MESOSCALE PRECIPITATION DISCUSSION 0772
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1122 AM EST SAT NOV 19 2016
 
AREAS AFFECTED...SOUTHWEST OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 191621Z - 200421Z
 
SUMMARY...AN APPROACHING SURFACE BOUNDARY AND INCREASING
INSTABILITY SHOULD LEAD WITH INCREASING RAIN RATES WITH TIME,
POTENTIALLY PEAKING IN THE 0.5-0.75" AN HOUR RANGE THIS AFTERNOON
AND EVENING.

DISCUSSION...AN OCCLUDED CYCLONE NEAR 44N 130.5W IS MOVING
NORTHEAST TOWARDS VANCOUVER ISLAND.  AROUND ITS SOUTHEAST SIDE, AN
OCCLUDED FRONT IS APPROACHING THE OR COAST.  PRECIPITABLE WATER
VALUES OF 0.4-0.6" EXIST ACROSS THE REGION PER GPS INFORMATION. 
MUCAPES OF 100-500 J/KG LIE JUST OFF THE COAST PER SPC
MESOANALYSES, WITH THE LIGHTNING DETECTION NETWORK SHOWING SOME
STRIKES OFFSHORE THE WEST COAST WITHIN SHALLOW CONVECTION BETWEEN
THE OLYMPIC PENINSULA AND NORTHWEST CA.  LOW-LEVEL INFLOW IS
SOUTH- SOUTHWEST AT 35-45 KTS PER REGIONAL VAD WIND PROFILES AT
850 HPA AND 700 HPA PRESSURE LEVELS.  A RECENT SAB/NESDIS BRIEFING
SHOWS INCREASING DIVERGENCE ALOFT TO THE EAST OF THE SYSTEM JUST
OFFSHORE THE OR/CA BORDER.

THE LOW-LEVEL INFLOW IS FORECAST TO RISE ABOVE 60 KTS AROUND 21Z,
WHICH ON ITS OWN WOULD INCREASE RAIN RATES.  THE CAM/MESOSCALE
GUIDANCE SHOWS DISCREPANCIES REGARDING WHEN THE HIGHEST RAIN RATES
WOULD APPROACH THE REGION, WITH ARW OUTPUT SHOWING WAVES OF
HEAVIER RAIN THROUGHOUT THE DAY WHILE THE 13Z HRRR SHOWS GREATER
POTENTIAL BEYOND 01Z.  AS THE OCCLUDED FRONT APPROACHES THE
REGION, PRECIPITABLE WATER VALUES RISE TO OR ABOVE 0.75" FROM 01Z
ONWARD IN RAP GUIDANCE.  RAP AND SREF GUIDANCE SHOWS INCREASING
INSTABILITY DURING THE DAY, WITH THE RAP INDICATING THE 500 J/KG
ISOPLETH NEARING THE COAST BY 20Z AND THE 1000 J/KG CONTOUR MOVING
WITHIN 100 NM OF SOUTHWEST OR BY 04Z.  AS THE INSTABILITY INCREASE
AND 0-6 KM BULK SHEAR VALUES OF 25+ KNOTS MOVE CLOSER/INTO TO THE
REGION, A THREAT OF SHORT TRAINING CONVECTIVE BANDS EXISTS WHICH
WOULD ALLOW HOURLY RAIN RATES TO RISE TO 0.5-0.75".  OVERALL,
BELIEVE THE HEAVY RAIN THREAT IS PRIMARILY BEYOND 20Z.  LOCAL
AMOUNTS OF 2" ARE INDICATED BY THE MESOSCALE GUIDANCE BETWEEN NOW
AND 04Z, WHICH SEEMS REALISTIC. 

ROTH

ATTN...WFO...EKA...MFR...

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

LAT...LON   43622416 43402379 42852361 42022355 41962427 
            42822458 43372444