MESOSCALE PRECIPITATION DISCUSSION 0742
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
816 PM EDT SUN OCT 16 2016
 
AREAS AFFECTED...CENTRAL SIERRAS AND INTO WESTERN NEVADA 
 
CONCERNING...HEAVY RAINFALL 
 
VALID 170016Z - 170516Z
 
SUMMARY...A PLUME OF ELEVATED MOISTURE FROM THE PACIFIC IS STILL
MOVING INLAND OVER CENTRAL CALIFORNIA, AND IT IS EXPECTED TO
PERSIST OVER THE NEXT SEVERAL HOURS BEFORE WEAKENING.  AS A
RESULT, HOURLY RAIN RATES REACHING 0.5" ARE POSSIBLE, WHICH COULD
LEAD TO LOCALIZED ISSUES IN RUGGED TERRAIN, BURN SCAR AREAS, AND
WHERE SOILS ARE CURRENTLY SATURATED FROM PREVIOUS RAINFALL. 

DISCUSSION...BOUNDARY LAYER MOISTURE CONVERGENCE WITHIN A
GRADUALLY WEAKENING ATMOSPHERIC RIVER CONTINUES PRODUCING HOURLY
RAIN RATES UP TO 0.4" OVER THE COASTAL RANGES AND SIERRA NEVADA OF
CENTRAL CALIFORNIA. MODERATE TO HEAVY RAINFALL IS ALSO LIKELY
AROUND THE RENO AREA AS THIS MOISTURE PLUME CONTINUES
NORTHEASTWARD ACROSS WESTERN NEVADA.  PRECIPITABLE WATER VALUES IN
THIS MOISTURE AXIS ARE ON THE ORDER OF 1.0" TO 1.3" PER LATEST RAP
GUIDANCE, WHICH ARE 2 TO 3 STANDARD DEVIATIONS ABOVE AVERAGE FOR
MID-OCTOBER.  THE LIMITING FACTOR HERE IS THE LACK OF INSTABILITY
WHICH WILL KEEP RAINFALL RATES FROM BECOMING HIGHER.

INFRARED AND WATER VAPOR IMAGERY INDICATE AN INTENSE 250MB UPPER
LEVEL JET STREAK (150+ KTS) SITUATED OVER NORTHERN CALIFORNIA AND
NORTHERN NEVADA EARLY THIS EVENING.  THIS IS HELPING TO SUSTAIN
LOW-LEVEL INFLOW ACROSS CENTRAL CALIFORNIA, WITH A 30-40 KT LOW
LEVEL JET AT 850MB.  THE MESOSCALE HIGH-RES GUIDANCE HAS A STRONG
SIGNAL FOR LOCAL AMOUNTS IN THE 1-2" RANGE ACROSS THE CENTRAL
SIERRA NEVADA RANGE THROUGH 05Z.  WHILE MOST MODEL PRECIPITATION
FORECASTS KEEP AMOUNTS GENERALLY UNDER 0.5" AN HOUR, HALF AN INCH
PER HOUR RAIN RATES ARE STILL POSSIBLE ON A LOCAL SCALE GIVEN THE
ORTHOGONAL COMPONENT OF THE FLOW OVER THE SIERRAS.  THESE RAINFALL
RATES COULD LEAD TO ISSUES NEAR BURN SCARS AND POSSIBLE DEBRIS
FLOWS IN/NEAR RUGGED TERRAIN.

HAMRICK

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            37211857 36651866 36481924 36901988 37502048 
            38392108 39202131 39802114 40132054