Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 052216
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
416 PM CST Thu Dec 5 2013
.SHORT TERM: (Through Tonight)
Issued at 356 PM CST Thu Dec 5 2013
Focus continues to be the ongoing winter wx system.
Latest mdl guidance is in fairly good agreement. However, seems to
be on the warm side regarding temps aloft based on latest reports of
sn/ip. Have therefore trended p-type turn over to sn a little faster
than based on progd soundings. Based on reports received within
the last half hour, precip is turning over to sleet, then sn
further S quicker than anticipated. Have therefore increased sn
amounts across sern portions of the CWA this evening. Some
uncertainty exists regarding how far E this heavier sn will make
it as some mdl guidance suggests the precip will weaken as it
Ongoing precip is expected gradually push s and sewd, before pulling
nwd again late tonight into Fri morning.
As for temps, have trended aob coolest MOS guidance.
No changes to headlines are expected based on tonight`s forecast,
but may be needed depending on precip rates this evening.
.LONG TERM: (Friday through Next Thursday)
Issued at 415 PM CST Thu Dec 5 2013
(Friday through Sunday)
Differences among mdls continue to plague the forecast process. Main
forecast problem is timing and placement of precip based on subtle
s/w within a mainly uniform flow. While the GFS/ECMWF are in good
agreement, the NAM/local WRF are suggesting a secondary band of
precip Fri morning across portions of central MO. This change
appears to be due to a stronger s/w in the NAM. While this s/w is
currently still across nrn portions of Mexico, there is some
legitimate concern this soln will verify.
Have therefore pulled POPS further NW and have also increased sn
amounts for Fri morning, esp across central and ern MO. With colder
air moving in, precip shield will struggle to move nw. However, due
to this cold air, some rather high SLRs may be realized over central
and into east central MO. If these trends continue in upcoming mdl
cycles, headlines may need to be upgraded and moved nwd this
SN is expected to pull ewd out of the area quickly Fri afternoon
with all precip expected to be E of the CWA by 00z Sat.
The next system to impact the area is expected to arrive late Sat
night into Sun. Latest mdl guidance has slowed the onset of this
precip. With uncertainty in timing, have lowered POPs, but have kept
basic message as the prev forecast.
With sn/ip expected across at least the srn half of the CWA, and
with strong CAA across the remainder of the area, have trended
colder again, esp with overnight lows over expected snowpack. Air
temps near zero will be possible Sat morning as clouds clear out of
the area. Since sfc winds are still expected to be around 8 to 10
kts, kept temps on the warmer side given how cold dewpoints are.
(Monday through Thursday)
Mean UA trof remains anchored over the CONUS into early next week,
with a very gradual transition to a more zonal flow regime by the
end of the work week. This should result in a very slow moderation
in temperatures during the extended period; however the overall
temperature trend during the Monday-Thursday time frame will remain
well below average for early December.
There are several shortwaves forecast to propagate through the trof
and across the nation`s midsection during this time. However,
surface ridging is forecast to dominate the mid-Mississippi Valley
during much of this time, and moisture is quite limited, so will
leave the forecast dry for now.
.AVIATION: (For the 18z TAFs through 18z Friday Afternoon)
Issued at 1023 AM CST Thu Dec 5 2013
Monitoring latest radar and model trends for snow potential this
afternoon/evening at terminals. It appears that St. Louis metro
sites will be on the northern edge of the snow shield with the
heaviest precipitation falling just south. The next round of snow
is expected to occur late tonight and into Friday. A few inches of
snow is possible. Ceilings and visibility will likely fall to
MVFR, if not IFR category with periods of snow.
Specifics for KSTL:
Light snow should build across the terminal this afternoon and
continue into early this evening. A break in the snow will likely
occur until early Friday morning when another round of light snow
occurs. Light snow accumulation is possible.
.PRELIMINARY POINT TEMPS/POPS:
Saint Louis 20 24 7 21 / 50 80 5 5
Quincy 14 22 3 20 / 10 30 5 5
Columbia 14 22 4 19 / 40 50 5 5
Jefferson City 14 23 4 19 / 50 60 5 5
Salem 23 26 9 20 / 100 90 10 5
Farmington 18 23 4 20 / 100 90 5 5
MO...WINTER WEATHER ADVISORY until 6 PM CST Friday FOR Crawford MO-
Jefferson MO-Washington MO.
WINTER STORM WARNING until 6 PM CST Friday FOR Iron MO-Madison
MO-Reynolds MO-St. Francois MO-Ste. Genevieve MO.
IL...WINTER WEATHER ADVISORY until 6 PM CST Friday FOR Bond IL-
Clinton IL-Fayette IL-Monroe IL-St. Clair IL.
WINTER STORM WARNING until 6 PM CST Friday FOR Marion IL-
Randolph IL-Washington IL.