Tuesday, 2/23/16 - Severe Weather Possible (School Closures)

MOBILE AFD (very long)

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOBILE AL
446 PM CST MON FEB 22 2016

...A SIGNIFICANT THREAT OF SEVERE STORMS IS FORECAST OVER THE LOCAL
AREA TUESDAY AFTERNOON THROUGH EARLY WEDNESDAY MORNING...

...POTENTIAL EXISTS FOR STRONG AND LONG TRACK TORNADOES TUESDAY
AFTERNOON INTO EARLY WEDNESDAY MORNING...

.NEAR TERM /NOW THROUGH TUESDAY/...A WEAK FRONTAL BOUNDARY EXTENDING
FROM SOUTHERN MISSISSIPPI UP TO THE NORTHEAST ACROSS CENTRAL ALABAMA
THIS EVENING WILL REMAIN NEARLY STATIONARY OR LIFT NORTH ACROSS THE
REGION TONIGHT. AN AREA OF RAIN WITH A FEW THUNDERSTORMS CURRENTLY
ORIENTED ALONG AND AHEAD OF THE FRONT WILL MOVE SLOWLY EAST ACROSS
WESTERN HALF OF OUR FCST AREA THIS EVENING AND INTO THE EARLY
PREDAWN MORNING HOURS TUESDAY. WE ARE EXPECTING COVERAGE TO DECREASE
AFTER MIDNIGHT AS WEAK SUPPORTING UPPER DYNAMICS WEAKEN OVER THE
AREA...BUT THERE WILL BE A CHANCE FOR SHOWERS AND ISOLATED
THUNDERSTORMS TO CONTINUE THROUGH THE NIGHT. LIGHT SOUTHERLY FLOW
CONTINUES TONIGHT...BRINGING EVER INCREASING MOISTURE INTO THE
REGION. OBSERVED SFC DEWPOINTS HAVE ALREADY BEEN RUNNING UP TO
AROUND 5 DEGREES ABOVE GUIDANCE...AND WE EXPECT THIS TO CONTINUE
OVERNIGHT. WITH THIS...AREAS OF FOG AGAIN POSSIBLE TONIGHT NEAR THE
COAST AND OUT OVER THE ADJACENT MARINE AREAS. LOWS TONIGHT IN THE
MID TO UPPER 50S OVER INTERIOR COUNTIES.

BIG CHANGES ON THE WAY TUESDAY...WITH THE AFTERNOON HOURS (AND
CONTINUING INTO THE EVENING HOURS...SEE SHORT TERM DISCUSSION
BELOW) EXPECT TO HAVE A SIGNIFICANT CHANCE OF SEVERE WEATHER. THE
DAY BEGINS WITH A RAPIDLY AMPLIFYING UPPER SYSTEM (BECOMING
NEGATIVELY TILTED DURING THE COURSE OF THE DAY) SWINGING EAST OUT OF
TEXAS TO NEAR NORTHEAST LOUISIANA BY THE END OF THE DAY. JUST TO THE
EAST OF THE UPPER LOW...VERY INTENSE AND DEEPENING SFC LOW PRESSURE
WILL LIFT NORTHEAST OUT OF SOUTHEAST COASTAL TEXAS TO NORTHEAST
LOUISIANA (WHERE SOME MODEL OUTPUTS INDICATES A PRESSURE AS LOW AS
988 MB). ALL INGREDIENTS COMING TOGETHER FOR ONSET OF A SIGNIFICANT
SEVERE WEATHER EVENT BY MID AFTERNOON (AND CONTINUING INTO THE
EVENING). THREAT FOR SEVERE WEATHER WILL RAPIDLY INCREASE AFTER ABOUT
2 PM...ESPECIALLY OVER INTERIOR SOUTHEAST MISSISSIPPI AND MOVING INTO
PORTIONS OF EXTREME SOUTHWEST ALABAMA THROUGH 6 PM. MODELS HAVE
ALREADY BEEN NOTED TO BE UNDERESTIMATING THE INSTABILITY...ESPECIALLY
THE GFS...WITH THE NAM AND ECMWF SEEMING TO ADJUST A LITTLE CLOSER
WITH CURRENT TRENDS. FOR THIS REASON WE LEANED TOWARD A COMBINATION
OF THESE TWO SOLUTIONS. WITH THE HIGHER MOISTURE LEVELS EXPECTED THAN
MODELS SUGGEST...BELIEVE THE 1500 MUCAPES ADVERTISED TO BE DEVELOPING
OVER OUR WESTERN FCST AREA BY LATE AFTERNOON BY THE NAM ARE NOT
UNREASONABLE. IN ADDITION TO THESE CAPE VALUES...0-1KM SR-HEL VALUES
APPROACHING 400 M2/S2 AND 0-3KM SR-HEL VALUES APPROACHING 500-600
M2/S2 OVER OUR SOUTHEAST MISSISSIPPI COUNTIES BY THE END OF THE DAY
AS LOW LEVEL 850 JET INCREASES TO AT LEAST 55 KNOTS. AS SUCH...SPC
HAS OUTLOOKED ALL OF OUR AREA UNDER A MODERATE RISK OF SEVERE WEATHER
ON TUESDAY...AND STRONG AND LONG TRACKED TORNADOES WILL BE POSSIBLE.
A WIND ADVISORY IS ALSO NOW IN EFFECT FOR THE ENTIRE AREA ON
TUESDAY...AND BOTH A HIGH SURF ADVISORY AND HIGH RIP CURRENT RISKS
ALONG THE COAST. HIGH TEMPS TUESDAY EXPECTED TO BE IN THE LOW TO MID
70S. 12/DS

