MESOSCALE PRECIPITATION DISCUSSION 0479
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
816 PM EDT WED JUL 18 2018

AREAS AFFECTED......CENTRAL AND NORTHERN ARIZONA...SOUTHEASTERN
NEVADA...FAR SOUTHWESTERN UTAH...

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

VALID 190014Z - 190314Z

SUMMARY...SCATTERED, SLOW-MOVING MONSOONAL THUNDERSTORMS WITH
HOURLY RAINFALL RATES UP TO 1.5-2.0 INCHES WILL CONTINUE TO POSE A
FLASH FLOOD RISK INTO THE EVENING HOURS.

DISCUSSION...LARGELY DEVOID OF UPPER LEVEL FORCING, CONVECTION
THIS AFTERNOON ONCE AGAIN INITIATED ACROSS THE MORE ELEVATED
TERRAIN WITH THE FAVORED UPSLOPE FLOW. ROBUST AVAILABLE DEEP-LAYER
INSTABILITY (MAXIMUM CAPE VALUES BETWEEN 1500-3000 J/KG) ALONG
WITH THE ABOVE-AVERAGE PW VALUES (BETWEEN 1-1.5 INCHES) WILL
CONTINUE TO SUPPORT HOURLY RAINFALL RATES IN THE 1.5 TO 2.0 INCH
RANGE INTO THE EARLY-MID EVENING HOURS, AS PER THE RECENT
OBSERVATIONAL AND RECENT WSR-88D RADAR ESTIMATES. THE WEAK
DEEP-LAYER FLOW AND INHERENT PULSE NATURE OF THE CONVECTION, ALONG
WITH THE DEGREE OF DOWNDRAFT CAPE, WILL MAINTAIN PROGRESSIVE
OUTFLOW BOUNDARIES WHICH WILL CONTINUE TO LIMIT THE DURATION HEAVY
RAINFALL (GENERALLY LESS THAN AN HOUR).

THE LATEST MESOSCALE GUIDANCE (INCLUDING MOST RECENT HRRR RUNS)
HAVE STRUGGLED WITH THE EVOLUTION OF THE CONVECTIVE PROGRESSION
MOVING OUT FROM THE HIGHER TERRAIN. NEVERTHELESS, THEY DO SHOW THE
POTENTIAL FOR 1.5-2.0"/HOUR RATES PERSISTING THROUGH 0300 UTC. THE
LATEST (1800 UTC) HREF 40 KM NEIGHBORHOOD PROBABILITIES DEPICT
THIS IDEA AS WELL.

HURLEY

ATTN...WFO...FGZ...LKN...PSR...SLC...TWC...VEF...

ATTN...RFC...CBRFC...CNRFC...

LAT...LON   38431433 37931363 37001360 36261330 35791288
            35341209 35321152 35811082 35570978 34940914
            34050907 33390979 33321064 33931269 34861403
            36701507 38161513