastward
into eastern KS by 12Z Monday.  A strong south-southwesterly low
level jet ahead of the low pressure system will bring relatively
strong low level warm air advection, moisture convergence and theta
e advection to much of the forecast area late tonight.  There may be
a few thunderstorms across central and southeast MO as the
atmosphere destabilizes with the approach of the dry slot.  It will
be unseasonably warm for mid December and the MOS guidance for
tonight appears a little too cool.

GKS

.LONG TERM:  (Monday through Next Sunday)
Issued at 331 PM CST Sun Dec 14 2014

Rain should spread eastward through the IL counties of our forecast
area Monday morning, then the best coverage of rain Monday afternoon
should occur across northeast MO and west central IL near the upper
level and surface low which should be over northeast MO and
southeast IA by 00z Tuesday.  The precipitation will be more
scattered further south and at most times lighter.  There may also
be a few thunderstorms, mainly underneath the upper level low and
during the afternoon hours.  Most of the precipitation will shift
northeast of the forecast area by late Monday night as colder and
drier air filters into the region behind the storm system.  Colder
more seasonable temperatures along with dry conditions can be
expected Tuesday through Wednesday as a surface ridge moves eastward
through our area.  Tuesday night should be quite cold due to good
radiational cooling with a mostly clear sky and fairly weak surface
winds as the surface ridge axis will be across western MO by
12Z Wednesday.  The ECMWF model brings precipitation back to our
area Wednesday night and Thursday morning as upper level divergence
increases ahead of an approaching southern stream shortwave over the
southern Plains.  It should be cold enough that most of this
precipitation will likely be in the form of snow.  The GFS is
weaker with this system and keeps the significant precipitation
south of our forecast area.  Will keep pops only in the chance
catagory due to these model differences.  A stronger storm system
may impact our area during the Friday through Saturday time frame,
although there are significant model differences with this storm
system as well.  The GFS model brings a negatively tilted upper
level low/trough and associated surface low northeastward through
southeast MO and southern IL Friday night with the potential for
accumulating snow, mainly north and west of St Louis.  The ECMWF
model is much further south with this storm system, keeping most of
the precipitation south of our forecast area. For now will just
include chance pops for Friday through Saturday with the highest
pops over the southern portion of the forecast area, but this system
will bear watching as it has the potential to bring the first
significant round of wintry weather to our area this season.

GKS

&&

.AVIATION:  (For the 06z TAFs through 06z Monday Night)
Issued at 1138 PM CST Sun Dec 14 2014

IFR flight condtions have backed right up into the St. Louis metro
area from Illinois this evening. Ceilings AOB 1000ft prevail
across much of Illinois with VFR flight conditions stretching back
across most fo the rest of Missouri. The band of rain moving
through cemtral Missouri will continue moving east through the
rest of the night into Monday morning. VFR and MVFR conditions
prevail under the rain, but some of the heavier pockets of rain
embedded in the band are producing visibilities at or below 2SM.
Believe this trend will continue with ceilings along and east of
the Mississippi river improving a bit as the rain moves in. Of
course, the pockets of heavier rain will likely continue to
temporarily reduce visibility conditions. Once the band moves
east, expect MVFR conditions to prevail with additional shower
activity to develop in the afternoon ahead of the cold front.

Specifics for KSTL:

The back edge of the IFR stratus over Illinois has backed into
Lambert, and it will likely stay put for several hours until the
band of rain now moving into the Columbia area gets into the Metro
area. It`s possible the IFR could push east before then, but seems
unlikely at this time. Think ceilings will improve with the onset
of rain, but pockets of heavier rain after the initial onset will
likely intermittantly drop the visibility to 2SM or less. Expect
MVFR conditions to prevail behind the rain band with slowly
improving conditions through the late morning and afternoon.
Additional shower activity is expected to develop during the
afternoon with MVFR ceilings continuing to prevail.


Carney

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX






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