Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS02 KWNS 210541
SWODY2
SPC AC 210540

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1240 AM CDT TUE APR 21 2015

VALID 221200Z - 231200Z

...THERE IS AN ENH RISK OF SVR TSTMS ACROSS PARTS OF SRN OK AND
NORTH TO NORTHEAST TX...

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF OK...SW
AR...TX...LA AND MS...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...ARKLATEX...LOWER MS VALLEY AND CNTRL GULF COAST STATES...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PARTS OF SOUTH FL...

...SUMMARY...
THUNDERSTORMS WITH WIND DAMAGE...LARGE HAIL AND POSSIBLY A FEW
TORNADOES ARE EXPECTED TO DEVELOP FROM THE SOUTHERN PLAINS
SOUTHEASTWARD ACROSS THE ARKLATEX AND INTO THE LOWER MISSISSIPPI
VALLEY. OTHER STORMS WITH HAIL AND WIND DAMAGE MAY DEVELOP IN
CENTRAL TEXAS AND THE TEXAS COASTAL PLAINS. MARGINALLY SEVERE
THUNDERSTORMS MAY DEVELOP ACROSS PARTS OF THE SOUTHERN HIGH PLAINS
AND IN SOUTH TEXAS. THUNDERSTORM DEVELOPMENT MAY ALSO OCCUR ACROSS
PARTS OF THE CENTRAL TO NORTHERN ROCKIES AND SIERRA NEVADA.

...SRN PLAINS/ARKLATEX/LOWER MS VALLEY...
AN UPPER-LEVEL RIDGE IS FORECAST TO BUILD NNWWD ACROSS THE SRN HIGH
PLAINS INTO THE CNTRL ROCKIES ON WEDNESDAY. AT THE SFC...A LOW IS
FORECAST TO DEEPEN IN NE NM WITH A WARM FRONT EXTENDING EWD ACROSS
SCNTRL OK INTO CNTRL AR. SOUTH OF THE BOUNDARY...SFC DEWPOINTS
SHOULD BE IN THE LOWER TO MID 60S F ACROSS NORTH TX AND SRN OK WHERE
MODERATE INSTABILITY SHOULD BE IN PLACE BY AFTERNOON. CONVECTION
APPEARS LIKELY TO INITIATE BY LATE AFTERNOON ALONG THE WARM FRONT IN
SW OK WITH AN MCS ORGANIZING AND MOVING ESEWD ACROSS SRN OK INTO NE
TX. THERE IS STILL SOME QUESTION ABOUT TIMING BUT THE GFS SOLUTION
SEEMS TO BE REASONABLE WITH A LATE AFTERNOON AND EARLY EVENING MCS.

NAM FORECAST SOUNDINGS FOR 00Z/THU AT FREDERICK OK AND VERNON TX
SHOW 1500 TO 2000 J/KG OF MLCAPE WITH VERY STEEP MID-LEVEL LAPSE
RATES APPROACHING 9.0 C/KM. IN ADDITION...AN IMPRESSIVE WIND-SHEAR
ENVIRONMENT IS FORECAST WITH SUBSTANTIAL VEERING WITH HEIGHT BELOW
850 AND 0-6 KM SHEAR NEAR 60 KT. THIS WOULD FAVOR THE DEVELOPMENT OF
SUPERCELLS WITH LARGE HAIL AND WIND DAMAGE EARLY IN THE EVENT.
HAILSTONES OF GREATER THAN 2 INCHES IN DIAMETER WILL BE POSSIBLE
WITH THE MORE DOMINANT CELLS. A FEW TORNADOES MAY OCCUR ESPECIALLY
WITH PERSISTENT ROTATING STORMS. A RELATIVELY FAST-MOVING MCS MAY
DEVELOP A LINEAR STRUCTURE AND COLD POOL EARLY WEDNESDAY EVENING
WHICH COULD RESULT IN AN ENHANCED WIND-DAMAGE THREAT. THE SEVERE
THREAT FROM THIS CONVECTIVE SYSTEM COULD EXTEND AS FAR SOUTHEAST AS
EAST TX AND NW LA DURING THE EVENING AND POSSIBLY DURING THE EARLY
OVERNIGHT OVER PARTS OF THE LOWER MS VALLEY.

...TX HILL COUNTRY/TX COASTAL PLAINS...
AN UPPER-LEVEL RIDGE IS FORECAST TO BE MAINTAINED ACROSS THE TX HILL
COUNTRY AND SRN HIGH PLAINS ON WEDNESDAY AS A WARM SECTOR REMAINS
LOCATED OVER MUCH OF THE SRN TWO-THIRDS OF TX. THE AIRMASS ACROSS
THE TX HILL COUNTRY AND THE TX COASTAL PLAINS...AWAY FROM THE
IMMEDIATE COAST...IS FORECAST TO BECOME MODERATELY TO STRONGLY
UNSTABLE BY WEDNESDAY AFTERNOON. FORECAST SOUNDINGS FOR 00Z/THU AT
AUSTIN AND COLLEGE STATION SHOW MLCAPE ABOVE 3000 J/KG WITH LOWER
70S F DEWPOINTS. IN ADDITION TO THE IMPRESSIVE
THERMODYNAMICS...DEEP-LAYER SHEAR SHOULD BE IN THE 50 TO 60 KT
RANGE. THIS SHOULD SUPPORT SEVERE THUNDERSTORM DEVELOPMENT WITH
SUPERCELLS THE FAVORED STORM MODE. CONVECTIVE COVERAGE IS THE MAIN
UNCERTAINTY WITH THE UPPER-LEVEL RIDGE TO THE WEST. EVEN THOUGH
STORM DEVELOPMENT SHOULD REMAIN ISOLATED...SUPERCELLS SHOULD BE
CAPABLE OF PRODUCING LARGE HAIL...WIND DAMAGE AND POSSIBLY A
TORNADO.

...SRN FL...
AN UPPER-LEVEL TROUGH IS FORECAST TO MOVE SLOWLY EWD ACROSS THE EAST
COAST AS A BELT OF STRONGER MID-LEVEL FLOW MOVES EWD ACROSS THE NRN
GULF OF MEXICO. A MOIST AIRMASS IS FORECAST ACROSS SOUTH FL WHERE
MODERATE INSTABILITY SHOULD DEVELOP BY MIDDAY. CELLS THAT CAN
INITIATE ACROSS SOUTH FL DURING THE EARLY AFTERNOON MAY OBTAIN A
MARGINAL WIND DAMAGE THREAT DUE TO MODERATE DEEP-LAYER SHEAR AND
UNIDIRECTIONAL WIND PROFILES.

..BROYLES.. 04/21/2015




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