Saturday, May 10, 2008

New "Day One" is out


Moderate risk


Hail/wind threat


Tornado threat

   DAY 1 CONVECTIVE OUTLOOK CORR 1
NWS STORM PREDICTION CENTER NORMAN OK
0135 AM CDT SAT MAY 10 2008

VALID 101200Z - 111200Z

...THERE IS A MDT RISK OF SVR TSTMS ACROSS EXTREME SERN OK...NERN
TX...THE SRN 2/3 OF AR...NRN LA...EXTREME SWRN TN...MUCH OF
MS...PARTS OF NRN AND CENTRAL AL...AND EXTREME W CENTRAL GA...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS A LARGE PORTION OF THE
SERN QUARTER OF THE CONUS...

CORRECTED FOR DESCRIPTION OF STATES IN MDT

...SYNOPSIS...
PROGRESSIVE/AMPLIFYING UPPER PATTERN IS FORECAST ACROSS THE CONUS
THIS PERIOD...AS THREE DISTINCT SHORT-WAVE TROUGHS -- ONE MOVING
INTO THE PAC NW...ONE MOVING INTO THE CENTRAL CONUS...AND A THIRD
SLOWLY VACATING THE NORTHEAST -- WILL SHIFT FROM W-E THROUGH THE
PERIOD.

THE MAIN FEATURE WITH RESPECT TO THE SEVERE/CONVECTIVE FORECAST WILL
BE THE CENTRAL U.S. TROUGH AND A MORE SUBTLE/LEAD WAVE -- COMPRISED
OF SEVERAL SMALL VORTICITY MAXIMA -- WHICH IS EXPECTED TO MOVE
ACROSS THE LOWER MS VALLEY AND GULF COAST STATES THROUGH THE
AFTERNOON.

AT THE SURFACE...A BAROCLINIC ZONE IS FORECAST TO LIE E-W FROM SC
WWD ACROSS NRN GA/NRN AL/NRN MS/SRN AR AND THEN NWWD TO A BROAD
SURFACE LOW CENTERED INVOF NWRN OK. THIS BROAD LOW IS FORECAST TO
SHIFT NEWD THROUGH THE DAY INTO NWRN MO BY 11/00Z...WITH A TRAILING
COLD FRONT FORECAST TO DIVE SEWD ACROSS THE CENTRAL AND INTO THE SRN
PLAINS BEHIND THIS LOW. AS THE FRONT REACHES WRN MO/ERN OK/N TX...A
DRYLINE WILL LIKELY HAVE MIXED EWD ACROSS CENTRAL TX. MEANWHILE...
THE W-E FRONT ACROSS THE GULF COAST STATES WILL HAVE BEGUN LIFTING A
BIT NWD ON ITS WRN FRINGE AS A WARM FRONT...AS THE LOW PROGRESSES
EWD.

THROUGH THE SECOND HALF OF THE PERIOD...THIS LOW SHOULD BEGIN
DEEPENING RAPIDLY...AS THE UPPER SYSTEM INTENSIFIES/EVOLVES INTO A
CLOSED LOW. BY THE END THE PERIOD...A ROUGHLY 990 MB LOW SHOULD LIE
INVOF CENTRAL IL...WITH AN ARCING COLD FRONT STRETCHING FROM SWRN
INDIANA SWD INTO MIDDLE TN...AND THEN SWWD ACROSS NWRN AL/MS AND
INTO SWRN LA/THE WRN GULF/DEEP S TX.

EACH OF THESE SURFACE BOUNDARIES -- THE COLD FRONT...THE DRYLINE...
AND THE W-E STATIONARY/WARM FRONT ACROSS THE GULF COAST

STATES -- EACH SHOULD SERVE AS FOCI FOR WIDESPREAD SEVERE
STORM
DEVELOPMENT.


...SERN QUARTER OF THE CONUS...
SIGNIFICANT/WIDESPREAD BUT COMPLEX SEVERE WEATHER EVENT IS LIKELY TO
UNFOLD THIS PERIOD...ACROSS A LARGE PORTION OF THE SERN QUARTER OF
THE U.S. FROM SERN KS/ERN OK/E TX EWD TO THE SOUTHEASTERN STATES
THIS PERIOD.

