MESOSCALE PRECIPITATION DISCUSSION 0046
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
502 AM EST WED FEB 08 2017
 
AREAS AFFECTED...PORTIONS OF NRN TO CNTRL CA...EXTREME SWRN OR 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 081001Z - 082130Z
 
SUMMARY...AN IMPRESSIVE SURGE IN LOW-LEVEL MOISTURE FLUX IS
EXPECTED TO REACH THE COAST THIS MORNING. RAIN RATES SHOULD
INCREASE ACROSS THE COASTAL RANGES OF NORTHERN CA AND SOUTHWESTERN
OR AS WELL AS THE CENTRAL AND NORTHERN SIERRA NEVADA. RATES NEAR
0.50 IN/HR ARE POSSIBLE AFTER 15Z.

DISCUSSION...AN ANOMALOUS PLUME OF MOISTURE IS BEING TRANSPORTED
NORTHEASTWARD THIS MORNING IN A CHANNEL OF 40-50 KT LOW-LEVEL FLOW
AHEAD OF A DEEPENING PACIFIC LOW PRESSURE SYSTEM. CURRENT BLENDED
TPW ESTIMATES INDICATE PWATS IN THE 1.25 TO 1.5 INCH RANGE IN THIS
PLUME. AMSU ESTIMATED RAINFALL RATES OFFSHORE ARE CURRENTLY IN THE
0.10 TO 0.25 IN/HR RANGE.

THE SURGE IN LOW-LEVEL MOISTURE FLUX/ATMOSPHERIC RIVER IS EXPECTED
TO REACH THE COAST LATER THIS MORNING, WITH RAINFALL RATES
GRADUALLY INCREASING ACROSS THE COASTAL RANGES AS WELL AS THE
SIERRA NEVADA. SSW FLOW OF 40-50 KT AT 850 HPA IS FORECAST TO
REACH THE COAST BETWEEN 12Z AND 15Z, WHICH SHOULD SUPPORT RAINFALL
RATES APPROACHING 0.50 IN/HR, ESPECIALLY IN FAVORED TERRAIN. RAIN
IS EXPECTED TO FALL EVEN AT THE HIGHER ELEVATIONS OF THE SIERRA
NEVADA WHERE THE PROLONGED PERIOD OF ONSHORE FLOW HAS INCREASED
SNOW LEVELS SUBSTANTIALLY. TOTAL RAINFALL AMOUNTS THROUGH 21Z OF 1
TO 4 INCHES ARE POSSIBLE. THESE RAINFALL AMOUNTS COULD EXACERBATE
ONGOING FLOODING PROBLEMS, EVEN FOR LOWER ELEVATION AREAS IN THE
SACRAMENTO VALLEY WHERE PROLONGED HEAVY RAIN AT HIGHER ELEVATIONS
ALONG WITH MELTING SNOW HAS LED TO SWOLLEN STREAMS AND RIVERS.

RYAN

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

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

LAT...LON   43552404 42782381 42082334 41932316 41632294 
            41492273 41532219 41342176 40612137 39922075 
            38561990 37911998 38262060 38772117 38882181 
            38752246 38522286 38622339 38982383 39712430 
            40472465 41542458 42812454