Mesoscale Discussion 2245

Issued

Dec 28, 2012, 9:41 AM CST (15:41 UTC)

Expired

Dec 28, 2012, 11:15 AM CST

In force

94 min

Issued by

the Storm Prediction Center

Chance of a watch

20%

Counties Acadia Parish, LA, Calcasieu Parish, LA, Cameron Parish, LA, Iberia Parish, LA, Jefferson Davis Parish, LA, Lafayette Parish, LA, Saint Martin Parish, LA, St. Mary Parish, LA, Vermilion Parish, LA

The Lake Charles radar (KLCH), 86 km from the middle of the area, began a volume at 15:41 UTC, the scan nearest the moment this went out.

Open the radar archive at this moment

The archived warnings, watches and discussions in force at that minute are drawn over the scan, this one among them.

313 
ACUS11 KWNS 281542
SWOMCD
SPC MCD 281541
LAZ000-TXZ000-281715-

MESOSCALE DISCUSSION 2245
NWS STORM PREDICTION CENTER NORMAN OK
0941 AM CST FRI DEC 28 2012

AREAS AFFECTED...SWRN-SOUTH CENTRAL LA

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 281541Z - 281715Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...POTENTIAL EXISTS FOR A BRIEF TORNADO THREAT ALONG AND
INLAND /1-2 TIERS OF PARISHES/ ACROSS SWRN TO SOUTH CENTRAL LA THIS
MORNING INTO THE EARLY AFTERNOON.  COVERAGE OF STRONGER CELLS
CAPABLE OF PRODUCING A TORNADO IS EXPECTED TO BE LOW TODAY...GIVEN
MARGINAL INSTABILITY.  FOR THIS REASON...WATCH ISSUANCE IS UNLIKELY
AT THIS TIME...BUT TRENDS WILL BE MONITORED FOR OUTLOOK UPGRADE AND
THE NEED FOR A WATCH.

DISCUSSION...AT 15Z...REGIONAL RADAR IMAGERY SHOWED A BROKEN LINE OF
TSTMS EXTENDING FROM CENTRAL-SWRN LA...TO THE UPPER TX COAST /20 S
KBPT/...AND THEN SWWD OFF THE REST OF THE TX COAST.  THE RADAR
IMAGERY ALSO SHOWED A FEW TRANSIENT...DISCRETE WARM SECTOR
CONVECTIVE CELLS SHOWING LOW LEVEL ROTATION.  SOME OF THIS ACTIVITY
WAS ALSO PRODUCING CG LIGHTNING STRIKES.  TRENDS IN SURFACE
OBSERVATIONS INDICATED A WARM FRONT HAD MOVED N OF KLCH...EXTENDING
SEWD THROUGH SOUTH CENTRAL LA /INVOF OF NEW IBERIA/ AND OFFSHORE THE
SERN LA COAST.  MODIFIED 12Z LCH SOUNDING SUGGESTS A SURFACE
DEWPOINT IN THE MID 60S IS REQUIRED FOR PARCELS TO BE
SURFACE-BASED...AND THUS REALIZE THE AVAILABILITY OF GREATER
EFFECTIVE SRH /400+ M2 PER S2/.  MODELS SHOWED DEWPOINTS IN THE
LOWER-MID 60S SHOULD SPREAD INLAND ACROSS SOUTH CENTRAL LA THIS
MORNING...AND EVENTUALLY SERN LA THIS AFTERNOON.

MORNING WATER VAPOR IMAGERY SHOWED A PRIMARY SHORTWAVE TROUGH MOVING
EWD ACROSS WRN OK/NWRN TX...WHILE A LEAD IMPULSE WAS MOVING ENEWD
THROUGH E TX TOWARD THE LOWER MS VALLEY. FORCING FOR ASCENT WITH
THIS LATTER FEATURE MAY BE WEAKENING THE MIDLEVEL CAP EVIDENT IN THE
12Z LCH SOUNDING...SUCH THAT DEEPER MOIST CONVECTION SHOULD CONTINUE
TO FORM WITHIN AND AHEAD OF THE NNE-SSW ORIENTED WIND SHIFT/CURRENT
CONVECTIVE LINE. 50-70 KT SWLY MIDLEVEL WINDS MOVING ACROSS LA AND
ATOP SWLY 40-50 KT LOW LEVEL FLOW ARE SUPPORTING MORE THAN
SUFFICIENT BULK SHEAR FOR PERSISTENT CELLS WITH ROTATION.
CLOUDINESS AND SCATTERED PRECIPITATION ONGOING ACROSS THE WARM
SECTOR SHOULD TEND TO INHIBIT STRONGER DESTABILIZATION TODAY AND THE
SPATIOTEMPORAL EXTENT OF STRONGER...PERSISTENT CELLS.
HOWEVER...GIVEN THE STRENGTH OF THE DEEP LAYER AND LOW LEVEL SHEAR
VALUES...A BRIEF TORNADO COULD DEVELOP ESPECIALLY CLOSER TO THE LA
COAST WHERE MOISTURE/INSTABILITY WILL BE RELATIVELY HIGHER.

..PETERS/HART.. 12/28/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...LIX...LCH...

LAT...LON   29299425 30149360 30409302 30299205 30049133 29539114
            29129110 28739118 28969247 29209359 29129424 29299425

Mesoscale Discussions in Louisiana, 2012Every mesoscale discussion in 2012

The product and its follow-ups from the Iowa Environmental Mesonet's archive of National Weather Service and Storm Prediction Center text; the sounding from the Mesonet's radiosonde archive; radar from the NEXRAD Level II archive.