518
FXUS05 KWBC 181231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU JUN 18 2009
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.
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.
THE MAIN FORECAST TOOLS ARE AS FOLLOWS:
7) STATISTICAL FORECAST TOOLS - CANONICAL CORRELATION ANALYSIS (CCA), SCREENING
MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOGUE (CA) AND ENSEMBLE CCA
(ECCA).
8) 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) IN THE EASTERN AND CENTRAL EQUATORIAL PACIFIC
OCEAN HAVE TRANSITIONED FROM BELOW NORMAL JUST A FEW MONTHS AGO TO ABOUT 0.5
DEGREES C ABOVE NORMAL IN THE RECENT TWO WEEKS. SSTS IN THIS REGION OF THE
PACIFIC OCEAN ARE A RELIABLE ENSO INDICATOR AND SHOW A TRANSITION FROM LA NINA
CONDITIONS EARLY IN THE YEAR TO NEUTRAL CONDITIONS IN MAY. THE CONTINUED
INCREASE IN SST ANOMALIES IN THIS REGION IN EARLY JUNE IS A STRONG INDICATION
THAT EL NINO CONDITIONS ARE LIKELY TO DEVELOP WITHIN THE NEXT FEW MONTHS.
WATER TEMPERATURES ARE WELL ABOVE NORMAL IN THE UPPER 200 METERS OF THE
TROPICAL PACIFIC OCEAN, MAKING IT LIKELY THAT ABOVE NORMAL SSTS WILL CONTINUE
INTO THE SUMMER. THE CFS MODEL CORRECTLY ANTICIPATED THIS RAPID TRANSITION IN
ITS FORECASTS FOR THE LAST FEW MONTHS, AND ITS CURRENT FORECAST SHOWS A
CONTINUED INCREASE IN SST ANOMALIES IN THE COMING FEW MONTHS, SUGGESTING THAT
MODERATE EL NINO CONDITIONS MAY SOON DEVELOP AND CONTINUE THROUGH THE END OF
THE YEAR. THE OUTLOOKS FOR TEMPERATURE AND PRECIPITATION FROM OND 2009 TO MAM
2010 ARE HEAVILY INFLUENCED BY THE POSSIBILITY OF EL NINO. IT IS STILL A BIT
EARLY TO PREDICT THE EL NINO STRENGTH FOR THE WINTER MONTHS, WHEN ITS INFLUENCE
ON U.S. CLIMATE IS STRONGEST. THE EVOLUTION OF SSTS IN THE EQUATORIAL PACIFIC
IN THE COMING MONTHS WILL BE CRITICAL TO WINTERTIME FORECAST IN THE U.S.
THE TEMPERATURE OUTLOOK FOR JAS 2009 CALLS FOR AN ENHANCED LIKELIHOOD OF BELOW
NORMAL TEMPERATURES FOR PORTIONS OF THE LOWER AND MIDDLE MISSISSIPPI VALLEY,
DUE MAINLY TO THE INFLUENCE OF INITIALLY WET SOIL MOISTURE CONDITIONS IN THE
AREA. ABOVE NORMAL TEMPERATURES ARE FAVORED FROM THE ROCKY MOUNTAINS WESTWARD,
EXCEPT ALONG THE PACIFIC COAST. ABOVE NORMAL TEMPERATURES ARE ALSO FAVORED IN
INTERIOR SECTIONS OF SOUTHERN ALASKA. ELSEWHERE, EQUAL CHANCES OF BELOW, NEAR,
AND ABOVE NORMAL TEMPERATURES ARE PREDICTED.
THE CHANCE OF BELOW MEDIAN PRECIPITATION IS ENHANCED FOR JAS 2009 FOR PARTS OF
THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKY MOUNTAINS. ABOVE MEDIAN
PRECIPITATION AMOUNTS ARE FAVORED FROM PARTS OF THE SOUTHWESTERN U.S. TO
SOUTHERN WYOMING. ABOVE MEDIAN PRECIPITATION AMOUNTS ARE FAVORED FOR FLORIDA
AND ALSO IN NEW ENGLAND. ELSEWHERE, EQUAL CHANCES OF BELOW, NEAR, AND ABOVE
MEDIAN PRECIPITATION ARE PREDICTED.
BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOKS
NOTE: FOR GRAPHICAL DISPLAYS OF THE FORECAST TOOLS DISCUSSED BELOW SEE:
HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/TOOLS/BRIEFING
CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS
SSTS IN THE EAST-CENTRAL EQUATORIAL PACIFIC CURRENTLY AVERAGE AROUND 0.5
DEGREES C ABOVE NORMAL, AND ANOMALIES HAVE INCREASED MARKEDLY IN THE PAST FEW
MONTHS. THE HEAT CONTENT IN THE UPPER 300 METERS OF THE CENTRAL AND EASTERN
PACIFIC ALONG THE EQUATOR HAS ALSO INCREASED MARKEDLY IN THE LAST FEW MONTHS
AND NOW AVERAGES CLOSE TO 1 DEGREE C ABOVE NORMAL. SST ANOMALIES IN THE NINO
3.4 REGION AVERAGED JUST UNDER .5 DEGREES C IN THE FIRST HALF OF JUNE.
ATMOSPHERIC CONDITIONS OVER THE EQUATORIAL PACIFIC OCEAN DURING MAY WERE
CONSISTENT WITH ENSO NEUTRAL CONDITIONS. LOW LEVEL WINDS WERE NEAR NORMAL NEAR
THE EQUATOR OVER THE CENTRAL PACIFIC, AND ATMOSPHERIC CONVECTION OVER THE
CENTRAL EQUATORIAL PACIFIC HAS RETURNED TO NEAR NORMAL VALUES AFTER HAVING BEEN
SUPRESSED FOR MOST OF THE PAST YEAR IN THE LA NINA EVENT.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE TRANSITION OF SST ANOMALIES FROM BELOW TO ABOVE NORMAL WAS PREDICTED BY
MOST DYNAMICAL SST PREDICTION MODELS FOR THE PAST FEW MONTHS, WITH STATISTICAL
PREDICTION TOOLS LAGGING BEHIND IN THEIR CONTINUATION OF NEAR TO BELOW NORMAL
SSTS. THE MOST RECENT DYNAMICAL SST FORECASTS FROM THE CFS AND OTHER MODELS
PREDICT SST ANOMALIES OF BETWEEN .5 AND 2 DEGREES C BY LATE SUMMER. FORECASTS
FROM THE STATISTICAL MODELS ARE NOW CONSIDERABLY WARMER THAN THEIR FORECASTS
LAST MONTH, ALTHOUGH MOST STILL LAG BEHIND THE DYNAMIC MODELS IN THEIR
PREDICTION OF ANOMALIES RANGING FROM 0 TO .5 DEGREES C BY LATE SUMMMER. THE
CPC CONSOLIDATION NINO 3.4 SST ANOMALY FORECAST INDICATES THE SST ANOMALIES
WILL REACH THE CRITICAL THRESHOLD FOR EL NINO CONDITIONS OF .5 DEGREES C OR
GREATER BY SON, AND CONTINUE AT THAT LEVEL THROUGH EARLY 2010. SINCE THE
DYNAMICAL MODELS HAVE PERFORMED CONSISTENTLY BETTER THAN THE STATISTICAL MODELS
THIS SPRING, AND SINCE WEEKLY SST ANOMALIES IN ALL FOUR NINO REGIONS ARE
ALREADY .5 DEGREES OR GREATER, IT IS QUITE LIKELY THAT SSTS IN THE NINO 3.4
REGION WILL BE ABOVE .5 DEGREES C FROM JULY 2009 THROUGH AT LEAST EARLY 2010,
AND THE CONDITIONS WILL BE FAVORABLE FOR THE ONSET OF EL NINO CONDITIONS IN THE
NEXT FEW MONTHS.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR JAS THROUGH SON 2009 ARE BASED
PRIMARILY ON THE CONSOLIDATION FORECAST (CON), A SKILL-WEIGHTED AND CALIBRATED
PROBABILISTIC FORECAST DERIVED FROM THE CFS, SMLR, OCN, CCA, AND ECCA FORECAST
TOOLS. OUTLOOKS BETWEEN OND 2009 AND MAM 2010 REFLECT THE LIKELY ONSET OF
MODERATE EL NINO CONDITIONS IN THE NEXT FEW MONTHS. THE CFS FORECAST AGREES
WELL WITH THE EL NINO COMPOSITES FROM OND THROUGH ITS FINAL LEAD TIME OF DJF
AND WAS USED TOGETHER WITH EL NINO COMPOSITES FOR THE PRECIPITATION FORECAST
FOR THESE SEASONS. THE TEMPERATURE FORECAST WAS ADJUSTED FROM THE CFS AND ENSO
COMPOSITES ON THE BASIS OF TRENDS AS INDICATED BY THE OCN TOOL AND THE CON.
