Hail and Damaging Wind in Missouri, April 19, 2011

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1219 AM CDT TUE APR 19 2011

.UPDATE...
/948 PM CDT MON APR 18 2011/

00Z SOUNDINGS INDICATE MID LEVEL CAP IS ALREADY FIRMLY ENTRENCHED
OVER W CENTRAL AND SW MO. HOWEVER...AS WARM AND MOIST AIR BENEATH
THE CAP ADVECTS EWD COOLER MID LEVEL TEMPS ALONG AND EAST OF THE
MISSISSIPPI RIVER SHOULD ALLOW A GOOD DEAL OF ELEVATED CONVECTION
TO DEVELOP...WITH HEAVY RAIN AND HAIL STILL POSSIBLE. HAVE KEPT
LIKELY AND HIGHER POPS GOING MOST AREAS FOR THE REST OF
TONIGHT...HOWEVER DID BACK POPS OFF TO CHANCE OVER MID
MISSOURI...AS THIS AREA SHOULD BE ON THE W AND/OR S FRINGES OF THE
OVERNIGHT CONVECTION. UPDATE OUT IN A SECOND.

TRUETT

&&

.DISCUSSION...
/204 PM CDT MON APR 18 2011/

...SEVERE THUNDERSTORM OUTBREAK TUESDAY AFTERNOON AND EVENING...

LATEST SURFACE ANALYSIS SHOWS SURFACE FRONT HAS STALLED ALONG THE
INTERSTATE 70 CORRIDOR...ESSENTIALLY BISECTING THE CWA.

SCATTERED THUNDERSTORMS ARE EXPECTED TO DEVELOP AFTER 21Z IN
VICINITY OF THE FRONTAL BOUNDARY. THIS WILL BE IN RESPONSE TO
INCREASING INSTABILITY AND A SERIES OF WEAK MID LEVEL VORTICES/
SURFACE WAVES TRAVERSING THE BOUNDARY. COVERAGE WILL CONTINUE TO
INCREASE ALONG AND NORTH OF THE BOUNDARY THIS EVENING AND OVERNIGHT
AS THE LOW LEVEL JET INCREASES. EXPECT A FEW OF THE THUNDERSTORMS
WILL BECOME SEVERE THIS AFTERNOON AND TONIGHT GIVEN 0-6KM SHEAR
VALUES AROUND 50KTS AND MUCAPES INCREASING TO AROUND 1000 J/KG.
ELEVATED NATURE OF THE CONVECTION AND LOW FREEZING LEVELS SUGGESTS
MAIN SEVERE THREAT WILL BE LARGE HAIL. ALTHOUGH...GIVEN INCREASING
LOW LEVEL MOISTURE...A THREAT OF LOCALLY HEAVY RAINFALL WILL ALSO
DEVELOP TONIGHT IF TRAINING CONVECTION OCCURS.

THIS FIRST ROUND OF THUNDERSTORM ACTIVITY SHOULD PUSH NORTH OF THE
AREA AS THE BOUNDARY LIFTS NORTH AS A WARM FRONT EARLY TUESDAY
MORNING. STILL THINK THERE WILL BE A LULL IN ACTIVITY BETWEEN 15Z
AND 21Z TOMORROW AS MUCH OF THE AREA IS CAPPED IN THE WARM SECTOR.

ALL THE MODEL DATA THAT WE CAN GET OUR HANDS ON CONTINUES TO PORTRAY
A RAPID DECREASE IN CIN LATE TOMORROW AFTERNOON AS STRONG ASCENT
OVERSPREADS THE REGION. CONVECTIVE INITIATION IS EXPECTED TO OCCUR
ROUGHLY AROUND 21Z...WITH SUPERCELLS BEING THE INITIAL STORM MODE.
LOCAL WRF CONTINUES TO PORTRAY THE MOST WORRISOME SCENARIO...WITH
TWO DISTINCT LINES OF CONVECTION DEVELOPING. AT THE ONSET THERE
CERTAINLY COULD BE TWO NORTH-SOUTH ORIENTATED LINES OF
SUPERCELLS...ONE ACROSS WESTERN/CENTRAL MISSOURI AND ANOTHER NEAR
THE MISSISSIPPI RIVER.

A MAJOR SEVERE WEATHER OUTBREAK IS EXPECTED TO OCCUR AS SHEAR AND
INSTABILITY PARAMETERS ARE CONDUCIVE FOR LONG TRACK SUPERCELLS
CAPABLE OF PRODUCING SIGNIFICANT/STRONG TORNADOES...VERY LARGE HAIL
AND DAMAGING STRAIGHT LINE WINDS. WE SHOULD SEE CONVECTION CONGEAL
INTO A SEVERE LINEAR MCS DURING THE EVENING AS IT PROGRESSES FURTHER
EAST...EXITING THE CWA SHORTLY AFTER 06Z.

COOLER WEATHER IS USHERED IN FOR MID WEEK WITH TEMPERATURES
STRUGGLING TO RISE OUT OF THE 50S WEDNESDAY AND THURSDAY.
MEANWHILE...THE FRONT WILL BEGIN MOVING BACK NORTH WITH A CLASSIC
OVERRUNNING/WARM ADVECTION PRECIPITATION EVENT OCCURRING THURSDAY
NIGHT INTO FRIDAY MORNING. ACTIVE WEATHER PATTERN CONTINUES THROUGH
THE WEEKEND WITH THE POTENTIAL OF HEAVY RAINFALL AND EPISODES OF
SEVERE WEATHER INCREASING AS QUASI-STATIONARY FRONTAL BOUNDARY
BECOMES PARKED ACROSS THE CWA. BUT LET'S GET THROUGH TOMORROW...

