MESOSCALE PRECIPITATION DISCUSSION 0023
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
233 AM EST WED JAN 18 2017
 
AREAS AFFECTED...OR COASTAL RANGE AND OR CASCADES/NORTHERN CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 180745Z - 181945Z
 
SUMMARY...A STRONG ATMOSPHERIC RIVER... WITH ITS ORIGINS OVER THE
CENTRAL PACIFIC...WILL DROP SOUTH FROM THE PACIFIC NORTHWEST COAST
TO NORTHERN CA DURING THE MORNING HOURS. A 65 TO 75 KNOT LOW LEVEL
JET WILL FOCUS THE DEEP MOISTURE PLUME ON THE FAVORED LOCATIONS IN
THE HIGHER TERRAIN...PRODUCING RAINFALL RATES OF 1/2 INCH OR
GREATER.

DISCUSSION...THE LATEST WATER VAPOR IMAGE SHOWED THE NOSE OF A 145
KNOT JET STREAK AT 250 MB NEAR 39N 132W EARLY THIS MORNING. A
0507Z AMSU PASS SHOWED PRECIPITABLE WATER VALUES CLOSE TO 1.5
INCHES IN ABOUT THE SAME LOCATION... AS SHORT WAVES EMBEDDED IN
THE VERY FAST FLOW TRANSPORT THE DEEP MOISTURE PLUME TO THE
PACIFIC NORTHWEST COAST. RAINFALL RATES...BASED ON THE KLGX AND
KRTX RADARS IN WA/OR RESPECTIVELY)...WERE GENERALLY BETWEEN 0.25
AND 0.50 INCHES...WITH THE GREATEST RATES DROPPING SOUTH INTO OR.

AS THE JET STREAK APPROACHES THE WEST COAST LATER THIS
MORNING...THE 65 TO 75 KNOT LOW LEVEL JET DROPS SOUTH FROM OR INTO
NORTHERN CA. THE LOW LEVEL JET TRANSPORTS A PLUME OF 1.25 INCH
PRECIPITABLE WATER AIR...FIRST TO THE OR COAST BETWEEN 09Z AND
13Z...THEN TO THE NORTHERN CA COAST BETWEEN 14Z AND 19Z. THE
STRONG LOW LEVEL JET WILL FOCUS THE RICH MOISTURE PLUME ON THE
SOUTHWEST FACING TERRAIN OF THE OR COAST RANGE AND THE OR CASCADES
DURING THE EARLY MORNING...THEN ACROSS THE RANGES IN NORTHERN CA
LATE THIS MORNING.

THERE IS A MULTI-MODEL SIGNAL FOR HOURLY RAINFALL RATES BETWEEN
0.50 AND LOCALLY 0.75 INCHES TO AFFECT THESE AREAS FROM NORTH TO
SOUTH...WITH THE GREATEST HOURLY RATES EXPECTED TO AFFECT THE
SOUTHERN OR COASTAL RANGE...THE SISKIYOU RANGE...AND THE SHASTA
AND TRINITY MOUNTAINS...MAINLY BETWEEN 15Z AND 19Z. 

GIVEN THE WET ANTECEDENT CONDITIONS ACROSS SOUTHWEST OR AND
NORTHERN CA DUE TO HEAVY RAINFALL IN THE PAST TWO WEEKS...THE
ADDITIONAL HEAVY RAIN COULD RESULT IN RUNOFF ISSUES.

HAYES

ATTN...WFO...EKA...MFR...MTR...PDT...PQR...REV...STO...

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

LAT...LON   46222412 46202342 45042325 43962327 43122323 
            43122267 44192244 45152219 45272172 44152138 
            42932141 42122143 41132109 40262066 39412056 
            39162099 39572138 40322172 40732234 40052261 
            38932236 38532267 38802333 39742381 40262429 
            41422408 42512414 44212418 45422429