Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 120807
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
307 AM CDT Wed Mar 12 2014
.SHORT TERM: (Through Late This Afternoon)
Issued at 303 AM CDT Wed Mar 12 2014
Deformation zone precipitation (largely snow based on recent surface
obs and intermittent spotter reports) which was ongoing across parts
of the CWA early this morning will taper off today as the main
system continues moving away from the region. No changes are planned
to the existing Winter Weather Advisory which expires at 12z.
Wind speeds will continue decreasing today as the pressure gradient
relaxes. No changes are planned to the existing Wind Advisory which
expires in 3 segments during 12-18z.
Today`s highs in the 30s and 40s will feel rather chilly compared
to yesterday`s highs in the 70s and 80s.
.LONG TERM: (Tonight through Tuesday)
Issued at 303 AM CDT Wed Mar 12 2014
NW flow aloft persists tonight followed by a brief period of
flattened shortwave ridging ahead of the next low pressure system
moving through Canada. Models depict a surface warm front extending
NNW-SSE through MN, IA, MO, and into TN by 18z Thu (this front is
associated with a strong low pressure system that will be located
over SK/MB on Thu), therefore expect to see warmer temperatures west
of the Mississippi River on Thu afternoon. Although a lead shortwave
is forecast to eject from a cutoff low over CA/NV/AZ, no
precipitation is expected with this feature as it crosses MO/IL on
Thu night since the H85 front will be east of the area.
Meanwhile, a strong low pressure system moving through southern
Canada towards the Great Lakes will send a cold front through the
Plains states on Thu/Thu night, eventually reaching our area on
Fri. The wind field induced by a new surface wave developing along
the baroclinic zone in TX will likely slow the southward advance
of the cold front on Fri, especially since it will be so far
removed from the parent cyclone. The cold front is forecast to
move through the LSX CWA on Fri night. Some precipitation is
possible across the southern CWA ahead of this front.
Models are still having difficulty with the timing, speed, and
strength of the cutoff low over CA/NV/AZ once it starts to eject
eastward. Instead of phasing it with a shortwave dropping out of
Canada, 00z EC/GFS runs now develop that shortwave into its own
cutoff low and retrograde it southwestward through Mexico towards
Baja California, leaving the remnants of the cutoff low to pass
south of MO/IL sometime between Fri and Sun. Some models also show
yet another vort max that could bring precipitation to MO/IL
sometime between Sat night and Sun night, but confidence remains
low due to model disagreement with these features.
.AVIATION: (For the 06z TAFs through 06z Wednesday Night)
Issued at 1145 PM CDT Tue Mar 11 2014
Low pressure passing just to the south of St. Louis with the cold
front through all terminals at this hour. North/northwest wind
will continue to increase and gust to 35 KT in wake of the storm
system. Rain will continue to mix with snow from north to south
tonight before ending. IFR conditions are likely with the heavier
rain/snow. A minor snow accumulation of a few inches is likely at
KUIN, with little if any expected at KCOU and St. Louis area
terminals. Ceiling should rise tomorrow in wake of the storm
system but overcast conditions are anticipated in cold cylonic
flow. Wind will decrease toward evening.
Specifics for KSTL:
Rain will continue into early Wednesday morning with a brief
changeover to snow before ending. Not expecting much accumulation
with surface temperatures and ground above freezing. A period of
IFR conditions is likely with the heavier rain/snow with improving
conditions on Wednesday. Gusty north/northwest wind will become
light Wednesday evening.
MO...WIND ADVISORY until 10 AM CDT this morning FOR Crawford MO-
Franklin MO-Iron MO-Jefferson MO-Madison MO-Reynolds MO-St.
Charles MO-St. Francois MO-St. Louis City MO-St. Louis MO-
Ste. Genevieve MO-Washington MO.
WIND ADVISORY until 7 AM CDT this morning FOR Audrain MO-Boone
MO-Callaway MO-Cole MO-Gasconade MO-Knox MO-Lewis MO-
Lincoln MO-Marion MO-Moniteau MO-Monroe MO-Montgomery MO-
Osage MO-Pike MO-Ralls MO-Shelby MO-Warren MO.
WINTER WEATHER ADVISORY until 7 AM CDT this morning FOR Lewis MO-
IL...WIND ADVISORY until 10 AM CDT this morning FOR Greene IL-Jersey
IL-Macoupin IL-Madison IL-Monroe IL-St. Clair IL.
WIND ADVISORY until 7 AM CDT this morning FOR Adams IL-Brown IL-
Calhoun IL-Pike IL.
WIND ADVISORY until 1 PM CDT this afternoon FOR Bond IL-Clinton
IL-Fayette IL-Marion IL-Montgomery IL-Randolph IL-
WINTER WEATHER ADVISORY until 7 AM CDT this morning FOR Adams IL-
Brown IL-Pike IL.