MESOSCALE PRECIPITATION DISCUSSION 0127
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
813 PM EDT FRI MAY 04 2018

AREAS AFFECTED...NORTHERN VT...NORTHERN NH...NORTHERN AND WESTERN
ME

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

VALID 050000Z - 050400Z

SUMMARY...SHORT TERM TRAINING ALONG A LINE OF FAST MOVING
CONVECTION COULD POSE A FLASH FLOOD THREAT IN AREAS WITH SATURATED
OR NEARLY SATURATED SOILS INTO THE LATE EVENING HOURS.

DISCUSSION...REGIONAL RADARS ACROSS NORTHERN NEW ENGLAND SHOWED
LINEAR CONVECTION AHEAD OF A COLD FRONT EXTENDING FROM NORTHERN VT
INTO CENTRAL NY STATE. THE CONVECTION WAS PROGRESSIVE AHEAD OF A
SHORT WAVE OVER FAR NORTHERN NY STATES. HOURLY RAINFALL RATES
ASSOCIATED WITH THIS CONVECTION WERE GENERALLY LESS THAN AN
INCH...ESPECIALLY OVER NORTHERN AND CENTRAL NY STATE.

FURTHER EAST...ELEVATED CONVECTION FORMING NORTH OF A WARM FRONT
EXTENDING FROM NORTHEAST VT INTO SOUTHERN ME WAS TAPPING AN AXIS
OF 1.25 INCH PRECIPITABLE WATER AIR (BASED ON THE MOST RECENT RAP
ANALYSIS AND BLENDED TPW PRODUCT) AND 500-1000 J/KG OF MUCAPE TO
PRODUCE HOURLY RAINFALL RATES CLOSER TO 1.25 INCHES OVER NORTH
CENTRAL VT.

SNOWMELT FROM HIGHER ELEVATION SNOW HAS RESULTED IN SATURATED OR
NEARLY SATURATED SOILS...RESULTING IN ONE HOUR FLASH FLOOD
GUIDANCE VALUES NEAR AN INCH OVER MUCH OF NORTHERN VT/NORTHERN NH
INTO THE WESTERN ME MOUNTAINS AND NORTHERN ME. SINCE THE
CONVECTION IS MOVING ALONG WITH THE STRONG MID LEVEL FLOW...IT
SHOULD SURVIVE THE EROSION OF ELEVATED INSTABILITY TO PRODUCE
LOCAL HOURLY RAINFALL RATES NEAR AN INCH (BASED ON THE MOST RECENT
HRRR) ACROSS THIS AREA.

THE FORWARD SPEED OF THE CONVECTION SHOULD LIMIT THE RAINFALL TO
SOME DEGREE. MUCH OF THE AVAILABLE HIGH RESOLUTION DOES SHOW LOCAL
1.00 TO 2.00 INCH RAINFALL AMOUNTS....WITH THE HIGHEST AMOUNTS
OVER NORTHERN VT/NORTHERNMOST NH INTO THE MOUNTAINS OF WESTERN ME
AND NORTHERN ME. GIVEN THE SATURATED SOILS...EVEN MODEST RAINFALL
AMOUNTS COULD RESULT IN AN ELEVATED FLASH FLOOD THREAT.

MUCH OF THE HIGH RESOLUTION GUIDANCE SHOWED THAT THE THREAT FOR
FLASH FLOODING FROM CONVECTION SHOULD DIMINISH FROM WESTERN TO
EAST BEFORE 05/05Z.

HAYES

ATTN...WFO...BTV...CAR...GYX...

ATTN...RFC...NERFC...

LAT...LON   46946796 45916749 44687000 43767259 44297353
            45047283 46237031