Flash Flood Guidance
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000
AWUS01 KWNH 092116
FFGMPD
CAZ000-ORZ000-100915-

MESOSCALE PRECIPITATION DISCUSSION 0791
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
415 PM EST FRI DEC 09 2016

AREAS AFFECTED...FAR SWRN OR INTO NRN CA

CONCERNING...HEAVY RAINFALL

VALID 092115Z - 100915Z

SUMMARY...INCREASING RAINFALL RATES AFTER 03Z ARE EXPECTED ALONG
THE NRN COAST OF CA INTO THE NRN SIERRA NEVADA/SRN CASCADE
MOUNTAINS. RAINFALL TOTALS PEAKING IN THE 3-4 INCH RANGE WILL BE
POSSIBLE THROUGH 09Z.

DISCUSSION...WATER VAPOR IMAGERY IN THE ERN PACIFIC SHOWED
CONFLUENT MID-UPPER LEVEL FLOW WITH THE AXIS OF DILATATION LOCATED
NEAR LATITUDE 40N. AT 20Z...A VORTICITY MAX WAS LOCATED NEAR 45N
155W IN NWLY FLOW. ANOTHER...MORE SHEARED VORTICITY MAX...WAS
LOCATED NEAR 37N 154W IN SWLY FLOW. DOWNSTREAM...GOES HD WINDS
CONFIRMED THE PRESENCE OF A 110-120 KT JET NEAR 250 MB WHERE THE
TWO STREAMS CAME TOGETHER. REGARDING MOISTURE...THE CIRA LAYERED
PW PRODUCT SHOWED A PLUME OF MODIFIED TROPICAL MOISTURE STREAMING
NORTH ACROSS HAWAII AND THEN NEWD TOWARD CALIFORNIA...WITH A
DIRECT CONNECTION TO THE ITCZ IN THE LOWER...MIDDLE AND UPPER
LEVELS OF THE TROPOSPHERE. BLENDED TPW IMAGERY AND RECENT RUNS OF
THE RAP SHOWED THE NOSE OF A SIZABLE PRECIPITABLE WATER PLUME OF
1.25 INCHES...REACHING NEAR 39N 130W IN SWLY LOW LEVEL FLOW.

SHORT TERM RAP FORECASTS TAKE THE TWO VORTICITY MAXIMA DOWNSTREAM
AND TIGHTEN THE CONFLUENT FLOW ALONG WITH A STRENGTHENING OF THE
250 MB JET TO 130-150 KTS. THE LEFT EXIT REGION OF THIS JET STREAK
IS FORECAST TO REACH THE CA/OR BORDER ALONG THE COAST BETWEEN
06-09Z ALONG WITH PRECIPITABLE WATER VALUES OF 1.0-1.2 INCHES
ALONG THE FAR NRN CA COAST AHEAD OF A WEAK SURFACE LOW. THE LOWER
LEVELS ARE EXPECTED TO SEE 850-700 MB WINDS OF ROUGHLY 30-40 KT
FROM THE WSW...PERPENDICULAR TO THE COASTAL RANGES OF DEL NORTE
AND HUMBOLDT COUNTIES WHERE RAINFALL RATES SHOULD APPROACH 0.5
IN/HR BUT THE STEADY DURATION OF FLOW ORTHOGONAL TO THE TERRAIN
COULD ALLOW 3-4 INCHES BY 09Z.

FARTHER SOUTH...MOISTURE IS EXPECTED TO REACH AS HIGH AS 1.4 TO
1.5 INCHES ALONG THE COAST OF MENDOCINO AND SONORA COUNTIES WITH
850-700 MB FLOW AS HIGH AS 50 KTS. THE ANOMALOUS MOISTURE WILL
EXTEND DOWNSTREAM INTO THE NRN SIERRA NEVADA WHERE SNOW MELT IS
EXPECTED WITH SNOW LEVELS RISING TO 10000 FT OVERNIGHT. IT IS HERE
WHERE THE HIGHEST RAINFALL RATES ARE EXPECTED...PERHAPS OWING TO
SOME WEAK INSTABILITY. RAINFALL RATES BETWEEN 0.50 AND 1.0 IN/HR
ARE EXPECTED IN THE 06-09Z RANGE ALONG THE COASTAL RANGES AND INTO
THE UPSLOPE REGIONS OF THE SIERRA NEVADA.

OTTO

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

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

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

LAT...LON   42652381 42522365 42182330 42012299 41782276
            41602254 41452206 41272182 40982168 40552140
            40252129 39872093 39672060 39352041 39112064
            39012093 39152134 39622163 39952200 40392217
            40422253 40012269 39592261 39212251 38922239
            38532252 38342275 38352310 38932385 39762417
            40452455 41432452 42102461 42432449 42542425
            42632403



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