056 
FXUS63 KLSX 112311
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
611 PM CDT Fri Oct 11 2013

.SHORT TERM:  (Through Late Tonight)
Issued at 318 PM CDT Fri Oct 11 2013

Although upstream front/dry line remain tranquil at 20z, believe 
that modest instability and convergence along the front should 
initiate scattered convection over the next few hours.  The coverage 
of this activity should then increase later tonight as upstream 
shortwave currently near the 4 corners works into the region.  It 
may take a while for the upstream convection to work into the CWA,  
but amount of moisture, instability, and lift all suggest scattered 
convection will threaten much of the CWA late tonight and during the 
predawn hours.  For now have placed the highest PoPs at 50% west of 
a KFAM-KTAZ line, with PoPs tapering off southeast of this line to 
low chance in KSLO area by daybreak.  For now have stayed with 
overnight lows in the 50s with the thinking that there should be a 
bit of cooling due to precip; however if convection does remain 
isolated these lows will likely be too cool by a cat or so.

Truett

.LONG TERM:  (Saturday through Next Friday)
Issued at 318 PM CDT Fri Oct 11 2013

Overall forecast trends appear on track for tomorrow with scattered 
showers and thunderstorms expected to persist from tonight into 
Saturday. A stacked low pressure system over the northern Plains 
will lift into Canada by tomorrow morning while at least one 
secondary vort max rotates around its back side, providing another 
source of lift for MO/IL. The occluding system will also continue to 
draw a narrow ribbon of moisture through the area ahead of the cold 
front (PW values will be near +2 SD). In addition, models are 
forecasting a coupled jet structure at H3 which places the LSX CWA 
beneath the favored region for enhanced lift, especially between 
12-18z. The combination of these factors should be sufficient for 
isolated to scattered precipitation, but this does not look like a 
widespread rainfall event because of the spatially limited moisture 
and overall weak forcing. 

Precipitation should end fairly quickly after the cold front moves 
through the region due to increasing subsidence with a 1025 hPa high 
pressure center that will be sliding into the northern Plains and 
western Great Lakes on Saturday night and Sunday. This area of high 
pressure will push the cold front to near the MO/AR border before 
cyclogenesis over the central Plains occurs and lifts the stalled 
boundary back northward as a warm front on Tuesday. There are still 
some model differences regarding the upper level disturbance which 
will be responsible for the surface low, but recent runs of the 
ECMWF/GFS/GEM all agree at that least a portion of that energy will 
lift through the central CONUS on Monday night and Tuesday. The 
moisture and dynamics are expected to be much better with the 
Mon/Tue system. Depending on how the upper level disturbance splits 
apart, the other half could move across the area during the middle 
or end of the week and provide additional precipitation chances. 

Kanofsky

&&

.AVIATION:  (For the 00z TAFs through 00z Saturday Evening)
Issued at 542 PM CDT Fri Oct 11 2013

Cold front extending from a sfc low over sern ND s-sw into cntrl
KS will move sewd through UIN and COU late tgt, and through the St
Louis metro area Saturday mrng. Scattered showers and a few
thunderstorms are expected along and just ahead of this front. A
band of VFR, low level clouds ahead of the front will move into
COU and UIN early this evng, and into the St Louis metro area late
this evng. Showers and a few storms should move through UIN and
COU around 06z Saturday, and through the St Louis metro area around
12z Saturday. The s-sely sfc wind should weaken this evng and lose
the gusts, then veer around to a nwly direction after fropa in
UIN and COU by early Saturday mrng and in the St Louis metro area
by late mrng. The low level clouds will clear out in the mrng in
UIN and COU, and in the aftn in the St Louis metro area as a ridge
of high pressure builds into the area behind the cold front.

Specifics for KSTL: Clouds at 4000-6000 ft will advect into STL
by late this evng with scattered showers moving into the STL area
by 12z Saturday. The showers will move out by late mrng with the
clouds clearing out in the aftn. Sely sfc wind will weaken tgt and
veer around to a swly direction Saturday mrng, and a nwly direction
Saturday aftn.

GKS

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$

WFO LSX