Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 241008
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
408 AM CST Mon Nov 24 2014
.SHORT TERM: (Through Late This Afternoon)
Issued at 405 AM CST Mon Nov 24 2014
Precip is in the process of winding down fairly quickly over the CWA
early this morning. As it does, colder air working into the back
edge of the rain has changed the precip over to snow as far east
as a UIN-Louisiana line as of 3 am, but it appears that freezing
level is staying just high enough from COU to STL that the
changeover is struggling to occur along the I70 corridor.
Could see some very minor accumulations in the UIN area by daybreak,
but based on radar trends over the past several hours measurable
precip may be negligible after 12z. Certainly by mid morning any
precip will be quite light, and limited to the northern half of the
CWA where CAA and low level cyclonic circulation may be enough to
generate a few spits of snow.
Cold front is just now reaching our far SE counties, and the intense
CAA in its wake will be causing a bit temp drop early this morning
before readings level off this afternoon. Elsewhere where the cold
air has already arrived, looking for a minimal rebound in temps due
to the clouds and strong cold air advection. Best chance for any
significant warming should be limited to our far s counties where
there could be a bit of sunshine.
.LONG TERM: (Tonight through Sunday)
Issued at 405 AM CST Mon Nov 24 2014
System to exit region with weak surface ridge building in tonight.
Low temps will be in the low to mid 20s. Then on Tuesday ahead of
next weather system, will see southwest to west winds, but
temperatures to stay below normal in the mid 30s to low 40s.
Tuesday night, clipper system to slide southeast towards forecast
area. So will see an increase in cloud cover as well as low level
moisture. Surface low to track just west of Mississippi river on
Wednesday. So highest pops will be over eastern sections of forecast
area. Precipitation to initially start off as light snow, then as
temperatures warm up during the day on Wednesday, the snow will
become mixed with light rain and change over to mostly rain before
coming to an end Wednesday afternoon. Lows Tuesday night will be in
the mid to upper 20s while highs on Wednesday will be in the upper
30s to upper 40s.
Extended models coming into better agreement with surface ridge
building in for Thanksgiving. So will see dry and colder weather on
Thursday before warming back up for the weekend ahead of next
system. Highs on Thursday will be in the low 30s to low 40s. Still
some timing differences on frontal boundary that will slide through
late this weekend. GFS is faster with front moving through during
the day on Saturday while the ECMWF has front sliding through
Saturday night. Moisture is limited with this system, so feel that
front to move through dry despite GFS showing some light qpf. Highs
by Saturday will be near normal in the 50s, before dropping off into
the 40s on Sunday behind this system.
.AVIATION: (For the 06z TAFs through 06z Monday Night)
Issued at 1111 PM CST Sun Nov 23 2014
A cold front had already moved through KCOU and KUIN but had not
yet reached the St. Louis metro area TAF sites as of 05z. Expect a
marked wind shift at KSUS/KCPS when fropa occurs between 06-08z.
An area of rain was also moving northeastwards towards the TAF
sites and had already reached KCOU at TAF issuance. Rain will
persist for several more hours then taper off. The rain could
briefly mix with snow at KCOU and KUIN just as the precipitation
is ending, but upstream METARs show that the post-frontal air
mass is warmer than previously anticipated, thus accumulating
snowfall looks less likely than it did during the previous TAF
cycle. Instability snow showers are possible during the afternoon.
Winds should start to taper off once the pressure gradient relaxes
by the late afternoon or early evening.
Specifics for KSTL: Expect a marked wind shift between 06-07z when
a cold front moves through the terminal. Rain will persist for
several more hours then taper off. Instability snow showers are
possible during the afternoon. This TAF is optimistic in that it
depicts a return to VFR cigs by late afternoon/early evening.