Watch Possible

SPC is considering a watch that would include a sizable portion of western and northwestern Alabama. Rather than rehash it, I’m posting the discussion below.

I will add that the latest High Resolution Rapid Refresh model runs have focused on the area between Mobile, Birmingham, and Montgomery in the time frame of 3 to 5 pm. Helicity values and CAPE values are best in that area in that time frame.

-Brian-

MESOSCALE DISCUSSION 0442
NWS STORM PREDICTION CENTER NORMAN OK
1041 AM CDT THU APR 11 2013

AREAS AFFECTED…ERN MS THROUGH NWRN AL AND MIDDLE TN

CONCERNING…SEVERE POTENTIAL…WATCH POSSIBLE

VALID 111541Z – 111745Z

PROBABILITY OF WATCH ISSUANCE…40 PERCENT

SUMMARY…STORMS ARE EXPECTED TO UNDERGO A SLOW BUT GRADUAL INCREASE
IN ORGANIZATION AND INTENSITY INTO THE AFTERNOON. PRIMARY THREAT
WILL BE ISOLATED DAMAGING WIND…BUT ISOLATED TORNADOES CANNOT BE
RULED OUT. AREA WILL CONTINUE TO BE MONITORED…AND ANY WW ISSUANCE
WILL ULTIMATELY DEPEND ON CONVECTIVE TRENDS.

DISCUSSION…EXPANSIVE SQUALL LINE EXTENDS FROM WEST OF NASHVILLE TN
SSWWD THROUGH ERN MS INTO SERN LA. A FEW SMALL BOWING SEGMENTS AND
MESO-VORTICES HAVE OCCASIONALLY BEEN OBSERVED WITHIN THE LINE…BUT
OVERALL STORMS HAVE BEEN NON-SEVERE THIS MORNING. SFC MESOANALYSIS
SHOW MOIST AXIS WITH DEWPOINTS FROM UPPER 60S OVER SERN MS/SRN AL TO
NEAR 60 OVER THE TN VALLEY. RICHER LOW-LEVEL MOISTURE WILL ADVECT
THROUGH SERN U.S. WARM SECTOR…BUT WIDESPREAD CLOUDS AND MODEST
LAPSE RATES SHOULD LIMIT MLCAPE TO AROUND 1500 J/KG OVER THE GULF
COASTAL STATES AND BELOW 1000 J/KG NORTHWARD INTO THE TN VALLEY.

MORNING RAOB FROM BIRMINGHAM INDICATE A CAPPING INVERSION PRESENT
JUST ABOVE 700 MB WHICH SHOULD TEND TO DELAY DEVELOPMENT OF MORE
ROBUST DISCRETE ACTIVITY WITH ERN EXTENT INTO THE WARM SECTOR. THIS
SUGGESTS MOST STORMS NEAR TERM WILL PROBABLY REMAIN CONFINED TO ZONE
OF FORCING ALONG THE OUTFLOW BOUNDARY ASSOCIATED WITH THE SQUALL
LINE. HOWEVER…RADAR TRENDS HAVE SHOWN AN INCREASE IN WARM SECTOR
CONVECTION OVER SERN MS. HERE…INFLUX OF MT AIR…A FEW CLOUD
BREAKS AND INFLUENCE FROM VORT MAX ROTATING THROUGH BASE OF UPPER
TROUGH MAY SUPPORT MORE ROBUST DISCRETE STORMS.

INITIALLY PRIMARY THREAT IS EXPECTED TO BE DAMAGING WIND AS STORMS
INTENSIFY AND BECOME BETTER ORGANIZED WITHIN THE ONGOING SQUALL
LINE. HOWEVER…DEEPENING OF CONVECTION IN WARM SECTOR MAY
EVENTUALLY OCCUR AS THE BOUNDARY LAYER GRADUALLY DESTABILIZES AND
CAPPING INVERSION ERODES. HODOGRAPHS AND EFFECTIVE BULK SHEAR WILL
REMAIN SUFFICIENT FOR A FEW EMBEDDED SUPERCELLS WITHIN THE LINE OR
WITH ANY CONVECTION THAT MAY DEEPEN IN WARM SECTOR DURING THE
AFTERNOON.

..DIAL/THOMPSON.. 04/11/2013

ATTN…WFO…OHX…BMX…HUN…MEG…JAN…

LAT…LON 32498759 32358885 32718914 33958827 34958766 36158663
36008589 34648640 33498695 32498759

Category: Alabama's Weather