791 
FXUS63 KLSX 132025
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
325 PM CDT WED MAR 13 2013

.SHORT TERM...(THROUGH LATE TONIGHT)
ISSUED AT 321 PM CDT WED MAR 13 2013

STRATO-CU WHICH HAS PERSISTED IN THE LOW LEVEL CYCLONIC FLOW OVER 
SOUTH CENTRAL ILLINOIS WILL DISSIPATE WITH THE LOSS OF DAYTIME 
HEATING.  SURFACE RIDGE CURRENTLY EXTENDING FROM CENTRAL IOWA INTO 
WESTERN MISSOURI WILL MOVE INTO THE CWA THIS EVENING AT THE SAME 
TIME THE SKIES WILL BE CLEARING. THIS WILL SET UP DECENT RADIATIONAL 
COOLING WHICH WILL ALLOW FOR A QUICK DROP IN TEMPERATURES EARLY THIS 
EVENING.  TEMPERATURES MAY BECOME STEADY OVER CENTRAL AND NORTHEAST 
MISSOURI LATE TONIGHT AS WINDS PICK UP FROM THE SOUTH AS THE RIDGE 
SHIFTS TO THE EAST.  WENT AT OR JUST BELOW MOS GUIDANCE TEMPERATURES 
GIVEN THE RADIATIONAL COOLING AND THE VERY DRY DEWPOINTS.

SHORTWAVE TROUGH CURRENTLY OVER MONTANA WILL DIVE SOUTHEASTWARD AND 
MOVE THROUGH MISSOURI/ILLINOIS EARLY ON THURSDAY.  THERE WILL BE 
SOME WEAK ASCENT MOVE INTO THE NORTHERN CWA LATE TONIGHT...HOWEVER 
THE DRY LOW LEVELS SHOULD KEEP MEASURABLE PRECIPITATION OUT OF THE 
AREA UNTIL AFTER 12Z.

BRITT

&&

.LONG TERM...(THURSDAY THROUGH NEXT WEDNESDAY)
ISSUED AT 321 PM CDT WED MAR 13 2013

THU/THU NIGHT...A VORT MAX WILL DIVE SEWD ACROSS THE AREA ON THU 
WITHIN A BROADER NW FLOW PATTN. THIS DISTURBANCE MAY SUPPORT ISO-SCT 
RAIN SHOWERS ACROSS THE ERN HALF OF THE CWA...ESPECIALLY DURING THE 
LATE MORNING AND EARLY AFTN HOURS WHEN ASCENT AHEAD OF THE VORT MAX 
WILL BE MAXIMIZED.

FRI/FRI NIGHT...A NW-SE ORIENTED SFC BAROCLINIC ZONE WILL BECOME 
ESTABLISHED ACROSS MO/IL...POSSIBLY RIGHT OVER STL. THERE COULD BE A 
FAIRLY LARGE DIFFERENCE IN AFTN HIGHS ACROSS THE GREATER ST. LOUIS 
METRO AREA IF THE GRADIENT IS SHARP ENOUGH AND FAVORABLY POSITIONED. 
IT LOOKS LIKE FRI WILL BE THE WARMEST DAY OUT OF THE NEXT 7 DAYS FOR 
MOST OF THE CWA...ESPECIALLY CENTRAL MO WHERE SOME LOCATIONS WILL 
EXPERIENCE AFTN HIGHS NEARLY 20 DEGREES ABOVE AVERAGE FOR THIS TIME 
OF YEAR. A MID/UPPER LEVEL VORT MAX MOVING THROUGH THE REGION ON FRI 
WILL INDUCE A SFC WAVE ALONG THE BAROCLINIC ZONE...PROBABLY 
SOMEWHERE IN SRN IA OR NRN MO. ISO-SCT PCPN IS POSSIBLE ON FRI NIGHT 
WHEN THIS SYSTEM MOVES EWD ACROSS THE AREA. 

SAT/SAT NIGHT...ONCE THE MID/UPPER VORT MAX MOVES EWD AND FLOW 
AROUND THE SFC WAVE HAS REORIENTED THE BAROCLINIC ZONE FM NW-SE TO 
W-E...THIS BDRY WILL SINK SWD AS A CDFNT AND EVENTUALLY STALL EITHER 
IN SRN MO OR NEAR THE MO/AR BORDER. THE SWD EXTENT OF THE CDFNT WILL 
DEPEND ON THE STRENGTH OF A SFC RIDGE SLIDING SWD OUT OF CANADA. THE 
SWD EXTENT OF THE CDFNT IS IMPORTANT NOT ONLY FOR THE TEMPERATURE 
FCST ON SAT BUT ALSO FOR DETERMINING PCPN CHCS ON SAT NIGHT BECAUSE 
A LLJ /ASSOCIATED WITH A DVLPG SFC LOW OVER OK AND TX WHICH WILL 
HAVE BEEN INDUCED BY A SHORTWAVE MOVING ACROSS THE SRN PLAINS/ IS 
FCST TO IMPINGE ON THE BDRY AND PRODUCE AN AREA OF SHRA/TSRA. 

SUN/SUN NIGHT...PCPN WILL LINGER INTO SUN THEN TAPER OFF BY SUN 
NIGHT AS THE LOW PRESSURE SYSTEM MOVES NEWD FM OK/TX THROUGH MO AND 
INTO IL/IN. FARTHER UPSTREAM...A STRONG SHORTWAVE WILL INDUCE LEE 
SIDE CYCLOGENESIS SOMEWHERE BETWEEN OK AND SD AS IT CROSSES THE 
ROCKIES.

MON/MON NIGHT...MODELS AGREE ON THE EXISTENCE OF A LOW PRESSURE 
SYSTEM SOMEWHERE IN THE NRN/CENTRAL PLAINS BUT DISAGREE ON SOME OF 
THE DETAILS. THERE IS A CHANCE OF RAIN ASSOCIATED WITH THIS SYSTEM 
GIVEN THE STRONG DYNAMICS AND FAVORABLE LOCATION. 

TUE/TUE NIGHT...A SFC HIGH PRESSURE CENTER WILL BUILD INTO THE 
REGION BENEATH CONFLUENT NW FLOW ALOFT IN THE WAKE OF THE PREVIOUS 
SYSTEM. NO PCPN IS EXPECTED ATTM UNLESS THE PREVIOUS SYSTEM IS
SLOWER THAN ANTICIPATED. 

KANOFSKY

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1212 PM CDT WED MAR 13 2013

DRY AND VFR CONDITIONS ARE EXPECTED THROUGH THE FORECAST PERIOD.
WINDS WILL BECOME LIGHT AND VARIABLE TONIGHT AS HIGH PRESSURE
CENTER MOVES ACROSS THE AREA. WINDS WILL THEN PICK UP OUT OF THE
SOUTH ON WEDNESDAY MORNING AS THE RIDGE MOVES BY.

SPECIFICS FOR KSTL...DRY AND VFR CONDITIONS ARE EXPECTED THROUGH
THE TAF PERIOD. WINDS WILL TURN LIGHT AND VARIABLE TONIGHT BEFORE
INCREASING FROM THE SOUTH ON THURSDAY MORNING. WINDS WILL SHIFT
WESTERLY BY MID AFTERNOON.

BRITT

&&

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

$$

WFO LSX