We have seen dramatic evidence in recent years that November is a secondary severe weather season here in the South. We may see that pinciple exhibited again on Tuesday as a developing weather situation unfolds across the southern U.S.
A strong trough of low pressure will move out of the Central Plains on Tuesday, drawing unstable air northward from the Gulf of Mexico. Very strong wind fields associated with the trough will enhance the threat of severe weather. For us here in Alabama, it appears that the main danger will come from damaging winds associated with a line of severe thunderstorms that will move through Tuesday night. But if the instability is stronger than expected, we can't rule out the possibility of supercell storms and tornadoes.
To the west of Alabama, the NWS Jacksion has been stressing the possibility of a significant outbreak of tornadoes Tuesday in their warning area. This was the headline on their technical discussion yesterday afternoon:
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
230 PM CST SAT NOV 20 2004
.HEADLINE...TORNADO OUTBREAK POSSIBLE TUESDAY AND TUESDAY NIGHT.
This was the forecaster's reasoning...
.LONG TERM...TUESDAY AND BEYOND. EVERY SINGLE SEVERE WEATHER PARAMETER SUGGESTS THAT THERE IS GOOD POTENTIAL FOR SIGNIFICANT ORGANIZED SEVERE CONVECTIVE ACTIVITY ON TUESDAY. DUE TO THE TIMING OF PASSAGE OF THIS SYSTEM (WHICH IS DURING THE LATE AFTERNOON)...APPEARS THAT IT WILL BE ABLE TO UTILIZE THE DAILY HEATING (THOUGH THE HEATING SHOULD BE SOMEWHAT LIMITED BY CLOUD COVER.) WARM AIR AND MOISTURE TRANSPORT INTO THE REGION FROM THE GULF WILL BE QUITE STRONG DURING THIS PERIOD. THIS SHOULD HELP INCREASE AND MAINTAIN THE INSTABILITY OVER THE AREA. THE SHEAR PROFILES ARE EXPECTED TO BECOME STRONGER AS A 60 KT SOUTHERLY LOW
LEVEL JET MOVES OVER THE AREA AND AS 80 KT SOUTHWESTERLY MID LEVEL JET POSITIONS ITSELF OVER ARKANSAS LATE TUESDAY AFTERNOON. FURTHERMORE...THE ARK-LA-MISS WILL BE UNDERNEATH A COUPLED UPPER LEVEL JET (IN THE RIGHT...ENTRANCE QUADRANT OF ONE AND IN THE LEFT...EXIT QUADRANT OF ANOTHER.) THIS POSITIONING OF THE JETS OVER THE AREA SHOULD SIGNIFICANTLY HELP THE CONVECTIVE DEVELOPMENT. ADDITIONAL LIFT WILL COME IN THE FORM OF AN EXTREMELY WELL DEFINED COLD FRONTAL BOUNDARY. TIME HIGHT PLOTS SHOW A RADICAL CHANGE IN
AIRMASSES. THOUGH THE POST FRONTAL AIRMASS WILL NOT BE VERY COLD...IT WILL BE EXTREMELY DRY. THIS IS IN STARK CONTRAST TO THE MOIST AIRMASS AHEAD OF THE FRONT. SPEAKING OF THE "WETNESS" OF THIS SYSTEM...THERE SHOULD BE SOME FLOODING CONCERNS ARISING TUESDAY AFTERNOON AS THE MAIN SYSTEM MOVES THROUGH. EVENT TOTAL PRECIPITATION AMOUNTS COULD BE NEAR 10 INCHES IN A FEW LOCATIONS WITH 4 TO 5 INCHES FALLING IN SOME AREAS DURING THE MAIN EVENT ON TUESDAY AND TUESDAY NIGHT. (THE LARGE EVENT TOTAL IS FOR THE PERIOD
TONIGHT THROUGH TUESDAY NIGHT.)
DESPITE THE CONCERN FOR SOME FLOODING...THE SEVERE THUNDERSTORM POTENTIAL REMAINS THE MAIN CONCERN. EARLY INDICATORS SHOW A SIGNIFICANT CONCERN FOR TORNADIC ACTIVITY ALONG WITH STRAIGHT LINE WINDS. GIVEN THE HIGHLY FAVORABLE DYNAMIC STATE OF THE ATMOSPHERE...SOME OF THE TORNADOES COULD BE QUITE STRONG. IF THE CURRENT MODEL SOLUTIONS HOLD...WHICH THEY SHOULD...WE ARE EXPECTING
THE DEVELOPMENT OF SUPERCELLS (SOME TORNADIC) OUT AHEAD OF A LARGE...STRONG SQUALL LINE THAT SHOULD MOVE FROM WEST TO EAST ACROSS THE AREA MONDAY AND MONDAY NIGHT. THE MAIN CONCERNS WITH THE SUPERCELLS SHOULD BE FOR TORNADOES AND HAIL. THE MAIN CONCERNS WITH THE SQUALL LINE SHOULD BE FOR STRAIGHT LINE WINDS AND ISOLATED TORNADOES.
