PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300PM EDT SUNDAY MAY 31 2015 30-DAY OUTLOOK DISCUSSION FOR JUNE 2015 THE OUTLOOK FOR JUNE 2015 IS UPDATED UTILIZING THE LATEST MODEL GUIDANCE FROM THE COUPLED CFS AND ECMWF ENSEMBLE SYSTEMS, WHICH COVERS NEARLY THE ENTIRE MONTH. OF COURSE, MUCH OF THE SKILL FROM THESE SYSTEMS IS OBTAINED FROM THE VERY HIGH FORECAST SKILL AFFORDED FROM THE FIRST TWO WEEKS OF THE PERIOD, INCLUDING EVENTS ON PURELY WEATHER TIMESCALES. RELATIVELY LITTLE CHANGE IS REQUIRED TO THE TEMPERATURE OUTLOOK, WITH PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES EXTENDED ACROSS THE NORTHERN TIER OF THE CONUS AND THE NORTHEAST. THIS IS LARGELY DUE TO ABOVE-NORMAL TEMPERATURES IN THE 3-10 DAY PERIOD. BEYOND THAT, THE SIGNAL IS ACTUALLY NEARER NORMAL, AND POTENTIALLY BELOW-NORMAL BY THE END OF THE MONTH. ALTOGETHER, THE OBJECTIVE GUIDANCE FAVORS A SLIGHT TILT TOWARD WARMER-THAN-NORMAL TEMPERATURES FOR THE MONTH. THE REGION FAVORING BELOW-NORMAL TEMPERATURES OVER THE SOUTH-CENTRAL CONUS HAS BEEN TWEAKED SLIGHTLY TO ACCOUNT FOR THE LATEST GUIDANCE, AS HAVE PROBABILITIES OVER ALASKA. SLIGHTLY MORE CHANGES WERE REQUIRED IN THE PRECIPITATION OUTLOOK. DUE TO HEAVY RAIN FORECAST EARLY IN THE PERIOD, ABOVE-MEDIAN PRECIPITATION IS NOW FAVORED OVER THE EASTERN CONUS. OVER THE CENTRAL PLAINS, THE REGION FAVORING ABOVE-MEDIAN RAINFALL WAS ADJUSTED TO ACCOUNT FOR THE LATEST GUIDANCE. PARTS OF TEXAS AND OKLAHOMA ARE NOW LESS LIKELY TO SEE ABOVE-MEDIAN PRECIPITATION IN JUNE, WHICH IS WELCOME NEWS GIVEN THE RECENT FLOODING IN THAT REGION. TWO REGIONS FAVORING BELOW-MEDIAN RAINFALL WERE ADDED OVER PARTS OF THE PACIFIC NORTHWEST AND GREAT LAKES REGIONS, RESPECTIVELY. THE LATTER IS LARGELY DUE TO A TENDENCY FOR DRY CONDITIONS OVER THE NEXT WEEK OR SO, WHILE THE FORMER IS DUE TO A FORECAST TENDENCY TOWARD BELOW-MEDIAN PRECIPITATION BEYOND THE FIRST WEEK OF THE MONTH. THE PREVIOUS DISCUSSION, ISSUED MAY 21, FOLLOWS BELOW, AND DISCUSSES SOME OF THE LARGE-SCALE CLIMATE SIGNALS AT WORK. ============================================================================ EQUATORIAL SEA-SURFACE TEMPERATURE (SST) ANOMALIES REMAINED ABOVE NORMAL FOR MUCH OF THE EQUATORIAL PACIFIC, AND ALONG THE WEST COAST OF MUCH OF NORTH AMERICA. COUPLING BETWEEN THE ATMOSPHERE AND OCEAN OVER THE TROPICAL PACIFIC REMAINS STRONG, WITH ENHANCED CONVECTION AND ANOMALOUS LOW-LEVEL WESTERLIES OBSERVED OVER THE PAST SEVERAL WEEKS NEAR THE DATE LINE. DYNAMICAL