Graphic for MPD #0008
MESOSCALE PRECIPITATION DISCUSSION 0008
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
309 PM EST SAT JAN 07 2017
 
AREAS AFFECTED...CENTRAL CALIFORNIA 
 
CONCERNING...HEAVY RAINFALL...FLASH FLOODING LIKELY 
 
VALID 072030Z - 080600Z
 
SUMMARY...STRENGTHENING MOISTURE FLUX WITH EMBEDDED DEEP
CONVECTIVE ELEMENTS DIRECTING TOWARD CENTRAL CA COAST WITH
LIKELIHOOD FOR RATES OVER 1"/HR POSING LIKELY FLASH FLOODING RISK
ESPECIALLY IN BURN SCARS. 

DISCUSSION...WV LOOP SHOWS CONFLUENCE OF MULTIPLE STREAMS OF
STRONG/MOIST FLOW SOUTHWEST OF CENTRAL CA ATTM.  DEEP UPPER LOW
OUT NEAR 30N145W SHOWS EXCELLENT ORIENTATION WITH STRONG DPVA
SUPPORTING BAROCLINIC SHIELD.  FURTHER EAST A MILD SWLY
SUBTROPICAL JET FLATTENS JUST NORTH OF 30N SETTING UP FAVORABLE
LEFT EXIT JET BROAD SCALE ASCENT.  BETWEEN THE TWO STREAMS A BROAD
MOIST PLUME OF ENHANCED MOISTURE WITH TPWS EXCEEDING 1.5" WHICH IS
OVER 3 STANDARD DEVIATIONS FROM NORMAL. COINCIDENT WITH THE DEEPER
MOISTURE THERE ARE INDICATIONS OF FAIRLY MODEST INSTABILITY WITH
MUCAPE EXCEEDING 500 J/KG CLOSER TO 1000 J/KG NEARER THE UPPER LOW
WELL SOUTH OF 30N.  WHILE THE COOLER COASTAL CURRENT AND LOWER
LEVEL MODIFIED TEMPS TEMPER THE VALUES A BIT AS IT APPROACHES THE
COAST THERE IS SOLID MODEL SIGNAL TO SUGGEST VALUES AROUND 250-500
J/KG WILL BE AVAILABLE FOR ASCENT.  STRONG MOISTURE CONVERGENCE
ALONG THE FRONTAL ZONE HAS ALREADY SUPPORTED DEEP CONVECTION WITH
A BROKEN QUASI-LINEAR BAND NOTED IN IR/VIS STARTING TO APPROACH
THE COAST. GIVEN THE AVAILABLE MOISTURE/INSTABILITY IT IS LIKELY
SOME OF THE DEEP CONVECTION WILL SUPPORT RAIN RATES UP TO AND
EXCEEDING 1.0" AT TIMES POSSIBLY AS HIGH AS 1.25"/HR.

GIVEN THE DEEPENING UPPER LOW FURTHER WEST LOW TO MID-LEVEL FLOW
WILL SLACKEN A BIT REDUCING SOME HIGHER FLUX VALUES. 
HOWEVER...THIS WILL SUPPORT REDUCING PROPAGATION VECTORS WITH A
DEEPENING NEARLY UNIDIRECITONAL STEERING LAYER SETTING UP A HIGHER
LIKELIHOOD FOR SOME TRAINING OF THE DEEP CONVECTION.  THERE IS
SOME QUESTION IF SIGNIFICANT COLD POOL GENERATION MAY ROB THE BEST
TRAINING (AS HINTED BY THE 12Z WRF-ARW) STILL EXPECTATION FOR 4-5"
ARE PROBABLE ALONG THE SANTA LUCIA RANGE THROUGH 06-07Z WITH FLASH
FLOODING CONDITIONS LIKELY PARTICULARLY IN RECENT BURN SCARS ALONG
THAT RANGE. HI-RES GUIDANCE SUGGEST SOME ISOLATED TOTALS OVER 6"
WITH THE MAJORITY FALLING BETWEEN 23-06Z PROVIDING FAIRLY HIGH
CONFIDENCE IN RAIN MAGNITUDE. THE BIGGEST REMAINING QUESTION IS
WITH RESPECT TO LOCATION ALONG THE RANGE...WITH HRRR/HRRR EXP/RAP
NORTH AND ARW/NMMB FURTHER SOUTH.  CURRENT TRENDS IN VIS/IR
SUPPORT A FURTHER SOUTH PLACEMENT OF HEAVIEST RAINS/TRAINING BUT
WITH THE STRENGTH OF THE SUBTROPICAL RIDGING THERE IS STILL SOME
QUESTION TO SPECIFIC PLACEMENT BETWEEN SAN LUIS OBISPO AND
MONTEREY COUNTY. 

INTO THE SOUTHERN SIERRAS...THOUGH LOSING THE LOWEST LAYER OF
MOISTURE TO THE COASTAL RANGE ALONG WITH REMAINING 
INSTABILTY...THE STRENGTH AND PERSISTENCE OF THE 800-650MB FLOW
REMAINS NICELY DIRECTED AT THE SOUTHERN SIERRAS/GREENHORN AND
PIUTE MTN RANGES.  THIS FLUX AND OROGRAPHIC ASCENT WILL LIKELY
CONTINUE TO SUPPORT RATES UP TO .5"/HR SUPPORTING 3-5" TOTALS
THROUGH 06Z. WHILE THESE RATES/TOTALS ARE NOT AS SIGNIFICANT AS
THE COAST WILL SEE THERE WILL REMAIN LOCALIZED FLOODING CONCERNS.
THIS WILL BE COMPOUNDED BY FREEZING LEVELS ABOVE 9000FT SHOULD
LEAD TO RAIN MELTING SNOW FROM EVENT FROM EARLIER THIS WEEK.       

GALLINA

ATTN...WFO...HNX...LOX...MTR...REV...STO...VEF...

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

LAT...LON   38231987 38091939 37881906 37201846 36531807 
            35871801 35311813 35101842 35311877 35271917 
            35271956 34902035 34792060 35132091 35372109 
            35792165 36372198 36782203 36872215 37012240 
            37282248 37392227 37142186 37242143 37282057 
            37512014 37962018 


Last Updated: 309 PM EST SAT JAN 07 2017