Wednesday, February 18, 2009

Moderate Risk in South Alabama


SPC Day One Tornado Probabilities


DAY 1 CONVECTIVE OUTLOOK  
NWS STORM PREDICTION CENTER NORMAN OK
1159 PM CST TUE FEB 17 2009

VALID 181200Z - 191200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF FAR ERN
MS...CNTRL AL AND SRN AL......

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE LOWER MS
VALLEY...TN VALLEY AND ERN GULF COAST STATES......

...LOWER MS VALLEY/TN VALLEY/ERN GULF COAST STATES...
AN UPPER-LEVEL TROUGH OVER THE NRN STATES WILL DIG SEWD INTO THE MS
VALLEY TODAY AS A POWERFUL 90 TO 100 KT MID-LEVEL JET MOVES EWD
ACROSS THE TN VALLEY AND SRN APPALACHIAN MTNS. SOUTHEAST OF THE
UPPER-LEVEL TROUGH...AN IMPRESSIVE 60 TO 70 KT LOW-LEVEL JET WILL BE
ORIENTED ALONG THE MS RIVER THIS MORNING WITH NUMEROUS ELEVATED
THUNDERSTORMS ONGOING ALONG THE AXIS OF THE JET. THE SRN EXTENT OF
THIS ACTIVITY SHOULD PERSIST EWD ACROSS TN...NRN AL AND NRN GA
THROUGH MIDDAY. FORECAST SOUNDINGS IN SRN TN...NRN MS AND NRN AL
SHOW COLD AIR ALOFT AND SUFFICIENT INSTABILITY FOR A HAIL THREAT
WITH THE ACTIVITY. BY THIS AFTERNOON...MODEL FORECASTS INITIATE
SFC-BASED THUNDERSTORMS FROM FAR ERN MS ENEWD ACROSS CNTRL AL INTO
WRN GA. STORM COVERAGE SHOULD GRADUALLY EXPAND WITH MCS DEVELOPMENT
APPEARING LIKELY BY THIS EVENING ACROSS SRN AL AND SW GA. THIS LINE
OF STORMS SHOULD REACH THE FL PANHANDLE AND THE NRN FL PENINSULA
DURING THE OVERNIGHT PERIOD.

AT THE SFC...A MOIST AXIS IS FORECAST TO BE LOCATED FROM SRN LA
EXTENDING ENEWD ACROSS SRN MS INTO WRN AL. THIS AREA SHOULD BE
MOSTLY FREE OF CONVECTION THROUGH MIDDAY ALLOWING FOR THE
DEVELOPMENT OF AN INSTABILITY/THERMAL AXIS EXTENDING ENEWD ACROSS
THE MODERATE RISK AREA. STRONG SFC-BASED THUNDERSTORMS APPEAR LIKELY
TO INITIATE FIRST IN NCNTRL AND NERN AL EARLY THIS AFTERNOON WITH
THE ACTIVITY EXPANDING WSWWD ACROSS THE MODERATE RISK AREA ALONG THE
INSTABILITY AXIS DURING THE AFTERNOON. FORECAST SOUNDINGS ACROSS
CNTRL AL SHOW STRONG VERTICAL SHEAR PROFILES/0-6 KM SHEAR OF 80 TO
90 KT/ WITH 0-3 KM SRH VALUES RANGING FROM 250 SOUTH OF TUSCALOOSA
TO 450 M2/S2 EAST OF MONTGOMERY. THIS SHOULD BE MORE THAN SUFFICIENT
FOR DISCRETE TORNADIC SUPERCELLS CAPABLE OF PRODUCING A FEW STRONG
TORNADOES. AS STORM COVERAGE EXPANDS ACROSS THE MODERATE RISK
AREA...THE SHEAR SHOULD KEEP THE STORMS DISCRETE RESULTING IN A
PERSISTENT TORNADO THREAT THROUGH EARLY EVENING. FURTHER WEST
SOUTHEAST INTO SCNTRL MS...ISOLATED SUPERCELLS WITH A TORNADO/HAIL
THREAT MAY ALSO INITIATE. HOWEVER...THE GREATER THUNDERSTORM
COVERAGE SHOULD EXIST ACROSS SRN AL AND SW AL AS THUNDERSTORMS
BECOME QUITE NUMEROUS DURING THE EVENING. A TRANSITION TO A MORE
LINEAR STRUCTURED MCS MAY OCCUR WITH THE WIND DAMAGE THREAT
INCREASING. ALTHOUGH A WIND DAMAGE THREAT MAY ALSO EXIST IN SW GA
DURING THE LATE EVENING...THUNDERSTORMS IN THE ERN PART OF THE
SLIGHT RISK AREA SHOULD BECOME ELEVATED DURING THE OVERNIGHT PERIOD.
THE WIND DAMAGE THREAT MAY CONTINUE INTO THE FL PANHANDLE LATE IN
THE PERIOD.

..BROYLES.. 02/18/2009

CLICK TO GET WUUS01 PTSDY1 PRODUCT


1 comment:

Storm Chasing Mikey said...

* Here are the latest severe weather parameters from the 6z (midnight) run of the NAM (North American Mesoscale) computer model, valid at Noon Today:
SBCAPE: 950 J/Kg
0-3KM SRH: 381
LI: -5.3
The CAPE approaches 1000, that means there should be plenty of instability to fuel storms. The SRH is a measure of how much the wind turns, values above 300 support tornadoes. And, the LI, Lifted Index, is an indicator of how prone the air is to rising - negative numbers mean rising air, which supports storms. Anything below -2 is supportive of severe storms.