PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
849 AM EST THU JAN 14 2010
VALID 12Z MON JAN 18 2010 - 12Z THU JAN 21 2010
...HEAVY RAINS AND SNOWS/FLOODING THREAT FOR THE WEST
COAST...
...POTENTIAL WIDESPREAD HVY RAINS LOWER MS VALLEY AND
GULF COAST...
GOOD MODEL OVERALL AGREEMENT THIS PERIOD AS THE FAST JET FINALLY
SHOWS EL NINO TRAITS AS IT DRIVES EASTWARD INTO THE WEST COAST
WITH A TYPICAL SPLITTING OF THE FLOW INTO TWO SEPERATE STREAMS.
THE NRN BRANCH TURNS NEWD AND THEN EAST ACROSS SRN CANADA AND THE
NRN TIER OF STATES KEEPING ABOVE AVERAGE HTS WITH A VERY NOTICABLE
POSITIVE HT ANOMALY OVER S CENTRAL CANADA EVENTUALLY CENTERING
UPON HUDSON BAY. THIS SHIFT OF THE WESTERLIES WILL KEEP COLD AIR
INTRUSIONS OUT OF CONUS THIS FORECAST PERIOD. THE MORE SOUTHERN
BRANCH WILL BE OVERWHELMINGLY THE DOMINANT FEATURE AS IT DRIVES
INTO CENTRAL AND THEN SRN CA AND BAJA AND EWD ACROSS THE SRN
CONUS/MEXICO BORDER AND EWD ACROSS THE GLFMEX. NEG EPAC HT
ANOMALIES INCREASE THRU THE PERIOD AS THE PAC/ASIAN JET CORE WITH
UPWARDS OF 200 KTS AT H250 DROPS SWD AND APPROACHS THE SRN CA
COAST. HT ANOMALIES AT H500 ARE IN THE 3 STANDARD DEVIATION RANGE
BUT THE APPROACHING LOW LEVEL JET FLOW EXCEEDS 5.
AS THE UPSTREAM FLOW MENTIONED ABOVE DEVELOPS AN EXITING CLOSED
SRN STREAM MID LEVEL LOW WHICH IS BASICALLY WELL AGREED UPON MOVES
EWD ON DAY 3 SUN INTO THE MID ATL STATES REGION AND EXITS
OFFSHORE. 00Z GFS REMAINS AN OUTLIER AS IT PHASES IN A NRN STREAM
SHORTWAVE INTO THE SRN STREAM FEATURE OVER THE OH VALLEY AND
RESULTS IN A PHASED STRONGER CLOSED OFF MID LEVEL LOW SOLUTION
OVER NEW ENG MON WITH A DEEP SFC LOW OFF THE NEW ENG COAST AND
BRINGING DOWN A COLD SURGE ON THE BACKSIDE ACROSS THE NERN QUARTER
OF CONUS. OTHER MODELS AND MEANS KEEP THIS UNPHASED RESULTING IN A
WEAKER MORE SRLY OFFSHORE TRACK OF THE SFC WELL LOW OFFSHORE. THIS
UNPHASED SOLUTION IS PREFERRED. MUCH MILDER CONDITIONS WILL
PREVAIL OVER ERN CONUS THRU MID WEEK.
ALONG THE WEST COAST THERE ARE AT LEAST 3 TO 4 SURGES COMING INTO
THE WEST COAST IN THE FAST PAC FLOW THIS PERIOD EACH WITH ROUNDS
OF HVY PCPN. AT THIS TIME THERE IS REASONABLE AGREEMENT ON THE
SHORTWAVES EMBEDDED IN THE FLOW TO COME IN AROUND
SAT-SUN..MON..TUES AND ANOTHER THURS-FRI WITH MORE TO FOLLOW.
MONDAYS SURGE HITS THE ENTIRE COAST FROM VANCOUVER SOUTH TO PT
CONCEPTION BUT THEN AS THE HTS FALL AND THE JET CORE SHIFTS SWD
THE TARGET AREA WILL BE MORE INTO CENTRAL CA AND SRN CA TUES
ONWARD. QPF TOTALS FROM MODEL GUIDANCE ARE VERY HIGH WITH AN
OVERALL RANGE OF 7-12 LIQUID INCHES DURING THIS FORECAST PERIOD
OVER COASTAL REGIONS/SIERRA AND ESPECIALLY SOCAL. SOME LOCAL
FAVORED TERRAIN AREAS WILL MOST LIKELY APPROACH 20 INCH LIQUID
AMOUNTS. VERY HVY SNOWS CAN BE EXPECTED OVER HIGHER TERRAIN AND A
FLOODING MUDSLIDE PROBLEMS APPEAR LIKELY. A HEAVY RAIN THEAT FOR
AZ APPEARS IN STORE THURS INTO SAT. SEE CPC THREAT ANALYSIS AND
LOCAL NWS OFFICE STATEMENTS/ADVISORIES AND EVENTUALLY WARNINGS.
HIGH CONFIDENCE EVENT WITH PAC RECON REQUESTED.
AS THE STRONG MID/UPPER JET CORE DRIVES EWD THE STRONGER SHORTWAVE
COMING ACROSS SOCAL WED WILL MOVE ACROSS TX BY THURSDAY. ALL
MODELS DEVELOP LOW PRESSURE WITH THIS SYSTEM AND A WEAKER
PRECEDING SHORTWAVE IN THE PLAINS. THIS SHORTWAVE/CLOSED LOW WILL
MOVE NEWD AS IT APPROACHS THE ERN CONUS RIDGE. ECMWF TAKES THIS
SHORTWAVE AND SFC LOW WEST OF OTHER MODELS UP THE CENTRAL MS
VALLEY AND INTO THE GREAT LAKES THURS-FRI WHILE GFS DRIVES NWD TO
OFF THE MID ATL COAST. CMC ORIGINATES A MORE SRLY TRACK INTIALLY
THEN TAKES IT UP THE WRN SIDE OF THE APPLCHN SPINE. THIS MORE SRN
DEVELOP AND OH VALLY TRACK IS PREFERED BY HPC FOR DAYS 6-7. THIS
WILL BREAK OUT ANOTHER AREA OF HEAVY RAINFALL IN THE LOWER MS
VALLEY THURS SPREADING EAST AND NORTHEAST FROM THE ERN GREAT LAKES
INTO FLORIDA. ABOVE AVG CONFIDENCE FORECAST.
HPC UPDATED PRELIM PROGS AND MODEL PREFERENCE IS A COMBINATION OF
ECMWF AND CMC WITH AN INCREASING AMOUNT OF THE CMC TO THE DOMINANT
MODEL BY DAY 7 THURS.
ROSENSTEIN
