402
FXUS05 KWBC 201230
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU AUG 20 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
BOREAL WINTER AND 2010. 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
INCREASE FROM HAVING LITTLE OR NO IMPACT FOR SON 2009 TO THE GREATEST IMPACT
DURING THE WINTER SEASONS. A WEAK TO MODERATE EL NINO EVENT IS EXPECTED DURING
WINTER, THOUGH A STRONGER EVENT IS 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 SON 2009 INDICATES AN ENHANCED LIKELIHOOD OF ABOVE
NORMAL TEMPERATURES FOR THE NORTHEAST US, THE WEST COAST, THE SOUTHWEST US, AND
ALASKA. WHERE THE LIKELIHOOD OF ABOVE OR BELOW NORMAL SEASONAL MEAN
TEMPERATURES ARE SIMILAR TO THE CLIMATOLOGY, EQUAL CHANCES OF BELOW, NEAR, AND
ABOVE NORMAL ARE INDICATED.
BELOW MEDIAN ACCUMULATED PRECIPITATION IS MOST LIKELY DURING SON 2009 FOR PARTS
OF THE PACIFIC NORTHWEST AND THE NORTHERN ROCKY MOUNTAINS. ABOVE MEDIAN
PRECIPITATION AMOUNTS ARE MORE LIKELY OVER THE GULF COAST AND FLORIDA, AND FOR
PARTS OF THE CENTRAL PLAINS. 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 IN 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 IN THE REGION BELOW 100 METERS DEPTH WEST OF ABOUT 160 W
AND JUST BELOW THE SURFACE IN THE EASTERN PACIFIC. HISTORICALLY, POSITIVE
TEMPERATURE ANOMALIES IN THE UPPER OCEAN PRECEDE THE ONSET AND FURTHER
DEVELOPMENT OF EL NINO EVENTS, AND TROPICAL PACIFIC TEMPERATURES ARE UNLIKELY
TO RETURN TO AN ENSO NEUTRAL STATE PRIOR TO JANUARY AFTER MAINTAINING AN EL
NINO STATE INTO AUGUST. THE TEMPERATURE STATE OF THE TROPICAL PACIFIC IS
UNUSUAL WITH POSITIVE ANOMALIES ACROSS THE ENTIRE BASIN AT AND BELOW THE
SURFACE.
THE MOST RECENT 30-DAY OUTGOING LONGWAVE RADIATION ANOMALIES INDICATE THAT
CONVECTION IS SUPPRESSED OVER THE MARITIME CONTINENT AND ENHANCED ACROSS THE
WESTERN PACIFIC TO THE INTERNATIONAL DATE LINE, AS WELL AS NORTH OF THE EQUATOR
TO THE EAST. WESTERLY WIND BURSTS OFTEN OCCUR OVER THE WESTERN EQUATORIAL
PACIFIC AS AN EL NINO EVENT DEVELOPS AS OCCURRED AT THE END OF JULY. 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 EXCEEDING +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 THE
BOREAL WINTER SEASON. THIS FORECAST IS NEAR THE TOP OF THE IRI MULTI-MODEL
ENSEMBLE PLUME. THE CPC STATISTICAL MODELS ARE GENERALLY FORECASTING A WEAK TO
MODERATE EL NINO EVENT PEAKING AROUND +1 TO +1.5 CELSIUS AROUND THE END OF
2009, WHERE THE CONSTRUCTED ANALOG METHOD PREDICTS THE GREATEST POSITIVE
ANOMALY. THE STATISTICAL MODEL FORECASTS ARE NOW CONSIDERABLY WARMER THAN THEY
WERE IN THEIR FORECASTS IN PREVIOUS MONTHS, AND REMAIN COOLER THAN THE
DYNAMICAL MODEL ENSO FORECASTS. THE CPC CONSOLIDATION OF NINO 3.4 SST
TEMPERATURE ANOMALY FORECASTS INDICATES THAT POSITIVE TROPICAL PACIFIC SST
ANOMALIES ARE MOST LIKELY TO CONTINUE INTO MAM 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 GIVEN
INCREASING WEIGHTS IN THE OUTLOOKS WITH THE CONTINUATION OF THE CURRENT WARM
PACIFIC STATE INTO AUGUST. OUTLOOKS FOR MAM 2010 AND LATER ARE BASED ON THE
CONSOLIDATION FORECASTS AND LARGELY ATTRIBUTABLE TO DECADAL CLIMATE TRENDS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2009 TO SON 2010
