547 
FXUS63 KLSX 280815
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
315 AM CDT FRI SEP 28 2012

.SHORT TERM...
ISSUED AT 313 AM CDT FRI SEP 28 2012
(TODAY)

THE PRIMARY FCST ISSUE FOR THIS FCST PD IS DETERMINING WHICH PARTS
OF THE CWA ARE MOST LIKELY TO RECEIVE PCPN THROUGH 00Z.

07Z METARS AND MSAS SATURATED EQUIVALENT POTENTIAL TEMPERATURE 
FIELDS DEPICTED AN E-W ORIENTED BDRY BISECTING THE CWA. ALOFT...A 
SHORTWAVE TROF WAS LOCATED OVER CENTRAL AND WRN MO PER WATER VAPOR 
SATELLITE IMAGERY ALONG WITH AN ANTICYCLONICALLY CURVED JET STREAK 
AT H25 OVER CENTRAL IL NOTED ON THE LATEST RUC ANALYSIS AND 
SUPPORTED BY AREA VWP/PROFILER OBS. LARGE SCALE LIFT AHEAD OF THIS 
SHORTWAVE AND RER DYNAMICS ASSOCIATED WITH THE CURVED JET STREAK 
WERE SUPPORTING ISO-SCT SHRA ACROSS THE SRN HALF OF THE CWA...MAINLY 
ALONG AND S OF THE BDRY. THESE FEATURES ARE EXPECTED TO MOVE E OF 
THE CWA BY DAYBREAK WITH PCPN DIMINISHING DUE TO SUBSIDENCE IN THE 
WAKE OF THE DEPARTING SHORTWAVE AND DRIER AIR FILTERING IN TO THE
REGION AS A SFC HIGH SINKS SWD. HOWEVER...THE BDRY WILL STILL BE
PRESENT /ALBEIT SLOWLY SINKING SWD/ ACROSS PART OF THE AREA
THROUGH THE AFTN HOURS...AND ANOTHER SHORTWAVE WAS LOCATED
UPSTREAM AT 07Z NEAR THE KS/CO BORDER. DESPITE THE DRIER AIR
FILTERING IN FROM THE NORTH...MODELS DO SHOW SOME 300-250MB
DIVERGENCE ACROSS THE SRN CWA DURING THE DAY AND WHEN COMBINED
WITH THE CO/KS SHORTWAVE THERE MAY BE ENOUGH SUPPORT FOR ISO-SCT
SHRA THIS AFTN INVOF THE BDRY. 

KANOFSKY

&&

.LONG TERM...
ISSUED AT 300 AM CDT FRI SEP 28 2012 
(TONIGHT - TUESDAY)

ZONAL FLOW ALOFT THAT HAS GIVEN US A PROLONGED PERIOD OF UNSETTLED 
WX THIS PAST WEEK WILL TRANSITION TO NW TO N FLOW THAT SHOULD GIVE 
US A QUIETER PERIOD FOR A BIT.  THIS CHANGE IN FLOW WILL INITIALLY 
BE HELPED OUT BY A POLAR VORTEX DIGGING INTO THE GRTLKS REGION THIS 
WEEKEND AND LATER BY A TROF THAT DIGS INTO THE CNTRL AND S CNTRL 
CONUS EARLY NEXT WEEK...WITH BOTH OF THESE FEATURES EXPECTED TO BE 
FAR ENOUGH AWAY TO HAVE LITTLE IMPACT.  THE SFC IS EXPECTED TO HAVE 
A WEAK RIDGE PREVAILING FOR MUCH OF THIS PERIOD...ALTHOUGH A TROF 
WILL TAKE A SWIPE MAINLY AT THE IL SIDE ON SATURDAY NIGHT AND 
SUNDAY.  

BELOW NORMAL PWATS FOR THIS WEEKEND...A STABLE ATMOSPHERE...AND MOST 
IMPORTANTLY...LIFTING MECHANISMS TOO WEAK...SHOULD PRECLUDE ANY PCPN 
DEVELOPMENT THIS WEEKEND.  NEAR AVERAGE TEMPS FOR LATE SEPTEMBER ARE 
EXPECTED...WHICH FAVOR THE MAV MOS NUMBERS WHICH IN MOST CASES ARE 
RUNNING A BIT LOWER THAN THE MET MOS. 