THE FORECASTS FROM JFM TO MAM 2010 ARE BASED ON EL NINO COMPOSITES, WITH THE
TEMPERATURE OUTLOOK ADJUSTED BY TRENDS. THE OUTLOOKS FOR AMJ TO JAS 2010 ARE
BASED ON THE CON FORECASTS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - JAS 2009 TO JAS 2010
TEMPERATURE:
THE TEMPERATURE OUTLOOK FOR JAS 2009 FAVORS ABOVE NORMAL TEMPERATURES FOR MOST
OF THE WESTERN U.S., EXCEPT ALONG THE IMMEDIATE WEST COAST AS INDICATED BY THE
CONSOLIDATION FORECAST TOOL. THIS AREA IS MOSTLY DUE TO RECENT TEMPERATURE
TRENDS. BELOW NORMAL TEMPERATURES ARE INDICATED IN PARTS OF THE CENTRAL CONUS
BY A NUMBER OF FORECAST TOOLS. INTIALLY WET SOIL MOISTURE CONDITIONS PLAY A
PART IN REDUCING TEMPERATURES IN THIS AREA ACCORDING TO THE SMLR TOOL, AND ARE
LIKELY A FACTOR IN THE CFS MODEL FORECAST AS WELL. THE ABOVE NORMAL
TEMPERATURES INDICATED ON LAST MONTHS OUTLOOK FOR JAS IN NEW ENGLAND HAVE BEEN
REMOVED DUE TO CONTRADICTING INDICATIONS FROM THE CFS SURFACE TEMPERATURE AND
UPPER LEVEL CIRCULATION FORECAST. ABOVE NORMAL TEMPERATURES IN ALASKA ARE
FAVORED BY CCA AND SMLR FORECASTS IN INTERIOR PORTIONS, WITH CONFLICTING
SIGNALS ON THE COASTAL AREAS LEADING TO A FORECAST OF EQUAL CHANCES.
THE TEMPERATURE OUTLOOK FOR ASO THROUGH OND ARE MAINLY BASED ON THE CON
FORECAST. FROM NDJ 2009/10 THROUGH FMA 2010 THE TEMPERATURE FORECAST WAS
SUBSTANTIALLY REVISED FROM LAST MONTHS FORECASTS FOR THE CORRESPONDING SEASONS
DUE TO INCREASED CONFIDENCE THAT EL NINO WILL INFLUENCE THE WINTERTIME
CIRCULATION. TEMPERATURES IN EL NINO WINTERS TEND TO BE BELOW NORMAL OVER MUCH
OF THE SOUTHERN CONUS, PARTIALLY COUNTERACTING TRENDS FOR WARMER WINTER
TEMPERATURES IN THE SOUTHWEST, AND ENTIRELY COUNTERACTING TRENDS IN THE
SOUTHEAST. CONFIDENCE IN ABOVE NORMAL TEMPERATURES OVER THE NORTHERN GREAT
PLAINS AND IN ALASKA IS INCREASED DUE TO ENSO TELECONNECTIONS.
