Flash Flood Guidance
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000
AWUS01 KWNH 182104
FFGMPD
CAZ000-190358-

MESOSCALE PRECIPITATION DISCUSSION 0025
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
403 PM EST WED JAN 18 2017

AREAS AFFECTED...NORTHERN AND CENTRAL CALIFORNIA COASTAL
RANGE/SIERRA NEVADA

CONCERNING...HEAVY RAINFALL

VALID 181958Z - 190358Z

SUMMARY...A STRONG ATMOSPHERIC RIVER... WITH ITS ORIGINS OVER THE
CENTRAL PACIFIC...WILL PUSH NORTHEAST ACROSS NORTHERN AND CENTRAL
CA DURING THE AFTERNOON HOURS. A 55 TO 65 KNOT LOW LEVEL JET WILL
FOCUS THE DEEP MOISTURE PLUME ON THE FAVORED LOCATIONS IN THE
HIGHER TERRAIN...PRODUCING RAINFALL RATES OF 1/2 INCH OR GREATER.

DISCUSSION...THE LATEST WATER VAPOR IMAGE SHOWED A LOW LEVEL JET
OF A 55 T0 65 KT TRANSPORTING
A PLUME OF 750+ KG/M/S INTEGRATED MOISTURE TRANSPORT ACROSS THE
COASTAL RANGES OF NORTHERN AND CENTRAL CALIFORNIA. A 1940Z AMSU
PASS SHOWED PRECIPITABLE WATER VALUES ~1.5 INCHES IN THIS SAME
LOCATION. HIGH RES HREF SHOWING A HIGH PROBABILITY OF RAINFALL
RATES IN THE 0.50 TO 0.75" RANGE
IN THIS AREA FROM 21Z-03Z...CORRESPONDING TO THE HIGH PW, RICH
MOISTURE PLUME COMING ASHORE.

THE GREATEST HOURLY RATES ARE EXPECTED TO BE CONCENTRATED FROM THE
CA COASTAL RANGES SOUTH TO NAPA...EXTENDING INTO THE SACRAMENTO
VALLEY AFTER 00Z.

GIVEN THE WET ANTECEDENT CONDITIONS ACROSS NORTHERN CA DUE TO
HEAVY RAINFALL IN THE PAST TWO WEEKS...THE ADDITIONAL HEAVY RAIN
COULD RESULT IN RUNOFF ISSUES.

MONTEFUSCO

...PLEASE SEE WWW.WPC.NCEP.NOAA.GOV FOR GRAPHIC PRODUCT...

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

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

LAT...LON   41112297 41062253 40972187 40892161 40602123
            40492099 40062074 39722057 39272039 38582045
            39302107 39392117 39512127 39562151 39562167
            39492190 39272196 38762178 38462171 38322165
            38242161 38062167 37932178 37812199 37692231
            37732263 37752278 37892310 38212347 38662378
            39062394 39472413 39962454 40392435 40342436
            40672411 41102370 41062373



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