MESOSCALE PRECIPITATION DISCUSSION 0009
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 PM EST THU JAN 14 2016
 
AREAS AFFECTED...NORTHWEST CA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 142000Z - 150000Z
 
SUMMARY...A STRONG SHORTWAVE TROUGH APPROACHING THE WEST COAST
WILL BE BRINGING A PERIOD OF HEAVY RAINFALL OVER THE NEXT COUPLE
OF HOURS TO PORTIONS OF NORTHWEST CA.

DISCUSSION...THE LATEST WV IMAGERY SHOWS A VERY STRONG SHORTWAVE
TROUGH APPROACHING THE WEST COAST...WITH AN AXIS OF ENHANCED LOW
LEVEL MOISTURE CONVERGENCE COINCIDING WITH ROBUST UPPER LEVEL JET
DYNAMICS/FORCING ENCROACHING ON ESPECIALLY NORTHWEST CA. THIS IS
RESULTING IN AN AXIS OF HEAVY SHOWERS AND A FEW THUNDERSTORMS
OFFSHORE THAT WILL BE OVERSPREADING THE COASTAL RANGES OF
NORTHWEST CA OVER THE NEXT COUPLE OF HOURS.

THE LATEST RAP ANALYSIS SHOWS A DISTINCT AREA OF 850 MB
CONVERGENCE OVERLAPPING WITH 250 MB DIVERGENCE FROM SOUTHWEST OR
DOWN ACROSS THE COASTAL RANGES OF NORTHWEST CA AHEAD OF THE ENERGY
AND AN ASSOCIATED FRONTAL ZONE. IN FACT...THERE IS A WELL-DEFINED
SOUTHWESTERLY LOW LEVEL JET AHEAD OF THE FRONT AS IDENTIFIED BY
850 MB WINDS THAT ARE EXCEEDING 60 KTS AS PER KBHX/EUREKA VWP DATA.

THE LAST COUPLE RUNS OF THE HRRR HAVE BEEN RATHER POOR IN HANDLING
THE LATEST CONVECTIVE TRENDS AS PER SATELLITE AND RADAR DATA.
COOLER CLOUD TOPS HAVE BEEN APPROACHING NORTHWEST CA AND THE
LATEST DUAL-POL ANALYSIS SHOWS A COUPLE OF WELL-DEFINED CONVECTIVE
LINE SEGMENTS WITH RAINFALL RATES EXCEEDING A 0.50 INCH/HR
APPROACHING THE COAST. THIS IS VALIDATED BY AT LEAST A COUPLE OF
RECENT AMSU PASSES WHICH HAVE SHOWED OFFSHORE RAINFALL RATES AT
LEAST APPROACHING A 0.50 INCH/HR.

AS THIS ENERGY MOVES INLAND OVER THE NEXT 2 TO 3 HOURS...THE
RAINFALL RATES WILL LIKELY BE ENHANCED FURTHER BY THE AFFECTS OF
STRONGER SOUTHWESTERLY ONSHORE FLOW INTO THE HIGHER TERRAIN IN
ASSOCIATION WITH THE AFOREMENTIONED LOW LEVEL JET.

EXPECT RAINFALL RATES TO LOCALLY APPROACH 1 INCH/HR WITHIN THE
STRONGER CONVECTIVE CORES AS THIS ENERGY MOVES INLAND...AND THIS
MAY RESULT IN SOME BRIEF RUNOFF PROBLEMS. THE LATEST GLD-LIGHTNING
DENSITY PRODUCT SHOWS A SMALL AREA OF STRIKES NORTHWEST OF ARCATA
WHICH WOULD LIKELY CORRELATE TO STRONGER FORCING AND RAIN RATES.
THE MAIN FOCUS FOR THE HEAVIEST RAINS SHOULD FOCUS FROM NEAR
ARCATA SOUTH DOWN TO JUST NORTH OF FORT BRAGG AND WEST ALONG THE
IMMEDIATE COASTAL RANGES.

ORRISON

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

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

LAT...LON   42022405 41902315 41242316 40142320 39332338 
            39352382 39742413 40262440 40912448 41692436