PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 830 AM EDT THU MAY 18 2017 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THE JUNE-JULY-AUGUST (JJA) 2017 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE FORECAST DOMAIN. FOR THE CONTIGUOUS U.S., ABOVE-NORMAL SEASONAL MEAN TEMPERATURES ARE MOST LIKELY FOR THE EASTERN U.S., ACROSS THE SOUTHERN STATES, AND WEST OF ROCKY MOUNTAINS. THE GREATEST ODDS ARE INDICATED FOR PARTS OF THE SOUTHWEST, THE GULF COAST AND ATLANTIC COASTAL REGIONS. ABOVE-NORMAL TEMPERATURES ARE ALSO FAVORED FOR MUCH OF ALASKA. THE JJA 2017 PRECIPITATION OUTLOOK INDICATES ENHANCED PROBABILITIES OF ABOVE-MEDIAN PRECIPITATION FOR PARTS OF THE ROCKIES AND HIGH PLAINS, CENTERED EAST OF THE CONTINENTAL DIVIDE, EXTENDING SOUTHWARD THROUGH THE SOUTHERN PLAINS. ABOVE-MEDIAN PRECIPITATION IS ALSO SLIGHTLY FAVORED FOR PARTS OF MAINLAND ALASKA. AS THE FORECAST PROGRESSES TOWARD THE COLD SEASON, A SLIGHT TILT TOWARD EL NINO (RELATIVE TO LA NINA) IS INDICATED BY THE LATEST OBJECTIVE GUIDANCE AND EXPERT ASSESSMENTS. THIS HAS A SMALL IMPACT ON THE TEMPERATURE AND PRECIPITATION FORECASTS FOR THE SEASONS SPANNING SON 2017 THROUGH FMA 2018. EQUAL CHANCES (EC) ARE FORECAST OVER AREAS WHERE ODDS OF ABOVE-, BELOW-, OR NEAR-NORMAL SEASONAL MEAN TEMPERATURES AND SEASONAL ACCUMULATED PRECIPITATION AMOUNTS ARE EXPECTED TO BE SIMILAR TO CLIMATOLOGICAL PROBABILITIES. BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE: HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/TOOLS/BRIEFING CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS OCEANIC AND ATMOSPHERIC OBSERVATIONS ACROSS THE EQUATORIAL PACIFIC AS A WHOLE INDICATE ENSO-NEUTRAL CONDITIONS ARE CONTINUING. THE LATEST WEEKLY SST ANOMALY MAP INDICATES THAT WEAKLY POSITIVE SST ANOMALIES EXIST ACROSS NEARLY THE ENTIRE EQUATORIAL PACIFIC BASIN, WITH HIGHER AMPLITUDE ANOMALIES LOCATED NEAR THE SOUTH AMERICAN COAST. THE HEAT CONTENT ANOMALY OF THE UPPER-OCEAN LAYERS, TO A DEPTH OF 300 METERS, SUMMED ACROSS THE BASIN FROM THE DATE LINE TO 100W HAS REBOUNDED FROM THE DECREASE OBSERVED LAST MONTH AND IS NOW POSITIVE. IN THE ATMOSPHERE OVER THE PAST MONTH, LOWER TROPOSPHERIC ZONAL WIND ANOMALIES WERE WEAK. OVER THE SAME PERIOD, MEASUREMENTS OF TROPICAL CONVECTION INDICATED THE DEVELOPMENT OF ENHANCED CONVECTION JUST SOUTH OF THE EQUATOR WITH WEAKLY ENHANCED CONVECTION CONTINUING OVER THE MARITIME CONTINENT. THIS COMBINATION OF THE ATMOSPHERIC AND OCEANIC EVOLUTION SUGGESTS A SHIFT FURTHER AWAY FROM THE REMNANT LA NINA BASE STATE. PROGNOSTIC DISCUSSION OF SST FORECASTS THE CPC NINO 3.4 SST INDEX CONSOLIDATION FORECAST, WHICH INCLUDES CANONICAL CORRELATION ANALYSIS (CCA), CONSTRUCTED ANALOG (CA), AND MARKOV STATISTICAL FORECASTS, ALONG WITH THE CFS DYNAMICAL MODEL, PREDICTS A MEDIAN TEMPERATURE ANOMALY OF BETWEEN +0.4C AND +0.5C FOR THE COMING SEASONS FROM APPROXIMATELY JJA THROUGH NDJ 2017, WITH EL NINO AS MOST LIKELY FROM LATE SUMMER THROUGH AUTUMN. THE CFS HAS BACKED OFF ITS EL NINO FORECAST IN A FAIRLY DRAMATIC FASHION OVER THE PAST MONTH, WHILE THE CA STATISTICAL