000
FXUS63 KLSX 062138
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
338 PM CST Fri Dec 6 2013

.SHORT TERM:  (Through Tonight)
Issued at 212 PM CST Fri Dec 6 2013

Plan to trim nrn edge of ongoing headlines where precip had ended
and will come to an end soon. Will determine which counties to
will be canceled closer to publish time.

Otherwise, focus will be temps and very cold wind chill values.

Ongoing sn is quickly pulling out of the area this afternoon.
Latest RADAR trends suggest, and mdls seem to agree, sn shud be
just E of the CWA by 00z. Have kept mention of flurries across ern
counties for a few hours this evening, but even flurries shud be
ending quickly with sunset. Clouds will also be quick to clear
out, but some mid clouds across wrn MO will move back into the
region as they break up this evening.

With clouds clearing out of the region, a nrly wind with persistent
CAA, and snowpack, temps shud plummet tonight. Have therefore
trended aob coolest MOS for tonight. Winds shud diminish somewhat,
but wind chill values will still be very close to advisory
criteria, which is -15 F. Have held off issuing an advisory
tonight, but one may be needed if winds do not diminish.

Tilly

.LONG TERM:  (Saturday through Next Friday)
Issued at 252 PM CST Fri Dec 6 2013

(Saturday through Monday)

Main focus will be the system impacting the region Sat night thru
Sun.

A brief mention for temps...have continued cold trend thru Sat for
obvious reasons.

For Sun, mdls lift the wrmfnt nwd thru the region late Sat night
and thru Sun as a s/w ejects out into the Plains. The
GFS/ECMWF/GEM are in rather good agreement with this fnt producing
some light precip as it lifts nwd. Have largely discounted the NAM
for this event for now. Latest guidance suggests this precip will
begin as sn. However, with the much warmer airmass lifting over
the snow field, granted it is only temps in the mid to upper 20s,
this shud present a FG problem as well as FZDZ. That said, there
are some locations that may switch back to SN due to a very cold
column that may reach the -10 C range to produce ice crystals
again. Uncertainty remains just how much ice accumulation this
system will generate. With sfc temps much colder than the current
system, only a trace of precip may have a huge impact on the area.
Latest mdl guidance suggests this precip will lift nwd thru the
region quicker than prev cycles and have adjusted POPs
accordingly.

(Tuesday through Friday)

Temps are expected to gradually moderate thru the period, but shud
finally reach above freezing late in the period as another system
approaches the area. Have kept POPs low given differences among
mdl guidance. However, what precip does fall is currently expected
to be rain. The forecast does mention FZRA as timing of onset will
determine type. Regardless, the rain will likely be falling onto a
very cold ground and may freeze even if air temps are above
freezing. This freezing will likely be short lived as temps
continue to warm.

Tilly

&&

.AVIATION:  (For the 18z TAFs through 18z Saturday Afternoon)
Issued at 1127 AM CST Fri Dec 6 2013

Ongoing snowfall expected to continue for areas south of I70 thru
the aftn. KCOU appears to have just missed the nthrn edge of the
precip shield. Snow is struggling against dry air near the surface
on the nthrn edge of the precip. This is esp evident in the STL
metro area where KCPS has IFR VSBYS and -SN this mrng and KSTL
has had flurries but KSUS has yet to see anything. Not confident
that the snow is going to able to overcome the dry layer...but if
it does...VSBYs will quickly go IFR. Local radar shows about 2kft
of dry air to overcome. The inherited fcst had IFR VSBYs in the
metro area so left them. Due to ongoing precip at KCPS...left IFR
VSBY as the predominant group. Due to uncertainty of snow at KSTL
and KSUS...backed off on the IFR From group to a TEMPO. Either
way...snow should wind down quickly late this aftn and skies
should clear out this evening. With high pressure remaining to
the north...winds will be steady out of the north thru the period.

Specifics for KSTL:

Terminal is on the fringe of the precip shield to the south. Snow
is having trouble overcoming dry air near the sfc. Not confident
that it ever will...but if it does...VSBYs will quickly drop to
IFR. The inherited fcst had a predominant group with IFR VSBY. Due
to uncertainty that steady snow will occur...back off to a 2 hr
IFR TEMPO group. Skies will clear by midnight with winds remaining
out of the north around 10kts.

Miller

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis      8  20  16  28 /  10   0  30  40
Quincy           4  18  12  27 /   5   0  10  70
Columbia         5  19  14  27 /   5   0  30  60
Jefferson City   5  20  14  28 /   5   0  40  50
Salem            5  17  14  28 /  10   0  20  30
Farmington       0  16  11  26 /  10   0  30  30

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...WINTER WEATHER ADVISORY until 6 PM CST this evening FOR Franklin
     MO-Gasconade MO-St. Louis City MO-St. Louis MO.

     WINTER STORM WARNING until 6 PM CST this evening FOR Crawford MO-
     Iron MO-Jefferson MO-Madison MO-Reynolds MO-St. Francois MO-
     Ste. Genevieve MO-Washington MO.

IL...WINTER WEATHER ADVISORY until 6 PM CST this evening FOR Bond IL-
     Fayette IL-Madison IL.

     WINTER STORM WARNING until 6 PM CST this evening FOR Clinton IL-
     Marion IL-Monroe IL-Randolph IL-St. Clair IL-Washington IL.

&&

$$

WFO LSX