MESOSCALE PRECIPITATION DISCUSSION 0011
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
107 PM EST SUN JAN 17 2016
 
AREAS AFFECTED...NORTHERN CA....FAR SOUTHWEST OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 171800Z - 180300Z
 
SUMMARY...AN ATMOSPHERIC RIVER AND ASSOCIATED FRONTAL ZONE WILL BE
MOVING INLAND THROUGH THE AFTERNOON. HEAVIER RAINS SHOULD
GRADUALLY SHIFT FARTHER SOUTH DOWN THROUGH NORTHERN AND CENTRAL CA.

DISCUSSION...IR AND WV IMAGERY SHOW A WELL-DEFINED ATMOSPHERIC
RIVER IMPACTING MUCH OF THE NORTHWEST WITH THE HEAVIEST RAINFALL
IMPACTING ESPECIALLY SOUTHWEST OR AND NORTHWEST CA. SOUTHWEST
FACING SLOPES OF THE COASTAL RANGES ARE INTERCEPTING A LOW LEVEL
JET OF 45 TO 50 KTS WHICH IS ENHANCING RAINFALL RATES WITHIN A
PLUME OF ALREADY 1.1 TO 1.25 INCH PWATS. 850/700MB MOISTURE FLUX
ANOMALIES ARE CURRENTLY RUNNING AT CLOSE TO 3 STANDARD DEVIATIONS
ABOVE NORMAL ACROSS THIS AREA.

OBSERVATIONAL DATA HAS ALREADY SHOWED LOCALIZED RAINFALL RATES OF
UP TO 0.75 INCHES/HR OVER THE HIGHER TERRAIN OF NORTHWEST CA
INVOLVING HUMBOLDT COUNTY. A 1538Z SSMI/S PASS INDICATED OFFSHORE
RAINFALL RATES AHEAD OF AN APPROACHING COLD FRONT STILL REACHING
CLOSE TO A 0.50 INCH/HR. THESE RATES WILL CONTINUE TO BE ENHANCED
THROUGH STRONGER UPSLOPE FLOW/OROGRAPHICS FOR THE COASTAL RANGES.

OVER THE NEXT FEW HOURS...AS A 110 KT+ 250MB JET MAX AND NEARBY
VORT IMPULSES LIFT NORTHEAST TOWARD THE COASTAL PACIFIC
NORTHWEST...A COLD FRONT WILL BE MOVING INLAND ACROSS WESTERN OR
AND WILL CROSS NORTHWEST CA WHICH WILL HELP TO PUSH THE FOCUS OF
DEEPER MOISTURE AND HEAVIER RAIN RATES FARTHER SOUTH AND MORE
TOWARD CENTRAL CA TOWARD EVENING. BY THIS EVENING...THE HIRES
GUIDANCE INDICATES A SLACKENING OF THE LOW LEVEL JET AHEAD OF THE
FRONT AND A REDUCTION IN RAINFALL RATES.

EXPECT ADDITIONAL RAINFALL AMOUNTS OF 2 TO 4 INCHES THROUGH THE
EARLY EVENING HOURS...MAINLY FOR NORTHERN CA IN VICINITY OF THE
SHASTA/SISKIYOU RANGES AND THE IMMEDIATE SOUTHWEST FACING COASTAL
RANGES. THIS WILL LIKELY CONTINUE TO PROMOTE THE THREAT FOR
FLOODING AND CONCERNS FOR DEBRIS FLOWS AND/OR MUDSLIDES GIVEN WET
ANTECEDENT CONDITIONS. SOME ISOLATED HEAVIER AMOUNTS OF NEAR 5
INCHES ARE POSSIBLE. ELSEWHERE...ADDITIONAL RAINFALL AMOUNTS OF
GENERALLY 1 TO 2 INCHES CAN BE EXPECTED.

ORRISON

ATTN...WFO...EKA...MFR...MTR...STO...

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

LAT...LON   42392397 42262352 41912293 41652196 41512166 
            40952174 40382254 39822272 38632233 38172243 
            37962313 38802382 39542425 40392446 41102425 
            42082425