Prognostic Meteorological Discussion
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000 FXUS07 KWBC 261231 PMD30D PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 830AM EDT THURSDAY MAR 19 2015 30-DAY OUTLOOK DISCUSSION FOR APRIL 2015 EQUATORIAL SEA-SURFACE TEMPERATURE (SST) ANOMALIES REMAIN ABOVE-NORMAL ACROSS MUCH OF THE WESTERN AND CENTRAL EQUATORIAL PACIFIC AND THE OCEAN HAS BEGUN TO SHOW BETTER COUPLING WITH THE ATMOSPHERE OVER THE LAST 1-2 MONTHS. CONSEQUENTLY, AN EL NINO ADVISORY WAS ISSUED EARLIER THIS MONTH. THE LATEST NINO 3.4 INDEX IS +0.5 C, WHILE THE NINO 4 INDEX IS +1.0 C. A STRONG MJO IS ALSO EVIDENT WITH THE ENHANCED CONVECTIVE PHASE LOCATED ACROSS THE WESTERN HEMISPHERE AND MOVING EASTWARD. BOTH OF THESE FACTORS PLAY A ROLE TO SOME DEGREE IN THE APRIL MONTHLY OUTLOOK, ALTHOUGH TELECONNECTIONS AND IMPACTS FROM THESE MODES OF CLIMATE VARIABILITY BEGIN TO RAPIDLY DECREASE DURING THE MONTH OF APRIL. ANOMALOUS SNOW COVER AND SOIL MOISTURE ALSO PLAYED A ROLE IN THE FORECAST FOR APRIL IN SEVERAL AREAS OF THE UNITED STATES. THE APRIL TEMPERATURE OUTLOOK SHOWS AN ENHANCED LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES FOR THE FAR WEST AND ALL OF ALASKA, WITH THE HIGHEST PROBABILITIES LOCATED ALONG THE COAST OF THE PACIFIC NORTHWEST AND THE SOUTHERN AREAS OF ALASKA. CONSIDERATIONS OF BELOW AVERAGE SNOW COVER, ONGOING DROUGHT CONDITIONS AND DYNAMICAL MODEL GUIDANCE ALL SUPPORT VARIOUS REGIONS OF THIS FORECAST AREA. BELOW AVERAGE TEMPERATURES ARE FAVORED IN TWO AREAS WITHIN THE CONUS, AN AREA CENTERED ACROSS WESTERN TEXAS AND ANOTHER SPANNING THE EASTERN GREAT LAKES, NORTHEAST AND NORTHERN MID-ATLANTIC. THE REGION NEAR TEXAS IS SUPPORTED BY EL NINO CONSIDERATIONS IN WHICH COMPOSITES AND REGRESSIONS INDICATE A BELOW NORMAL SIGNAL IN THAT REGION. PROBABILISTIC NMME AND IMME DYNAMICAL MODEL GUIDANCE AND TO SOME DEGREE MJO COMPOSITES FOR RMM PHASES 2 AND 3 ALSO SUPPORT THIS REGION. DYNAMICAL MODEL GUIDANCE CONTINUES TO INDICATE A MEAN TROUGH ACROSS EASTERN NORTH AMERICA AS HAS BEEN OBSERVED THROUGHOUT MUCH OF FEBRUARY AND MARCH. THE CFS, PROBABILISTIC NMME AND IMME GUIDANCE FAVOR ELEVATED ODDS FOR BELOW NORMAL TEMPERATURES IN THIS AREA. POSITIVE SNOW COVER AND DEPTH ANOMALIES IN SOME OF THESE AREAS ALSO FAVORS BELOW NORMAL TEMPERATURES AS DO MJO COMPOSITES FOR FORECAST MJO EVOLUTION FOR THE REMAINDER OF MARCH INTO EARLY APRIL. THE APRIL PRECIPITATION OUTLOOK DEPICTS ELEVATED PROBABILITIES FOR ABOVE MEDIAN PRECIPITATION ACROSS THE SOUTHWEST, SOUTHERN AND CENTRAL ROCKIES AND FROM SOUTHERN TEXAS TO THE SOUTHEAST CONUS. DYNAMICAL MODEL GUIDANCE FROM THE CFS, PROBABILISTIC NMME AND IMME ARE IN GOOD AGREEMENT ACROSS THE SOUTHWEST FOR ANOMALOUS WETNESS WHILE EL NINO CONDITIONS, THE MJO (EARLY IN THE MONTH), AND DYNAMICAL MODEL GUIDANCE SUPPORT THE FORECAST IN THE SOUTHEAST. THE FAVORED UPPER-AIR HEIGHT PATTERN AT THE CURRENT TIME ESPECIALLY DURING THE FIRST HALF OF THE MONTH IS FOR RIDGING (TROUGHING) ACROSS WESTERN (EASTERN) NORTH AMERICA WHICH SUPPORTS ELEVATED ODDS FOR BELOW MEDIAN PRECIPITATION FOR PARTS OF THE NORTHERN PLAINS AND WESTERN GREAT LAKES. BELOW MEDIAN PRECIPITATION IS ALSO FAVORED BY DYNAMICAL MODEL GUIDANCE FOR THE FAR PACIFIC NORTHWEST. 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: JON GOTTSCHALCK 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 APR WILL BE ISSUED ON TUE MARCH 31 2015 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$

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