PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EDT THURSDAY JUN 20 2013

30-DAY OUTLOOK DISCUSSION FOR JULY 2013

ATMOSPHERIC AND OCEANIC CONDITIONS OVER THE TROPICAL PACIFIC INDICATE 
PERSISTENT ENSO-NEUTRAL CONDITIONS. EQUATORIAL SEA SURFACE TEMPERATURES (SSTS) 
REMAIN NEAR LONG-TERM CLIMATOLOGICAL NORMALS WEST OF 130 W LONGITUDE AND BELOW 
NORMAL OVER THE EASTERN PACIFIC FROM 130 W TO THE SOUTH AMERICAN COAST. AVERAGE 
SUBSURFACE OCEAN TEMPERATURES TO A DEPTH OF 300 METERS IN THE EQUATORIAL 
PACIFIC HAVE WARMED SLIGHTLY IN THE LAST MONTH AND ARE NOW SLIGHTLY ABOVE 
NORMAL. THERE IS A LARGE VOLUME OF WARMER THAN NORMAL WATER BELOW 50 METERS IN 
MUCH OF THE EQUATORIAL PACIFIC TO THE WEST OF 100 W LONGITUDE, AND A REGION OF 
COOLER THAN NORMAL WATER NEAR THE SURFACE TO THE EAST OF 120W. DURING THE LAST 
MONTH TROPICAL CONVECTION WAS ENHANCED IN THE REGION AROUND THE MARITIME 
CONTINENT AND SUPPRESSED OVER THE CENTRAL AND EASTERN EQUATORIAL PACIFIC. THE 
ENHANCED CONVECTIVE PHASE OF THE MADDEN-JULIAN OSCILLATION (MJO) HAS BEEN 
RECENTLY ACTIVE OVER THE MARITIME CONTINENT. MODEL FORECASTS FROM MOST 
AVAILABLE ENSEMBLE AND HIGH-RESOLUTION OPERATIONAL MODELS INDICATE PROGRESSION 
OF MJO CONVECTION EASTWARD ACROSS THE PACIFIC OCEAN AND INTO THE WESTERN 
HEMISPHERE DURING THE NEXT COUPLE WEEKS.

THE JULY 2013 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE GENERATED USING THE 
LATEST MODEL GUIDANCE FROM THE NCEP CLIMATE FORECAST SYSTEM (CFS) AND OTHER 
MODELS USED IN THE NATIONAL MULTI-MODEL ENSEMBLE (NMME). STATISTICAL TOOLS WERE 
USED TO DETERMINE THE IMPACT OF LONG-TERM CLIMATE TRENDS AND OTHER CLIMATE 
SIGNALS ON JULY TEMPERATURES AND PRECIPITATION AMOUNTS. THIS MONTH THE RELEASE 
OF THE MONTHLY OUTLOOKS ARE NEAR ENOUGH TO THE BEGINNING OF THE TARGET MONTH 
THAT MODELS THAT EXTEND OUT TO ONLY 15 DAYS CAN BE CONSIDERED, SUCH AS 
FORECASTS FROM THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS) CALIBRATED USING 
MULTI-DECADAL REFORECASTS GENERATED BY THE NOAA EARTH SYSTEM RESEARCH 
LABORATORY (ESRL) AND FROM THE NORTH AMERICAN ENSEMBLE FORECAST SYSTEM (NAEFS), 
A MULTI-MODEL ENSEMBLE THAT COMBINES THE NCEP GEFS AND THE ENVIRONMENT CANADA 
ENSEMBLE PREDICTION SYSTEM.

THE TEMPERATURE OUTLOOK FOR JULY 2013 INDICATES ENHANCED PROBABILITIES FOR 
ABOVE NORMAL MEAN TEMPERATURES FOR MOST OF THE WESTERN U.S. AND FOR THE CENTRAL 
AND SOUTHERN PLAINS, FOR NEW ENGLAND, AND FOR NORTHERN ALASKA. THESE FORECASTS 
ARE LARGELY SUPPORTED BY RECENT DYNAMICAL MODEL GUIDANCE FROM THE NMME, AND 
CONSISTENT WITH DECADAL CLIMATE TRENDS AS WELL. THE ABOVE NORMAL FORECAST FOR 
NORTHERN ALASKA ARE SUPPORTED PRIMARILY BY CLIMATE TRENDS RELATED TO THE LOSS 
OF SEA ICE DURING RECENT DECADES. THE POTENTIAL FOR AN ACTIVE NORTH AMERICAN 
MONSOON MODERATES PROBABILITIES OF ABOVE NORMAL TEMPERATURES IN THE SOUTHWEST.

THE PRECIPITATION OUTLOOK FOR JULY 2013 INDICATES INCREASED PROBABILITIES OF 
ABOVE MEDIAN PRECIPITATION OVER THE SOUTHWEST WITH MODEL GUIDANCE, SUCH AS THE 
REFORECAST CALIBRATED GEFS, INDICATING AN ACTIVE MONSOON EARLY IN THE MONTH. 
THE ENHANCED CONVECTIVE PHASE OF THE MJO NOW OVER THE MARITIME CONTINENT IS 
FORECAST TO PERSIST AND PROGRESS ACROSS THE PACIFIC AS JULY BEGINS. IMPACTS DUE 
TO AN ACTIVE MJO CONVECTIVE PHASE OVER THE WESTERN HEMISPHERE INCLUDE GREATER 
CHANCES FOR ABOVE MEDIAN PRECIPITATION IN THE SOUTHWEST WITH THE POTENTIAL FOR 
MOISTURE SURGES FROM THE EASTERN PACIFIC. THE JULY OUTLOOK CALLS FOR INCREASED 
PROBABILITIES OF BELOW MEDIAN PRECIPITATION TO THE EAST OF THE MONSOON REGION 
OVER WESTERN TEXAS AND ENHANCED PROBABILITIES OF ABOVE MEDIAN PRECIPITATION 
OVER MUCH OF THE SOUTHEAST WITH SUPPORT FROM MODEL GUIDANCE. AN INDICATION OF 
GREATER CHANCES OF BELOW MEDIAN PRECIPITATION FOR PARTS OF THE PACIFIC 
NORTHWEST ARE RELATED TO DECADAL TRENDS FOR BELOW AVERAGE PRECIPITATION OVER 
THE REGION DURING SUMMER MONTHS.

IN AREAS WHERE THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES AND MONTHLY 
ACCUMULATED PRECIPITATION AMOUNTS ARE SIMILAR TO CLIMATOLOGICAL PROBABILITIES, 
EQUAL CHANCES (EC) IS SHOWN.

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 15-YEAR MEAN OF TEMPERATURE OR 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 (CFS) 
AND FOR THE 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: DAN COLLINS


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 JUL WILL BE ISSUED ON SUN JUNE 30 2013


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.

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