MESOSCALE PRECIPITATION DISCUSSION 0530
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1016 AM EDT TUE SEP 29 2015
 
AREAS AFFECTED...SOUTHWEST VIRGINIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 291415Z - 291915Z
 
SUMMARY...A TROPICAL AIRMASS WITH NEAR RECORD PRECIPITABLE WATER
WILL RESULT IN A CONTINUED FLOOD AND FLASH FLOOD THREAT INTO THIS
AFTERNOON.


DISCUSSION...SATELLITE AND RADAR SHOW ONE AREA OF SHOWERS AND
EMBEDDED THUNDERSTORMS MOVING WEST OFF THE ATLANTIC INTO NC AND
SOUTHWEST VA. MEANWHILE AN UPPER LOW OVER NORTHEAST GA HAS AN AREA
OF STEADY RAINFALL WITH IT. THIS REGION HAS BEEN VERY WET THE PAST
SEVERAL DAYS...AND PORTIONS OF SOUTHWEST VA HAVE RECEIVED 2-6" OF
RAIN ALREADY THIS MORNING. THIS RAINFALL HAS SATURATED THE GROUND
AND THUS MADE FLOODING/FLASH FLOODING MORE PROBABLE WITH ANY
ADDITIONAL RAINFALL.

FORCING FROM THE SHORTWAVE IN GA AND A GENERALLY DIVERGENT PATTERN
ALOFT IS HELPING FORCE ASCENT ON THE LARGE SCALE...WITH 20-30 KTS
OF LOW LEVEL UPSLOPE FLOW AIDING IN LIFT. LAYERED PRECIPITABLE
WATER PRODUCTS SHOW AN IMPRESSIVE COMBINATION OF FACTORS
CONTRIBUTING TO THE NEAR RECORD PRECIPITABLE WATER VALUES ACROSS
THIS REGION. A CONNECTION TO THE PACIFIC AND TROPICAL STORM MARTY
CAN BE SEEN IN THE MID/UPPER LEVELS...WITH A DEEP LAYER CONNECTION
TO THE GULF OF MEXICO AND ALSO TROPICAL STORM JOAQUIN IN THE
ATLANTIC. THIS IS ALL RESULTING IN A VERY EFFICIENT ATMOSPHERE FOR
HEAVY RAIN RATES. THE ONE THING LACKING IS INSTABILITY...BUT AT
LEAST SOME DOES EXIST ACROSS THE AREA AS NOTED BY SOME LIGHTNING
AND COLDER CLOUD TOPS.

AS THE UPPER LOW PROGRESSES NORTHEAST...EXPECT THE LOW LEVEL
UPSLOPE FLOW TO DECREASE ACROSS NORTHWEST NC AND FAR SOUTHWEST VA.
THIS COMBINED WITH AN ERODING OF INSTABILITY SHOULD EVENTUALLY
LEAD TO A DECREASE IN RATES BY LATER THIS MORNING. HOWEVER STILL
WILL HAVE THE RAINFALL FROM THE UPEPR LOW TO DEAL WITH INTO THE
AFTERNOON...WHICH MAY STILL HAVE SOME CONVECTIVE ELEMENTS TO IT.
THIS COMBINED WITH THE SATURATED GROUND WILL CONTINUE THE
FLOOD/FLASH FLOOD RISK.

THE BIGGER THREAT LATER THIS MORNING INTO EARLY AFTERNOON WILL
MOVE NORTH INTO WEST CENTRAL AND NORTHWEST VA. THIS IS WHERE THE
STRONGEST UPSLOPE FLOW WILL FOCUS...WITH THE BANDS OF LOCALLY
HEAVY RAIN CURRENTLY OVER SOUTHERN VA LIKELY SHIFTING INTO THIS
REGION. THE HRRR AND EXPERIMENTAL HRRR SEEM TO HAVE A DECENT
HANDLE ON THE EVOLUTION AND SUGGEST AN ADDITIONAL 1-3"...WITH
LOCALLY HIGHER AMOUNTS THROUGH 20Z ACROSS THIS REGION.

   
CHENARD

ATTN...WFO...GSP...LWX...MRX...RLX...RNK...

ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...

LAT...LON   38957892 38637854 38067851 37467878 36997912 
            36547948 36278026 36298050 36278206 36678161 
            37328121 38358015 38907954