MESOSCALE PRECIPITATION DISCUSSION 0740
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
715 AM EDT SUN OCT 16 2016
 
AREAS AFFECTED...NORTHERN CA, WESTERN OR, AND WESTERN WA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 161114Z - 162314Z
 
SUMMARY...ONSHORE FLOW AND GREATER THAN NORMAL INSTABILITY NEAR A
DEEP CYCLONE SHOULD LEAD TO HOURLY RAIN RATES GREATER THAN 0.5"
AND LOCAL AMOUNTS IN THE 3-5" RANGE FROM TIME TO TIME THROUGH 23Z.

DISCUSSION...A COLD AND DEEP CYCLONIC CIRCULATION, THE THIRD IN
THE SERIES, IS LOCATED NEAR 49N 134.5W.  INFRARED IMAGERY REVEALS
LOW-TOPPED CONVECTION OFFSHORE OR AND WA WITH THE LIGHTNING
DETECTION NETWORK SHOWING WIDELY SCATTERED THUNDERSTORMS MOVING
INTO THE PACIFIC NORTHWEST COAST EXTENDING WESTWARD PAST THE 130TH
MERIDIAN WEST.  THIS CONFIRMS RECENT SPC MESOANALYSES OF 500-1000
J/KG MUCAPE LYING JUST OFF THE COAST.  PRECIPITABLE WATER VALUES
ARE ~0.75" IN THE COASTAL RANGES OF WA, OR, AND NORTHWEST CA, AND
AROUND 0.65" IN THE OREGON CASCADES.  INFLOW AT 850 HPA IS
SOUTH-SOUTHWEST AT 30-40 KTS PER VAD WIND PROFILES IN THE AREA.  A
SLIGHTLY CURVED JET STREAK IS SEEN IN RECENT WATER VAPOR IMAGERY
IN THE 130S LONGITUDE, MOVING TOWARDS THE AREA.

FOR MUCH OF THE REGION, THE ABOVE ATMOSPHERIC VARIABLES REMAIN
STEADY STATE DURING THE DAY TODAY, WITH LOW-LEVEL INFLOW PEAKING
IN THE 50 KT RANGE FROM TIME TO TIME.  THE EXCEPTION IS ACROSS THE
NORTHERNMOST COAST OF CA AND THE SOUTHERN COAST OF OR, WHERE RAP
MASS FIELDS INDICATE BOUNDARY LAYER MOISTURE CONVERGENCE, A
POSSIBLE FRONTAL ZONE/BAROCLINIC TROUGH, MOVES INTO THE REGION
AFTER 20Z WHICH IS LIKELY TO ENHANCE RAIN RATES (INTO THE
0.5-0.75" AN HOUR RANGE) AND TOTALS.  THE MESOSCALE GUIDANCE SHOWS
A STRONG SIGNAL FOR LOCAL AMOUNTS IN THE 3-5" RANGE IN THIS
SOUTHERN AREA THROUGH 23Z, WHICH COULD LEAD TO ISSUES IN BURN
SCARS, SENSITIVE RIVER BASINS, AND AREAS WHERE SOILS ARE
SATURATING FROM RECENT RAINS.  

DUE TO THE GREATER THAN NORMAL INSTABILITY OFFSHORE, HOURLY RAIN
RATES ARE EXPECTED TO RISE TOWARDS THE PW VALUES, LOCALLY REACHING
0.5-0.75" ACROSS THE RANGES OF WESTERN OR AND COASTAL RANGES OF
WESTERN WA.  THE CYCLONIC CIRCULATION OFF THE COAST IS ACCOMPANIED
BY UNIDIRECTIONAL FLOW WITH HEIGHT, SO THERE IS THE POSSIBILITY OF
SHORT TRAINING CONVECTIVE SEGMENTS NEAR THE COAST/COASTAL RANGES
THROUGH THE DAY TODAY, WITH THE BEST CHANCE OF THAT OCCURRING IN
WESTERN WA AND PORTIONS OF WESTERN OR DOWNSTREAM OF THE BEST
INSTABILITY.  LOCAL AMOUNTS OF 2-3" ARE SLATED HERE THROUGH 23Z,
BUT THOSE AMOUNTS COULD FALL WITHIN A RELATIVELY SHORT PERIOD OF
TIME.

ROTH

ATTN...WFO...EKA...MFR...OTX...PDT...PQR...SEW...STO...

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

LAT...LON   49012224 48822062 47102100 45782151 44732158 
            42542187 42112215 42482305 41512297 41662191 
            41002205 40652239 40672315 40052268 39532367 
            39922445 40382460 41402427 42822467 45022411 
            46562421 48342485 48382404 48212297 48172259 
            46532293 46332274 47212205 48212211