MODEL GUIDANCE IS GENERALLY IN GOOD AGREEMENT ON BOTH THE TEMPERATURE AND PRECIPITATION FORECASTS FOR JUNE. A PLETHORA OF DYNAMICAL GUIDANCE WAS CONSULTED, INCLUDING DETERMINISTIC AND PROBABILISTIC GUIDANCE FROM THE WMO GLOBAL PRODUCING CENTERS, WHICH INCLUDES MODELS FROM THE ECMWF AND UKMET, AMONG OTHERS. GIVEN THE LATE TIME AT WHICH THIS FORECAST WAS ISSUED, THE MAPS WERE SLIGHTLY TWEAKED TO REFLECT THE LATEST GUIDANCE ON WEEKS 3 AND 4 FROM THE ECMWF AND CFS COUPLED SYSTEMS. THE STATISTICAL GUIDANCE CONSULTED INCLUDED THE FOLLOWING: CONSTRUCTED ANALOG BASED ON SOIL MOISTURE, COMPOSITE ANALOG BASED ON TROPICAL AND MIDLATITUDE SSTS NEAR NORTH AMERICA, AND SEASONAL CORRELATIONS BETWEEN ENSO AND SURFACE PARAMETERS FOR JJA. THESE TOOLS GENERALLY AGREED WITH THE LARGEST SIGNALS FROM THE DYNAMICAL MODELS, HOWEVER, THEY INTRODUCED UNCERTAINTY OVER THE NORTHEAST, WHERE THE NMME SUITE FAVORED ABOVE-NORMAL TEMPERATURES, AS WELL AS OVER THE SOUTHWEST, WHERE THE DYNAMICAL MODELS MAY HAVE BEEN A BIT WARM. IT MAY INTEREST THE USER THAT THE FORECAST IS ALSO CONSISTENT WITH 2-MONTH LAGGED CORRELATIONS BETWEEN THE PDO AND AMO INDICES. THAT INFORMATION IS PARTLY CONTAINED WITHIN THE AFOREMENTIONED COMPOSITE ANALOG BASED ON SST. THE LARGEST SIGNAL FOR BELOW-NORMAL TEMPERATURES IS CENTERED OVER NORTH TEXAS/OKLAHOMA, WHERE SOIL MOISTURE CURRENTLY EXCEEDS THE 90TH PERCENTILE AND ALL GUIDANCE IS IN AGREEMENT. LIKEWISE, THE TOOLS ARE IN GOOD AGREEMENT OVER THE PACIFIC NORTHWEST AND SOUTHERN ALASKA, WHERE THE BEST CHANCES OF ABOVE-NORMAL TEMPERATURES RESIDE. UNCERTAINTY IS LARGEST NEAR THE EAST COAST AND GREAT LAKES, WHERE EVERYTHING WAS SUBJECTIVELY COMBINED TO YIELD THE MAP AS IT STANDS. THE ONLY SUBSTANTIAL SIGNALS FOR PRECIPITATION COME FROM UNANIMOUS DYNAMICAL AGREEMENT FAVORING ABOVE-MEDIAN RAINFALL OVER PARTS OF THE WEST-CENTRAL CONUS, EXTENDING TOWARD THE SOUTHEAST. STATISTICAL GUIDANCE IS REASONABLY ON BOARD WITH THIS, THOUGH PROBABILITIES ARE GENERALLY LOW TO REFLECT HISTORICALLY POOR FORECAST SKILL IN THE 0.5 MONTH LEAD PRECIPITATION OUTLOOK. IN AREAS WHERE THERE ARE NO STATISTICALLY SIGNIFICANT CLIMATE SIGNALS, SUCH THAT THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES OR MONTHLY ACCUMULATED PRECIPITATION AMOUNTS ARE EQUAL 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: STEPHEN BAXTER 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 JUL ... WILL BE ISSUED ON THU JUN 18 2015 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$