789
FXUS05 KWBC 171231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU SEP 17 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.
CURRENT EL NINO CONDITIONS ARE EXPECTED TO STRENGTHEN AND PERSIST INTO THE
NORTHERN HEMISPHERE WINTER 2009-10. THE INCREASING LIKELIHOOD OF A CONTINUING
EL NINO EVENT INFLUENCES THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR OND
2009 THROUGH MAM 2010. THE IMPACT OF EL NINO ON THE CLIMATE OVER NORTH AMERICA
IS EXPECTED TO BE GREATEST DURING THE WINTER SEASONS. A MODERATE STRENGTH EL
NINO IS MOST LIKELY DURING THE WINTER, ALTHOUGH A STRONGER OR WEAKER EVENT
REMAINS POSSIBLE. UNCERTAINTY IN THE FUTURE STRENGTH AND DURATION OF THIS EVENT
IS CONSIDERED IN THE SEASONAL FORECASTS, ESPECIALLY AT LONGER LEAD TIMES.
THE TEMPERATURE OUTLOOK FOR OND 2009 INDICATES AN ENHANCED LIKELIHOOD OF ABOVE
AVERAGE TEMPERATURES FOR THE WESTERN HALF OF THE CONUS AND MUCH OF ALASKA.
WHERE THE CHANCE OF ABOVE OR BELOW AVERAGE SEASONAL MEAN TEMPERATURES ARE
SIMILAR TO THE CLIMATOLOGY, EQUAL CHANCES OF BELOW, NEAR, AND ABOVE AVERAGE ARE
INDICATED.
BELOW MEDIAN ACCUMULATED PRECIPITATION IS MOST LIKELY DURING OND 2009 FOR PARTS
OF THE PACIFIC NORTHWEST. ABOVE MEDIAN PRECIPITATION AMOUNTS ARE MOST LIKELY
ALONG THE GULF COAST FROM TEXAS TO FLORIDA. WHERE THE LIKELIHOOD OF ABOVE OR
BELOW MEDIAN SEASONAL PRECIPITATION IS SIMILAR TO THE CLIMATOLOGY, EQUAL
CHANCES OF BELOW, NEAR, AND ABOVE MEDIAN PRECIPITATION ARE INDICATED.
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
MONTHLY SEA SURFACE TEMPERATURE (SST) ANOMALIES EXCEED +0.5 CELSIUS ACROSS MOST
OF THE EQUATORIAL PACIFIC OCEAN AND ARE FROM +1 TO +1.5 CELSIUS NEAR THE DATE
LINE AND IN PARTS OF THE THE EASTERN HALF OF THE BASIN. SUBSURFACE HEAT CONTENT
IS GENERALLY ABOVE NORMAL IN THE UPPER 200 METERS OF THE TROPICAL PACIFIC OCEAN
WITH TEMPERATURE ANOMALIES EXCEEDING +2 CELSIUS AT THERMOCLINE DEPTH BETWEEN
170E AND 110W. HISTORICALLY, POSITIVE TEMPERATURE ANOMALIES IN THE UPPER OCEAN
PRECEDE THE ONSET AND FURTHER DEVELOPMENT OF EL NINO EVENTS. THUS TROPICAL
PACIFIC TEMPERATURES ARE UNLIKELY TO RETURN TO AN ENSO NEUTRAL STATE PRIOR TO
JANUARY 2010.
