Area Forecast Discussion
Issued by NWS St. Louis, MO
FXUS63 KLSX 121152
AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
652 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 12z TAFs through 12z Thursday Morning)
Issued at 637 AM CDT Wed Mar 12 2014
Surface low that intensified over the region overnight has now
surged into the Upper Ohio Valley, with the last of precipitation
associated with tail end of deformation zone exiting STL area at
this time. The back edge of MVFR cigs lag the back edge of this
precip shield by several hours, but this edge also continues to
pull east with the low. If the cloud trend of the past few hours
continue...the MVFR cigs over STL area should clear out by 15z.
There is another strong shortwave that is clearly visible on water
vapor imagery over NE IA, and as this feature drops south expect
additional cloudiness...with bases aoa 3kft...to either advect or
develop along and east of the Mississippi River during the late
morning and early afternoon hours. Additional clouds with bases
aoa 5kft expected across the area tonight as warm advection
intensifies upstream over the mid Missouri Valley. Intense
pressure gradient produced by the surface low will maintain strong
and gusty NW winds into early afternoon, with speeds quickly
diminishing by late in the day.
Specifics for KSTL: MVFR cigs ovr area should exit to the east by
15z, with additional, diurnally driven clouds aoa 3kft
redeveloping durnig the late morning and into the early afternoon
hours. NW winds with gusts to near 30 knots are expected into
the early afternoon.
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.
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-