PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300PM EDT FRIDAY JUL 31 2015

30-DAY OUTLOOK DISCUSSION FOR AUGUST 2015

SEA SURFACE TEMPERATURES (SSTS) CONTINUE TO BE MORE THAN ONE DEGREE C ABOVE 
NORMAL ALONG THE EQUATOR IN THE PACIFIC OCEAN FROM THE INTERNATIONAL DATE LINE 
EASTWARD TO THE SOUTH AMERICAN COAST. SST ANOMALIES ARE GREATER THAN +2.0 
DEGREES C IN THE EAST PACIFIC FROM ABOUT 135 W LONGITUDE TO THE SOUTH AMERICAN 
COAST AND EXCEED +3.0 C EASTWARD OF 100 W LONGITUDE. THERE CONTINUES TO BE A 
LARGE AREA OF POSITIVE SST ANOMALIES OVER MUCH OF THE NORTH PACIFIC ALONG THE 
WEST COAST OF NORTH AMERICA. SUBSURFACE OCEAN TEMPERATURES NEAR THE EQUATOR 
HAVE BEEN PERSISTENTLY ABOVE NORMAL TO DEPTHS EXCEEDING 100 METERS EAST OF THE 
INTERNATIONAL DATE LINE, CONTRIBUTING TO SUSTAINED POSITIVE SST ANOMALIES. 
NEGATIVE OLR ANOMALIES ABOVE THE EASTERN PACIFIC TO THE NORTH OF THE EQUATOR 
INDICATE ANOMALOUSLY ACTIVE CONVECTION. ANOMALOUS LOW-LEVEL (850-HPA) WESTERLY 
WINDS EXTENDED FROM THE WEST PACIFIC TO THE EAST-CENTRAL EQUATORIAL PACIFIC. 
ANOMALOUS UPPER-LEVEL (200-HPA) EASTERLIES WERE OBSERVED OVER THE EAST-CENTRAL 
EQUATORIAL PACIFIC. THESE ATMOSPHERIC AND OCEANIC CONDITIONS INDICATE STRONG 
OCEAN-ATMOSPHERE COUPLING ASSOCIATED WITH EL NINO CONDITIONS. 

THE MONTHLY UPDATE TO THE AUGUST 2015 U.S. CLIMATE OUTLOOK IS BASED LARGELY ON 
DYNAMICAL MODEL FORECASTS, INCLUDING WEATHER PREDICTION MODELS FOR THE FIRST 
WEEK IN THE MONTH, AS WELL AS THE NORTH AMERICAN ENSEMBLE FORECAST SYSTEM 
(NAEFS) AND THE REFORECAST-CALIBRATED GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS) 
FOR THE SECOND WEEK, THE ECMWF ENSEMBLE PREDICTION SYSTEM FORECASTS FOR THE 
THIRD AND FOURTH WEEK, AND THE NCEP CLIMATE FORECAST SYSTEM (CFS) FOR THE FULL 
MONTH.

THE UPDATE TO THE AUGUST TEMPERATURE OUTLOOK INDICATES ONLY SMALL CHANGES TO 
THE TEMPERATURE PATTERN RELATIVE TO THE HALF-MONTH LEAD OUTLOOK. ENHANCED 
PROBABILITIES OF BELOW-NORMAL TEMPERATURES OVER THE SOUTHWEST EXTEND FURTHER 
NORTHWARD INTO THE CENTRAL ROCKIES AND NORTHERN PLAINS FOLLOWING CHANGES IN 
DYNAMICAL MODEL GUIDANCE. GUIDANCE ALSO INDICATES INCREASING LIKELIHOODS OF 
ABOVE-NORMAL TEMPERATURES FOR AN EXPANDED AREA OF EAST TEXAS AND THE SOUTHEAST.

