MESOSCALE PRECIPITATION DISCUSSION 0737
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
701 AM EDT FRI OCT 14 2016
 
AREAS AFFECTED...NORTHWEST OR & WESTERN WA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 141100Z - 142300Z
 
SUMMARY...A DEEP CYCLONE AND ITS ASSOCIATED COLD POOL ALOFT WILL
BRING INCREASING AMOUNTS OF LOW-LEVEL INFLOW AND INSTABILITY
ASHORE THE REGION TODAY.  HOURLY RAIN RATES IN EXCESS OF 0.5" ARE
ANTICIPATED.

DISCUSSION...A DEEP CYCLONE NEAR 48N 130.5W WITH A CENTRAL
PRESSURE AROUND 972 HPA IS MOVING STEADILY TOWARDS VANCOUVER
ISLAND, APPROACHING THE PACIFIC NORTHWEST.  PRECIPITABLE WATER
VALUES OF 0.75" EXIST ACROSS THE AREA PER GPS VALUES, AND
INSTABILITY JUST OFFSHORE IS UNCHARACTERISTICALLY HIGH, WITH
MUCAPES IN THE 500-1000 J/KG RANGE PER SPC MESOANALYSES.  MODEL
SOUNDINGS SHOW STEEP LAPSE RATES DUE TO THE SYSTEM'S COLD POOL
ALOFT.  THIS HAS LED TO A RECENT INCREASE IN
THUNDERSTORMS/LIGHTNING ACTIVITY JUST OFFSHORE NORTHWEST OR AND
WESTERN WA, WITH THE STORMS STARTING TO MOVE INLAND AT THIS TIME. 
INFLOW AT 850 HPA IS ~40 KTS OUT OF THE SOUTHWEST PER VAD WIND
PROFILES.

DURING THE DAY TODAY, THE AMOUNT OF MOISTURE/INSTABILITY ACROSS
THE REGION IS EXPECTED TO REMAIN RELATIVELY STEADY STATE.  THE
CAM/MESOSCALE GUIDANCE SHOWS LOCAL AMOUNTS IN THE 3-5" RANGE
THROUGH 23Z, PARTICULARLY ACROSS THE OLYMPIC PENINSULA, WITH
LOW-LEVEL INFLOW INCREASING INTO THE REGION THROUGH 17Z BEFORE
SLOWLY DROPPING OFF THEREAFTER AROUND THE TIME THE CYCLONE MAKES
LANDFALL IN VANCOUVER ISLAND.  THE 06Z SSEO NEIGHBORHOOD
PROBABILITIES SUGGEST THE HEAVY RAINS IN THE CASCADES WOULD
MAXIMIZE IN THE 17-22Z TIME FRAME.  THE COMBINATION OF PACIFIC
INFLOW AND INSTABILITY SHOULD LEAD TO HOURLY RAIN RATES EXCEEDING
0.50", WHICH COULD LEAD TO/PROLONG HEAVY RAIN RELATED ISSUES IN
AREAS WITH BURN SCARS AND MORE SENSITIVE RIVER BASINS.

ROTH

ATTN...WFO...OTX...PDT...PQR...SEW...

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

LAT...LON   49072123 48102090 46742151 46212158 45682197 
            45782247 45992294 45782323 45512336 45292371 
            45572408 46982423 48312477 48132296 47872265 
            46722289 46442281 47292203 48072202 48972250