MESOSCALE PRECIPITATION DISCUSSION 0173
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
807 PM EDT SAT MAY 19 2018

AREAS AFFECTED...SW OK...WRN N TX

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 200006Z - 200436Z

SUMMARY...THE FLASH FLOOD RISK WILL INCREASE THIS EVENING AS COLD
POOLS BECOME ESTABLISHED AND MOIST LOW LEVEL INFLOW
INCREASES...RESULTING IN SEVERAL POCKETS OF TRAINING. THE REGION
HAS SEEN SOMEWHAT ABOVE NORMAL PRECIPITATION RECENTLY...SO RAPID
RUNOFF IS MORE LIKELY.

DISCUSSION...APPROACHING 00Z ALL THE INGREDIENTS WERE IN PLACE FOR
A ROUND OF STRONG THUNDERSTORMS AND HEAVY RAINFALL TO PERSIST FOR
AT LEAST A FEW HOURS ACROSS THE TX SOUTH PLAINS TO WESTERN NORTH
TEXAS AND FAR SOUTHWEST OKLAHOMA. THE AFTERNOON CONVECTIVE
EVOLUTION OWED TO A WELL TIMED UPPER LEVEL SHORTWAVE TROUGH
EVIDENT IN GOES-16 WATER VAPOR IMAGERY. DEEP LAYER FLOW WAS STRONG
ENOUGH FOR FORWARD MOTION...ESPECIALLY GIVEN LARGE T/TD SPREADS AT
THE SURFACE. FLASH FLOODING HAD BECOME AN ISSUE...HOWEVER..AS CELL
MERGERS AND REDEVELOPMENT ALONG FLANKS OR THE INCIPIENT LARGER
SCALE OUTFLOW BOUNDARIES LED TO HEAVY RAINFALL.

GIVEN NEW CONVECTIVE GROWTH NEAR THE DRYLINE TRIPLE POINT EAST OF
LUBBOCK...IT APPEARS A NEARLY WEST TO EAST COMBINED OUTFLOW
BOUNDARY WILL BECOME ESTABLISHED FROM NEAR LBB TO NEAR SPS...JUST
AS BOUNDARY LAYER DECOUPLING LEADS TO INCREASING 850 MB FLOW. THE
ACCELERATING LOW LEVEL INFLOW WILL NOT ONLY BOOST UPDRAFT
STRENGTH...BUT MAY ALSO RESULT IN SLOWER CELL MOTION
INITIALLY...UNTIL SUCH TIME WHEN THE MODELS HANDLING THIS
ACTIVITY...NAMELY THE 20Z HRRR AND 12Z WRF-NMMB...SUGGEST A
FORWARD PROPAGATING MCS TOWARD THE EAST. UNTIL CONVECTION
DISLODGES...PW VALUES OF AROUND 1.25 INCHES AND MODERATE TO STRONG
CAPE SHOULD SUPPORT LOCAL RAIN RATES 2.0 INCH PER HOUR...EVEN
DESPITE THE PRESENCE OF LARGE HAIL. THESE RATES WOULD EASILY
SURPASS FLASH FLOOD GUIDANCE WHICH HAD BEEN LOWERED BY THE RECENT
WET PATTERN.

PARTS OF HARMON AND HARDEMAN COUNTIES FLOODED EARLIER THIS
AFTERNOON MAY CONTINUE TO RECEIVE SOME ELEVATED CONVECTION AS THE
SYNOPTIC BACKGROUND REMAINS FAVORABLE...ALTHOUGH THE MORE ROBUST
NEW ACTIVITY SHOULD OCCUR FARTHER SOUTH.

BURKE

ATTN...WFO...FWD...LUB...MAF...OUN...SJT...

ATTN...RFC...ABRFC...WGRFC...

LAT...LON   34879942 33459800 32570079 32890170 33760153