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Official 90-day Outlooks are issued once each month near mid-month at 8:30am Eastern Time. Please consult the schedule of 30 & 90-day outlooks for exact release dates.

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    0.5mn SON 2015
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    0.5mn Sep 2015


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HOME> Outlook Maps>Seasonal Forecast Discussion
 
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EDT THURSDAY AUG 20 2015

30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2015

SEA SURFACE TEMPERATURES (SSTS) ARE CURRENTLY MORE THAN TWO DEGREES C ABOVE
NORMAL ALONG THE EQUATOR IN THE PACIFIC OCEAN FROM THE SOUTH AMERICAN COAST
WESTWARD TO NEAR 150 W. SOME DEPARTURES ARE GREATER THAN +3.0 DEGREES C IN THE
EASTERN PACIFIC. ABOVE NORMAL SSTS EXTEND NORTHWARD FROM THE EQUATOR TO COVER
AN EXTENSIVE AREA OF THE NORTH PACIFIC TO THE WEST OF NORTH AMERICA. IN THE
ATMOSPHERE, ENHANCED CONVECTION CONTINUES TO BE OBSERVED FROM WEST OF THE DATE
LINE ACROSS THE EQUATORIAL PACIFIC TO JUST WEST OF THE AMERICAS, SLIGHTLY NORTH
OF THE EQUATOR. LARGE SCALE WESTERLY WIND ANOMALIES AT LOW LEVELS ARE EVIDENT
OVER THE WEST AND CENTRAL PACIFIC. ANTICYCLONIC CIRCULATIONS IN THE UPPER
LEVELS ARE ALSO EVIDENT, BOTH NORTH AND SOUTH OF THE EQUATOR, IN THE EAST
CENTRAL PACIFIC. THESE NOTED OCEAN-ATMOSPHERIC OBSERVATIONS SUGGEST STRONG
OCEAN-ATMOSPHERE COUPLING AND INDICATE A SIGNIFICANT AND STRENGTHENING EL NINO
EVENT.

STATISTICAL AND DYNAMICAL SST FORECASTS INDICATE EL NINO CONDITIONS MOST LIKELY
WILL PERSIST THROUGH WINTER AND EL NINO IS LIKELY CONTRIBUTING TO RECENT
CLIMATE ANOMALIES OVER NORTH AMERICA. EL NINO IS FORECAST TO HAVE SOME
INFLUENCE ON CLIMATE ANOMALIES IN SEPTEMBER.

A REVIEW OF RECENT SOIL MOISTURE ANOMALIES INDICATES ANOMALOUSLY WET CONDITIONS
CONTINUE FOR AN AREA FROM THE SOUTHWEST CONUS NORTH AND EASTWARD TO THE OHIO
VALLEY FROM ANTECEDENT RAINFALL. DRIER THAN NORMAL SOIL MOISTURE IS INDICATED
FOR MANY AREAS IN THE PACIFIC NORTHWEST. THESE SIGNALS WERE ALSO CONSIDERED IN
THE SEPTEMBER OUTLOOK.

IN ADDITION TO THE EL NINO BACKGROUND STATE AND SOIL MOISTURE ANOMALIES,
DYNAMICAL MODEL GUIDANCE FROM THE CFS AND NMME PLAYED A SUBSTANTIAL ROLE IN THE
SEPTEMBER OUTLOOK. THESE CLIMATE MODEL FORECASTS HAVE REMAINED QUITE CONSISTENT
OVER THE LAST FEW MONTHS AND AGREE REASONABLY WELL, IN GENERAL, WITH THE
TEMPERATURE AND PRECIPITATION ANOMALIES ASSOCIATED WITH PAST EL NINO EVENTS. AT
THE CURRENT TIME, THE MJO IS INACTIVE AND PLAYED NO ROLE IN THE SEPTEMBER
OUTLOOK.

THE SEPTEMBER TEMPERATURE OUTLOOK DEPICTS ENHANCED ODDS FOR ABOVE NORMAL
TEMPERATURES FROM CALIFORNIA NORTHWARD TO INCLUDE THE PACIFIC NORTHWEST, PARTS
OF THE NORTHERN ROCKIES AND ALASKA. THIS HIGHLIGHTED REGION IS BASED ON SEVERAL
FACTORS, WHEN APPROPRIATE, WHICH INCLUDES DYNAMICAL MODEL GUIDANCE,
ABOVE-AVERAGE SSTS IN THE NORTH PACIFIC OCEAN, EL NINO CONDITIONS AND
ANOMALOUSLY DRY SOIL MOISTURE IN SOME AREAS. ABOVE NORMAL TEMPERATURES ARE ALSO
FAVORED FOR PARTS OF THE GULF COAST AND SOUTHEAST BASED ON DYNAMICAL MODEL
GUIDANCE AND TO A LESSER EXTENT DRY SOIL MOISTURE CONDITIONS. BELOW NORMAL
TEMPERATURES ARE MORE LIKELY FOR A REGION FROM THE SOUTHWEST NORTHEASTWARD INTO
THE INTERIOR PORTION OF THE CONUS. THIS AREA IS HIGHLIGHTED BASED ON
CORRELATION WITH EL NINO CONDITIONS, NEAR-TO-BELOW AVERAGE TEMPERATURE
FORECASTS FROM THE NMME AND ANOMALOUSLY WET SOIL MOISTURE CONDITIONS IN SOME
AREAS.

EL NINO CONDITIONS, AND STRONG AND CONSISTENT SIGNALS FROM DYNAMICAL MODEL
GUIDANCE SUPPORT AN AREA OF FAVORED ABOVE-MEDIAN PRECIPITATION FROM SOUTHERN
CALIFORNIA NORTHWARD AND EASTWARD TO INCLUDE SOME OF THE GREAT BASIN, MUCH OF
THE ROCKIES, SOUTHWEST AND CENTRAL AND SOUTHERN PLAINS. ABOVE MEDIAN
PRECIPITATION IS ALSO HIGHLIGHTED FOR THE SOUTH CENTRAL COAST OF ALASKA
CONSISTENT WITH EL NINO CONDITIONS. BELOW MEDIAN PRECIPITATION IS INDICATED
ALONG THE GULF COAST, FOR PARTS OF THE SOUTHEAST AND LOWER MID-ATLANTIC BASED
ON DYNAMICAL MODEL GUIDANCE AND CORRELATIONS WITH EL NINO CONDITIONS THIS TIME
OF THE YEAR.

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: 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 SEP WILL BE ISSUED ON MON AUGUST 31 2015


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

$$

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