THE MOST RECENT 30-DAY OUTGOING LONGWAVE RADIATION ANOMALIES INDICATE THAT
CONVECTION IS SUPPRESSED OVER THE MARITIME CONTINENT AND SLIGHTLY ENHANCED
ACROSS THE WESTERN PACIFIC. LOW LEVEL WESTERLY WIND BURSTS OFTEN OCCUR OVER
THE WESTERN EQUATORIAL PACIFIC DURING THE DEVELOPMENT OF EL NINO EVENTS AS
OCCURRED AT THE END OF JULY AND AGAIN DURING EARLY SEPTEMBER. TROPICAL OCEANIC
AND ATMOSPHERIC ANOMALIES REFLECT THE CURRENT EL NINO STATE.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE CURRENT MEAN ENSEMBLE CFS FORECAST INDICATES SST ANOMALIES IN THE NINO 3.4
REGION PEAKING NEAR +1.5 CELSIUS BEFORE THE END OF 2009, WITH THE ENSEMBLE
SPREAD RANGING FROM +1 TO ABOUT +2 CELSIUS, THUS CALLING FOR MODERATE TO STRONG
EL NINO CONDITIONS BY EARLY NORTHERN HEMISPHERE WINTER. THIS FORECAST IS AMONG
THE WARMEST IN THE IRI MULTI-MODEL ENSEMBLE PLUME. THE CPC STATISTICAL MODELS
ARE GENERALLY FORECASTING A MODERATE EL NINO EVENT PEAKING BETWEEN +1 TO +1.5
DEGREES CELSIUS DURING THE EARLY PART OF THE WINTER. THE CONSTRUCTED ANALOG
MODEL PREDICTS THE LARGEST POSITIVE ANOMALY, SLIGHTLY GREATER THAN +1.5 DEGREES
CELSIUS. THE CPC CONSOLIDATION OF NINO 3.4 SST TEMPERATURE ANOMALY FORECASTS
INDICATES THAT THE CURRENT EL NINO WILL WEAKEN AND END BY AMJ 2010.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON THE CONSOLIDATION
FORECAST, A SKILL-WEIGHTED AND CALIBRATED PROBABILISTIC FORECAST DERIVED FROM
THE CFS, SMLR, OCN, CCA, AND ECCA FORECAST TOOLS. EL NINO COMPOSITES ARE THE
MAJOR FORECAST TOOL FOR FORECASTS FROM OND 2009-10 THROUGH MAM 2010.
PROGNOSTIC DISCUSSION OF OUTLOOKS - OND 2009 TO OND 2010
TEMPERATURE:
THE TEMPERATURE OUTLOOKS FOR OND 2009 THROUGH OND 2010 INDICATE THAT
THREE-MONTH MEAN TEMPERATURES ARE MOST LIKELY TO BE IN THE ABOVE NORMAL
CATEGORY FOR MUCH OF THE WESTERN US MAINLY DUE TO THE TREND SIGNAL. ALL
OUTLOOKS TO SOME EXTENT USE THE CPC CONSOLIDATION FORECAST AS A STARTING POINT
WITH MODIFICATIONS DUE TO THE INFLUENCE OF THE EXPECTED IMPACT OF EL NINO FROM
OND THROUGH FMA. THE STATISTICAL CONSOLIDATION DOES NOT ACCOUNT FOR INCREASES
IN THE SKILL OF FORECASTS THAT INCLUDE AN ENSO SIGNAL. BEGINNING IN OND 2009
AND CONTINUING TO SOME DEGREE THROUGHOUT THE NEXT 12 MONTHS, ABOVE NORMAL MEAN
TEMPERATURES ARE MOST LIKELY IN THE US SOUTHWEST, PRIMARILY AS A RESULT OF THE
LOCAL TEMPERATURE TREND. THE PROBABILITY OF WARMER THAN AVERAGE TEMPERATURES IN
THIS REGION ARE DECREASED SIGNIFICANTLY FROM DJF TO FMA 2010 BY THE EXPECTED
IMPACT OF EL NINO. SEASONAL MEAN TEMPERATURES ARE MOST LIKELY TO BE IN THE
BELOW AVERAGE CATEGORY FOR THE SOUTHEAST AND ALONG THE GULF COAST FROM NDJ 2009
TO FMA 2010 AS A RESULT OF EL NINO.