FORECAST HAS BECOME THE WARMEST CONSTITUENT MEMBER OF THE CONSOLIDATION FORECAST. THE LATEST FORECASTS FROM THE DYNAMICAL SUITE OF MODELS FROM THE NMME CONTINUE TO FAVOR EL NINO DEVELOPMENT, THOUGH NOT AS STRONGLY AS LAST MONTH. THE LATEST OFFICIAL ENSO OUTLOOK FROM CPC/IRI PLACES THE ODDS OF EL NINO AND ENSO NEUTRAL AT ROUGHLY 45% FROM JJA THROUGH DJF. THE CONSENSUS FORECAST INDICATES THE LIKELIHOOD OF A REPEAT LA NINA EVENT TO BE SMALL DURING THIS FORECAST PERIOD. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS THE PRIMARY TOOLS USED FOR THIS SET OF SEASONAL OUTLOOKS INCLUDED BOTH STATISTICAL AND DYNAMICAL MODEL FORECAST GUIDANCE, AND IN PARTICULAR AT LONGER LEADS, DECADAL TEMPERATURE AND PRECIPITATION TRENDS. THE CALIBRATED DYNAMICAL MODEL GUIDANCE FROM THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND, TO LESSER EXTENT, ITS INDIVIDUAL MODELS, INCLUDING THE NCEP CFS, WERE IMPORTANT CONTRIBUTORS TO THE OUTLOOKS THROUGH OND 2017. ANTECEDENT SOIL MOISTURE AND SNOWPACK ANOMALIES IN CERTAIN REGIONS ALSO IMPACTED THE OUTLOOKS AT EARLY LEADS. WHILE THE ENSO FORECAST REMAINS HIGHLY UNCERTAIN, THE SLIGHT TILT TOWARD EL NINO WAS CONSIDERED IN THE TEMPERATURE AND PRECIPITATION FROM SON THROUGH FMA. PROGNOSTIC DISCUSSION OF OUTLOOKS - JJA 2017 TO JJA 2018 TEMPERATURE THE LATEST JJA AND JAS 2017 TEMPERATURE OUTLOOKS INDICATE ABOVE-NORMAL TEMPERATURES ARE MOST LIKELY FOR MUCH OF THE FORECAST DOMAIN, WITH THE EXCEPTION OF PARTS ROCKIES AND PLAINS. THE CHANCES OF ABOVE-NORMAL SEASONAL MEAN TEMPERATURES ARE SLIGHTLY ENHANCED FOR MUCH OF THE PACIFIC NORTHWEST, BUT THE PROBABILITY OF ABOVE-NORMAL TEMPERATURES IS MODERATED BY RECENT POSITIVE SNOW AND SOIL MOISTURE ANOMALIES. ABOVE-NORMAL TEMPERATURES ARE PARTICULARLY ENHANCED FOR A REGION STRETCHING FROM THE SOUTHWEST, EASTWARD ACROSS THE FAR SOUTHERN TIER OF THE CONUS INTO THE EASTERN U.S. THE GREATEST PROBABILITIES EXCEED 50% FOR PARTS OF THE SOUTHWEST AND ALONG THE GULF AND ATLANTIC COASTS, FOLLOWING THE CALIBRATED PROBABILISTIC GUIDANCE FROM THE NMME. NEGATIVE SOIL MOISTURE ANOMALIES IN THE SOUTHEAST REGION ALSO CONTRIBUTE TO THE LIKELIHOOD OF ANOMALOUS WARMTH. DECADAL CLIMATE TRENDS ALSO SUPPORT THE OUTLOOK AND ARE A COMPONENT OF THE DYNAMICAL MODEL GUIDANCE. THESE FORECAST TOOLS ALSO SUPPORT ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES FOR ALASKA. POSITIVE SOIL MOISTURE ANOMALIES, COMBINED WITH PROBABILITIES FAVORING ABOVE-MEDIAN PRECIPITATION, SUPPORT SOME EXPANION OF THE RELATIVE TEMPERATURE WEAKNESS OVER PARTS OF THE ROCKIES AND PLAINS STATES FOR JJA AND JAS. ADDITIONALLY, ANTECEDENT TROPICAL AND EXTRATROPICAL SST BOUNDARY CONDITIONS MAY INDICATE SOME COMPONENT OF INTERANNUAL VARIABILITY THAT COULD DESTRUCTIVELY INTERFERE WITH LONGER TERM WARMING TRENDS OVER PARTS OF THE CENTRAL AND EASTERN CONUS. WHILE THE FORECAST STILL BROADLY FAVORS ABOVE-NORMAL TEMPERATURES, THE PROBABILITIES ARE NOT EXCEPTIONAL, AND INDEED THE NMME FORECAST AND THE OFFICIAL FORECAST SUGGEST A SLIGHTLY COOLER FORECAST FOR THE CONUS AS A WHOLE THAN THAT ISSUED FOR LAST SUMMER FOR JJA AND JAS. SUBTLE