A BROAD ZONE OF 60 TO 70 KT WLYS AT MID LEVELS -- S OF
THE CENTRAL U.S. TROUGH -- WILL ADVECT STEEP LAPSE RATES EWD INTO
THE SERN QUARTER OF THE COUNTRY THROUGH THE DAY...ATOP A VERY MOIST
BOUNDARY LAYER /UPPER 60S TO LOW 70S DEWPOINTS/.
THIS WILL RESULT IN MODERATE TO STRONG DESTABILIZATION AS DIURNAL
HEATING INCREASES THROUGH MIDDAY. BY MID AFTERNOON...EXPECT
3000 TO 4000 J/KG
MIXED-LAYER CAPE AHEAD
OF THE CENTRAL TX DRYLINE
..AND 1500 TO 2500 J/KG
ACROSS ERN OK/SRN AR/LA EWD ACROSS THE SOUTHEAST INVOF THE W-E
BOUNDARY.

INITIAL DEVELOPMENT MAY OCCUR EARLY IN THE PERIOD ACROSS PARTS OF
OK/N TX WITHIN ZONE OF WARM ADVECTION ASSOCIATED WITH A LOW-LEVEL
JET...FOLLOWED BY MORE WIDESPREAD DEVELOPMENT ALONG THE W-E BOUNDARY
FROM THE ARKLATEX EWD TO THE SOUTHEAST STATES. WITH VERY STRONG
DEEP-LAYER WIND FIELD...ANY STORMS WHICH DEVELOP SHOULD RAPIDLY
ORGANIZE/BECOME SEVERE...WITH A COMPLEX/MIXED STORM MODE EXPECTED.
WHILE ISOLATED STORMS SHOULD ALSO BEGIN TO DEVELOP SWWD ALONG THE
DRYLINE TOWARD CENTRAL TX THROUGH THE AFTERNOON...GREATEST SEVERE
THREAT THROUGH MID TO LATE AFTERNOON IS EXPECTED FROM SERN OK/NERN
TX EWD ACROSS THE LOWER MS VALLEY INTO SWRN TN/MS...AS LOW-LEVEL JET
SHIFTS EWD AND STRONGER WLY FLOW ALOFT SPREADS TOWARD THE CENTRAL
GULF COAST REGION. ALONG WITH AN EXPANSION IN STORM
COVERAGE...INCREASINGLY-FAVORABLE DEEP-LAYER SHEAR PROFILES WILL
SUPPORT LONG-LIVED/INTENSE SUPERCELLS. WHERE STORMS MERGE INTO
CLUSTERS...THE VERY STRONG/SOMEWHAT UNIDIRECTIONAL WLY FLOW ABOVE
THE BOUNDARY LAYER WOULD ALSO SUPPORT FAST-MOVING/BOWING STORM
SEGMENTS CAPABLE OF WIDESPREAD/SIGNIFICANT WIND DAMAGE.
FINALLY...LOW-LEVEL SHEAR -- PARTICULARLY NEAR AND JUST N OF THE W-E
SURFACE BOUNDARY -- WILL BE QUITE FAVORABLE FOR LOW-LEVEL
ROTATION...AND THUS THE POTENTIAL FOR MULTIPLE/DAMAGING TORNADOES
WILL ALSO EXIST.

SEVERE POTENTIAL WILL SHIFT EWD WITH TIME...AS SURFACE COLD FRONT
CONTINUES MOVING SEWD ACROSS THE CENTRAL CONUS. WHILE
SUPERCELL/TORNADO THREAT WILL CONTINUE INTO THE OVERNIGHT

HOURS...POTENTIAL FOR WIDESPREAD/DAMAGING WINDS COULD BECOME
THE
MAIN SEVERE THREAT AS MULTIPLE CLUSTERS OF STORMS LIKELY
EVOLVE.
GIVEN VERY FAST FLOW ALOFT...A DERECHO EVENT WILL BE
POSSIBLE ACROSS
THE GULF COAST REGION. SEVERE THREAT COULD
EXTEND AS FAR E AS THE SC/GA COASTS OVERNIGHT GIVEN FAST-MOVING
STORMS/STORM CLUSTERS.

..GOSS.. 05/10/2008

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