MESOSCALE PRECIPITATION DISCUSSION 0530
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
800 AM EDT TUE JUL 24 2018

AREAS AFFECTED......EASTERN AND NORTHERN VA...D.C....MD...EASTERN
PA...FAR SOUTHERN NY...

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

VALID 241159Z - 241559Z

SUMMARY...GIVEN THE WET ANTECEDENT SOILS, ADDITIONAL SHOWERS AND
THUNDERSTORMS THIS MORNING WILL MAINTAIN AN ELEVATED FLOOD AND/OR
FLASH FLOOD THREAT THIS MORNING.

DISCUSSION...A PERSISTENT, FAVORABLE SYNOPTIC PATTERN REMAINS IN
PLACE FOR HEAVY RAINFALL ACROSS THE MID ATLANTIC REGION, WITH A
HIGHLY-AMPLIFIED UPSTREAM TROUGH/ DOWNSTREAM RIDGE MAINTAINING AN
ELONGATED AXIS OF FAVORABLE ALONG-STREAM DIVERGENCE ALOFT AND A
CORRESPONDING CONFLUENT, MOIST FLOW IN THE LOW LEVELS. PW VALUES
REMAIN ANOMALOUS -- NEAR 2.25" -- OWING TO THE SUBTROPICAL INFLUX
ALOFT FROM THE CARIBBEAN (500-300 MB LAYER PW VALUES OF 0.25+
INCH) ALONG WITH THE CONFLUENCE OF HIGHER LOW-LEVEL THETA-E FROM
THE EASTERN GULF AND THE ATLANTIC GULF STREAM.

NARROW/SKINNY DEEP-LAYER INSTABILITY (MUCAPES GENERALLY 500-1000
J/KG), COINCIDING WITH THE FAVORABLE SYNOPTIC FORCING AND DEGREE
OF DEEP-LAYER MOISTURE, WILL FOSTER HOURLY RAINFALL RATES OF
1.5-2.0" UNDERNEATH THE STRONGEST BANDS THIS MORNING WITHIN THE
OUTLOOK AREA. GIVEN THE WET ANTECEDENT CONDITIONS AND LARGE AREA
OF LOW FLASH FLOOD GUIDANCE (AN INCH OR LESS WITHIN 3 HOURS ACROSS
THE MAJORITY OF THE AREA), ADDITIONAL FLASH FLOODING AND/OR
CONTINUED FLOODING IS LIKELY.

HURLEY

ATTN...WFO...AKQ...BGM...BUF...CTP...LWX...PHI...

ATTN...RFC...MARFC...NERFC...OHRFC...

LAT...LON   42467719 42337645 41917591 41107542 40217535
            39607597 38767610 38067644 37977704 38327749
            38767784 39247813 40217837 40667852 41687843
            42287795