National Weather Service Raw Text Product

187 
FXUS63 KLSX 261705
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1205 PM CDT FRI APR 26 2013

.UPDATE...
ISSUED AT 908 AM CDT FRI APR 26 2013

INCREASED POPS TODAY AS FIRST WAVE OF RAIN SHOWERS STEADILY MARCH
NORTHEAST INTO THE FORECAST AREA. DRY LOW LEVELS ARE FIGHTING A
LOSING BATTLE AND MEASURABLE PRECIPITATION HAS BEEN OBSERVED AS
FAR EAST AS FARMINGTON ALREADY. COULD SEE A BREAK ALONG THE I-70
CORRIDOR THIS AFTERNOON BEFORE ROUND NUMBER TWO OVERSPREADS THE
AREA IN ASSOCIATION WITH THE MAIN SHORTWAVE CURRENTLY LOCATED
OVER COLORADO.

CVKING

&&

.SHORT TERM...(THROUGH LATE THIS AFTERNOON)
ISSUED AT 353 AM CDT FRI APR 26 2013

THE PRIMARY FCST ISSUE FOR TODAY IS PCPN COVERAGE.

EARLY MORNING WATER VAPOR IMAGERY AND RUC 1.5 PVU ANALYSES DEPICTED 
A COMPACT VORT MAX OVER MN AS WELL AS A SHORTWAVE NEAR THE FOUR 
CORNERS REGION. A BROAD AREA OF SHRA/TSRA HAS DEVELOPED ACROSS PARTS 
OF KS/OK/MO/AR IN RESPONSE TO A COMBINATION OF H9 FRONTOGENESIS AND 
H85-H7 MOISTURE CONVERGENCE FM THE LLJ AHEAD OF THE FOUR CORNERS 
SHORTWAVE. THIS 40-50KT SWLY LLJ /PER AREA VWP AND PROFILER OBS/ WAS 
TRANSPORTING MOISTURE INTO THE AREA AND LEADING TO AN INCREASE IN 
PCPN COVERAGE. ALTHOUGH MODELS GENERALLY SHOW A DECREASE IN THE LLJ 
THROUGH MID MORNING ACROSS MO/IL...THEY ALSO SHOW PERSISTENT AREAS 
OF ISENTROPIC ASCENT ALONG THE 295-305K SFCS /ESPECIALLY ACROSS THE 
SWRN CWA/ ALONG WITH AREAS OF INCREASED FRONTOGENESIS ALOFT. 
ALTHOUGH THE BEST FORCING FOR LARGE SCALE ASCENT WILL NOT ARRIVE 
UNTIL LATER TONIGHT AND THE LOW LEVEL AIR MASS WILL INITIALLY BE 
SOMEWHAT DRY...THE AFOREMENTIONED LIFTING MECHANISMS APPEAR 
SUFFICIENT TO CONTINUE POPS FOR SCT-INTERMITTENT SHRA TODAY. 

42

.LONG TERM...(TONIGHT THROUGH THURSDAY)
ISSUED AT 353 AM CDT FRI APR 26 2013

(TONIGHT - SATURDAY)

A LARGELY NEUTRAL UPPER LEVEL FLOW WILL EXIST THRU SATURDAY...BUT 
THIS PERIOD WILL BE MOST MARKED BY A STRONG SHORTWAVE SLOWLY PASSING 
THRU.  THE PROGRESSION OF THIS SYSTEM THRU THE BI-STATE WILL BE 
SLOW...WITH IT NOT EXPECTED TO PULL AWAY UNTIL LATE SATURDAY NIGHT.  
UNTIL SUNDAY...LOOK FOR CLOUDY SKIES WITH HI RAIN PROBS...EVEN 
THOUGH SOME AREAS MAY ONLY RECEIVE A FEW HUNDREDTHS WITH EXPECTED 
NATURE OF PCPN FOR MUCH OF THIS EVENT TO BE SHOWERY.

MAIN AREAS TO KEY ON FOR RAIN TONIGHT WILL BE WHAT SHOULD BE A 
PERSISTENTLY STRONG REGION OF WAA AND H850-700 FRONTOGENESIS OVER 
SERN MO AND FAR SRN IL WHICH WILL REPRESENT THE BEST CHANCES FOR 
MEASURABLE...BUT A MORE BROADSCALE REGION OF MID LEVEL LIFT SHOULD 
ALSO WORK IN FOR THE REMAINDER OF THE AREA...ESPECIALLY W OF THE MS 
RIVER FOR ADDITIONAL LIGHT RAIN AMOUNTS.