CVKING

&&

.AVIATION...
/1206 AM CDT TUE APR 19 2011/

SOME QUESTION REMAINS REGARDING CONVECTION TONIGHT. AREA OF PRECIP
WILL LINGER NEAR UIN OVERNIGHT. NEAR COU/SUS...CONVECTION MAY
BEGIN LATER TONIGHT AS LLJ BEGINS TO INCREASE. OTHERWISE...CIGS
WILL REMAIN LOW MVFR TO IFR OVERNIGHT WITH CIGS GRADUALLY
LOWERING. UIN IS EXPECTED TO REMAIN N OF THE WRMFNT ON TUES AND
SHUD THEREFORE EXPERIENCE LOW MVFR CIGS FOR THE ENTIRE TAF PERIOD.
KEPT PRECIP VAGUE AS UNCERTAIN HOW WIDESPREAD PRECIP WILL BE N OF
THE WRMFNT. FOR COU/SUS...EXPECT TSRA...VERY POSSIBLE SEVERE...
JUST AHEAD OF THE APPROACHING CDFNT AND SFC LOW. TIMING OF THIS
CDFNT REMAINS SOMEWHAT UNCERTAIN...BUT IS A LITTLE FASTER THAN
PREVIOUS GUIDANCE. BEHIND THE FNT...CIGS WILL RAPIDLY DROP INTO
THE LOW MVFR RANGE AGAIN. CAN NOT RULE OUT LIGHT FG AS WELL...BUT
WILL KEEP OUT OF TAF FOR NOW.

SPECIFICS FOR KSTL...SOME QUESTION REMAINS REGARDING CONVECTION
TONIGHT. CONVECTION MAY BEGIN LATER TONIGHT AS LLJ BEGINS TO
INCREASE AND VEER. OTHERWISE...CIGS WILL REMAIN LOW MVFR AND
EXPECTED TO DRIP TO IFR OVERNIGHT. FOR TUESDAY...EXPECT
TSRA...VERY POSSIBLE SEVERE...JUST AHEAD OF THE APPROACHING CDFNT
AND SFC LOW. TIMING OF THIS CDFNT REMAINS SOMEWHAT UNCERTAIN...BUT
IS A LITTLE FASTER THAN PREVIOUS GUIDANCE. BEHIND THE FNT...CIGS
WILL RAPIDLY DROP INTO THE LOW MVFR RANGE AGAIN. CAN NOT RULE OUT
LIGHT FG AS WELL...BUT WILL KEEP OUT OF TAF FOR NOW.

TILLY

&&

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

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
318 PM CDT MON APR 18 2011

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-191230-
GREENE IL-MACOUPIN IL-MONTGOMERY IL-BOND IL-FAYETTE IL-CLINTON IL-
MARION IL-WASHINGTON IL-RANDOLPH IL-ADAMS IL-BROWN IL-PIKE IL-
CALHOUN IL-JERSEY IL-MADISON IL-ST. CLAIR IL-MONROE IL-KNOX MO-
LEWIS MO-SHELBY MO-MARION MO-MONROE MO-RALLS MO-PIKE MO-BOONE MO-
AUDRAIN MO-MONITEAU MO-COLE MO-OSAGE MO-CALLAWAY MO-MONTGOMERY MO-
LINCOLN MO-GASCONADE MO-WARREN MO-ST. CHARLES MO-FRANKLIN MO-
ST. LOUIS MO-ST. LOUIS CITY MO-JEFFERSON MO-CRAWFORD MO-
WASHINGTON MO-ST. FRANCOIS MO-STE. GENEVIEVE MO-IRON MO-
MADISON MO-REYNOLDS MO-
318 PM CDT MON APR 18 2011

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF EASTERN AND
CENTRAL MISSOURI AS WELL AS WEST CENTRAL AND SOUTHWEST ILLINOIS.

.DAY ONE...TONIGHT

SCATTERED THUNDERSTORMS WILL DEVELOP AND INCREASE IN COVERAGE
ACROSS THE REGION THIS EVENING AND CONTINUE OVERNIGHT. ISOLATED
SEVERE THUNDERSTORMS ARE POSSIBLE WITH THE MAIN THREAT BEING HAIL
UP TO THE SIZE OF QUARTERS. LOCALLY HEAVY RAINFALL WILL ALSO BE
POSSIBLE.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

A SIGNIFICANT OUTBREAK OF SEVERE THUNDERSTORMS IS EXPECTED TUESDAY
AFTERNOON AND TUESDAY EVENING OVER MUCH OF THE AREA. THE
STRONGEST THUNDERSTORMS WILL BE CAPABLE OF PRODUCING STRONG TORNADOES...
HAIL LARGER THAN GOLF BALL SIZE AND DAMAGING STRAIGHT LINE WIND
GUSTS. LOCALLY HEAVY RAINFALL IS ALSO POSSIBLE.

THUNDERSTORMS ARE LIKELY THURSDAY NIGHT THROUGH FRIDAY NIGHT AS
ANOTHER STORM SYSTEM MOVES ACROSS THE REGION. THERE IS SOME
POTENTIAL FOR ADDITIONAL SEVERE WEATHER DURING THIS PERIOD.

THERE IS A CONTINUED CHANCE OF THUNDERSTORMS SATURDAY NIGHT AND
SUNDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTERS ARE ASKED TO RELAY ALL SEVERE WEATHER REPORTS AND
RAINFALL AMOUNTS OVER AN INCH TO THE NATIONAL WEATHER SERVICE IN
ST. LOUIS.

CVKING