|WPC Met Watch|
Mesoscale Precipitation Discussion: #1039 (2018) |
(Issued at 1026 AM EST Thu Dec 06 2018
Mesoscale Precipitation Discussion 1039
NWS Weather Prediction Center College Park MD
1026 AM EST Thu Dec 06 2018
Areas affected...Greater Los Angeles Area
Concerning...Heavy rainfall...Flash flooding possible
Valid 061526Z - 062126Z
Summary...Showers and isolated thunderstorms will continue to
develop off the southern CA coast and shift inland ahead of a
surface low over the Channel Islands. Rain rates up to half an
inch per hour are likely and may cause flash flooding and debris
flows, particularly in recent burn scar areas.
Discussion...A combination of forcing from a low pressure system
off the southern CA coast, PW of 0.9 to 1 inch per GPS data,
MUCAPE of 250-500 J/kg per the RAP, and 30 to 40 kt of bulk shear
(also from the RAP) will result in localized heavy rain. Rainfall
of 0.4" in an hour around 14Z was reported in Topanga Canyon in 30
to 40 dBZ echoes from KVTX. Reflectivity has since blossomed
across and off Ventura County with rates likely to reach or exceed
0.5" an hour. This activity is headed toward the Woolsey Fire burn
scar with the potential for one to two inches rainfall through 17Z
there. Based on extrapolation from radar coverage, that amount can
be expected east of there across the Los Angeles metro area with a
localized flood threat through noon.
Recent HRRR runs have initialized with this reflectivity and
support localized heavy rain over the great LA area through 20Z.
The low pressure system will continue to drift southeast along the
southern CA coast with QPF also shifting toward the San Diego area
this afternoon where further localized impacts are possible.
LAT...LON 34631984 34611854 34051757 33501771 33481806
Last Updated: 1026 AM EST Thu Dec 06 2018