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...GLOBAL MODELS
ARE IN EXCELLENT AGREEMENT ALOFT AND AT THE SURFACE WITH THE POTENT
STORM SYSTEM LIFTING UP ACROSS THE LOWER MISSISSIPPI RIVER VALLEY AND
MID-SOUTH TUESDAY EVENING. A STRONGLY REFLECTED NEGATIVE TILT
CONFIGURATION TO THE MID LEVEL GEO-POTENTIAL HEIGHT FIELDS WILL
INCREASE LARGE SCALE ASCENT WITHIN A WELL DEFINED WARM SECTOR TUESDAY
EVENING OVER THE CENTRAL GULF COAST THAT IS FORECAST TO CONTAIN MODEST
INSTABILITY. SUBSTANTIAL H50 HEIGHT FALLS TO BETWEEN 15 AND 20
DECAMETERS ROLLING ACROSS THE LOWER MISSISSIPPI RIVER DELTA RESULTS
IN THE RAPID INTENSIFICATION TO A FRONTAL SURFACE LOW WHICH
PROPAGATES NORTHEAST TO THE MID-SOUTH BY MIDNIGHT EARLY WEDNESDAY
MORNING. BETWEEN THE MODEL SOLUTIONS...CENTRAL PRESSURES LOWER TO A
RANGE OF 988 TO 993 MILLIBARS NEAR MONROE LOUISIANA BY EARLY TUESDAY
EVENING. FROM THERE...THE INTENSE LOW TRACKS NORTHEAST TO BETWEEN
GREENVILLE AND OXFORD MISSISSIPPI BY MIDNIGHT EARLY WEDNESDAY AM TO
JACKSON TENNESSEE BY DAYBREAK WEDNESDAY. THE ENSEMBLES INDICATE THAT
THE STRENGTH OF THIS LOW IS AN ANOMALY WITH SURFACE CENTRAL PRESSURES
SOME 3 TO 4 STANDARD DEVIATIONS BELOW THE MEAN. CONSIDERING THIS AND
THE REPRESENTATION OF THE PHYSICAL SOLUTIONS IN THE SPECTRAL
MODELS...THE WIND PROFILES IN THE LOWER LEVELS OF THE ATMOSPHERE ARE
FORECAST TO BE INTENSE OVER THE LOCAL AREA DURING THE EVENING.
CONSIDERING THIS...SOUTHWESTERLY 0-3 KM BULK SHEAR MAGNITUDES
TRENDING BETWEEN 45 AND 55 KNOTS COUPLED WITH STRONGLY BACKED SURFACE
WINDS...HODOGRAPHS ARE STRONGLY CURVED WITH 0-1 KM STORM RELATIVE
HELICITY VALUES BECOMING EXTREMELY HIGH...EXCEEDING 500 M2/S2. THIS
FAVORS WELL DEFINED ROTATION IN STRONGLY DEVELOPED SUPERCELLS...WITH
CONCERNS THAT WE COULD BE DEALING WITH INSTANCES OF STRONG AND LONG
TRACK TORNADOES. OTHER SEVERE WEATHER THREATS WILL BE DAMAGING WINDS
IN EXCESS OF 70 MPH AND GOLFBALL SIZE HAIL OR LARGER. FORECASTERS
STRONGLY ENCOURAGE EVERYONE TO PLAN AHEAD...BE WEATHER AWARE AND
VIGILANT INTO TUESDAY NIGHT. WITH THE EXPECTED STORM MOTION FORECAST
TO BE RAPID...IT IS IMPORTANT TO MOVE QUICKLY TO A PLACE OF SAFETY IN
THE EVENT A WARNING IS ISSUED FOR YOUR AREA.

COLD FRONT IS FORECAST TO SWEEP EAST OF THE LOCAL AREA ON
WEDNESDAY...BRINGING MUCH COOLER CONDITIONS TO THE LOCAL AREA.
FORECASTERS EXPECT IT TO CONTINUE TO BE BREEZY TO WINDY AS STRONG
PRESSURE GRADIENT REMAINS IN PLACE TO THE SOUTHWEST OF THE LARGE
SURFACE LOW LIFTING UP ACROSS THE OHIO RIVER VALLEY. WILL CONTINUE IN
A COOL NORTHWEST FLOW ON THURSDAY. WEDNESDAY AND THURSDAY NIGHTS
COLDER WITH MID/UPPER 30S INTERIOR TO UPPER 30S/LOWER 40S COAST
WEDNESDAY AND THURSDAY.

.LONG TERM /FRIDAY THROUGH MONDAY/...SURFACE HIGH PRESSURE MOVES EAST
ACROSS THE GULF COAST DURING THE OUTLOOK. HIGHS IN THE MID TO UPPER
50S FRIDAY WILL MODERATE INTO THE MID/UPPER 60S SUNDAY AND MONDAY.
COLDEST NIGHT FRIDAY NIGHT WITH A FEW AREAS POSSIBLY SINKING TO NEAR
FREEZING OVER SOME AREAS OF THE INTERIOR. OVERNIGHT LOWS MODERATE
INTO THE WEEKEND. /10