THE LIKELIHOOD OF ABOVE AVERAGE TEMPERATURES INCREASES IN THE NORTH-CENTRAL US
FROM OND 2009 THROUGH FMA 2010. THOUGH MEAN WINTER TEMPERATURES IN THE NORTHERN
PLAINS HAVE MOST OFTEN BEEN ABOVE AVERAGE IN THE LAST DECADE, THIS DECADAL
TEMPERATURE SIGNAL IS EXPECTED TO BE ENHANCED BY THE DEVELOPING EL NINO, AS
INDICATED BY SIGNIFICANTLY GREATER PROBABILITIES FOR BOTH THE NORTHERN PLAINS
AND PACIFIC NORTHWEST. MUCH OF ALASKA IS INDICATED TO HAVE AN ENHANCED
LIKELIHOOD OF ABOVE AVERAGE TEMPERATURES DUE TO THE LONG TERM CLIMATE TREND,
CONSISTENT WITH THE CFS AND OCN FORECASTS.
FORECAST LEADS FROM MAM 2010 THROUGH SON 2010 ARE BASED ON THE CONSOLIDATION
FORECAST AND ATTRIBUTABLE TO TEMPERATURE TRENDS AND WEAK INTERANNUAL SIGNALS.
PRECIPITATION:
THE PRECIPITATION OUTLOOKS FOR OND 2009 THROUGH FMA 2010 LEAN HEAVILY ON THE
CONSOLIDATION FORECAST AND THE EXPECTED IMPACTS OF A PROBABLE EL NINO EVENT,
WHILE THE LONGER LEAD FORECASTS FROM AMJ TO OND 2010 ARE MAINLY BASED ON THE
CONSOLIDATION.
THE AREA OF ENHANCED PROBABILITY OF BELOW MEDIAN PRECIPITATION FORECAST FOR THE
PACIFIC NORTHWEST FROM OND 2009 THROUGH MAM 2010 IS A RESULT OF BOTH THE
DECADAL CLIMATE TREND AND THE EXPECTED IMPACTS OF EL NINO. BELOW MEDIAN
PRECIPITATION IS ALSO MOST LIKELY FOR PARTS OF THE MISSISSIPPI AND OHIO VALLEYS
FROM DJF 2009-10 THROUGH MAM 2010 LARGELY DUE TO EL NINO. LIKELY ABOVE MEDIAN
PRECIPITATION FOR THE GULF COAST AND FLORIDA INTO THE SPRING OF 2010 IS MAINLY
A RESULT OF THE LIKELY IMPACT OF EL NINO BEGINNING WITH OND 2009 AND PEAKING IN
JFM 2010. THE ENHANCED PROBABILITY OF ABOVE MEDIAN PRECIPITATION ACROSS THE
ENTIRE SOUTHERN US DURING THE WINTER SEASONS WHICH EXTENDS INTO THE SOUTHERN
PLAINS DURING JFM 2010 IS DUE TO EXPECTED EL NINO IMPACTS. DUE TO THE
UNCERTAINTY IN THE POTENTIAL STRENGTH OF THE EL NINO, THE SHIFTS IN THE
PROBABILITY DISTRIBUTION ACROSS THE SOUTHWEST AND CALIFORNIA IS FAIRLY SMALL.
USING THE CONSOLIDATION FORECASTS AS A GUIDE, SIGNALS PRIMARILY DUE TO
PRECIPITATION TRENDS ARE INDICATED IN JJA 2010 TO SON 2010. PARTS OF THE
PACIFIC NORTHWEST ARE MOST LIKELY TO RECEIVE BELOW MEDIAN PRECIPITATION DURING
THE SUMMER OF 2010. A DECADAL PRECIPITATION TREND LEADS TO THE ENHANCED
PROBABILITY OF ABOVE MEDIAN PRECIPITATION EAST OF THE CENTRAL ROCKIES. FLORIDA
AND PARTS OF THE SOUTHERN ATLANTIC COAST ARE MOST LIKELY TO RECEIVE ABOVE
MEDIAN PRECIPITATION FOR PARTICULAR SEASONS FROM JJA TO SON 2010 DUE TO DECADAL
TRENDS IN TROPICAL PRECIPITATION.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: MIKE HALPERT
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 OCT 15 2009
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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