MESOSCALE PRECIPITATION DISCUSSION 0130
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
904 PM EDT MON MAY 25 2015
 
AREAS AFFECTED...SOUTHEAST TO EAST-CENTRAL TX...WESTERN LA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 260100Z - 260600Z
 
SUMMARY...VERY HEAVY SHOWERS AND THUNDERSTORMS WILL ARRIVE THIS
EVENING WITH RAINFALL RATES OF 2 TO 3 INCHES/HR. LOCALLY
SIGNIFICANT FLASH FLOODING IS POSSIBLE.

DISCUSSION...THE SOUTHERN PORTION OF AN EXPANSIVE MCS NOW
APPROACHING THE LOWER MS VALLEY HAS BEEN PRODUCING EXTREMELY HEAVY
RAINFALL RATES AND IS CHARACTERIZED BY CLOUD TOP TEMPERATURES AS
COLD AS -80C OVER PARTS OF EASTERN TX.

THE CONVECTION CONTINUES TO TAKE ADVANTAGE OF A COMBINATION OF
ROBUST DEEP LAYER ASCENT AROUND THE SOUTHERN FLANK OF A DEPARTING
VORT CENTER...ALONG WITH A VERY MOIST AND VERY UNSTABLE AIRMASS
POOLED ACROSS SOUTHEAST TX AND LA. IN FACT...THE LATEST RAP
ANALYSIS DEPICT SBCAPE VALUES OF 4000 TO 5000 J/KG VALUES ALONG
THE IMMEDIATE SOUTHEAST TX COASTAL PLAIN...AND MEANWHILE
PERSISTENT SOUTHERLY H85 FLOW OF 30 TO 40 KTS IN OFF THE WESTERN
GULF OF MEXICO IS FOCUSING PWATS OF 1.75 TO 2 INCHES OUT AHEAD OF
THE MCS.

THE SOUTHERN PORTION OF THE MCS HAS BEEN INCREASINGLY BECOMING
ORIENTED SW/NE OVER THE LAST COUPLE OF HOURS...AND IS BECOMING
MORE ALIGNED MEAN WITH THE DEEPER MEAN FLOW. UNFORTUNATELY...THIS
WILL SET THE STAGE FOR VERY HEAVY RAINFALL AMOUNTS THIS EVENING
OVER SOUTHEAST TX...WITH A HIGH LIKELIHOOD OF TRAINING CELLS. THE
12Z ARW AND LATEST HRRR RUN SUGGEST THE MCS FOCUSING AS MUCH AS 4
TO 6 INCHES OF RAIN WITH LOCALLY HEAVIER AMOUNTS THROUGH 06Z.
SIGNIFICANT FLASH FLOODING IS EXPECTED AT LEAST LOCALLY AS A
RESULT.

EXPECT SOMEWHAT LOWER AMOUNTS OVER NORTHWEST LA AS THIS PART OF
THE CONVECTIVE LINE IS EXPECTED TO BE A BIT MORE PROGRESSIVE.
HOWEVER...WITH SUCH INTENSE RAINFALL RATES...FLASH FLOODING WILL
BE A CONCERN HERE AS WELL.

ORRISON

ATTN...WFO...CRP...EWX...HGX...JAN...LCH...SHV...

ATTN...RFC...LMRFC...WGRFC...

LAT...LON   32929356 32889196 32049166 30909211 30029309 
            29579416 28809565 28209694 28269789 28869824 
            29569775 30399637 30849588 31669476