This morning's discussion has a similar tone...
FOR THIS MAIN SYSTEM...NOTHING MUCH HAS CHANGED. IF ANYTHING THE NEWER MODEL RUNS ARE TRENDING STRONGER AND A BIT FURTHER SOUTH!! WHAT I AM EXPECTING IS A SQUALL LINE TO DEVELOP ALONG THE PREFRONTAL TROUGH AND RAPIDLY SHIFT EAST AS THE MID-LEVEL JET (60-75KTS) AND UPPER JET (110-120KTS) OVERSPREAD THE WARM SECTOR. THIS LINE WILL LIKELY CONTAIN BOWING SEGMENTS AND HIGH POTENTIAL OF DAMAGING WINDS
AS WELL AS SOME POTENTIAL FOR SIG WIND (>65KTS)! OF GREATER CONCERN WILL BE IF ANY SUPERCELLS CAN DEVELOP AHEAD OF THE LINE. AT THIS TIME...IT SEEMS VERY LIKELY THERE WILL BE SOME! THESE WILL POSE THE MOST SIG THREAT WITH ANY ONE OF THEM CONTAINING LARGE HAIL AND TORNADOES. DUE TO THE KINEMATICS OF THIS SYSTEM AND THE STRONG WIND SHEAR THAT WILL BE IN PLACE...THE POTENTIAL EXISTS FOR ANY SUPERCELL TO PRODUCE A STRONG TORNADO! THE MAIN THING TO FOCUS ON IS THAT THIS IS ALL ABOUT PATTERN RECOGNITION AND IF WHAT THE MODELS SHOW
ACTUALLY OCCURS! HOWEVER...DUE TO THE VERY CONVINCING CONSISTENCY THE PAST 4 DAYS...CONFIDENCE IS HIGH THAT SOMETHING WILL OCCUR TO THE EXTENT I JUST DESCRIBED!
Needless to say, we will be monitoring the situation carefully. We will have more information in our afternoon forecast package.
A strong trough of low pressure will move out of the Central Plains on Tuesday, drawing unstable air northward from the Gulf of Mexico. Very strong wind fields associated with the trough will enhance the threat of severe weather. For us here in Alabama, it appears that the main danger will come from damaging winds associated with a line of severe thunderstorms that will move through Tuesday night. But if the instability is stronger than expected, we can't rule out the possibility of supercell storms and tornadoes.
To the west of Alabama, the NWS Jacksion has been stressing the possibility of a significant outbreak of tornadoes Tuesday in their warning area. This was the headline on their technical discussion yesterday afternoon:
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON MS
230 PM CST SAT NOV 20 2004
.HEADLINE...TORNADO OUTBREAK POSSIBLE TUESDAY AND TUESDAY NIGHT.
This was the forecaster's reasoning...
.LONG TERM...TUESDAY AND BEYOND. EVERY SINGLE SEVERE WEATHER PARAMETER SUGGESTS THAT THERE IS GOOD POTENTIAL FOR SIGNIFICANT ORGANIZED SEVERE CONVECTIVE ACTIVITY ON TUESDAY. DUE TO THE TIMING OF PASSAGE OF THIS SYSTEM (WHICH IS DURING THE LATE AFTERNOON)...APPEARS THAT IT WILL BE ABLE TO UTILIZE THE DAILY HEATING (THOUGH THE HEATING SHOULD BE SOMEWHAT LIMITED BY CLOUD COVER.) WARM AIR AND MOISTURE TRANSPORT INTO THE REGION FROM THE GULF WILL BE QUITE STRONG DURING THIS PERIOD. THIS SHOULD HELP INCREASE AND MAINTAIN THE INSTABILITY OVER THE AREA. THE SHEAR PROFILES ARE EXPECTED TO BECOME STRONGER AS A 60 KT SOUTHERLY LOW
