PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300PM EDT SUNDAY AUG 31 2014 30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2014 THE SEPTEMBER MONTHLY OUTLOOK IS UPDATED AT THE END OF AUGUST USING THE LATEST DYNAMICAL MODEL GUIDANCE, INCLUDING THE NCEP CLIMATE FORECAST SYSTEM (CFS), THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS) CALIBRATED USING RETROSPECTIVE FORECASTS FOR 1985-2010 GENERATED BY THE NOAA EARTH SYSTEM RESEARCH LABORATORY (ESRL), AND THE NORTH AMERICAN ENSEMBLE FORECAST SYSTEM (NAEFS, A MULTI-MODEL ENSEMBLE THAT COMBINES BIAS-CORRECTED OUTPUT FROM THE NCEP GEFS AND THE ENVIRONMENT CANADA ENSEMBLE PREDICTION SYSTEM). THE UPDATE TO THE SEPTEMBER 2014 TEMPERATURE OUTLOOK CONTINUES TO INDICATE ENHANCED PROBABILITIES OF ABOVE NORMAL OVER MUCH OF THE WESTERN U.S. FROM THE PACIFIC COAST TO THE ROCKY MOUNTAINS. THE PROBABILITIES OF ABOVE NORMAL HAVE BEEN REDUCED FOR THE PACIFIC NORTHWEST WHERE MODEL FORECASTS FOR EARLY SEPTEMBER INDICATE AN INCREASED LIKELIHOOD OF BELOW NORMAL TEMPERATURES. RECENT CFS AND CALIBRATED GEFS FORECASTS SUPPORT THE FORECAST FOR ABOVE NORMAL MONTHLY MEAN TEMPERATURES BEGINNING WITH THE SECOND WEEK OF THE MONTH. THE PROBABILITIES OF ABOVE NORMAL TEMPERATURES HAVE BEEN INCREASED AND THE AREA HAS BEEN EXPANDED OVER THE SOUTHEAST AND ALONG THE ATLANTIC COASTAL STATES AS INDICATED BY THE CFS, THE CALIBRATED GEFS, AND THE NAEFS. THE PROBABILITIES OF BELOW NORMAL TEMPERATURES ARE NOW GREATER THAN CLIMATOLOGY OVER PARTS OF MONTANA, NORTH DAKOTA AND SOUTH DAKOTA WITH A TROUGH OVER THE REGION IN MODEL FORECASTS. THE UPDATE TO THE SEPTEMBER 2014 PRECIPITATION OUTLOOK CONTINUES TO INDICATE AN ENHANCED PROBABILITY OF ABOVE MEDIAN PRECIPITATION OVER THE SOUTHWEST MONSOON REGION EXTENDING INTO THE CENTRAL PLAINS WITH SOME REDUCTIONS IN THE AREA AND PROBABILITIES IN THE UPDATE. THIS OUTLOOK IS PRIMARILY SUPPORTED BY THE CALIBRATED GEFS AND THE NAEFS FOR THE SECOND WEEK OF THE MONTH. PROBABILITIES OF ABOVE MEDIAN PRECIPITATION ARE NOW ENHANCED FOR THE UPPER MISSISSIPPI VALLEY AND THE WESTERN GREAT LAKES REGION AHEAD OF THE MEAN LOCATION OF A PREDICTED TROUGH AS INDICATED BY THE CFS. AN AREA OF ENHANCED PROBABILITIES OF ABOVE MEDIAN PRECIPITATION OVER SOUTHERN TEXAS AND THE WESTERN GULF COAST IS INDICATED FOR EARLY IN THE MONTH BY DYNAMICAL MODEL FORECASTS AND FOR THE MONTHLY PRECIPITATION TOTALS FROM THE CFS. ENHANCED PROBABILITIES FOR BELOW MEDIAN PRECIPITATION OVER AN AREA OF THE WESTERN PACIFIC NORTHWEST IS SUPPORTED BY CFS FORECASTS FOR SEPTEMBER. IN AREAS WHERE CLIMATE SIGNALS ARE WEAK SUCH THAT THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES OR MONTHLY ACCUMULATED PRECIPITATION ARE SIMILAR TO CLIMATOLOGICAL PROBABILITIES, EQUAL CHANCES (EC) IS INDICATED. THE DISCUSSION FROM THE HALF-MONTH-LEAD SEPTEMBER OUTLOOK RELEASED AUGUST 21 IS BELOW: --- RECENT ATMOSPHERIC AND OCEANIC CONDITIONS ACROSS THE TROPICAL PACIFIC INDICATE CURRENT ENSO-NEUTRAL CONDITIONS. CLIMATE MODEL FORECASTS AND THE CPC/IRI ENSO OUTLOOK INDICATE THE EXPECTED DEVELOPMENT OF EL NINO IN LATE SUMMER OR EARLY AUTUMN. MOST FORECASTS INDICATE EL NINO TO PEAK AT WEAK OR MODERATE STRENGTH IN LATE AUTUMN INTO EARLY WINTER. DURING THE PAST FEW WEEKS, POSITIVE SST ANOMALIES PERSISTED IN THE EASTERN EQUATORIAL PACIFIC AND WEST OF THE DATE LINE, WHILE ANOMALIES ARE NEAR ZERO IN THE EAST-CENTRAL PACIFIC. THE LATEST WEEKLY SST ANOMALY IN THE NINO 3.4 REGION IS +0.0C. POSITIVE ANOMALIES IN AVERAGE OCEANIC HEAT CONTENT BASED ON SUBSURFACE TEMPERATURE ANOMALIES IN THE UPPER 300-METERS OF THE EASTERN AND