REMAINING FORECAST LEADS FROM AMJ 2010 THROUGH JAS 2010 ARE BASED ON THE
CONSOLIDATION FORECAST AND LARGELY REFLECT TEMPERATURE TRENDS.
PRECIPITATION:
THE PRECIPITATION OUTLOOKS FOR JAS THROUGH SON 2009 ARE BASED PRIMARILY ON THE
CONSOLIDATION FORECAST, AND INDICATE INCREASED CHANCES OF ABOVE MEDIAN
PRECIPITATION AMOUNTS OVER PARTS OF THE CENTRAL AND SOUTHERN ROCKY MOUNTAINS
AND THE SOUTHWEST, BASED MOSTLY ON FORECASTS FROM THE CFS AND ECCA. THE AREA
OF THE TREND-RELATED DRY FORECAST FOR THE PACIFIC NORTHWEST HAS BEEN REDUCED
FROM THAT INDICATED IN PREVIOUS OUTLOOKS DUE TO AMPLE PRECIPITATION AND
FAVORABLE SOIL MOISTURE CONDITIONS IN JUNE IN PARTS OF THE NORTHERN GREAT
BASIN. THE CON FORECAST CONTINUES TO SHOW INCREASED CHANCES FOR ABOVE MEDIAN
PRECIPITATION AMOUNTS IN NEW ENGLAND AND ALSO IN FLORIDA. THE CHANCE OF ABOVE
MEDIAN PRECIPITATION AMOUNTS FROM ASO TO OND IS ENHANCED ALONG THE SOUTH COAST
OF ALASKA AND IS BASED ON INDICATIONS FROM THE CFS. EL NINO PRECIPITATION
COMPOSITES WERE USED TOGETHER WITH THE CFS FORECAST FROM OND 2009 THROUGH MAM
2010. THESE INDICATE INCREASED CHANCES OF ABOVE MEDIAN PRECIPITATION FOR THE
SOUTHERN CONUS, BEGINING IN CENTRAL SECTIONS OF THE REGION IN OND, EXPANDING TO
MAXIMUM COVERAGE IN LATE WINTER, AND THEN DIMINISHING IN AREA BY MAM. BELOW
MEDIAN PRECIPITATION IS FAVORED IN EL NINO WINTERS FOR THE PACIFIC NORTHWEST
AND PARTS OF THE OHIO AND TENNESSEE RIVER VALLEYS. THERE ARE NO CLEAR SIGNALS
FOR PRECIPITATION FROM AMJ TO JJA 2010, RESULTING IN A FORECAST FOR EQUAL
CHANCES FOR BELOW, NEAR, OR ABOVE MEDIAN PRECIPITATION AMOUNTS NATIONWIDE. A
TREND-RELATED SIGNAL FOR ENHANCED CHANCES OF BELOW MEDIAN PRECIPITATION IN THE
PACIFIC NORTHWEST, AND ABOVE MEDIAN PRECIPITATION FOR FLORIDA APPEARS IN THE
OUTLOOK FOR JAS 2010.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: DAVID UNGER
FOR A DESCRIPTION OF OF THE STANDARD FORECAST TOOLS - THEIR SKILL- AND THE
FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT
HTTP:/WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/PREDICTIONS/90DAY/DISC.HTML
(USE LOWER CASE LETTERS)
INFORMATION ON THE FORMATION OF SKILL OF THE CAS FORECASTS MAY BE FOUND AT:
HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML (USE LOWERCASE LETTERS)
NOTES - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR
VALID PERIOD. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM
RANGE FORECASTS SHOULD BE CONSULTED.
THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT
MONTH ON THU JUL 16 2009
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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