MESOSCALE PRECIPITATION DISCUSSION 0241
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
228 AM EDT THU MAY 31 2018

AREAS AFFECTED...NWRN VIRGINIA...PANHANDLE OF WV...FAR WRN
MARYLAND

CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY

VALID 310627Z - 311030Z

SUMMARY...VERY HEAVY RAIN WILL CONTINUE IN TROPICAL RAIN BANDS
EARLY THIS MORNING WITH RAIN RATES POSSIBLY REACHING 2 IN/HR. ONE
PROMINENT RAIN BAND CONTINUED TO FOCUS NEAR THE BLUE RIDGE
MOUNTAINS AND HAS PRODUCED RADAR ESTIMATED RAINFALL IN EXCESS OF 8
INCHES JUST WEST OF CHARLOTTESVILLE VA. CONTINUED TRAINING OF THE
RAIN BAND IN THIS GENERAL VICINITY SHOULD CONTINUE TO LEAD TO
SIGNIFICANT AND LIFE-THREATENING FLASH FLOODING.

DISCUSSION...A NEARLY STATIONARY CONVECTIVE RAIN BAND HAS REMAINED
FOCUSED ALONG AND NEAR THE BLUE RIDGE MOUNTAINS FOR MUCH OF THE
NIGHT...PRODUCING VERY HEAVY RAIN RATES FROM ALBERMARLE COUNTY
NORTHEAST TO MADISON COUNTY IN NORTHWEST VIRGINIA. KLWX DUAL POL
RAINFALL TOTALS ARE IN EXCESS OF 4 INCHES FOR MUCH OF THAT
SWATH...AND IN EXCESS OF 8 INCHES IN ALBERMARLE COUNTY JUST WEST
OF KCHO. THE MEAN POSITION OF THE CONVECTIVE BAND HAS SHIFTED OFF
THAT QPE MAX AND IS NOW TIED MORE TO THE TERRAIN...BUT PERSISTENCE
FOR SEVERAL HOURS HAS DELIVERED AT LEAST 4 INCHES TO THOSE AREAS
WITH RAIN CONTINUING AS OF 06Z.

HI-RES MODELS HAVE STRUGGLED TO ADEQUATELY MODEL THE EVOLUTION OF
THIS CONVECTIVE BAND...TENDING TO LIFT MOST OF THE RAIN NORTHEAST
WITH AN ELEVATED (925-850MB) WARM FRONT AND A PWAT AXIS.
HOWEVER...A REGION OF MLCAPE AROUND 500-800 J/KG WITH LIMITED CINH
WAS SITUATED ACROSS PORTIONS OF CENTRAL VIRGINIA IN THE INFLOW
REGION FOR THE CONVECTIVE BAND...WITH BOUNDARY LAYER WINDS OUT OF
THE S-SE. THIS HAS LIKELY HELPED SUSTAIN THE CONVECTION...VERY
MOIST LOW-LEVEL INFLOW INTERCEPTING THE TERRAIN (AND PERHAPS A
WEAK SURFACE CONVERGENCE ZONE ALONG THE BLUE RIDGE MTNS) WITH A
SUPPLY OF CONVECTIVE INSTABILITY THAT IS NOT BEING EXHAUSTED.
THEREFORE...DESPITE THE SUGGESTIONS OF THE HI-RES MODELS...IT
SEEMS PLAUSIBLE THAT THE CONVECTIVE BAND COULD BE SUSTAINED FOR AT
LEAST A FEW MORE HOURS.

EVEN IF THE CONVECTIVE BAND BEGINS TO DIMINISH...VERY HEAVY RAIN
RATES AT THE TIME OF THIS DISCUSSION (0630Z) ON ALREADY SATURATED
SOIL SHOULD PRODUCE FLASH FLOODING AND EXCESSIVE RUNOFF EARLY THIS
MORNING IN THE VICINITY OF THE BLUE RIDGE MTNS. SOME OF THE FLASH
FLOODING WAS VERY LIKELY SIGNIFICANT...WITH LIFE-THREATENING DEEP
INUNDATION...PARTICULARLY IN LOW LYING AREAS AND NEAR STREAMS AND
CREEKS. IF THE CONVECTIVE BAND MANAGES TO BE SUSTAINED FOR SEVERAL
MORE HOURS...DOMINANT WARM RAIN PROCESSES AND ANOMALOUSLY HIGH
PRECIPITABLE WATER VALUES SHOULD SUPPORT HIGHLY EFFICIENT RAINFALL
PRODUCTION AND HEAVY RAIN RATES POSSIBLY EXCEEDING 2 IN/HR AT
TIMES. THIS WOULD CONTINUE TO EXACERBATE ANY ONGOING FLOODING.

THE DISCUSSION AREA WAS DRAWN TO INCLUDE AREAS TO THE NORTH AND
NORTHWEST...TO ACCOUNT FOR SOME SHOWERS DEVELOPING NEAR THE WV-VA
BORDER...AND THE POSSIBILITY THAT SIMILAR RAIN BANDS MAY BEGIN TO
FOCUS ON OTHER TERRAIN FEATURES IN BROAD S-SE LOW-LEVEL INFLOW.
HOWEVER...A LIMITING FACTOR TO THE NORTH AND NORTHWEST WOULD TEND
TO BE MORE LIMITED CONVECTIVE INSTABILITY.

LAMERS

ATTN...WFO...AKQ...LWX...RNK...

ATTN...RFC...MARFC...

LAT...LON   39717801 39437746 38577774 38107818 37777865
            37667910 37907935 38367937 38947909 39547859