Severe Thunderstorm Warning 117, NWS Mobile, AL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOBILE AL
241 PM CDT TUE APR 22 1997

SERIES OF MID LEVEL S/WAVES SEEN IN WV LOOP WILL CONTINUE TO MOVE
ACROSS CWA THROUGH TONIGHT...EXITING BY EARLY WEDNESDAY MORNING.  18Z
SURFACE ANALYSIS DEPICTS SURFACE LOW IN NORTHWEST AL ASSOCIATED WITH
LEADING S/WAVE AND ASSOCIATED PREFRONTAL TROF.  KJAN LOOP SHOWS
COMPLEX PATTERN OF SEVERAL LINES OF TSRA/+TSRA ASSOCIATED WITH
SURFACE REFLECTIONS OF MID LEVEL S/WAVES AND INTERACTIONS WITH
OUTFLOW BOUNDARIES.  MODIFIED 18Z MOBILE SOUNDING SHOWED CAPES NEAR
3500 WITH LI VALUES NEAR -10 WITH PLENTY OF DRY AIR STILL IN PLACE
ABOVE H7 AND WET BULB ZERO VALUES NEAR 9100.  MODIFIED MOBILE
SOUNDING ALSO SHOWED A 2-3C DEGREE CAP FROM H85-75...DECREASING TO NO
CAP AT JAN.  RADAR TRENDS INDICATE THAT CAP IS WEAKENING
PROGRESSIVELY FURTHER SOUTH...WITH TSRA NOW FORMING IN EXTREME
SOUTHEAST MS...AND SO WILL EXPECT FURTHER SOUTHWARD DEVELOPMENT
THROUGH THIS EVENING AFFECTING NORTHWEST FLORIDA AND COASTAL ALABAMA.
AXIS OF MOST UNSTABLE AIR SHIFTS EASTWARD THIS EVENING AND REMAINS
MOSTLY OVER THE COASTAL SECTIONS WITH CAPES LATER DROPPING QUICKLY TO
BELOW 1500 OVER NORTHWEST FLORIDA BY 1 AM TONIGHT.  MAIN SURFACE LOW
LOCATED IN WEST CENTRAL MS PER 18Z ANALYSIS ADVANCES NORTHEAST TO
NORTHWEST GA BY 1 AM WITH ASSOCIATED COLD FRONT ENTERING SOUTHWEST AL
BY MIDNIGHT AND LATER EXITING CWA DURING WEDNESDAY MORNING.  SURFACE
HIGH PRESSURE SETTLES INTO THE REGION THROUGH THURSDAY WITH CLEARING
WEDNESDAY AND CONTINUED CLEAR CONDITIONS THROUGH THURSDAY.

SOUTHWEST WINDS AT 15 TO 20 KNOTS OVER THE MARINE AREA WILL BEGIN TO
SWITCH TO THE NORTHWEST NEAR 20 KNOTS LATE TONIGHT OVER THE ALABAMA
COASTAL WATERS AS A COLD FRONT WINDS OVER THE MARINE AREA...AND
SWITCH TO THE NORTHWEST OVER THE FLORIDA COASTAL WATERS WEDNESDAY
MORNING.  SCA WILL BE REQUIRED TONIGHT AND WEDNESDAY FOR WIND SHIFT
AND SCATTERED TSRA.

MOB 58/74/50/78 6100    PNS 61/74/53/78 6100
DTS 64/73/51/74 6100    EVR 57/69/46/76 9100 29

ALZ051>64-MSZ067-075-076-078-079-FLZ001>006-230600-

AREAL THUNDERSTORM OUTLOOK FOR
SOUTHWEST AL...NORTHWEST FL AND SOUTHEAST MS
NATIONAL WEATHER SERVICE MOBILE AL
1105 AM CDT TUE APR 22 1997

THERE IS A MODERATE RISK FOR SEVERE THUNDERSTORMS FOR SOUTHWEST
ALABAMA...NORTHWEST FLORIDA AND SOUTHEAST MISSISSIPPI FROM MID
AFTERNOON THROUGH TONIGHT.

ABUNDANT LOW LEVEL MOISTURE...COOL TEMPERATURES IN THE MID AND UPPER
LEVELS OF THE ATMOSPHERE...AND HEATING OF THE SURFACE BY THE SUN WILL
RESULT IN AN EXTREMELY UNSTABLE ATMOSPHERE ACROSS THE REGION BY
AFTERNOON.  A LOW LEVEL CAP WILL INHIBIT THUNDERSTORM DEVELOP ACROSS
THE AREA THROUGH THE EARLY AFTERNOON HOURS BUT WILL WEAKEN WEST OF
INTERSTATE 65 AS A STRONG UPPER LEVEL DISTUBANCE WITH A SURFACE LOW
PRESSURE SYSTEM ADVANCES INTO EAST CENTRAL MISSISSIPPI BY THE MID
AFTERNOON.  AS THE CAP DISINTEGRATES WEST OF INTERSTATE 65 WITH THE
APPROACH OF THE LOW PRESSURE SYSTEM...A LINE OF STRONG TO SEVERE
THUNDERSTORMS WILL BEGIN TO ENTER SOUTHEAST MISSISSIPI DURING THE MID
AFTERNOON HOURS AND ADVANCE TO A LINE FROM CAMDEN TO GROVE HILL TO
MOBILE DURING THE DINNER HOUR.  AS THE LOW PRESSURE SYSTEM PROGRESSES
FURTHER EAST INTO CENTRAL ALABAMA...THE LINE OF STRONG TO SEVERE
STORMS WILL CONTINUE EAST OF THIS LINE DURING THE EVENING HOURS.

DUE TO THE EXTREMELY UNSTABLE ATMOSPHERE...ISOLATED SEVERE
THUNDERSTORM DEVELOPMENT IN ADVANCE OF THE MAIN LINE OF SEVERE STORMS
CANNOT BE RULED OUT.

THE COMBINATION OF WARM...MOIST AIR AT LOW LEVELS AND COOL...DRY
CONDITIONS ALOFT...AND EXTREMELY UNSTABLE CONDITIONS WILL BE
CONDUCIVE TO THE DEVELOPMENT OF VERY LARGE HAIL AND DAMAGING SURFACE
WINDS WITH THE POSSIBILITY OF ISOLATED TORNADOES.

THE THREAT OF SEVERE STORMS WILL DIMINISH IN THE WAKE OF THE LINE OF
SEVERE STORMS AS TEMPERATURES IN THE LOWER LEVELS WILL HAVE COOLED
DUE TO THE PREVIOUS THUNDERSTORMS RAIN COOLER AIR...THUS HAVING A
STABLIZING EFFECT ON THE ATMOSPHERE.  A COLD FRONT WILL BEGIN TO
ENTER SOUTHEAST MISSISSIPPI BY MIDNIGHT AND PUSH ACROSS SOUTHWEST
ALABAMA AND NORTHWEST FLORIDA THROUGH THE LATE NIGHT HOURS.  DUE TO
THE DECREASED INSTABILITY IN THE WAKE OF THIS AFTERNOONS AND EVENINGS
LINE OF STRONG TO SEVERE STORMS...ONLY SCATTERED SHOWERS AND GENERAL
THUNDERSTORMS ARE EXPECTED WITH THE COLD FRONTAL PASSAGE.

ACTIVATION OF STORM SPOTTERS AND EMERGENCY MANAGEMENT PERSONNEL WILL
LIKELY BE REQUIRED BY MID AFTERNOON THROUGH TONIGHT.