MESOSCALE PRECIPITATION DISCUSSION 0208
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
432 PM EDT SAT MAY 14 2016
 
AREAS AFFECTED...NORTHEAST OR 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE 
 
VALID 142031Z - 150231Z
 
SUMMARY...INCREASING CONVECTIVE COVERAGE LEADING TO AN ISOLATED
FLASH FLOOD RISK.

DISCUSSION...DAYTIME HEATING HAS ALLOWED FOR THE DEVELOPMENT OF A
MARGINALLY UNSTABLE AIRMASS ACROSS PORTIONS OF CENTRAL OREGON THIS
AFTERNOON...WITH AROUND 500 J/KG OF CAPE ANALYZED. THIS
INSTABILITY IS MAINLY FOCUSED ALONG AND SOUTH OF A STATIONARY
BOUNDARY THAT IS STRETCHED FROM JUST NORTH OF REDMOND EAST ACROSS
NORTH CENTRAL OREGON. MOISTURE POOLING NEAR THIS BOUNDARY HAS ALSO
RESULTED IN INCREASED PRECIPITABLE WATER VALUES. THERE IS A PRETTY
NARROW OVERLAP OF 0.75" AND GREATER PWAT VALUES AND THE MARGINAL
INSTABILITY...AND IT IS HERE WHERE THE GREATEST THREAT FOR LOCALLY
HEAVY RAINFALL EXISTS. PLENTY OF SYNOPTIC FORCING AHEAD OF A
STRONG SHORTWAVE IMPULSE IN A VERY DIFFLUENT PATTERN ALOFT IS
SUPPORTIVE OF CONTINUED SCATTERED CONVECTIVE DEVELOPMENT INTO THE
AFTERNOON ACROSS THE AREA.

THE HIGH RESOLUTION GUIDANCE IS GENERALLY IN GOOD AGREEMENT WITH
THE EVOLUTION OF CONVECTION INTO THE EVENING HOURS. MOST OF THE
CONVECTION ALLOWING MODELS...INCLUDING THE HRRR TIME LAGGED
ENSEMBLE...SUGGEST HOURLY RAINFALL TOTALS GENERALLY AROUND 0.5" AN
HOUR. ALTHOUGH THERE IS A SIGNAL FOR LOCAL AMOUNTS AROUND 1" AN
HOUR...AND AROUND 1.5" IN THREE HOURS. THESE AMOUNTS ARE
APPROACHING VALUES WHERE AT LEAST AN ISOLATED FLASH FLOOD RISK IS
EXPECTED TO DEVELOP THROUGH THE AFTERNOON HOURS. THINK THE FLASH
FLOOD THREAT GENERALLY DECREASES AS YOU GET NORTH OF THE OR/WA
BORDER...WHERE A LACK OF INSTABILITY SHOULD KEEP RAINFALL RATES
GENERALLY BELOW A HALF INCH AN HOUR.

CHENARD 

ATTN...WFO...BOI...PDT...

ATTN...RFC...NWRFC...

LAT...LON   45891874 45731795 45451708 45101698 44971724 
            44911736 44531800 44411853 44281921 44072004 
            44052103 44412144 44802147 45472110 45881965