CENTRAL EQUATORIAL PACIFIC (180W TO 100W) DECREASED IN THE LAST FEW MONTHS, BECOMING SLIGHTLY NEGATIVE IN RECENT WEEKS, BEFORE RETURNING TO AN AVERAGE ANOMALY NEAR ZERO. IN RECENT WEEKS A POSITIVE SUBSURFACE TEMPERATURE ANOMALY EMERGED IN THE WESTERN PACIFIC AT ABOUT 100 TO 200 METERS DEPTH, WHILE A LARGE AREA OF POSITIVE TEMPERATURE ANOMALIES AT DEPTH IN THE CENTRAL AND EASTERN EQUATORIAL PACIFIC DECREASED IN SIZE AND MAGNITUDE AND IS NOW LOCATED FROM ABOUT 145W TO 85W EXTENDING ONLY TO A DEPTH OF ABOUT 75 METERS. DURING THE PAST 30-DAYS, POSITIVE OLR ANOMALIES, INDICATING SUPPRESSED CONVECTION AND PRECIPITATION, WERE OBSERVED OVER INDONESIA AND NEAR THE DATE LINE. LOW-LEVEL 850-HPA WINDS WERE NEAR AVERAGE ACROSS THE EQUATORIAL PACIFIC, AND EASTERLY UPPER-LEVEL 200-HPA WIND ANOMALIES WERE OBSERVED OVER THE EAST-CENTRAL PACIFIC. THE SEPTEMBER 2014 TEMPERATURE AND PRECIPITATION OUTLOOKS RELY MAINLY ON CLIMATE MODEL FORECASTS WITHOUT AN EXPECTATION OF SIGNIFICANT IMPACTS ON THE CLIMATE OF NORTH AMERICA BY NEXT MONTH FROM POTENTIAL EL NINO DEVELOPMENT. A GREATER LIKELIHOOD OF ABOVE-NORMAL MONTHLY MEAN TEMPERATURES FOR SEPTEMBER 2014 IS PREDICTED FOR THE GULF COAST AND PARTS OF THE SOUTHEAST FROM THE TEXAS COAST TO EASTERN NORTH CAROLINA. THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES IS GREATEST FOR SOUTHERN AND EASTERN PARTS OF THE REGION. THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES IS ALSO ENHANCED FOR NEW ENGLAND. ABOVE-NORMAL TEMPERATURES ARE ALSO MOST LIKELY FOR ALASKA AND MUCH OF THE WEST INCLUDING THE NORTHERN ROCKIES, GREAT BASIN AND PACIFIC COASTAL STATES, WITH THE GREATEST PROBABILITIES ALONG THE WEST COAST AND THE SOUTHERN COAST OF ALASKA. THE TEMPERATURE OUTLOOK IS SUPPORTED BY RECENT CLIMATE MODEL FORECASTS FROM THE CFS, NMME AND IMME. POSITIVE SEA SURFACE TEMPERATURE ANOMALIES OVER THE NORTH PACIFIC AND ALONG THE SOUTHERN CALIFORNIA, EASTERN GULF AND NEW ENGLAND COASTS MAY INCREASE THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES NEAR THE COAST. CLIMATE MODELS AS SHOWN IN CFSV2 FORECASTS INDICATE ABOVE-NORMAL MID-LEVEL 700-HPA HEIGHTS OVER ALASKA, THE PACIFIC COAST AND THE EAST, SUPPORTING AN ENHANCED LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES. THE MONTHLY OUTLOOK FOR SEPTEMBER 2014 INDICATES A GREATER THAN NORMAL LIKELIHOOD OF ABOVE-MEDIAN PRECIPITATION FOR A LARGE AREA OF THE SOUTHWEST FROM SOUTHERN CALIFORNIA TO WESTERN TEXAS AND OKLAHOMA AND NORTHEASTWARD TO UTAH, SOUTHERN WYOMING, NEBRASKA AND KANSAS. THE PRECIPITATION OUTLOOK FOR SEPTEMBER 2014 IS SUPPORTED BY CLIMATE MODEL FORECASTS FROM THE NMME AND IMME. ABOVE-NORMAL EASTERN PACIFIC SEA SURFACE TEMPERATURES AND THE PREDICTED ATMOSPHERIC CIRCULATION INDICATE AN INCREASED FLOW OF ATMOSPHERIC MOISTURE FROM THE TROPICS INTO THE SOUTHWEST. IN AREAS WHERE CLIMATE SIGNALS ARE WEAK SUCH THAT THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES OR MONTHLY ACCUMULATED PRECIPITATION AMOUNTS ARE SIMILAR TO CLIMATOLOGICAL PROBABILITIES, EQUAL CHANCES (EC) IS INDICATED. THE MAIN FACTORS THAT 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) PERSISTENTLY 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 VERSION 2 (CFS) AND FOR THE ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS). AN EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL MULTI-MODEL ENSEMBLE (NMME), COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED. FORECASTER: DAN COLLINS 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 OCT ... WILL BE ISSUED ON THU SEP 18 2014 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$