THE UPDATE TO THE AUGUST PRECIPITATION OUTLOOK SHOWS ONLY SMALL CHANGES IN THE 
PREDICTED PRECIPITATION PATTERN COMPARED TO THE HALF-MONTH LEAD OUTLOOK. A 
LARGE AREA WITH ENHANCED PROBABILITIES OF ABOVE-MEDIAN PRECIPITATION FROM THE 
SOUTHWEST NORTHWARD INTO THE CENTRAL ROCKIES AND EASTWARD ACROSS THE CENTRAL 
PLAINS TO THE MISSISSIPPI RIVER EXTENDS FARTHER TO THE NORTH IN THE UPDATED 
OUTLOOK AS INDICATED BY MOST DYNAMICAL MODEL GUIDANCE, INCLUDING THE CFS. AN 
AREA OF ENHANCED PROBABILITIES OF BELOW-MEDIAN PRECIPITATION WAS REMOVED FROM 
THE PACIFIC NORTHWEST IN THE UPDATED OUTLOOK, AS MODEL GUIDANCE FOR THE FIRST 
TWO WEEKS OF AUGUST FORECASTS INCREASED PRECIPITATION AMOUNTS. AN AREA OF 
ENHANCED PROBABILITIES OF BELOW-MEDIAN PRECIPITATION FOR SOUTH FLORIDA WAS 
REMOVED FOLLOWING MODEL GUIDANCE FOR THE MONTH.

BELOW IS THE DISCUSSION FROM THE HALF-MONTH LEAD, AUGUST, MONTHLY FORECAST 
ISSUED JULY 16, 2015.

SEA SURFACE TEMPERATURES (SSTS) ARE CURRENTLY MORE THAN ONE DEGREE C ABOVE 
NORMAL ALONG THE EQUATOR IN THE PACIFIC OCEAN FROM THE SOUTH AMERICAN COAST 
WESTWARD TO JUST WEST OF THE INTERNATIONAL DATE LINE. SST ANOMALIES ARE GREATER 
THAN +2.0 DEGREES C IN THE EAST PACIFIC FROM ABOUT 130 W LONGITUDE TO THE SOUTH 
AMERICAN COAST. ABOVE NORMAL SSTS EXTEND NORTHWARD FROM THE EQUATOR TO COVER AN 
EXTENSIVE AREA OF THE NORTH PACIFIC TO THE WEST OF NORTH AMERICA. SUBSURFACE 
OCEAN WATER TEMPERATURES TO A DEPTH OF ABOUT 100 METERS ARE CONSIDERABLY ABOVE 
NORMAL THROUGHOUT THE EASTERN EQUATORIAL PACIFIC OCEAN.  RECENT ATMOSPHERIC 
OBSERVATIONS OVER THE EASTERN AND CENTRAL TROPICAL PACIFIC OCEAN SUGGEST STRONG 
OCEAN-ATMOSPHERE COUPLING, WITH UNUSUALLY ACTIVE CONVECTION ACROSS THE CENTRAL 
AND EAST-CENTRAL EQUATORIAL PACIFIC TOGETHER WITH LARGE SCALE WESTERLY WIND 
ANOMALIES AT LOW LEVELS OVER THE WEST AND CENTRAL PACIFIC. ATMOSPHERIC AND 
OCEANIC CONDITIONS SUGGEST CONTINUED STRENGTHENING OF EL NINO CONDITIONS. 
STATISTICAL AND DYNAMICAL SST FORECASTS INDICATE EL NINO CONDITIONS WILL 
PERSIST THROUGH WINTER, AND ANOMALIES IN SST ARE LIKELY TO GROW INTO THE 
BEGINNING OF WINTER AS THE CLIMATOLOGY OF SST COOLS. EL NINO IS LIKELY 
CONTRIBUTING TO RECENT CLIMATE ANOMALIES OVER NORTH AMERICA AND IS EXPECTED TO 
HAVE AN INFLUENCE ON CLIMATE ANOMALIES IN AUGUST.

