PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 830AM EDT THURSDAY APR 17 2014 30-DAY OUTLOOK DISCUSSION FOR MAY 2014 RECENT ATMOSPHERIC AND OCEANIC CONDITIONS IN THE TROPICAL PACIFIC BASIN CONTINUE TO INDICATE ENSO-NEUTRAL CONDITIONS IN EARLY APRIL. PACIFIC SEA SURFACE TEMPERATURE (SST) ANOMALIES HAVE BEEN STEADILY RISING ALONG EQUATOR THROUGHOUT MUCH OF THE CENTRAL AND EASTERN PACIFIC OCEAN AND ARE NOW ABOVE AVERAGE EXCEPT ALONG THE SOUTH AMERICAN COAST. THERE ARE MANY INDICATORS THAT SUGGEST THAT THE ENSO STATE IS EVOLVING TOWARD EL NINO. THESE INCLUDE RECENTLY OBSERVED WESTERLY WIND ANOMALIES OVER MUCH OF THE CENTRAL AND WESTERN EQUATORIAL PACIFIC, A MARKED INCREASE IN SUB-SURFACE OCEANIC HEAT CONTENT IN THE PAST FEW WEEKS, AND A SLOW PROGRESSION OF ENHANCED CONVECTION ALONG THE EQUATOR TOWARD THE CENTRAL PACIFIC. IN ADDITION, THERE IS AN INCREASING CONSENSUS AMONG DYNAMICAL AND STATISTICAL FORECASTS THAT POSITIVE SST ANOMALIES IN THE ENSO CRITICAL REGIONS OF THE PACIFIC WILL REACH MINIMAL THRESHOLDS FOR EL NINO CONDITIONS BY SUMMER 2014. COMPOSITES OF PAST YEARS IN WHICH EL NINO CONDITIONS DEVELOPED IN SUMMER WERE CONSIDERED FOR THE MAY OUTLOOK. THE MAY OUTLOOK FOR MONTHLY MEAN TEMPERATURES INDICATES ELEVATED CHANCES FOR BELOW-NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN ROCKIES, THE NORTHERN GREAT PLAINS, AND THE UPPER GREAT LAKES. THIS IS DUE TO INDICATIONS FROM THE BOTH SMLR AND CFS, AND IS CONSISTENT WITH TEMPERATURES FROM COMPOSITES OF PAST YEARS WITH DEVELOPING EL NINO CONDITIONS. ABOVE-NORMAL SOIL MOISTURE CONTENT IN THE NORTHERN ROCKIES MAY ALSO ENHANCE THE CHANCES FOR BELOW-NORMAL TEMPERATURES. THE CHANCES FOR BELOW-NORMAL TEMPERATURES NEAR THE SHORES OF THE GREAT LAKES ARE FURTHER ENHANCED BY THE SIGNIFICANTLY BELOW-NORMAL WATER TEMPERATURES THAT ARE EXPECTED TO PERSIST INTO MAY. MOST TOOLS INDICATE ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE SOUTHWESTERN QUARTER OF THE CONUS AND PARTS OF THE SOUTHERN GREAT PLAINS. DRY SOIL MOISTURE CONDITIONS ARE EXPECTED TO HELP INCREASE THE ODDS OF ABOVE NORMAL TEMPERATURES IN THESE REGIONS. ABOVE-NORMAL SSTS NEAR SOUTHERN FLORIDA HELP ELEVATE CHANCES FOR ABOVE-NORMAL AIR TEMPERATURES THERE. MANY MODELS AND STATISTICAL TOOLS POINT TO AN INCREASED CHANCE FOR ABOVE-NORMAL TEMPERATURES ALONG THE WEST COAST OF NORTH AMERICA AND MOST OF ALASKA. IN AREAS WHERE CLIMATE SIGNALS ARE WEAK AND/OR NOT RELIABLE, EQUAL CHANCES (EC) OF BELOW-, NEAR- AND ABOVE-NORMAL MEAN MONTHLY TEMPERATURES ARE INDICATED. THE NMME, IMME AND CFS, FAVOR BELOW-MEDIAN PRECIPITATION IN THE PACIFIC NORTHWEST AND ALSO THE ALASKA PANHANDLE. THE NMME FAVORS ABOVE-MEDIAN PRECIPITATION AMOUNTS NEAR FLORIDA. COMPOSITES BASED ON YEARS WITH DEVELOPING EL NINO CONDITIONS ALSO SUPPORT DRY TENDENCIES IN THE PACIFIC NORTHWEST, AND TENDENCIES FOR WET CONDITIONS IN FLORIDA. ELSEWHERE, THE LACK OF CONSISTENT SIGNALS AMONG TOOLS SUGGEST EQUAL CHANCES (EC) FOR BELOW- NEAR- OR ABOVE-MEDIAN PRECIPITATION AMOUNTS. IT IS NOTEWORTHY THAT THE VARIOUS MODELS IN THE NMME SHOW NO CONSISTENT SIGNAL FOR THE SOUTHERN HIGH PLAINS AND WEST TEXAS IN SPITE OF VERY DRY INITIAL SOIL MOISTURE CONDITIONS IN SOME OF THESE REGIONS. 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: DAVID UNGER 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 MAY WILL BE ISSUED ON WED APRIL 30 2014 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$