Here’s the forecast discussion for September, October and November from the Climate Prediction Center.

SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS 

THE MAIN FACTORS WHICH USUALLY INFLUENCE THE SEASONAL CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH COMPRISE EL NINO/SOUTHERN OSCILLATION OR ENSO.
IMPACTS OF THESE EVENTS ARE SUMMARIZED BY SEPARATING 3-MONTH OBSERVATIONS FROM
3 OR MORE DECADES INTO EL NINO, NEUTRAL, AND LA NINA SETS, AVERAGING EACH
SEPARATELY, AND THEN COMPUTING ANOMALIES.  THESE ARE CALLED "ENSO COMPOSITES",
AND ARE USED 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
1971-2000).
3) THE TROPICAL 30-60 DAY OSCILLATION - SOMETIMES CALLED MADDEN JULIAN
OSCILLATION (MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE NORTH ATLANTIC OSCILLATION (NAO) AND THE PACIFIC NORTH AMERICAN (PNA)
PATTERNS - WHICH AFFECT THE TEMPERATURE ANOMALY PATTERN ESPECIALLY DURING THE
COLD SEASONS. THESE PHENOMENA ARE CURRENTLY KNOWN TO BE PREDICTABLE ONLY OVER A
WEEK OR SO.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE
VARIABILITY AFFECTING BOTH 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 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 TOOLS - CANONICAL CORRELATION ANALYSIS (CCA), SCREENING
MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOGUE (CA) AND ENSEMBLE CCA
(ECCA).
  DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM (CFS).
9) AN OBJECTIVE CONSOLIDATION (ABBREVIATED CON IN THE TEXT) OF THE OCN, CCA,
SMLR, ECCA, AND CFS FORECASTS IS USED AS A FIRST GUESS IN PREPARING THE
FORECAST MAPS. THIS TECHNIQUE MAKES OPTIMUM USE OF THE KNOWN SKILL OF OUR
FORECAST TOOLS.
 
SEA SURFACE TEMPERATURES (SSTS) ALONG THE EQUATOR IN THE EAST-CENTRAL PACIFIC
HAVE DECREASED DRAMATICALLY FROM ABOVE NORMAL IN APRIL, TO WELL BELOW NORMAL
THROUGH JULY 2010. THE WEEKLY SST DEPARTURE FROM NORMAL FOR THE NINO 3.4 REGION
(FROM 120 TO 170 DEGREES WEST LONGITUDE AND FROM 5 DEGREES SOUTH TO 5 DEGREES
NORTH LATITUDE)HAS BEEN IN EXCESS OF 1 DEGREES CELSIUS SINCE THE MIDDLE OF
JULY.  THIS INDICATES THAT THE ENSO STATE HAS CHANGED FROM EL NINO TO LA NINA
IN A MATTER OF MONTHS. 

THE SON 2010 TEMPERATURE OUTLOOK FAVORS ABOVE NORMAL SEASONAL MEAN TEMPERATURES
IN THE DESERT SOUTHWEST, EXTENDING EASTWARD INTO WEST TEXAS AND MUCH OF THE
EASTERN HALF OF THE CONTIGUOUS UNITED STATES EXCEPT IN THE SOUTHEAST. ABOVE
NORMAL TEMPERATURES IN THE EASTERN U.S. ARE CONSISTENT WITH THE DEVELOPING LA
NINA AND WITH DECADAL TEMPERATURE TRENDS IN PARTS OF THE NORTHEAST AS WELL,
WHILE LA NINA CONDITIONS AND DECADAL WARMING TRENDS CONTRIBUTE TO THE ENHANCED
PROBABILITY OF ABOVE NORMAL TEMPERATURES IN THE SOUTHWEST.  ABOVE NORMAL
TEMPERATURES ARE ALSO FAVORED FOR NORTHERN ALASKA, WHERE A RELIABLE WARMING
TREND HAS BEEN OBSERVED. 

LA NINA CONDITIONS FAVOR ABOVE MEDIAN PRECIPITATION AMOUNTS IN SON FOR THE
NORTHWEST AND BELOW MEDIAN PRECIPITATION AMOUNTS IN THE SOUTHWEST AND THE
CENTRAL MISSISSIPPI VALLEY. THE CHANCES OF ABOVE MEDIAN PRECIPITATION AMOUNTS
ARE ALSO ENHANCED OVER PARTS OF THE CENTRAL AND NORTHERN PLAINS DUE TO TRENDS. 

IN LOCATIONS WHERE THE LIKELIHOODS OF SEASONAL MEAN TEMPERATURES AND SEASONAL
PRECIPITATION AMOUNTS ARE SIMILAR TO THE CLIMATOLOGICAL PROBABILITIES, EQUAL
CHANCES OF BELOW, NEAR, AND ABOVE AVERAGE TEMPERATURE AND PRECIPITATION ARE
INDICATED. 

PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2010 TO SON 2011 

TEMPERATURE 

ABOVE NORMAL TEMPERATURES ARE FAVORED IN SON 2010 FOR MOST OF THE LOWER 48
STATES EXCLUDING THE PACIFIC COAST, THE NORTHWEST AND SOUTHEAST.  PROBABILITIES
ARE PARTICULARLY ENHANCED FOR THE DESERT SOUTHWEST, AND THE GREAT LAKES AND
NORTHEAST, DUE PRIMARILY TO DECADAL TEMPERATURE TRENDS AND LA NINA CONDITIONS. 

FOR OND 2010, ABOVE NORMAL TEMPERATURES ARE FAVORED FOR A REGION STRETCHING
FROM THE SOUTHERN U.S. TO THE NORTHEAST, ASSOCIATED WITH BOTH EXPECTED LA NINA
CONDITIONS AND TEMPERATURE TRENDS. 

THE OUTLOOKS FOR NDJ 2010-11 THROUGH MAM 2011 PRIMARILY REFLECT EXPECTED LA
NINA IMPACTS. THE PROBABILITIES OF BELOW NORMAL TEMPERATURES ARE ENHANCED IN
MOST OF ALASKA, THE PACIFIC NORTHWEST, THE NORTHERN ROCKIES, AND INTO THE
NORTHERN PLAINS - FOR THE LATER LEADS THIS IS SUPPORTED BY TRENDS AS WELL.  THE
PROBABILITIES OF ABOVE NORMAL TEMPERATURES ARE ENHANCED IN MUCH OF THE SOUTHERN
U.S. BY THE PROSPECT OF LA NINA CONDITIONS. 

THE OUTLOOKS FOR AMJ THROUGH SON 2011 PRIMARILY REFLECT DECADAL VARIABILITY IN
THE LONG TERM CLIMATE STATE FAVORING ABOVE NORMAL TEMPERATURES FOR MUCH OF THE
WEST, AND FOR SOME AREAS IN THE NORTHEAST.  AN ELEVATED CHANCE OF BELOW NORMAL
TEMPERATURES IN THE NORTHERN PLAINS IN AMJ AND MJJ 2011 REFLECTS RECENT DECADAL
VARIABILITY IN THIS REGION.  ABOVE NORMAL TEMPERATURES ARE ALSO FAVORED FOR
ALASKA IN THESE LATER LEADS WHERE AND WHEN WARMING TRENDS HAVE BEEN RELIABLE
INDICATORS OF SEASONAL MEAN TEMPERATURES. 

PRECIPITATION 

THE PRECIPITATION OUTLOOK FOR SON 2010 INDICATES INCREASED CHANCES FOR
ABOVE MEDIAN PRECIPITATION FOR AREAS IN THE NORTHWEST AND IN THE CENTRAL PLAINS
THE FORMER DUE TO LA NINA, THE LATTER DUE TO LONG TERM TRENDS. LA NINA, WHEN
CONSIDERED IN ISOLATION, FAVORS BELOW MEDIAN RAINFALL IN MUCH OF THE SOUTH BUT
THIS IS CONTRADICTED IN SOME AREAS BY OTHER TOOLS, FOR EXAMPLE ALONG THE GULF
COAST IN AN ACTIVE HURRICANE SEASON. BOTH TRENDS AND LA NINA COMPOSITES AGREE
ON INCREASED CHANCES FOR BELOW MEDIAN PRECIPITATION IN THE SOUTHWEST AND THE
CENTRAL MISSISSIPPI VALLEY. 

THE OUTLOOKS FOR OND 2010 THROUGH MAM 2011 SHOW THE EXPECTED IMPACT OF LA NINA
CONDITIONS ON PRECIPITATION.  LA NINA CONDITIONS ENHANCE THE PROBABILITIES OF
ABOVE MEDIAN PRECIPITATION IN THE PACIFIC NORTHWEST AND NORTHERN ROCKIES IN THE
FALL AND WINTER SEASONS AND IN THE CENTRAL INTERIOR REGIONS OF THE EASTERN U.S.
IN WINTER.  PROBABILITIES OF BELOW MEDIAN PRECIPITATION AMOUNTS ARE ENHANCED
ACROSS MOST OF THE SOUTHERN U.S. IN THE WINTER BY THE INCREASING LIKELIHOOD OF
LA NINA CONDITIONS, ESPECIALLY IN THE SOUTHEAST. 

BOTH THE IMPACT OF LA NINA CONDITIONS AND THE CONFIDENCE IN ENSO PREDICTIONS
DECREASE IN THE SPRING OF 2011 SUCH THAT THERE IS NO SIGNAL FOR PRECIPITATION
ANOMALIES FROM AMJ THROUGH MJJ 2011.  DECADAL TRENDS LEAD TO ENHANCED CHANCES
OF BELOW MEDIAN PRECIPITATION IN THE PACIFIC NORTHWEST AND OF ABOVE MEDIAN
PRECIPITATION IN FLORIDA AND THE CENTRAL PLAINS IN THE LATER LEADS. 

NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).