PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 
300PM EDT SUNDAY MAR 31 2013 
 
30-DAY OUTLOOK DISCUSSION FOR APRIL 2013 
 
THE ZERO LEAD UPDATE FOR APRIL 2013 TURNED OUT TO BE NEAR IMPOSSIBLE FOR 
SEVERAL REASONS. FIRST THE PATTERN OBSERVED IN MARCH, WHICH IS QUITE THE 
OPPOSITE OF THE LONG LEAD APRIL FORECAST MADE IN MID MARCH, HAS PERSISTED UNTIL 
TODAY AND IS FORECAST TO PERSIST FOR ANOTHER WEEK ROUGHLY. FOR EXAMPLE, TO 
FOCUS ON ONE AREA TO EXPLAIN THE DIFFICULTY, THE MID-ATLANTIC HAS BEEN COLD IN 
MARCH AND WILL BE COLD IN THE 1ST WEEK OF APRIL, WHILE THE LONG LEAD CLIMATE 
SIGNALS FOR APRIL ARE CONFIDENTLY WARM. SECOND THE CFS, OUR BEST TOOL FOR THE 
MONTHLY UPDATE AT ZERO LEAD BECAUSE IT UPDATES EVERY DAY AND COMBINES NWP 
INFORMATION WITH CLIMATE SIGNALS, PREDICTED A COLD MID ATLANTIC FOR WEEK 2-4 
DAY AFTER DAY UNTIL ABOUT 2 DAYS AGO. IT IS ONLY SINCE THE 29TH OF MARCH THAT 
WEEK 2 HAS GONE WARMER IN THE MID ATLANTIC IN THE CFS, AND ONLY SINCE TODAY 
THAT WEEK 3 AND 4 WILL BE WARM. WE ARE THUS ACTING ON THE VERY LATEST, A 16 
MEMBER ENSEMBLE OF CFS FORECASTS. 
 
CHANGES FROM THE LONG LEAD FORECAST RELEASED IN MID-MARCH ARE LARGE, ESPECIALLY 
FOR PRECIPITATION WHERE WE MADE 2 CLASS CHANGES, WHICH IS NORMALLY NOT 
RECOMMENDED FOR WHAT IS SUPPOSED TO BE AN ADJUSTMENT. 
 
THE APRIL 2013 ZERO LEAD TEMPERATURE OUTLOOK INDICATES ENHANCED PROBABILITIES 
FOR ABOVE NORMAL TEMPERATURES ACROSS THE SOUTH FROM ARIZONA TO THE GULF AND 
ATLANTIC COASTS AS WELL AS IN THE MID-ATLANTIC, THE GREAT LAKES AND NEW 
ENGLAND. KEEP IN MIND THAT IN MANY OF THESE AREAS THE START OF THE MONTH 
DIFFERS FROM THE FORECAST FOR THE MONTHLY MEAN. INDICATIONS FOR ENHANCED 
PROBABILITIES FOR BELOW NORMAL TEMPERATURES EXIST ONLY IN EASTERN NORTH DAKOTA 
PLUS PORTIONS OF ADJACENT STATES, AS WELL AS IN MUCH OF ALASKA. 
 
THE APRIL 2013 ZERO LEAD PRECIPITATION OUTLOOK CALLS FOR AN ENHANCED LIKELIHOOD 
OF ABOVE-MEDIAN PRECIPITATION ALONG THE GULF COAST FROM TEXAS TO NORTH FLORIDA 
AND THE GEORGIA ATLANTIC COAST. THIS IS ENTIRELY FROM A PRECIPITATION EVENT 
SETTING UP IN THAT AREA ACCORDING TO NWP IN THE FIRST DAYS OF APRIL. ENHANCED 
CHANCES OF BELOW-MEDIAN PRECIPITATION HAVE ALL BEEN REMOVED BECAUSE OF 
CONTRADICTIONS IN THE TOOLS AT HAND AT ZERO LEAD. 
 
AREAS WHERE THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURE AND MONTHLY ACCUMULATED 
PRECIPITATION AMOUNTS ARE SIMILAR TO CLIMATOLOGICAL PROBABILITIES OF BELOW, 
NEAR AND ABOVE AVERAGE TEMPERATURE OR PRECIPITATION ARE SHOWN AS EQUAL CHANCES 
(EC). 
 
OLD TEXT: CONSIDERATIONS AT LONG LEAD: 
 
ACROSS THE EQUATORIAL PACIFIC, SST ANOMALIES REMAIN SLIGHTLY BELOW NORMAL. WITH 
THE LATEST WEEKLY NINO 3.4 ANOMALY NOT REACHING -0.5 C ENSO IS NOT MUCH OF A 
CONSIDERATION IN THE OUTLOOK. THE MJO REMAINS ACTIVE DURING MARCH BUT IS WEAKER 
NOW THAN IN FEBRUARY. 
 
THERE IS SURPRISINGLY HIGH AGREEMENT AMONG LONG LEAD FORECAST TOOLS. THE 
SPATIAL PATTERNS OF THE NMME, IMME AND LONG TERM TRENDS AS EXPRESSED BY OCN ARE 
SURPRISINGLY SIMILAR OVER CONUS FOR APRIL 2013. THE TRADITIONAL TOOLS DO LEND 
SUPPORT, BUT COVER SMALLER AREAS. IN ALL, WE HAVE HIGH COVERAGE, BUT ONLY 
MODEST PROBABILITIES. CONFIDENCE IS SUPPRESSED BECAUSE WE NEED A LARGE CHANGE 
IN THE CURRENT CIRCULATION PATTERN FOR THIS FORECAST TO VERIFY.  FOR INSTANCE 
MARCH 2013 HAS BEEN COLDER THAN NORMAL FROM THE DAKOTAS INTO THE SOUTHEAST, AND 
THIS PATTERN APPEARS TO STAY IN PLACE UNTIL THE END OF MARCH, AT LEAST. THE 
PREDICTION OF ELEVATED CHANCES FOR ABOVE AVERAGE IN APRIL FOR MUCH OF THE 
COUNTRY (EXCEPT THE NORTH WEST) MAY BE AT ODDS WITH EARLY APRIL OBSERVATIONS. 
THE OUTLOOK WILL BE UPDATED MARCH, 31. 
 
 
 
AREAS WHERE THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURE AND MONTHLY ACCUMULATED 
PRECIPITATION AMOUNTS ARE SIMILAR TO CLIMATOLOGICAL PROBABILITIES OF BELOW, 
NEAR AND ABOVE AVERAGE TEMPERATURE OR PRECIPITATION ARE SHOWN AS EQUAL CHANCES 
(EC). 
 
THE MAIN FACTORS WHICH 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) PERSISTANTLY 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 (CFS) 
AND FOR ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM 
(GEFS). THE EARLIER VERSION OF THE CFS MODEL WAS DISCONTINUED AS OF OCTOBER, 
2012. AN EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL MULTI-MODEL ENSEMBLE 
(NMME), COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED. 
 
 
FORECASTER: HUUG VAN DEN DOOL 
 
 
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 MAY ... WILL BE ISSUED ON THU APR 18 2013 
 
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. 
 
$$