ON SATURDAY THE MEAT OF THE SYSTEM MOVES THRU WITH GENERALLY WEAK 
YET DEEP LIFT THRU A MOIST COLUMN...AND BUMPED POPS TO LIKELY FOR 
WIDESPREAD LIGHT RAINFALL AMOUNTS.  THIS FINALLY BEGINS TO EXIT 
SATURDAY NIGHT WITH MOISTURE SLOWLY SCOURING OUT ALTHOUGH COULD SEE 
SHRA SIMPLY BE REPLACED BY DRIZZLE EARLY SUNDAY MORNING WITH LO 
CLOUDS BEING THE MOST STUBBORN OF ALL TO LEAVE.

THE WARMER MAV MOS IS PREFERRED FOR MINS TONIGHT...WHILE WENT WITH 
THE COOLER MET MOS FOR MAXES SATURDAY TO PROMOTE A LO DIURNAL SWING 
WITH WHAT SHOULD BE THICK AND LO CLOUD COVER.  AGAIN PREFERRED 
WARMER MAV MOS FOR SATURDAY NIGHT MINS. 

(SUNDAY - TUESDAY)

UPPER LEVEL LONGWAVE RIDGE WILL BUILD OVER ERN NOAM WHILE A TROF 
DIGS IN THE W...RESULTING IN A WARM AND DRY PERIOD...WITH TEMPS 
PUSHING ABOVE AVERAGE FOR A COUPLE OF DAYS AT LEAST.  WHILE DID 
UNDERCUT MOS MAX TEMPS ON SUNDAY DUE TO WHAT SHOULD BE STUBBORN LO 
CLOUD HANGING AROUND AND FINALLY LEAVING...MONDAY AND TUESDAY ARE 
EXPECTED TO FEATURE PLENTY OF SUNSHINE AND A DECENT S FLOW WITH 
RISING H500 HEIGHTS OVERHEAD.  FCST H850/H900 TEMPS...IF THEY PAN 
OUT...WILL RESULT IN 75-80F FOR MONDAY AND AROUND 78-82F FOR 
TUESDAY.  

BUILDING RIDGE WILL EFFECTIVELY DEFLECT ANY SYSTEMS TO OUR N AND 
SHOULD KEEP OUR REGION DRY. 

(WEDNESDAY - THURSDAY)

ALL OF THIS IS SHORT-LIVED...WITH THE UPPER LEVEL ERN NOAM RIDGE TO 
BREAKDOWN EITHER WEDNESDAY OR THURSDAY DEPENDING ON THE MODEL AND 
WILL BE ACCOMPANIED BY A STOUT CDFNT BACKED BY A STRONG CANADIAN 
AIRMASS.  THE ECMWF PREFERS A SLOWER TIMING ON THURS WHILE THE GFS 
FAVORS WEDNESDAY.  HAVE STRETCHED POPS FOR WED-THU TO COVER TIMING 
DIFFS WITH FRONT AND DID NOT HIT THE COLD AIR AS MUCH ON THURSDAY 
FOR THE SAME REASONS.

TES

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1156 AM CDT FRI APR 26 2013

LIGHT RAIN SHOWERS CONTINUE TO DEVELOP ACROSS THE FORECAST AREA
EARLY THIS AFTERNOON. CONDITIONS SHOULD REMAIN VFR THROUGH THE
AFTERNOON OUTSIDE OF HEAVIER RAIN WHICH IS LOCATED ACROSS THE FAR
SOUTHERN PART OF THE CWA. GENERALLY BELIEVE THAT THE MAIN THRUST
OF RAIN SHOULD COME THIS EVENING AND INTO THE OVERNIGHT AS MAIN
UPPER LEVEL ENERGY PUSH INTO THE REGION. HAVE BROUGHT CEILING DOWN
TO MVFR CATEGORY BUT AM NOT SOLD ON IFR CONDITIONS YET...WOULD
RATHER TAKE A WAIT AND SEE APPROACH. OTHERWISE...WITH UPPER LEVEL
SYSTEM MOVING OVERHEAD ON SATURDAY...COULD SEE SHOWERS AND LOWER
CEILINGS LINGER THROUGH THE DAY. SOUTH WIND WILL BECOME EAST.

SPECIFICS FOR KSTL...

ISOLATED TO SCATTERED LIGHT RAIN SHOWERS WILL CONTINUE THIS
AFTERNOON WITH A RAMPING UP OF COVERAGE AND INTENSITY THIS EVENING
AS UPPER LEVEL SYSTEM APPROACHES. COULD BE A PERIOD OF IFR
CONDITIONS IN HEAVIER RAIN...BUT WILL HAVE TO NOWCAST THIS BASED
ON RADAR AS WE GET CLOSER. OTHERWISE...CEILING TO LOWER TO MVFR
AND SHOWERS TO CONTINUE INTO SATURDAY WITH UPPER LOW TRACKING
OVERHEAD. 

CVKING

&&

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

$$

WFO LSX