UP UNTIL THIS POINT THERE IS GOOD AGREEMENT BETWEEN THE MODELS.  WE 
START TO SEE SOME DISAGREEMENT BEGINNING MONDAY WHERE THE ECMWF 
DRAGS A CDFNT THRU WHEREAS THE GFS KEEPS IT WEST OF THE FA WHERE IT 
THEN DISSIPATES IT AND RE-ESTABLISHES THE RIDGE.  IT APPEARS WITH 
RESPECT TO THE BOTTOM LINE...THIS IS A MINOR QUIBBLE AS THE ECMWF 
STRUGGLES TO BRING ANY MOISTURE UP IN TIME FOR WHEN IT BRINGS THE 
CDFNT THRU...AND IF THIS DOES HAPPEN...SHOULD GO THRU DRY AS A 
SYSTEM FURTHER TO THE SE WILL STEAL THE SHOW AND HOG THE SENSIBLE 
WX.  WILL NEED TO WATCH EXACTLY WHERE THIS SERN CONUS SYSTEM GOES AS 
IT COULD EDGE SOME PARTS OF SERN MO AND SRN IL ON MONDAY.  TEMPS 
COULD BE A BIGGER SOURCE OF ERROR HERE...NAMELY IF THE FRONT 
ACTUALLY GOES THRU OR NOT...BUT TEMPS AT OR A BIT ABOVE AVERAGE SEEM 
THE BETTER BET.  

(WEDNESDAY - THURSDAY)

GFS AND ECMWF CONTINUE THEIR STANDOFF INTO THE MID AND LATER PARTS 
OF NEXT WEEK.  THE ECMWF FEATURES ZONAL FLOW RETURNING BUT MORE IN 
THE FORM OF A PLATEAUED OUT BUILDING RIDGE FROM THE SW WHILE THE GFS 
MAINTAINS A TROF OVER THE LOWER MS VALLEY WHICH THEN LIFTS NEWD INTO 
THE LOWER OH VALLEY AS IT GETS ABSORBED.  EITHER WAY...BOTH ARE 
TAKING ANOTHER...STRONGER...CDFNT THRU THE AREA DURING THIS TIME BUT 
THE DIFFS IN FLOW ALOFT WILL MAKE FOR A TIMING QUANDARY WITH THE 
FRONT BY AS MUCH AS 24HRS.  THE GFS TAKES THE CDFNT THRU WEDNESDAY 
WHILE THE ECMWF DOESN/T UNTIL THURSDAY.  BUT ONCE AGAIN...MOISTURE 
RETURN FROM THE GULF IS EFFECTIVELY BLOCKED AND WILL MAKE FOR 
LIMITED AMOUNTS TO WORK WITH.  VERY QUESTIONABLE WHETHER OR NOT 
FRONT CAN GENERATE PCPN HERE BUT IF STRENGTH OF COLD AIR BEHIND IS 
SUFFUCIENT...IT MAY.  ABOVE AVERAGE TEMPS TO CONTINUE AHEAD OF 
FRONT.

TES

&&

.AVIATION...
ISSUED AT 1152 PM CDT THU SEP 27 2012

HAVE ADDED VCSH AT KCOU AND THE ST. LOUIS METRO TAFS OVER THE NEXT
6 HOURS AS SCATTERED -RA HAS DEVELOPED OVER WRN MO AND WILL MOVE
EAST OVERNIGHT. OTHERWISE...NOT CERTAIN IF CIGS WILL FALL INTO THE
MVFR RANGE THROUGH 14Z...SO HAVE CIGS IN THE BKN035-040 RANGE.
AFTER 15Z...EXPECT DRY AND VFR CONDITIONS THE REST OF THE PERIOD.

SPECIFICS FOR KSTL...HAVE ADDED VCSH FROM 08-11Z TO REFLECT RECENT
DEVELOPMENT OF -RA OVER CNTRL/WRN MO. THERE IS STILL SOME POSSIBILITY
THAT CIGS WILL FALL INTO THE MVFR RANGE OVERNIGHT...BUT WITH PERSISTENT
10-15KT WINDS BETWEEN 1-3K FT NOTED ON THE KLSX AND TSTL WIND
PROFILES THAT WILL IS BRINGING DRY AIR INTO THE REGION...DO NOT
FEEL CONFIDENT ENOUGH AT THIS POINT TO INCLUDE IN A PREDOMINANT
GROUP IN THE TAF. OTHERWISE...EXPECT DRY AND VFR CONDITIONS TO
RETURN TO THE AREA BY MID-MORNING FRIDAY.

BRITT

&&

.PRELIMINARY POINT TEMPS/POPS...
ST LOUIS        75  52  75  56 /  10   0   0   0 
QUINCY          71  47  76  50 /   5   0   0   0 
COLUMBIA        73  48  75  51 /  10   0   0   0 
JEFFERSON CITY  73  49  74  51 /  20   5   0   0 
SALEM           72  48  72  50 /  10   0   0   5 
FARMINGTON      72  50  73  50 /  20   5   0   0 

&&

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

$$

WFO LSX