Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 030014
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
614 PM CST Mon Dec 2 2013
.SHORT TERM: (Through Late Tonight)
Issued at 315 PM CST Mon Dec 2 2013
Persistent stratus clouds across cntrl MO in COU and JEF should
dissipate later this aftn with continued daytime heating, drying and
mixing, and as a weak warm front over our area lifts n-newd with
increasing s/swly sfc/low level winds south of the front. The mid
level cloudiness across portions of ern MO and wrn IL associated
with low-mid level waa ahead of a weak shortwave should shift east
of our forecast area by early evng, although more mid-high level
cloudiness will likely advect e-sewd into our area tgt. Any
sprinkles out of the mid level clouds across nern MO and w cntrl IL
should also shift east of our area by early evng. With sly/swly
sfc/low level winds tgt, and warmer temperatures not expecting
significant fog late tgt, but could not rule out some patchy stratus
clouds, especially over the srn portion of our forecast area with
relatively high sfc dew points. Due to the 850 mb temperatures
continuing to warm from sw to ne tgt low temperatures tgt will be
warmer than the previous ngt, and about 10-15 degrees above normal
for early December.
.LONG TERM: (Tuesday through Next Monday)
Issued at 315 PM CST Mon Dec 2 2013
Another mild day on tap with minimal chances for rain.
Upper flow will be in the process of transitioning from a NW flow to
SW, with weak upper level disturbances continuing to slide overhead.
These systems will also only have marginal moisture to work with,
and as such, PoPs will be minimal. Cannot rule out sprinkles during
this period, but will lean on previous forecast of dry for now, as
evidence is pretty scant at the moment.
Previous forecast of max temps in the 60s still looks on track with
some sunshine expected and the warm front to our N: giving us a
warmer day than persistence.
(Wednesday - Saturday)
Wintry precipitation still looks likely for Thursday thru Friday,
especially for areas near and S of I-70. However, the vast majority
of the forecast will hinge on ability to accurately forecast timing
and depth of shallow Arctic airmass into our region.
The 12z run of the models today is the first run where the main
storm system that will create the setup that looks to give us our
first shot of accumulating wintry pcpn is over land. It is then no
surprise that the broad spread of model solutions at the surface
have come into better agreement, but there is still a significant
enough difference between the fastest and slowest to make for a
tricky forecast with respect to precipitation type. For instance:
at STL on 18z/Thu, the GEM has 33, the GFS/EC have 37, and the NAM
28. Better, but still not optimal to make hi confidence decisions
on pcpn-type. Given this choice, I prefer a tempered version of the
NAM on lo level cold air, with the NAM`s timing of the front good
with respect to consistency of our previous fcsts and what should be
its long-standing ability to diagnose Arctic air intrusions the
best. Aloft, it will be hard to disagree with the more consistent
GFS which brings a slug of warm air with the pcpn on Thursday and
then gradually cools it down Thursday night and Friday as the Arctic
With this in mind, the timing of the wintry precipitation still
looks the same: Thursday (mainly afternoon), and for some areas,
continuing into Thursday night and much of Friday. The pcpn-type
remains lo confidence due to model spread, but am going with more of
a wintry mix for areas further NW than 24hrs ago but it still looks
like UIN/COU/JEF will be all snow, with mainly sleet-snow for most
of STL metro. Liquid pcpn is expected to predominate further S and
E on Thursday, changing to sleet-snow Thursday night.
Lo confidence of pcpn-types will result in a pretty wide-open debate
on amounts. Will just leave it at this: there is good potential
for accumulating snow and sleet of an inch or more for a swath from
central MO thru the NW half of STL metro and into IL headed towards
SPI. For a narrower area to the SE into parts of SE MO and S IL,
including FAM and SLO, there is good potential for ice accretion
from FZRA but the window looks narrow because of lo confidence of 2m
temp values at this time. The persistence of pcpn beyond Thursday
is also a concern, where additional light accums of snow and some
sleet are likely for at least parts of SE MO and S IL.
Being what looks like our first widespread winter event of the year,
will issue a SPS to highlight some of these items.
Temps will be cold from Friday on, with max temps only in the 20s
and mins in the single digits and teens.
(Sunday - Next Monday)
The cold continues with the Arctic hi in the neighborhood. EC and
GFS both show another system for Sunday, but tracks are all over the
place with the EC a warmer solution but also more questionable.
Will continue with chance for snow on Sunday. Monday looks dry with
hi pres re-asserting control.
.AVIATION: (For the 00z TAFs through 00z Tuesday Evening)
Issued at 606 PM CST Mon Dec 2 2013
A weak warm frontal bndry currently extends from SE IL NW to just
S of the STL metro then NNW to KDSM. This wind shift is expected
to slowly lift N this evening and should be well N of KUIN by 6Z.
After FROPA...expect S/SE winds of 6-12 kts and SCT/BKN mid/high
level cloudiness thru the period. There is the possibility of some
MVFR fog around sunrise. This depends on the amount of clearing
and subsequent cooling.
Specifics for KSTL:
VFR fcst with S/SE winds of 6-12 kts and CIGS aoa 12kft.