MESOSCALE PRECIPITATION DISCUSSION 0463
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
715 PM EDT SUN JUL 15 2018

AREAS AFFECTED...NORTHERN CA...SOUTH-CENTRAL OR

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 152315Z - 160330Z

SUMMARY...SLOW-MOVING AND LOCALLY BACKBUILDING SHOWERS AND
THUNDERSTORMS WILL BRING THE POTENTIAL FOR SOME FLASH FLOODING
CONCERNS OVER THE NEXT 2 TO 3 HOURS.

DISCUSSION...THE LATEST GOES-16 WV IMAGERY SHOWS AN UPPER LOW
OFFSHORE OF NORTHERN CA THAT IS DRIFTING OFF TO THE EAST AND IS
INTERACTING WITH A NOSE OF ANOMALOUS MOISTURE AND MODERATE
INSTABILITY. THE LATEST RADAR AND CG LIGHTNING DATA SHOWS A
PERSISTENT AREA OF CONVECTION OVER TRINITY AND SISKIYOU COUNTIES
AND CLOUD TOP TEMPERATURES CONTINUE TO COOL.

THE UPSTREAM UPPER LOW IS EXPECTED TO DRIVE A DIVERGENT FLOW
PATTERN ALOFT WITH FAVORABLE DYNAMICS WORKING IN TANDEM WITH THE
AFOREMENTIONED INSTABILITY TO SUSTAIN THE CONVECTIVE THREAT FOR
THE NEXT FEW HOURS. IN FACT...THE LATEST RAP ANALYSIS SHOWS MLCAPE
VALUES OF NEAR 1000 J/KG NOSED UP ACROSS NORTHERN CA AHEAD OF THE
OFFSHORE HEIGHT FALLS.

EXPECT HEAVY RAINFALL RATES OF AS MUCH AS 1 INCH/HR WITH LOCALLY
HEAVIER RATES GIVEN THE FAVORABLE OROGRAPHIC SET-UP AND
THERMODYNAMIC PROFILES. THE CONVECTION RECENTLY HAS BEEN TENDING
TO GET ANCHORED OVER THE SHASTA/SISKIYOU RANGES AND THERE MAY WELL
BE SOME STORM TOTALS OF 2 TO 3 INCHES BEFORE THE CONVECTION
EVOLVES OVER THE ADJACENT TERRAIN. ADDITIONAL AREAS THAT WILL NEED
TO BE MONITORED INCLUDE THE HIGHER TERRAIN OF SOUTH-CENTRAL OR AS
WELL SINCE STRONGER DYNAMICS AND INSTABILITY TRANSPORT ARRIVING
MAY TEND TO FOCUS MORE CONVECTION HERE AROUND 00Z.

GIVEN THE SLOW CELL MOTION AND TENDENCY FOR CONVECTION TO
BACKBUILD...FLASH FLOODING WILL BE POSSIBLE OVER THE NEXT FEW
HOURS.

ORRISON

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

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

LAT...LON   42652097 42132027 41592040 40852029 40782044
            40752072 41162127 41252177 40692255 40572302
            40982325 41232335 41762297 42242221