637 
FXUS63 KLSX 301427
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
927 AM CDT Wed Oct 30 2013

.SHORT TERM:  (Through Late Tonight)
Issued at 926 AM CDT Wed Oct 30 2013

Based on latest obs, will extend the current dense fog advisory
for our southwest Illinois counties through 11 am. Visibilities
over Missouri (including MO portion of STL metro) and west central
Illinois have improved enough that advisory no longer needed in
these areas.

Truett

.LONG TERM:  (Tonight through Tuesday)
Issued at 349 AM CDT Wed Oct 30 2013

(Tonight - Thursday Night)

Guidance continues to be in good agreement with the strong upper 
system over the Rockies, so have made few changes to the going 
forecast.  The closed low will open up and move into the Great 
Plains and then further east tonight into Thursday.  It should be a 
fairly wet period with the Gulf of Mexico wide open, and a 40-60kt 
low level jet pumping moisture up into the Mid-Mississippi Valley.  
Moisture convergence along with dynamic lift from the approaching 
upper level trof will be plenty of forcing to produce showers and 
thunderstorms across the area.  The probability of rain is almost as 
close to certain as it ever gets, but exact timing and amounts are 
still in question.  Feel pretty confident that the entire area will 
see measurable precipitation tonight and Thursday, but it's likely 
there will also be some dry periods.  The hourly details of the 
convective forecast are impossible to nail down at this time, so 
have stuck with 6-12 hour blocks of categorical pops.  HPC qpf 
guidance continues to look pretty reasonable so have stuck with it.  
SPC backed the day2 slight risk back up into the southern portion of 
our CWFA across the eastern Ozarks and southwest Illinois.  The 
kinematics will be very strong in this case with 0-6km bulk shear in 
excess of 70kts and 0-1km shear in excess of at least 40kts across 
the slight risk area.  Models only have show about 200-300 J/kg of 
CAPE though.  Personally I'd like to see CAPE values greater than 
400-500 J/kg, but given the ludicrous shear I can't say there won't 
be severe thunderstorms.  At any rate, the surface front should 
sweep through by early-mid evening effectively ending the rain and 
any severe threat across the area.

(Friday - Tuesday)

Friday through Sunday should be dry as a Pacific high builds across 
the country.  The center of the high should be down across the Lower 
Tennessee Valley by 12Z Sunday.  Temperatures on Friday will remain 
mild in westerly flow with highs running around 5 degrees above 
normal.  For Saturday and Sunday the wind will turn to the northwest 
allowing some cooler air to filter across the Mississippi Valley 
and temperatures will be near or a few degrees below normal.  The 
ridge moves east on Monday, and the wind will shift back to a 
southerly direction, and low level moisture will begin to move back 
into the region as another longwave trof sharpens up over the 
Rockies.  Medium range guidance remains in good agreement in 
producing another round of rain over the area as the low level jet 
ramps up Monday into Tuesday.

Carney

&&

.AVIATION:  (For the 12z TAFs through 12z Thursday Morning)
Issued at 704 AM CDT Wed Oct 30 2013

Warm front continues to make very slow progress to the north, so
dealing with dense fog at taf sites this morning. Went with
quarter to half mile vsbys through 14z, then conditions improve.
As for cigs, sites along Interstate 70 to see cigs lift to mvfr by
14z, then to vfr after 17z. However, KUIN to remain socked in with
ifr cigs til 17z when front lifts north of KUIN. East winds to
veer to the south and increase after front moves through. As for
pcpn chances, hard to pin down. Will just see scattered activity
this morning with better chances later this afternoon and into the
overnight hours. Best thunderstorm chances will be along and south
of I-70, so have mention in these tafs between 17z and 22z, then
just have showers with vcts mention.

Specifics for KSTL:
Warm front continues to make very slow progress to the north, so
dealing with dense fog in metro area this morning. Went with
quarter mile vsby through 14z, then conditions improve. As for
cigs, ifr/mvfr cigs to lift to vfr by 17z. Southeast winds to veer
to the south and increase by 14z. As for pcpn chances, hard to
pin down. Will just see scattered activity this morning with
better chances later this afternoon and into the overnight hours.
Best thunderstorm chances will be between 19z and 22z, then just
have showers with vcts mention through rest of forecast period.

Byrd

&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...DENSE FOG ADVISORY until 11 AM CDT this morning FOR Bond IL-
     Clinton IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Marion IL-Montgomery IL-St. Clair IL-Washington 
     IL.

&&

$$

WFO LSX