LEVEL JET MOVES OVER THE AREA AND AS 80 KT SOUTHWESTERLY MID LEVEL JET POSITIONS ITSELF OVER ARKANSAS LATE TUESDAY AFTERNOON. FURTHERMORE...THE ARK-LA-MISS WILL BE UNDERNEATH A COUPLED UPPER LEVEL JET (IN THE RIGHT...ENTRANCE QUADRANT OF ONE AND IN THE LEFT...EXIT QUADRANT OF ANOTHER.) THIS POSITIONING OF THE JETS OVER THE AREA SHOULD SIGNIFICANTLY HELP THE CONVECTIVE DEVELOPMENT. ADDITIONAL LIFT WILL COME IN THE FORM OF AN EXTREMELY WELL DEFINED COLD FRONTAL BOUNDARY. TIME HIGHT PLOTS SHOW A RADICAL CHANGE IN
AIRMASSES. THOUGH THE POST FRONTAL AIRMASS WILL NOT BE VERY COLD...IT WILL BE EXTREMELY DRY. THIS IS IN STARK CONTRAST TO THE MOIST AIRMASS AHEAD OF THE FRONT. SPEAKING OF THE "WETNESS" OF THIS SYSTEM...THERE SHOULD BE SOME FLOODING CONCERNS ARISING TUESDAY AFTERNOON AS THE MAIN SYSTEM MOVES THROUGH. EVENT TOTAL PRECIPITATION AMOUNTS COULD BE NEAR 10 INCHES IN A FEW LOCATIONS WITH 4 TO 5 INCHES FALLING IN SOME AREAS DURING THE MAIN EVENT ON TUESDAY AND TUESDAY NIGHT. (THE LARGE EVENT TOTAL IS FOR THE PERIOD
TONIGHT THROUGH TUESDAY NIGHT.)
DESPITE THE CONCERN FOR SOME FLOODING...THE SEVERE THUNDERSTORM POTENTIAL REMAINS THE MAIN CONCERN. EARLY INDICATORS SHOW A SIGNIFICANT CONCERN FOR TORNADIC ACTIVITY ALONG WITH STRAIGHT LINE WINDS. GIVEN THE HIGHLY FAVORABLE DYNAMIC STATE OF THE ATMOSPHERE...SOME OF THE TORNADOES COULD BE QUITE STRONG. IF THE CURRENT MODEL SOLUTIONS HOLD...WHICH THEY SHOULD...WE ARE EXPECTING
THE DEVELOPMENT OF SUPERCELLS (SOME TORNADIC) OUT AHEAD OF A LARGE...STRONG SQUALL LINE THAT SHOULD MOVE FROM WEST TO EAST ACROSS THE AREA MONDAY AND MONDAY NIGHT. THE MAIN CONCERNS WITH THE SUPERCELLS SHOULD BE FOR TORNADOES AND HAIL. THE MAIN CONCERNS WITH THE SQUALL LINE SHOULD BE FOR STRAIGHT LINE WINDS AND ISOLATED TORNADOES.
This morning's discussion has a similar tone...
FOR THIS MAIN SYSTEM...NOTHING MUCH HAS CHANGED. IF ANYTHING THE NEWER MODEL RUNS ARE TRENDING STRONGER AND A BIT FURTHER SOUTH!! WHAT I AM EXPECTING IS A SQUALL LINE TO DEVELOP ALONG THE PREFRONTAL TROUGH AND RAPIDLY SHIFT EAST AS THE MID-LEVEL JET (60-75KTS) AND UPPER JET (110-120KTS) OVERSPREAD THE WARM SECTOR. THIS LINE WILL LIKELY CONTAIN BOWING SEGMENTS AND HIGH POTENTIAL OF DAMAGING WINDS
AS WELL AS SOME POTENTIAL FOR SIG WIND (>65KTS)! OF GREATER CONCERN WILL BE IF ANY SUPERCELLS CAN DEVELOP AHEAD OF THE LINE. AT THIS TIME...IT SEEMS VERY LIKELY THERE WILL BE SOME! THESE WILL POSE THE MOST SIG THREAT WITH ANY ONE OF THEM CONTAINING LARGE HAIL AND TORNADOES. DUE TO THE KINEMATICS OF THIS SYSTEM AND THE STRONG WIND SHEAR THAT WILL BE IN PLACE...THE POTENTIAL EXISTS FOR ANY SUPERCELL TO PRODUCE A STRONG TORNADO! THE MAIN THING TO FOCUS ON IS THAT THIS IS ALL ABOUT PATTERN RECOGNITION AND IF WHAT THE MODELS SHOW
ACTUALLY OCCURS! HOWEVER...DUE TO THE VERY CONVINCING CONSISTENCY THE PAST 4 DAYS...CONFIDENCE IS HIGH THAT SOMETHING WILL OCCUR TO THE EXTENT I JUST DESCRIBED!
Needless to say, we will be monitoring the situation carefully. We will have more information in our afternoon forecast package.
on November 22, 2004, 1:22 am
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