Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 150000
AFDLSX

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

.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 00z TAFs through 00z Monday Evening)
Issued at 539 PM CST Sun Dec 14 2014

VFR flight conditions are expected to prevail across most of the
area for most of the evening. Some low MVFR and IFR stratus is
lingering over parts of central and south central Illinois...and I
expect it will continue to hang there through the evening. Should
see MVFR ceilings develop from the southwest during the evening
over southwest Missouri and move into central Missouri before 06Z.
the band of rain over eastern Kansas/Oklahoma will also move into
Missouri this evening and sweep through our area overnight and
Monday morning. MVFR ceilings ahead of the rain will fall to IFR
as the rain moves through. Should see wind pick up on Monday behind
the rain and ceilings are expected to rise up to between
2000-3000ft. May see additional rain and possibly a few
thunderstorms Monday afternoon ahead of the cold front which will
pass through Monday evening.

Specifics for KSTL:

Expect VFR flight conditions to prevail through the evening at
Lambert. The stratus deck to the east over Illinois should stay
out there, however do want to point out that some model guidance
is hinting the low ceilings could begin backing to the west later
this evening, so will be watching for this closely. Band of rain
to over eastern Kansas/Oklahoma will continue moving east and
should affect Lambert well before sunrise. I do expect another
MVFR deck to develop ahead of the rain and move in from the west
overnight, tho timing and height of the deck is still uncertain.
Ceilings will likely fall to IFR range with the rain and slowly
improve after the rain ends Monday morning. Wind will pick up and
we could see some gusts in excess of 20kts, but the current
guidance seems to indicate the better gusts will stay west of
Lambert. Another band of showers and possibly thunderstorms may
develop Monday afternoon if there is sufficient heating ahead of
the cold front. At this time, it looks like the front will pass
through the STL Metro area around 03Z Tuesday.

Carney

&&

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

$$

WFO LSX






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