Mesoscale Precipitation Discussion 1019...Corrected
NWS Weather Prediction Center College Park MD
144 AM EST Thu Nov 22 2018

Corrected for addition of "flash flooding possible" into header

Areas affected...portions of central to southern CA

Concerning...Heavy rainfall...Flash flooding possible

Valid 220604Z - 221200Z

Summary...A localized and dwindling flash flood threat will exist
for another few hours across the southern Sierra Nevada and
Transverse ranges of southern CA. Rainfall rates should drop below
0.5 in/hr by 12Z, likely ending the flash flood threat for burn
scar regions.

Discussion...As a large scale upper level trough and its
associated cold front continue to move into CA, the highest
remaining precipitable water values were located in the northern
San Joaquin Valley and along the southern CA coast, south of Point
Conception with values peaking between 1.0 and 1.2 inches. VAD
wind data through 0545Z from KVBX has shown 850 mb winds have
veered and dropped in magnitude from 30 kt from the SSW to WSW at
20 kt. Earlier observed rainfall rates were as high as .83 in/hr
(ending 0300Z) in western San Luis Obispo County and .58 in/hr
just east of Point Conception (ending 0430Z).

The strongest low level moisture flux was located in eastern Santa
Barbara County at 0545Z, co-located with an axis of moderate to
heavy rain, steadily progressing toward the east. 850 mb winds of
30 kt were estimated to be located within the moisture flux axis,
oriented perpendicular to the Santa Ynez Mountains. As the upper
level trough axis continues moving east over the next 6 hours,
short term forecasts from the RAP show precipitable water values
falling below 1 inch across inland locations with 850 mb flow
weakening and veering from west to east along the coast of
southern CA.

The potential for an additional 0.5 to 1.0+ inches of rain exists
for the southern CA mountain ranges with 1 to 2 inches farther
north into the southern Sierra Nevada through 1200Z. Given the
prominent Thomas and Woolsey burn scars in Santa Barbara, Ventura
and Los Angeles counties and remnant burn scars farther to the
north in the Sierra Nevada Mountains, a flash flood threat is
expected to linger for another few hours with a consensus of the
00Z hi-res models and recent HRRR guidance suggesting rainfall
rates falling below 0.5 in/hr by 12Z and beyond with rapidly
weakening moisture flux values.

Otto

ATTN...WFO...HNX...LOX...SGX...

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

LAT...LON   37781962 37371907 37201883 36951867 36681859
            36371846 36091832 35881820 35631813 35311821
            35001829 34791815 34651791 34551769 34421754
            34061758 33761797 33551888 34192003 34792006
            35011938 35271903 35621891 36261914 37411992