CLIMATE MODEL FORECASTS FROM THE LAST FEW MONTHS HAVE SHOWN CONSISTENT NORTH 
AMERICAN SURFACE TEMPERATURE AND PRECIPITATION ANOMALY PATTERNS. MODEL 
PREDICTIONS AGREE REASONABLY WELL WITH THE TEMPERATURE AND PRECIPITATION 
ANOMALIES ASSOCIATED WITH PAST EL NINO EVENTS, ALTHOUGH THE AVERAGE OF CLIMATE 
MODELS CONTRIBUTING TO THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) IS 
SUBSTANTIALLY WARMER ACROSS THE NORTHERN U.S. FROM THE NORTHERN ROCKIES INTO 
THE NORTHEAST. THE CLIMATE FORECAST SYSTEM (CFS) FORECAST FOR AUGUST APPEARS IN 
CLOSER AGREEMENT WITH ANOMALIES ASSOCIATED WITH EL NINO IMPACTS. THE CLIMATE 
OUTLOOK FOR AUGUST 2015 IS BASED PRIMARILY ON FORECASTS FROM CLIMATE MODELS OF 
THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND REGRESSIONS OF NORTH 
AMERICAN SURFACE TEMPERATURE AND PRECIPITATION TO THE NINO 3.4 INDEX.  

THE FORECAST PREDICTS ELEVATED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES FOR 
THE U.S. WEST AND ALASKA. BELOW NORMAL TEMPERATURES ARE MORE LIKELY IN AREAS 
THAT HAVE OBSERVED RECENT ABOVE AVERAGE RAINFALL SUCH AS THE SOUTHERN ROCKY 
MOUNTAINS AND CENTRAL PLAINS. THIS SIGNAL IS LIKELY IN PART ASSOCIATED WITH 
ABOVE AVERAGE SOIL MOISTURE AND INCREASED CHANCES OF CONTINUING ANOMALOUSLY WET 
SOILS IN THE NEXT MONTH. THERE IS CONSENSUS AMONG CLIMATE ENSEMBLE MODELS FOR 
ABOVE NORMAL TEMPERATURES ALONG THE GULF COAST, THE SOUTH ATLANTIC COAST AND 
NORTHERN NEW ENGLAND.  

THERE CONTINUES TO BE CONSENSUS AMONG CLIMATE ENSEMBLE MODELS FOR ABOVE-MEDIAN 
PRECIPITATION AMOUNTS OVER A LARGE AREA OF THE SOUTHWEST EXTENDING INTO THE 
CENTRAL PLAINS. ENHANCED TROPICAL STORM ACTIVITY IN THE EASTERN PACIFIC IS 
LIKELY TO CONTINUE TO PROVIDE ANOMALOUS ATMOSPHERIC MOISTURE TO THE U.S. 
SOUTHWEST. CLIMATE MODELS PREDICT ENHANCED PROBABILITIES OF ABOVE MEDIAN 
PRECIPITATION AS A NORTHWARD EXTENSION OF A LARGE AREA OF ABOVE MEDIAN RAINFALL 
OVER THE TROPICAL EASTERN PACIFIC OCEAN. REGRESSIONS OF PRECIPITATION AGAINST 
THE NINO 3.4 INDEX INDICATE ABOVE-MEDIAN PRECIPITATION OVER A LARGE AREA OF THE 
CENTRAL CONUS AND BELOW-MEDIAN PRECIPITATION OVER A LARGE AREA OF THE CARIBBEAN 
EXTENDING INTO PARTS OF THE SOUTHERN FLORIDA PENINSULA AND THE GULF COAST OF 
TEXAS AND LOUISIANA. THIS PATTERN OF PRECIPITATION ANOMALIES IS CONSISTENT IN 
THE CONSENSUS OF CLIMATE MODELS FROM THE NMME. THERE IS ALSO CONSENSUS AMONG 
THE NMME MODELS FOR BELOW MEDIAN PRECIPITATION OVER PARTS OF THE PACIFIC 
NORTHWEST.

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: 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.



THE NEXT MONTHLY OUTLOOK...FOR SEP ... WILL BE ISSUED ON THU AUG 20 2015


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

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