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Mesoscale Discussion 425 |
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MESOSCALE DISCUSSION 0425
NWS STORM PREDICTION CENTER NORMAN OK
1121 AM CDT THU APR 23 2015
AREAS AFFECTED...SRN LA
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 231621Z - 231745Z
PROBABILITY OF WATCH ISSUANCE...60 PERCENT
SUMMARY...INCREASING CONVECTIVE DEVELOPMENT /AND ASSOCIATED SEVERE
RISK/ ACROSS SRN LA OVER THE NEXT COUPLE OF HOURS SUGGESTS POSSIBLE
WW ISSUANCE.
DISCUSSION...LATEST SURFACE ANALYSIS SHOWS A QUASI-STATIONARY FRONT
LYING ROUGHLY W-E ACROSS SRN LA ATTM...SEPARATING A VERY MOIST GULF
BOUNDARY LAYER TO THE S FROM A COOLER/DRIER -- AND CONVECTIVELY
CONTAMINATED -- AIRMASS ACROSS NRN LA AND CENTRAL/NRN MS.
SCATTERED CLOUD COVER NEAR AND S OF THE FRONT HAS PERMITTED MODEST
HEATING...WHICH HAS HELPED TO PUSH MIXED-LAYER CAPE VALUES ACROSS
SRN LA INTO THE 500 TO 1000 J/KG RANGED. MODIFYING THE MORNING LIX
/SLIDELL LA/ RAOB FOR CURRENT BOUNDARY LAYER TEMP/DEWPOINT SHOWS
THAT A WEAK CAP AROUND 900 MB IS NEARLY ERODED -- AND CONVECTIVE
DEVELOPMENT OVER THE PAST HALF HOUR OR SO JUST N OF LFT /LAFAYETTE
LA/ WHERE ASCENT IS BEING MAXIMIZED INVOF THE FRONT CONFIRMS THIS
CAP EROSION. AS SUCH...EXPECT STORMS TO DEVELOP ACROSS SRN LA INVOF
THIS FRONT OVER THE NEXT 1-2 HOURS.
WHILE LOW-LEVEL SHEAR -- EVEN TO THE COOL SIDE OF THE FRONT -- IS
RELATIVELY WEAK WHICH SHOULD LIMIT ANY TORNADO RISK...RAPIDLY
INCREASING WLY FLOW WITH HEIGHT THROUGH THE 700 TO 500 MB LAYER IS
CONTRIBUTING TO DEEP-LAYER SHEAR SUFFICIENT FOR ORGANIZED/ROTATING
STORMS. WHILE FLOW ALOFT ALIGNED ROUGHLY ALONG THE FRONT SUGGEST
THAT CELLULAR STORM MODE WILL LIKELY NOT BE SUSTAINED
LONG-TERM...LOCALLY DAMAGING WINDS AND HAIL WILL BE POSSIBLE WITH
ANY STORM/STORM CLUSTER ACROSS THIS REGION. AS THREAT
INCREASES...WW ISSUANCE MAY BE NEEDED.
..GOSS/GRAMS.. 04/23/2015
ATTN...WFO...JAN...LIX...LCH...
LAT...LON 29949295 30279367 30989350 31309276 30939028 30098931
29528950 29449028 29949295
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