Mesoscale Discussion 563

Issued

Apr 17, 2012, 12:41 PM CDT (17:41 UTC)

Expired

Apr 17, 2012, 2:45 PM CDT

In force

2 hr

Issued by

the Storm Prediction Center

670 
ACUS11 KWNS 171742
SWOMCD
SPC MCD 171741
MSZ000-LAZ000-171945-

MESOSCALE DISCUSSION 0563
NWS STORM PREDICTION CENTER NORMAN OK
1241 PM CDT TUE APR 17 2012

AREAS AFFECTED...SERN MS...SERN LA

CONCERNING...HEAVY RAINFALL

VALID 171741Z - 171945Z

AREAS OF HEAVY RAIN WILL IMPACT PORTIONS OF SERN MS AND SERN LA INTO
THE MID AFTERNOON HOURS...WITH RAINFALL RATES OF 1-2 IN/HR POSSIBLE.
ALSO...AN ISOLATED SVR TSTM CAPABLE OF PRODUCING A MARGINALLY SVR
WIND GUST OR TWO AND PERHAPS A WEAK/BRIEF TORNADO CANNOT BE RULED
OUT...AND A WW WILL NOT BE ISSUED.

SFC MESOANALYSIS AROUND 17Z DEPICTS A SUBSYNOPTIC-SCALE LOW CENTERED
30 ENE OF MCCOMB MS...WITH A STATIONARY FRONT EXTENDING NEWD FROM
THE LOW INTO CNTRL AL AND A SLOW-MOVING COLD FRONT TRAILING SSW OF
THE LOW TO THE COAST OF S-CNTRL LA. WITH CONTINUED MOISTURE
TRANSPORT INTO THE REGION AND ISENTROPIC ASCENT NEAR AND NORTH OF
THE STATIONARY FRONT...BANDS OF THUNDERSTORMS WITH HEAVY RAINFALL
WILL CONTINUE TO IMPACT THE AREA INTO THE AFTERNOON. A WELL DEFINED
CONVECTIVE LINE EXTENDS FROM 20 S OF JACKSON MS TO 20 ESE OF MCCOMB
MS AS OF 1720Z. JACKSON VWP DATA DEPICT A NEARLY UNIDIRECTIONAL SLY
WIND PROFILE FROM JUST ABOVE THE SFC TO AROUND 4.5 KM AGL -- I.E.
ORIENTED NEARLY PARALLEL TO THIS CONVECTIVE LINE. THIS SCENARIO WILL
SUPPORT TRAINING OF MESO-BETA ELEMENTS WITHIN THE LINE...WHILE
ADDITIONAL N-S-ORIENTED BANDS OF CONVECTION EVOLVE WITHIN THE WARM
SECTOR THROUGH THE AFTERNOON HOURS. HIGH PRECIPITATION EFFICIENCY
WILL BE SUPPORTED OWING TO /1/ PW VALUES AROUND 1.55-1.65 INCHES PER
GPS DATA AND 12Z JACKSON MS AND SLIDELL RAOBS -- I.E. AROUND 160-175
PERCENT OF NORMAL PER BLENDED AMSU/SSMI SATELLITE DATA -- AND /2/
WARM-CLOUD-LAYER DEPTHS AROUND 4 KM PER THE RAOB DATA. AS
SUCH...RAINFALL RATES OF 1-2 IN/HR WILL OCCUR WITH TRAINING
CONVECTIVE ELEMENTS. WITH THE APPROACH OF A MID-LEVEL VORT MAX NEAR
THE SABINE RIVER VALLEY...THE MID-LEVEL FLOW WILL ATTAIN MORE OF A
WLY COMPONENT AFTER 20Z -- I.E. SOME ORTHOGONAL COMPONENT TO
PREVIOUSLY ESTABLISHED CONVECTIVE LINES. ACCORDINGLY...CONVECTIVE
TRAINING AND THE THREAT FOR HEAVY RAINFALL WILL BECOME LESS LIKELY
LATER THIS AFTERNOON...AS ADVECTION PROCESSES SHIFT CONVECTION EWD.

ADDITIONALLY...ISOLATED TO SCATTERED THUNDERSTORMS ARE DEVELOPING
WITHIN THE WARM SECTOR. WITH 20-25 KT OF EFFECTIVE BULK SHEAR ACROSS
THE AREA...OCCASIONALLY ORGANIZED STORM STRUCTURES MAY ENSUE WITH A
THREAT FOR ONE TO TWO MARGINALLY SVR WIND GUSTS IN WET MICROBURSTS
AIDED BY WATER-LOADING PROCESSES. FURTHERMORE...LATEST VWP DATA FROM
SLIDELL DEPICT SOME CURVATURE IN THE LOW-LEVEL HODOGRAPH AS WINDS
MODESTLY VEER WITH INCREASING HEIGHT ABOVE THE SFC. AND...GIVEN THE
RICH TROPOSPHERIC MOISTURE CONTENT IN PLACE...A WEAK/BRIEF TORNADO
CANNOT BE RULED OUT WITH THE MOST INTENSE CONVECTION...PARTICULARLY
NEAR THE SFC LOW AND STATIONARY FRONT WHERE SFC WINDS ARE RELATIVELY
MORE BACKED.

..COHEN.. 04/17/2012

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

ATTN...WFO...MOB...JAN...LIX...

LAT...LON   31859021 32208994 32358949 32388896 32058853 30648857
            29228918 29069056 29579095 30349040 30909014 31529032
            31859021

Mesoscale Discussions in Mississippi, 2012Mesoscale 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.