PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830AM EDT THURSDAY AUG 16 2012

30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2012

ENSO NEUTRAL CONDITIONS CONTINUED DURING THE MONTH OF AUGUST. POSITIVE 
EQUATORIAL PACIFIC SEA SURFACE TEMPERATURE (SST) ANOMALIES HAVE BEEN OBSERVED 
IN THE CENTRAL AND EASTERN PACIFIC WITH WEEKLY NINO34 BEING AROUND 0.5 -1.0. EL 
NINO CONDITIONS ARE LIKELY LATER IN THE FALL BUT THIS IS A MINOR CONSIDERATION 
FOR SEPTEMBER ONLY.

THE LONG LEAD SEPTEMBER 2012 TEMPERATURE OUTLOOK DEPICTS ENHANCED ODDS FOR 
ABOVE-NORMAL MEAN TEMPERATURES ACROSS MOST OF THE CONTIGUOUS UNITED STATES AND 
NORTHERN ALASKA. THIS IS BASED ON CONSISTENT SIGNATURES FROM CLIMATE MODEL 
FORECASTS (CFSV2, IMME AND NMME), AND THE CAS WHICH ACTS ON VERY LOW SOIL 
MOISTURE CONDITIONS ACROSS A LARGE AREA OF THE EAST-CENTRAL CONUS. STATISTICAL 
TOOLS INDICATE WARMTH TO EXTEND ALSO INTO THE SOUTHWEST, AND THIS IS IN PART 
DUE TO LONG TERM TEMPERATURE TRENDS AND TEMPERATURE OBSERVATIONS OVER THE PAST 
30-DAYS. THE PROBABILITIES ARE KEPT MODEST BECAUSE THE NWP FORECAST FOR THE 
NEXT TWO WEEKS, I.E. BEFORE THE PERIOD STARTS, HAS A TROUGH OVER EAST-CENTRAL 
CONUS. IN NORTHERN ALASKA, ODDS FAVOR ABOVE-NORMAL TEMPERATURES DUE PRIMARILY 
TO THE CFSV2 AND ABNORMALLY WARM SSTS. BELOW-NORMAL SEPTEMBER MEAN TEMPERATURES 
ARE FAVORED FOR ALL COASTAL REGIONS FROM SOUTHERN ALASKA TO CALIFORNIA, 
SUPPORTED IN PART BY THE CFSV2 AND ABNORMALLY COOL SSTS. ELSEWHERE THERE ARE 
EITHER VERY WEAK OR CONFLICTING SIGNALS AMONG TOOLS, AND SO EQUAL CHANCES FOR 
BELOW-, NEAR-, OR ABOVE-NORMAL SEPTEMBER MEAN TEMPERATURES ARE INDICATED.

THE SEPTEMBER 2012 PRECIPITATION OUTLOOK FAVORS ABOVE-MEDIAN PRECIPITATION FOR 
ARIZONA AND SOUTHERN CALIFORNIA IN RELATION TO AN ACTIVE SEASON FOR BOTH THE 
MONSOON AND EAST PACIFIC TROPICAL CYCLONES. THE NMME INDICATES AN ACTIVE 
MOISTURE FLOW FROM MEXICO INTO THE SOUTHERN GULF STATES. ABOVE MEDIAN 
PRECIPITATION IS FURTHER INDICATED IN CENTRAL PORTIONS OF ALASKA. THE LATTER 
HAS SOME SUPPORT FROM THE CFSV2 MODEL AND THE NMME. ODDS FOR BELOW-MEDIAN 
PRECIPITATION ARE ELEVATED OVER PORTIONS OF BOTH THE MISSISSIPPI VALLEY AND 
GREAT PLAINS REGION. THIS IS STRONGLY INDICATED BY NMME, AND MAY BE ATTRIBUTED 
TO REINFORCING, NEGATIVE FEEDBACKS ASSOCIATED WITH DRY SOILS COMMON DURING THE 
SUMMER SEASON, AND IN THIS EXTREME CASE, WE ASSUME INTO SEPTEMBER AS WELL. ODDS 
FOR BELOW-MEDIAN PRECIPITATION ARE FURTHER ELEVATED OVER THE PACIFIC NORTHWEST, 
THE ALASKA PANHANDLE. THIS IS DUE PRIMARILY TO THE CFSV2 MODEL AND TRENDS. 
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 UPDATED SEPTEMBER 2012 TEMPERATURE AND PRECIPITATION OUTLOOKS WILL BE BASED 
ON A NUMBER OF FACTORS, SUCH AS THE MOST RECENT EXTENDED-RANGE MODEL GUIDANCE, 
CLIMATE MODELS SUCH AS THE CFSV2 AND NMME, SOIL MOISTURE CONDITIONS, SEA 
SURFACE TEMPERATURES (SST), AND RECENT OBSERVED TEMPERATURE AND PRECIPITATION 
PATTERNS.

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: HUUG VAN DEN DOOL


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.



AN UPDATED MONTHLY OUTLOOK... FOR SEP WILL BE ISSUED ON FRI AUGUST 31 2012


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

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