HEAVY RAIN, SEVERE WEATHER: April 5 & 6, 2014

High shear and low CAPE events tend to overproduce. This system looks to have plenty of shear. Lack of instability is keeping this from being a more serious outbreak.

Folks, this Sunday afternoon/Sunday night looks like it's going to be pretty nasty starting in Louisiana and moving NW through Mississippi and Alabama.  I'm emphasizing this because this is more of an event that looks like it'll impact more of the board members and it's April, a climatologically bad month for the SE US.  Both GFS and Euro show a neutral to negatively tilted trough swinging through the area Sunday right with rapid development of a low in Louisiana.  It's going to rapidly intensify...the GFS is showing it at 999mb in North Mississippi similar to the Euro.  This means a large part of the Central Gulf Coast will be in the warm sector.  Shear is going to be roaring across the area at 60-70 kts from the SW with a surface flow from the S/SE...conducive for rotating storms.  CAPE will be modest at 750-1000 J/kg, but that looks sufficient for supercells with the type of shear that will be occurring. 

Shear for Sunday evening/night (notice the pinks and purples):


Shows the differences in direction of winds through the column:



Negative tilt is apparent:

From LIX. I'll place this in both threads:

MOBILE:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MOBILE AL
400 PM CDT THU APR 3 2014

...ACTIVE WEATHER EXPECTED THIS WEEKEND WITH POTENTIAL FOR HEAVY RAIN
AND INSTANCES OF SEVERE THUNDERSTORMS...

.SHORT TERM [TONIGHT THROUGH FRIDAY NIGHT]...SFC HIGH PRESSURE RIDGE WILL
CONTINUE OVER THE FCST AREA TONIGHT WITH NO WEATHER EXPECTED...AND
THEN BREAK DOWN ON FRIDAY AS A COLD FRONT APPROACHES FROM THE WEST.
THE COLD FRONT WILL LIKELY BE MOVING INTO OUR WESTERN FCST ZONES
(SOUTHEAST MISSISSIPPI) BY LATE MORNING OR EARLY AFTERNOON FRIDAY
AND APPROACHING THE I-65 CORRIDOR MID/LATE AFTERNOON AND THEN
FINALLY MOVING EAST OF THE FCST AREA TO THE SOUTHEAST DURING THE
EARLY EVENING HOURS FRIDAY. A BROKEN LINE OF THUNDERSTORMS JUST
AHEAD OF THE FRONT WILL IMPACT THE AREA FROM WEST TO EAST DURING THE
DAY FRIDAY. SOME OF THE STORMS ALONG THE LINE COULD BE STRONG TO
OCNLY SVR...WITH THE PRIMARY THREAT BEING DAMAGING WIND GUSTS.
OVERALL THOUGH...CHANCES FOR SVR WEATHER WILL BE LOW...AND PRIMARILY
OVER OUR INTERIOR AND WESTERN COUNTIES. COULD SEE A FEW ISOLATED
DISCRETE THUNDERSTORMS DEVELOP OUT AHEAD OF THE LINE BUT RIGHT NOW
ANY TORNADO THREAT WITH THESE APPEARS TO BE VERY LOW. RAINFALL
TOTALS TOMORROW WITH THE PASSAGE OF THE LINE WILL GENERALLY BE ONE
HALF TO ONE INCH ACROSS THE AREA...WITH THE HIGHER ONE INCH AMOUNTS
MORE LIKELY OVER SOUTHEAST MISSISSIPPI AS THE LINE IS LIKELY TO BE
WEAKENING SLIGHTLY AS IT WORKS ITS WAY EAST ACROSS THE AREA. PARTS
OF THE FLORIDA PANHANDLE WILL PROBABLY SEE LOWER RAINFALL TOTALS...
ON THE ORDER OF ONE QUARTER TO ONE HALF INCH AT THE MOST. OTHERWISE...
A TEMPERATURE FCST. LOWS TONIGHT IN THE MID/UPPER 60S OVER COASTAL
AND WESTERN PORTIONS OF THE FCST AREA CLOSER TO THE WESTERN
PERIPHERY OF THE SFC RIDGE...AND IN THE LOWER 60S OVER INTERIOR
EASTERN COUNTIES WHICH WILL BE BETTER INFLUENCED BY THE RIDGE. HIGH
TEMPS FOR TOMORROW WILL BE A LITTLE COOLER THAN PAST SEVERAL DAYS
WITH MORE CLOUD COVER AND PCPN...WITH HIGHS GENERALLY IN THE UPPER
70S. 12/DS