CHANGES WERE MADE TO LATER LEADS, FROM ASO TO FMA, BASED ON THE LATEST MODEL GUIDANCE AND STATISTICAL FORECASTS THAT EMPHASIZE A SLIGHT TILT TOWARD EL NINO IMPACTS. GENERALLY THIS IS SEEN AS A SLIGHT INCREASE IN PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURE ACROSS THE NORTHERN TIER OF THE CONUS, AND A REDUCTION OF THE SAME ACROSS THE FAR SOUTHERN TIER. HIGH PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE INDICATED FOR THE NORTH SLOPE OF ALASKA DURING SON AND OND 2017 DUE TO DECADAL TRENDS IN THE SEASONAL CYCLE OF SEA ICE. PRECIPITATION FOR PRECIPITATION, THE JJA AND JAS 2017 OUTLOOKS INDICATE ABOVE-MEDIAN PRECIPITATION FOR AREAS OF THE ROCKY MOUNTAINS AND TO THE EAST, INCLUDING PARTS OF THE CENTRAL AND NORTHERN PLAINS. IN THE CASE OF JJA, A SLIGHT ENHANCEMENT OF PROBABILITIES FAVORING ABOVE-MEDIAN TEMPERATURES EXTENDS SOUTHWARD THROUGH TEXAS. FROM ASO THROUGH OND 2017, INCREASING CHANCES FOR EL NINO CONDITIONS AND DYNAMICAL MODEL FORECASTS OF GREATER THAN AVERAGE SSTS IN THE EASTERN TROPICAL PACIFIC LEAD TO A SOUTHWARD SHIFT OF THIS REGION OF LIKELY ABOVE-MEDIAN PRECIPITATION INTO THE SOUTHWEST CONUS, EXTENDING ACROSS THE FAR SOUTHERN TIER OF THE CONUS WITH STILL MODEST PROBABILITIES. FOR LATE AUTUMN AND WINTER, FROM NDJ 2017-2018 THROUGH JFM 2018, THE LOW PROBABILITY OF A LA NINA AND ELEVATED CHANCES FOR A POSSIBLE EL NINO NOW RESULT IN THE INTRODUCTION OF PROBABILITIES ASSOCIATED WITH A CANONICAL EL NINO, ALBEIT AT VERY LOW AMPLITUDE AND COVERAGE DUE TO THE HIGH UNCERTAINTY. FOLLOWING JFM 2018, WEAK SIGNALS DUE TO DECADAL TRENDS IN PRECIPITATION ARE INDICATED, INCLUDING BELOW-MEDIAN PRECIPITATION FOR PARTS OF THE SOUTHWEST BEGINNING WITH THE MAM 2018 SEASON AND ABOVE-MEDIAN PRECIPITATION IN THE NORTHERN-CENTRAL CONTIGUOUS U.S. BEGINNING WITH MAM 2018. OVER ALASKA, CALIBRATED DYNAMICAL GUIDANCE FAVORS A SHIFT TOWARD ABOVE-MEDIAN PRECIPITATION FOR PARTS OF THE MAINLAND DURING THE EARLY LEADS. DURING SON, MODEST PROBABILITIES FAVORING ABOVE-MEDIAN PRECIPITATION ARE INTRODUCED OVER SOUTHERN ALASKA TO ACCOUNT FOR THE TILT TOWARD EL NINO; THAT SIGNAL CONTINUES IN THE FORECASTS THROUGH JFM 2018. FORECASTER: STEPHEN BAXTER THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING THE WORLD METEROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3 COMPLETE DECADES AS THE CLIMATIC 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. FOR A DESCRIPTION OF OF THE STANDARD FORECAST TOOLS - THEIR SKILL- AND THE FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/LONG_RANGE/TOOLS.HTML (USE LOWER CASE LETTERS) INFORMATION ON THE FORMATION OF SKILL OF THE CAS FORECASTS MAY BE FOUND AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/SOILMST_MONITORING/US/OUTLOOK/OUTLOOK.SHTM L (USE LOWERCASE LETTERS) NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR VALID PERIOD. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM RANGE FORECASTS SHOULD BE CONSULTED. THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT MONTH ON JUN 15 2017 1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011 FORECAST RELEASE. $$