PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300PM EDT SUNDAY SEP 30 2012

30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2012

ENSO NEUTRAL CONDITIONS CONTINUED DURING THE MONTH OF SEPTEMBER. VERY WEAK 
POSITIVE EQUATORIAL PACIFIC SEA SURFACE TEMPERATURE (SST) ANOMALIES HAVE BEEN 
OBSERVED IN THE CENTRAL AND EASTERN PACIFIC WITH WEEKLY NINO3.4 VALUES 
GENERALLY AROUND 0 TO +0.5 C. ANY INFLUENCE OF THESE WEAK EL NINO-LIKE SSTS IN 
THIS FORECAST COMES SOLELY THROUGH ITS (LIKELY NEGLIGIBLE) IMPACTS UPON THE 
DYNAMICAL MODEL FORECAST GUIDANCE.

THE END-OF-MONTH, ZERO-LEAD, OCTOBER 2012 TEMPERATURE AND PRECIPITATION UPDATE 
OUTLOOKS ARE BASED PRIMARILY ON DYNAMICAL MODEL FORECAST GUIDANCE FROM THE GFS, 
NAEFS, ECMWF, AND CANADIAN.  THIS FORECAST UPDATES ONE MADE ON SEP 20.  THAT 
FORECAST WAS BASED ON A NUMBER OF FACTORS WHICH INCLUDE CLIMATE MODELS SUCH AS 
THE CFSV2 AND NMME, SOIL MOISTURE CONDITIONS, SEA SURFACE TEMPERATURES (SST), 
AND RECENT OBSERVED TEMPERATURE AND PRECIPITATION PATTERNS. THE DIFFERENCES IN 
INPUTS TO THE EARLIER AND LATER FORECASTS LARGELY ACCOUNT FOR THE CHANGES 
BETWEEN THEM.

THE OCTOBER 2012 UPDATED TEMPERATURE OUTLOOK DEPICTS ENHANCED ODDS FOR 
ABOVE-NORMAL MEAN TEMPERATURES IN ALASKA AND WESTERN CONUS. BELOW-NORMAL 
OCTOBER MEAN TEMPERATURES ARE FAVORED FOR COASTAL REGIONS OF CALIFORNIA, 
SUPPORTED IN PART BY ABNORMALLY COOL OBSERVED SSTS, AND FOR MUCH OF THE EASTERN 
HALF OF CONUS, EXCLUDING NEW ENGLAND AND THE FLORIDA PENINSULA. THIS IS BASED 
ON GOOD AGREEMENT AMONG THE VARIOUS EXTENDED RANGE DYNAMICAL MODELS (GFS, 
ECMWF, CANADIAN) UPON THE DEVELOPMENT OF A BLOCKING PATTERN IN THE GULF OF 
ALASKA, WITH A DOWNSTREAM TROUGH OVER NORTH AMERICA.  ELSEWHERE THERE ARE 
EITHER VERY WEAK OR CONFLICTING SIGNALS AMONG TOOLS, AND SO EQUAL CHANCES FOR 
BELOW-, NEAR-, OR ABOVE-NORMAL OCTOBER MEAN TEMPERATURES ARE INDICATED.

THE OCTOBER 2012 UPDATED PRECIPITATION OUTLOOK FAVORS ABOVE-MEDIAN 
PRECIPITATION FOR ALASKA, DUE TO THE LIKELY OCCURRENCE OF SOUTHERLY FLOW IN THE 
REGION, AND FOR THE GREAT LAKES AND SECTIONS OF THE EAST COAST STATES. 
SUB-MEDIAN PRECIPITATION IS MOST LIKELY FROM SOUTHERN SECTIONS OF THE ALASKA 
PANHANDLE THROUGH THE WEST COAST STATES, WESTERN NEVADA, ARIZONA AND 
SOUTHWESTERN SECTIONS OF NEW MEXICO. ELSEWHERE, WHERE THERE ARE EITHER WEAK OR 
CONFLICTING SIGNALS AMONG THE TOOLS, EQUAL CHANCES (EC) OF BELOW-, NEAR-, AND 
ABOVE-MEDIAN PRECIPITATION IS PROJECTED.

THE MAIN FACTORS WHICH USUALLY INFLUENCE THE MONTHLY CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH COMPRISE ENSO. IMPACTS OF THESE EVENTS ARE 
SUMMARIZED BY SEPARATING 3-MONTH OBSERVATIONS FROM THREE OR MORE DECADES INTO 
EL NINO, NEUTRAL AND LA NINA SETS, AVERAGING EACH SEPARATELY, AND THEN 
COMPUTING ANOMALIES. THESE ARE CALLED "COMPOSITES" AND USED AT TIMES TO 
SUBJECTIVELY MODIFY THE FORECAST.
2) TRENDS - APPROXIMATED BY THE OCN TOOL AS THE DIFFERENCE BETWEEN THE MOST 
RECENT 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN OF PRECIPITATION FOR A GIVEN 
LOCATION AND TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY 
1981-2010).
3) THE TROPICAL 30-60 DAY OSCILLATION - CALLED THE MADDEN JULIAN OSCILLATION 
(MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE ARCTIC OSCILLATION (AO), THE SIMILAR NORTH ATLANTIC OSCILLATION (NAO), 
AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE 
ANOMALY PATTERN ESPECIALLY DURING BOREAL WINTER AND ARE GENERALLY CONSIDERED TO 
HAVE LOW PREDICTABILITY.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE 
VARIABILITY AFFECTING THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN 
REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO.
6) PERSISTANTLY DRY OR WET SOILS IN THE SPRING AND SUMMER AND SNOW AND ICE 
COVER ANOMALIES IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS 
AND ACT AS A KIND OF MEMORY IN THE CLIMATE SYSTEM.
7) STATISTICAL FORECAST MODELS - CANONICAL CORRELATION ANALYSIS (CCA), 
SCREENING MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOG (CA), AND 
ENSEMBLE CCA (ECCA).
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM (CFS) 
AND FOR ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM 
(GEFS). THE UPGRADED VERSION OF THE CFS (CFSV2) BECAME OPERATIONAL IN LATE 
MARCH OF 2011. BOTH VERSIONS OF CFS ARE CURRENTLY RUN IN PARALLEL. AN 
EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL MULTI-MODEL ENSEMBLE (NMME), 
COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED.


FORECASTER: ED O'LENIC


THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING
THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3 
COMPLETE DECADES AS THE CLIMATE REFERENCE PERIOD.  THE PROBABILITY ANOMALIES
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT
SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.



THE NEXT MONTHLY OUTLOOK...FOR NOV ... WILL BE ISSUED ON THU OCT 18 2012


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.

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