Scientific Forecaster Discussion
Area forecast discussion
National Weather Service St Louis MO
305 PM CST Mon Dec 9 2013
Short term: (through tonight)
issued at 233 PM CST Mon Dec 9 2013
Focus tonight will be approaching system with another quick shot at
Latest mdl guidance has shifted sn a little further nwd tonight and
have adjusted pops nwd somewhat. Snow is beginning to reach the ground
across sern Kansas and nrn OK and will continue to push ENE into swrn MO
this afternoon. Light sn may reach srn portions of the County Warning Area by late
this afternoon, but accumulations are expected to be minimal thru
the afternoon hours. This current band is expected to diminish over
swrn MO with another redeveloping just to the south. This recycling
band will probably occur again as the upper trof approaches the
Mdls also increased amount of liquid precip with this system with
some areas across the ern Ozarks possibly receiving around one tenth
of an inch of liquid precip. With a fairly sizable portion of the
atmo within the dgz, have used a high slr. Cobb algorithm suggests
an slr of 15 to 20 to one. To account for the entire area, have used
a conservative 16:1 ratio.
Would not be surprised to have a couple locations end up with around
three inches of snowfall from this system. However, believe most
areas will receive two inches of sn or less. Have therefore held off
on any headlines for now.
As for temps tonight, with snowpack over much of the area and with
clouds expected to clear late tonight, have trended twd coldest
guidance again tonight.
Long term: (tuesday through next monday)
issued at 304 PM CST Mon Dec 9 2013
Next shortwave expected to move north of the County Warning Area Tuesday night,
sending a cold front across the region on Wednesday. Believe
snowfall with this feature will remain north of the County Warning Area. Another
cold surface ridge will build into the Midwest Wednesday night and
Thursday morning providing ideal radiational cooling conditions.
Have went below guidance for low temperatures, especially across
areas that have snow on the ground.
Southerly flow ramps up ahead of the next shortwave Thursday night
with clouds and precipitation rapidly developing northeast across
the County Warning Area on Friday. Have tried to nail down some precipitation type
trends with the lastest model guidance. Conceptially it appears that
area will still have cold/dry airmass overhead when precipitation
develops, which will support snow/sleet at the onset.
Temperatures will try to warm on Friday, but 2m temperatures
forecast by the models show a persistent dip in the isotherms
across the County Warning Area indicating the power of evaporative cooling.
Precipitation will probably transition to freezing rain or rain
along and south of I-70, depending on surface temperatures, Friday
afternoon as 850mb temperatures briefly rise above freezing.
Colder air will begin to transition the winter mix back to snow from
northwest to southeast Friday night as the inverted trof/surface low
passes east of the County Warning Area. Tad early to determine amounts of any
winter precipitation but it certainly looks like at least an
advisory type event. Have increased pops to likely and will include
in the hazardous weather outlook.
Aviation: (for the 18z tafs through 18z Tuesday afternoon)
issued at 1124 am CST Mon Dec 9 2013
An approaching system is expected to bring another round of sn,
but is currently expected to remain just S of all terminals.
However, as the system passes sus/cps may see some flurries with
MVFR cigs. Any accumulating snow is expected to remain S of these
sites. Timing remains uncertain and may persist later than
currently forecast, but current tempo shud at least capture onset.
Elsewhere, very small bands of MVFR cigs have developed and may
briefly impact cou/uin. These cigs may also support a period of
flurries as well. Location and timing of these MVFR cigs is very
uncertain, if they reach these terminals at all. Have kept out of
the fcst for now and will update if they are expected to persist.
Cigs are expected to improve overnight with clouds clearing. Winds
will pick up with gusts to around 20 kts Tue morning.
Specifics for kstl: accumulating sn is expected to remain S of the
terminal tonight, but flurries/light sn is possible this eve. Wly
winds will eventually become nwly before backing again tonight.
Clouds will clear out overnight with winds picking up again Tue
morning with gusts to around 20 kts.
Preliminary point temperatures/pops:
Saint Louis 13 33 18 31 / 50 0 0 0
Quincy 5 27 17 24 / 10 0 10 10
Columbia 8 32 18 28 / 10 0 0 0
Jefferson City 9 35 18 30 / 20 0 0 0
Salem 16 27 12 30 / 90 0 0 0
Farmington 16 29 13 33 / 80 0 0 0
Weather forecast office lsx