EF0 tornado, Shelbina to Lakenan, Missouri, February 27, 2011

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
550 PM CST SUN FEB 27 2011

.DISCUSSION...
/345 PM CST SUN FEB 27 2011/

THERE BE A PLETHORA OF WX HAZARDS TO DEAL WITH OVER THE NEXT 24HRS.

FIRST WILL BE THE SVR WX THREAT. A STRENGTHENING FRONTAL ZONE FROM
JUST S OF KPPQ TO KMYJ WILL REMAIN QUASI-STATIONARY THRU THE EVENING
HRS BEFORE MAKING ITS FINAL PUSH SEWD THRU THE FA. STEEP MID LEVEL
LAPSE RATES...ONLY KEPT AT BAY BY A STOUT CAP...BUT THAT WILL NOT BE
MUCH OF AN ISSUE SOON AS DEEP LIFT FROM A STRONG SHORTWAVE LIFTS
THIS LAYER AND REMOVES THE CAP. THIS SHOULD BE ALL COMING TOGETHER
AROUND 00Z AND WILL CONTINUE THRU THE EVENING AND INTO THE EARLY
OVERNIGHT. FOR MOST AREAS IN THE NRN FA...ROUGHLY N OF I-70...THE
PRIMARY THREAT WILL BE LARGE HAIL WITH A BRIEF SPINUP TORNADO
POSSIBLE WITH ANY SUPERCELLS THAT CROSS THE LO LEVEL FRONTAL ZONE.
FOR THE I-70 CORRIDOR AND AREAS S...A GREATER THREAT FOR DAMAGING
WINDS WILL EXIST TO ACCOMPANY THE LARGE HAIL...AS WELL AS TORNADOES.
THE MODELS STILL HAVE SOME ISSUES WITH EXACT STRUCTURE OF THE
SYSTEM...BUT MOST AGREE THAT A SEPARATION OF PCPN AREAS WILL OCCUR
WITH THE NRN AREA EVOLVING INTO LESS THUNDER AND MORE STRATIFORM
RAIN WITH TIME THIS EVENING AND WILL TEND TO BE A MORE STEADY ZONE
OF PCPN. THE SRN AREA WILL LIKELY GO THRU THE STL METRO AREA AND
AREAS TO THE S AND E...AND WILL BE THE PRIMARY SVR WX THREAT ZONE
WITH THIS SYSTEM. A DRY SLOT IS ULTIMATELY EXPECTED TO PUNCH THRU
LATE THIS EVENING AND EARLY OVERNIGHT AND WIND DOWN THE SVR THREAT
SIGNIFICANTLY.

ANOTHER HAZARD WILL BE FLOODING...AND AN AREAL FLOOD WATCH WAS
ISSUED EARLIER THIS AFTN FOR THE NRN FA TO ADDRESS SMALL CREEKS AND
STREAMS RUNNING OUT OF BANKFULL WITH THE EXPECTED INCH OR SO OF
RAINFALL THAT IS EXPECTED...IN ADDITION TO THE MELTING SNOW PACK AND
ALREADY SATURATED GROUND AND/OR STILL SOMEWHAT FROZEN GROUND
DEPENDING ON EXACTLY WHERE.

YET ANOTHER HAZARD IS DENSE FOG. THIS HAS FORMED WHERE MUCH HIGHER
DWPTS WITH FRONTAL ZONE HAVE INTERSECTED THE REMNANT SNOW PACK AND
PERSISTENT STRATUS TO CREATE A REGION OF POOR VSBYS. BELIEVE THIS
WILL PERSIST UNTIL THE FRONTAL ZONE BEGINS TO MAKE A GO TO THE
SOUTHEAST LATE THIS EVENING OR EARLY OVERNIGHT. DENSE FOG ADVISORY
HAS BEEN ISSUED.

AND FINALLY...SOME WINTRY WX IS EXPECTED AS THE SYSTEM PULLS OUT.
SOME IMPRESSIVE TEMP GRADIENTS EXIST ACROSS MO THANKS TO THIS
FRONTAL ZONE...FROM LOWER 30S JUST N OF IT TO NEAR 70 TO THE S. THIS
COLDER AIR WILL EXPAND SWD...BUT NOT TOO CONFIDENT THE COLD AIR WILL
GET MUCH STRONGER THAN WHAT IS ALREADY THERE AS IT APPEARS TO BE
TAPPED OUT. BELIEVE THE REGION OF LOW-MID 30S TEMPS WILL EXPAND SEWD
WITH THE ADVANCING FRONTAL ZONE LATER TONIGHT AND MONDAY AND THIS
WILL RESULT IN THE LEFTOVER PCPN CHANGING OVER TO SLEET OR SNOW AS
THE WARM WEDGE OF AIR ALOFT ERODES. SOME FZRA POSSIBLE...BUT BELIEVE
THE LACK OF A LARGE AREA OF SUB-FRZG TEMPS WILL LARGELY PRECLUDE
THAT BUT WILL MONITOR CLOSELY THIS EVENING. INITIAL SNOW ACCUMS WITH
SOME SLEET COULD BE NEAR AN INCH WHEN IT ENDS BY LATE MONDAY
MORNING.

