Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 061113
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
513 AM CST Fri Dec 6 2013
.SHORT TERM: (Through Late This Afternoon)
Issued at 310 AM CST Fri Dec 6 2013
Snowstorm will continue across the sern half of our forecast area
today as another sw flow shortwave comes out of the srn Plains
inducing low-mid level waa over the sfc/850 mb front southeast of
our area. The models depict strong upper level divergence across
the srn portions of MO and IL today. Areas across sern MO and
swrn IL have already received 5-7 inches of snow with the potential
for storm totals to double by the time the snow tapers off late this
aftn. Should start to see snow move back into cntrl portions of MO
later this mrng with areas from around JEF to STL receiving an
additional inch of snow today, with only a dusting further north of
this area. With slightly higher snowfall amounts forecast today
will be shifting the winter storm warnings and winter weather
advisories slightly further north. High temperatures today will be
about 20 degrees below normal for early December with the Arctic air
mass over our area and 850 mb temperatures continuing to slowly fall
from nw to se. Areas with persistent snowfall will not see much of
a diurnal rise in temperatures today. Precipitation type should be
all snow with increasing SLR values as the low-mid levels continue
to cool. Storm total values for this event will range from only a
dusting in Quincy to around 2 inches in St Charles county to near 13
inches in Ste Genevieve and Randolph counties.
.LONG TERM: (Tonight through Thursday)
Issued at 310 AM CST Fri Dec 6 2013
(Tonight - Monday)
Main focus will be on Sunday, when another storm system is expected
to impact our region with wintry weather.
A longwave TROF will remain situated over the Rockies and Plains--or
to our west--and will serve to steer storm systems thru our area for
a bit longer. As a result, we are looking at another system doing a
swing-by on Sunday. However the track of this system will be
further to the N than the previous tracks of the past day or so and
will thus confine the best chances for measurable precipitation to
areas N and W of STL Metro, including COU and UIN.
Even though the Arctic airmass that began to build into our region
on Wednesday will be on the retreat by Sunday, it will still have
plenty of residual cold air in place. The real problem will be will
there be enough higher/colder cloud in place for the presence of
ice. Unfortunately, it looks like outside the direct influence of
the lift from the system, which will be most felt in NE/central MO
and W IL, the rest of our region will be stuck with "snizzle": at
times light snow or flurries and other times, freezing drizzle.
High anticipated liquid to snow ratios from the magnitude of cold
still in place will allow for the potential of up to 2" of snow
mainly in NE MO with up to an inch for sections of central MO and W
IL and only a dusting elsewhere with some glaze potential as well
from the FZDZ.
Temps will be tricky anytime we are dealing with snow cover.
Anticipated deep snow cover over SE MO and S IL will not be going
anywhere anytime soon with losses expected primarily due to
sublimation and settling. This will limit ability to warm in the
day, and where decoupling can occur with approaching Arctic air, the
nighttime temp can really tank, with sub-zero values not out of the
question. The best chance for sub-zero temps for the deep snowpack
areas will be on early Saturday morning. Single digits look to be
(Tuesday - Thursday)
The base of the longwave TROF will pass thru on Tuesday, with a
lo-amplitude NW flow thereafter. This looks to be a quiet period
with continued cold, thanks to the presence of a strong hi pressure,
but a more moderated cold from what we will be dealing with this
.AVIATION: (For the 12z TAFs through 12z Saturday Morning)
Issued at 449 AM CST Fri Dec 6 2013
Another round of snow will move into the St Louis metro area
later this mrng, possibly grazing COU as well ahead of an upper
level disturbance moving out of the srn Plains. The cloud ceiling
in the St Louis metro area will drop to 1000-2000 ft with this
snow and the visibility will drop down to as low as 1-2sm. The
snow should taper off later this aftn, followed by a clearing sky
this evng as a strong sfc ridge over the nrn Plains builds sewd
into MO. N-nwly sfc winds will continue through the period.
Specifics for KSTL: Should see another round of snow during the
late mrng and early aftn. At this time the visibility should fall
as low as 1-2sm in light snow along with the ceiling dropping down
to 1000-2000 ft. The snow should taper off late this afn with VFR
conditions returning by about 00z Saturday. The sky will clear out
by late evng. N-nwly sfc winds will continue through the forecast
period, with wind speeds of around 11-13 kts today and 7-9 kts tgt
and Saturday mrng.
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.