FRONTAL BOUNDARY IS PROGGED TO MAKE PASSAGE FRIDAY EVENING TO OFF THE
CENTRAL GULF COAST. UPPER LEVEL DYNAMICS WILL HAVE MOVED WELL OFF TO
THE NORTHEAST...SO RISK OF SEVERE WEATHER ENDS. ALTHOUGH FRONTAL
PASSAGE OCCURS...DEEP LAYER MOISTURE IS NOT SCOURED OUT WITH
PRECIPITABLE WATER VALUES ~1.5 INCHES BECOMING ALIGNED WEST TO EAST
OVER THE NORTHERN GULF COAST. WITH THE PRESENCE OF A MID LEVEL SHEAR
AXIS/WEAK UPPER LEVEL IMPULSES MOVING EASTWARD ATOP THE FRONTAL ZONE
AND MOISTURE...HAVE THE HIGHER PROBABILITIES OF MEASUREABLE RAIN
ORIENTED OVER THE SOUTHERN HALF OF THE AREA. OVERNIGHT LOWS LOOK TO
RANGE FROM THE LOWER 50S FAR NORTHERN ZONES...TO UPPER 50S/LOWER 60S
BEACH AREAS. /10

.LONG TERM [SATURDAY THROUGH THURSDAY]...STALLED FRONTAL ZONE OVER
THE NORTHERN GULF ON SATURDAY BEGINS TO TRANSITION TO A WARM FRONT
AND BEGIN MOVING SLOWLY NORTHWARD SATURDAY NIGHT. WITH THE PRESENCE
OF THE BOUNDARY...ALONG WITH A MORE ACTIVE SOUTHWESTERLY FLOW ALOFT
(ENHANCED ASCENT) AND PRESENCE OF DEEP MOISTURE RESULTS IN SHOWERS TO
BECOME LIKELY ONCE AGAIN AREA WIDE WITH A CHANCE OF STORMS. GULF
MOISTURE IS WIDE OPEN WITH PRECIPITABLE WATER VALUES OF ~1.6 INCHES
BEING NEARLY 2 STANDARD DEVIATIONS ABOVE NORMAL FOR THIS TIME OF
YEAR. THUS...THE STAGE IS SETTING UP FOR ORGANIZED STORMS TO BE
EFFICIENT IN DROPPING LOCALLY HEAVY RAINFALL. GRIDDED STORM TOTAL
RAINFALL FROM FRIDAY MORNING TO MONDAY MORNING ADDS UP TO BETWEEN 3
AND 5 INCHES WITH THE HIGHER AMOUNTS IN THIS RANGE ORIENTED OVER
INTERIOR SOUTHEAST MISSISSIPPI AND INTERIOR SOUTHWEST ALABAMA.
LOCALLY HIGHER AMOUNTS ARE HIGHLY POSSIBLE. DUE TO ANTECEDENT SOIL
MOISTURE CONDITIONS FROM RECENT RAINS FROM LAST WEEKEND...ADDITIONAL
HEAVY RAINS THIS WEEKEND WILL LIKELY LEAD TO RUNOFF AND FLOODING
PROBLEMS. ANOTHER ISSUE ARE RIVERS. INCREASED RIVER STAGES WILL BE
HIGHLY DEPENDENT ON WHERE THE HEAVIER RAINS SET UP.

DURING THE DAY SUNDAY...THE GLOBAL WEATHER MODELS ARE IN AGREEMENT ON
BRINGING A LARGE SWATH OF MID LEVEL HEIGHT FALLS EASTWARD OUT OF TEXAS.
THIS CAUSES A WAVE OF SURFACE LOW PRESSURE TO DEVELOP ON THE WESTERN
PERIPHERY OF NORTHERN GULF FRONT. THE DEVELOPING LOW LIFTS NORTHEAST
UP ACROSS LOUISIANA LATE SUNDAY AFTERNOON...THEN UP ACROSS THE LOWER
MISSISSIPPI RIVER VALLEY SUNDAY EVENING. IN ADDITION TO THE POTENTIAL
OF MORE HEAVY RAINS ON SUNDAY...AN ORGANIZING AREA OF STORMS WILL
LIKELY DEVELOP OVER THE CENTRAL GULF COAST. THIS OCCURS AS THE
GEOPOTENTIAL HEIGHT FIELD BECOMES STRONGLY DIFFLUENT/INCREASED
SURFACE BASED CONVERGENCE IN THE PRESENCE OF DEEP MOISTURE AND
INSTABILITY. AT SAME TIME...A STRENGTHENING H85 SOUTHWESTERLY LOW
LEVEL SPEED MAX BETWEEN 40 AND 50 KNOTS DEVELOPS BY LATE SUNDAY
AFTERNOON CONTINUING INTO THE EVENING WHICH POSES CONCERNS FOR
ANOTHER ROUND OF SEVERE WEATHER DURING THIS TIME PERIOD. CONSIDERING
THE SPEED MAX/STRONG VEERING IN THE LOW LEVELS/INCREASED SHEAR...0-1
KM HELICITY VALUES INCREASING BETWEEN 200 TO 300 M2/S2 FAVORS THE
POTENTIAL FOR MORE ORGANIZED...POTENTIALLY ROTATING UPDRAFTS/ISOLATED
TORNADOES IN ADDITION TO A DAMAGING WIND RISK IN SEVERE STORMS. STAY
TUNED. /10