DRY WX AND CLEAR SKIES WILL THEN TAKE HOLD FOR MONDAY NIGHT THRU
WEDNESDAY WITH NEAR OR SLIGHTLY ABOVE AVERAGE TEMPS. ANOTHER CDFNT
FOR TUESDAY NIGHT BUT THIS SHOULD PASS THRU WITH LITTLE FANFARE.

FOR THE EXTENDED PERIOD (WEDNESDAY NIGHT - SUNDAY)...ZONAL H500 FLOW
WILL GIVE WAY TO A STRONG SHORTWAVE HEADING INTO NEXT WEEKEND...BUT
THE 00Z/06Z MODELS ARE IN SHARP DISAGREEMENT ON HOW TO HANDLE IT AS
IT MOVES INTO THE CNTRL AND ERN CONUS. THE ECMWF WANTS TO CUT THIS
SYSTEM OFF AND SLOW IT DOWN AND DEEPEN IT OVER THE LOWER MS VALLEY
AND RESULT IN A PROLONGED PCPN EVENT FROM FRIDAY THRU THE END OF THE
PERIOD AT LEAST. THE GFS WANTS TO KEEP THINGS MORE PROGRESSIVE...
WHILE SLOWING DOWN THE TRANSLATIONAL SPEED SOME AND RESULT IN A PCPN
EVENT FROM FRIDAY UNTIL SATURDAY. PREFER THE GFS SOLUTION FOR NOW AS
IT HAS BETTER CONTINUITY AND ACKNOWLEDGES THE NEED TO SLOW THE
TIMING DOWN SOME IF THE SHORTWAVE DIGS AS DEEP AS NOW APPEARS IT
MIGHT...AND SO HAVE PUSHED THE CHANCES FOR RAIN BACK A BIT BUT KEPT
SUNDAY DRY. AT OR SLIGHTLY ABOVE AVERAGE TEMPS WILL ACCOMPANY THE
ZONAL FLOW AT THE BEGINNING OF THE PERIOD...BUT WILL BE CUT BACK TO
BELOW AVERAGE IN THE SECOND HALF OF THE PERIOD GIVEN EXPECTED CLOUDS
AND RAIN AND CDFNT MOVING THRU.

TES
&&

.AVIATION...
/550 PM CST SUN FEB 27 2011/

WARM FRONT HAS REMAINED SOUTH OF KUIN...SO WILL SEE DENSE FOG LINGER
FOR AT LEAST ANOTHER HOUR OR SO TIL THUNDERSTORM COMPLEX MOVES INTO
AREA. STILL SOME UNCERTAINTY ON WHERE THUNDERSTORMS WILL TRACK...SO
JUST KEPT VCTS MENTION FROM 01Z TO 05Z...THEN LINGERING RAIN ON
BACKSIDE OF SYSTEM CHANGING TO ALL SNOW BY 11Z BEFORE COMING TO AN
END AROUND 15Z. WILL SEE CIGS SCATTER OUT BY 21Z MON. AS FOR
WINDS...TO REMAIN FROM THE NORTH...THOUGH WILL SEE GUSTS TO NEAR
25KTS DURING THE DAY ON MONDAY...BEFORE DIMINISHING AS RIDGE BUILDS
IN. AS FOR KCOU...INITIAL COMPLEX MAY REMAIN NORTH OF TAF SITE...SO
FOR NOW JUST HAVE VCTS WITH ADDITIONAL ACTIVITY POSSIBLE TIL FRONT
MOVES THROUGH AROUND 05Z. THEN SEE LINGERING LIGHT RAIN...CHANGING
TO SNOW BY 12Z MON BEFORE COMING TO AN END. WINDS AT KCOU TO REMAIN
FROM THE SOUTH TIL FRONT MOVES THROUGH...THEN VEER TO THE NORTH.
PLEASE REFER TO THE STL DISCUSSION BELOW FOR SUS INFORMATION.