THE UPPER TROUGH AND SURFACE LOW WILL LIFT NORTHEASTWARD TOWARD THE
OHIO VALLEY MONDAY...WHILE A COLD FRONT MEANWHILE PUSHES ACROSS OUR
FORECAST AREA MONDAY AFTERNOON. A DRIER AIRMASS WILL BRING A GRADUAL
END TO PRECIPITATION CHANCES MONDAY AFTERNOON/EVENING. HOWEVER...
ANOTHER MID LEVEL TROUGH CLIPPING THROUGH THE MISSISSIPPI VALLEY
REGION MAY BRING AN INCREASING CHANCE OF SHOWERS TUESDAY AND TUESDAY
NIGHT...WITH DRY WEATHER THEN LOOKING TO RETURN BY WEDNESDAY IN THE
WAKE OF THIS FEATURE. AN EVEN COOLER AIRMASS LOOKS TO ARRIVE IN THE
WAKE OF THE NEXT FRONT TUESDAY AND WEDNESDAY...AND TEMPERATURES MAY
RETURN TO BELOW NORMAL VALUES BOTH DAYS. /21

Already a Slight Risk for Day 3, Sunday:





DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0131 AM CDT FRI APR 04 2014

VALID 061200Z - 071200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM SRN LA INTO CNTRL AND SRN
MS AND AL...AND THE WRN FL PANHANDLE...

...SYNOPSIS...
A SHORTWAVE TROUGH WILL MOVE EWD ACROSS THE SRN PLAINS AND INTO THE
LOWER MS VALLEY BY SUNDAY NIGHT. A SURFACE LOW IS FORECAST TO DEEPEN
LATE IN THE PERIOD FROM LA INTO MS...WITH SHEAR AND INSTABILITY
INCREASING THROUGH THE PERIOD DUE TO INCREASING SLY LOW-LEVEL WINDS.
THE RESULT SHOULD BE A THREAT OF SEVERE WINDS AND A FEW TORNADOES
FROM LA INTO MS AND AL.

...LA/MS/AL...
WHILE SOME TIMING DIFFERENCES EXIST BETWEEN THE VARIOUS
MODELS...CYCLOGENESIS IS LIKELY TO OCCUR BY LATE AFTERNOON OR
EVENING ACROSS LA OR MS IN ADVANCE OF THE SHORTWAVE TROUGH. SHEAR
PROFILES WILL INCREASE ATTENDANT TO THE TROUGH AND MOISTURE WILL
INCREASE THROUGHOUT THE PERIOD. IN THE WAKE OF EARLY-DAY
PRECIPITATION...MID 60S F BOUNDARY LAYER DEWPOINTS ARE PROBABLE
ACROSS THE DEVELOPING WARM SECTOR...FROM SERN LA INTO CNTRL AND SRN
MS AND AL. THIS WILL CREATE MODEST BUT SUFFICIENT INSTABILITY FOR A
SEVERE WIND AND TORNADO THREAT WITH DETAILS TO BE DETERMINED IN
LATER OUTLOOKS.

..JEWELL.. 04/04/2014

JACKSON:

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

CONFIDENCE CONTINUES TO INCREASE THAT HEAVY RAIN WILL AFFECT PORTIONS
OF THE ARKLAMISS SUNDAY INTO SUNDAY NIGHT. RAINFALL AMOUNTS OF 2 TO 4
INCHES WILL BE POSSIBLE WITH LOCALLY HIGHER AMOUNTS. THIS COULD LEAD
TO LOCALIZED FLASH FLOODING CONCERNS FOR THE MAJORITY OF CENTRAL AND
SOUTHEAST MISSISSIPPI...AS WELL AS PORTIONS OF NORTHEAST LOUISIANA...
SUNDAY THROUGH SUNDAY NIGHT.

IN ADDITION...SEVERE THUNDERSTORMS CAPABLE OF PRODUCING WIND GUSTS OF
60 MPH OR GREATER WILL BE POSSIBLE ACROSS PORTIONS OF SOUTH CENTRAL AND
SOUTHEAST MISSISSIPPI SUNDAY AFTERNOON AND EVENING.

.SPOTTER CALL TO ACTION STATEMENT...
THE ACTIVATION OF STORM SPOTTERS...HAM RADIO OPERATORS...AND
EMERGENCY MANAGEMENT PERSONNEL IN SUPPORT OF SEVERE WEATHER
OPERATIONS MAY BE NEEDED FOR PORTIONS OF THE REGION SUNDAY
NIGHT.