SPECIFICS FOR KSTL...
FOR STL METRO AREA...SOME SHOWERS AND STORMS HAVE DEVELOPED TO THE
SOUTHWEST OF AREA...BUT FEEL BEST CHANCES OF SEVERE WEATHER WILL BE
BETWEEN 04Z AND 07Z. ACTIVITY TO PERSIST OVER REGION THROUGH 09Z
WHEN COLD FRONT MOVES THROUGH. EXACT TIMING AND COVERAGE OF STORMS
STILL UNCERTAIN...SO FOR NOW JUST HAVE VCTS MENTIONED IN TAF...THEN
UPDATE AS NEEDED. ONCE FRONT MOVES THROUGH WILL SEE LINGERING RAIN
WITH IT CHANGING OVER TO LIGHT SNOW AND SLEET TOWARDS DAYBREAK
BEFORE COMING TO AN END. AS FOR WINDS...TO PERSIST FROM THE
SOUTH...THEN GRADUALLY VEER TO THE SOUTHWEST...THEN TO THE NORTH
BEHIND THE FRONT. WILL SEE GUSTS TO NEAR 25KTS DURING THE DAY ON
MONDAY...BEFORE DIMINISHING AS RIDGE BUILDS IN AND CIGS SCATTER OUT
AROUND 23Z MON.

BYRD
&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...FLOOD WATCH THROUGH LATE TONIGHT FOR AUDRAIN MO-BOONE MO-
     CALLAWAY MO-COLE MO-KNOX MO-LEWIS MO-LINCOLN MO-MARION MO-
     MONITEAU MO-MONROE MO-MONTGOMERY MO-PIKE MO-RALLS MO-SHELBY
     MO.

     DENSE FOG ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR AUDRAIN MO-
     KNOX MO-LEWIS MO-MARION MO-MONROE MO-PIKE MO-RALLS MO-
     SHELBY MO.

IL...FLOOD WATCH THROUGH LATE TONIGHT FOR ADAMS IL-BROWN IL-CALHOUN
     IL-GREENE IL-PIKE IL.

     DENSE FOG ADVISORY UNTIL MIDNIGHT CST TONIGHT FOR ADAMS IL-BROWN
     IL-PIKE IL.
&&

WFO LSX

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE ST LOUIS MO
407 PM CST SUN FEB 27 2011

ILZ058>060-064-065-069-070-074-079-095>102-MOZ018-019-026-027-
034>036-041-042-047>052-059>065-072>075-084-085-099-281200-
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-
407 PM CST SUN FEB 27 2011

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

.DAY ONE...TONIGHT

AN OUTBREAK OF SEVERE THUNDERSTORMS IS EXPECTED MAINLY FOR THIS
EVENING...ALTHOUGH IT MAY CONTINUE PAST MIDNIGHT FOR SOME AREAS.
FOR AREAS MAINLY NORTH OF INTERSTATE 70...LARGE HAIL IS EXPECTED
TO BE THE MAIN SEVERE THREAT. FOR AREAS ALONG AND SOUTH OF THE
INTERSTATE 70 CORRIDOR...THE SEVERE THREATS WILL INCLUDE LARGE
HAIL...DAMAGING WINDS...AND POSSIBLY A FEW TORNADOES. FOR FURTHER
INFORMATION ON CONVECTIVE WATCHES...PLEASE REFER TO THE LATEST
STORM PREDICTION CENTER WATCH PRODUCTS.

THE COMBINATION OF SATURATED GROUND OR PARTIALLY FROZEN GROUND
WITH EXISTING AND MELTING SNOW COVER AND A PERSISTENT AREA OF
SHOWERS AND THUNDERSTORMS WILL RESULT IN AN INCREASED RISK FOR
FLOODING FROM STREAMS AND SMALL RIVERS TONIGHT FOR AREAS IN
NORTHEAST AND CENTRAL MISSOURI AND WEST CENTRAL ILLINOIS. PLEASE
SEE THE FLOOD WATCH PRODUCT FOR FURTHER INFORMATION.

WIDESPREAD DENSE FOG...REDUCING VISIBILITIES TO ONE QUARTER MILE
OR LESS AT TIMES...IS EXPECTED ACROSS PARTS OF CENTRAL AND
NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS THROUGH THIS
EVENING WITH IMPROVEMENT EXPECTED BY MIDNIGHT. PLEASE SEE THE
DENSE FOG ADVISORY PRODUCT FOR FURTHER INFORMATION.

ENOUGH COLD AIR WILL SPILL IN BEHIND THE FRONT TO CHANGE THE
PRECIPITATION OVER TO SLEET AND SNOW AFTER MIDNIGHT FOR PARTS OF
NORTHEAST MISSOURI AND WEST CENTRAL ILLINOIS. MINOR ACCUMULATIONS
OF SNOW AND SLEET ARE POSSIBLE.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

SNOW AND SOME SLEET IS EXPECTED FOR MONDAY MORNING FOR AREAS
MAINLY TO THE NORTH AND EAST OF SAINT LOUIS. SNOW ACCUMULATIONS
ARE EXPECTED TO BE LESS THAN AN INCH.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS LIKELY ANYTIME FROM THIS AFTERNOON THROUGH
TONIGHT.

TES

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