TEMPERATURE:
THE TEMPERATURE OUTLOOKS FOR SON 2009 THROUGH SON 2010 INDICATE THAT
THREE-MONTH MEAN TEMPERATURES ARE MOST LIKELY TO BE IN THE ABOVE NORMAL
CATEGORY FOR MUCH OF THE US WITH A SIGNIFICANT CLIMATE SIGNAL. ALL OUTLOOKS TO
SOME EXTENT FOLLOW THE CPC CONSOLIDATION FORECAST WITH MODIFICATIONS DUE TO THE
INFLUENCE OF THE EXPECTED IMPACT OF AN EL NINO STATE. THE STATISTICAL
CONSOLIDATION DOES NOT ACCOUNT FOR INCREASES IN THE SKILL OF FORECASTS THAT
INCLUDE A CLEAR ENSO SIGNAL. AREAS OF LIKELY WARMER THAN NORMAL MEAN
TEMPERATURES ARE AN INDICATION OF THE CURRENT CLIMATE STATE, PARTLY
ATTRIBUTABLE TO DECADAL CLIMATE TRENDS, BUT ALSO DUE TO INTERANNUAL VARIABILITY
ATTRIBUTABLE TO THE ENSO STATE. BEGINNING IN SON 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 NORMAL TEMPERATURES 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 NORMAL CATEGORY FOR THE
SOUTHEAST AND ALONG THE GULF COAST FROM NDJ 2009 TO FMA 2010 AS A RESULT OF EL
NINO IMPACTS. BEGINNING IN THE NORTHEAST FOR SON 2009 AND BECOMING MORE LIKELY
OVER THE NORTHERN CENTRAL US DURING THE WINTER SEASONS, MEAN TEMPERATURES ARE
MOST LIKELY TO BE IN THE ABOVE NORMAL CATEGORY. THOUGH MEAN WINTER TEMPERATURES
IN THE NORTHERN PLAINS HAVE MOST OFTEN BEEN ABOVE NORMAL IN THE LAST DECADE,
THIS DECADAL TEMPERATURE SIGNAL SHOULD BE ENHANCED DUE TO THE DEVELOPING EL
NINO WHICH IS 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 NORMAL TEMPERATURES DUE TO THE CLIMATE TREND AND
FOLLOWING THE CFS AND OCN FORECASTS.
THE CFS FORECASTS FOR OND 2009 THROUGH MAM 2010 INDICATE A STRONG EL NINO AND
IMPACTS RESULTING FROM AN EL NINO CLIMATE STATE. THE CFS OUTLOOKS HAVE
INFLUENCED THE FORECAST ALONG WITH ENSO COMPOSITES, THROUGH THE CON AND AS A
REPRESENTATION OF POSSIBLE EL NINO IMPACTS. THE FORECASTS ARE SOMEWHAT
CONSERVATIVE COMPARED TO THE CFS, BECAUSE THE STRENGTH OF THE DEVELOPING EL
NINO IS STILL UNCERTAIN.
FORECAST LEADS FROM AMJ 2010 THROUGH SON 2010 ARE BASED ON THE CONSOLIDATION
FORECAST AND ATTRIBUTABLE TO TEMPERATURE TRENDS AND WEAK INTERANNUAL SIGNALS.
PRECIPITATION:
THE PRECIPITATION OUTLOOK FOR SON 2009 IS BASED PRIMARILY ON THE CONSOLIDATION
FORECAST, AS ARE THE LATER LEADS FROM AMJ TO SON 2010. FOR THE FORECASTS FROM
OND 2009 THROUGH MAM 2010 SIGNIFICANT WEIGHT HAS BEEN GIVEN TO THE EXPECTED
IMPACTS OF A PROBABLE EL NINO EVENT. THE CFS PRECIPITATION FORECAST AND ENSO
COMPOSITES HAVE BEEN USED AS A GUIDE TO PREDICTABLE IMPACTS. CONFIDENCE IN THE
IMPACTS OF A PREDICTED EL NINO EVENT HAS INCREASED SINCE LAST MONTH.
THE AREA OF ENHANCED PROBABILITY OF BELOW MEDIAN PRECIPITATION FORECAST FOR THE
PACIFIC NORTHWEST FROM SON 2009 THROUGH FMA 2010 IS A RESULT OF BOTH THE
DECADAL CLIMATE TREND AND THE IMPACT OF AN EL NINO. BELOW MEDIAN PRECIPITATION
IS ALSO MOST LIKELY FOR PARTS OF THE MISSISSIPPI AND OHIO VALLEYS FROM DJF
THROUGH MAM 2010 LARGELY DUE TO EL NINO. LIKELY ABOVE MEDIAN PRECIPITATION FOR
THE GULF COAST AND FLORIDA INTO THE SPRING OF 2010 IS ALMOST ENTIRELY DUE TO
THE CLIMATE TREND IN THE FIRST SON 2009 SEASON AND MAINLY A RESULT OF THE
LIKELY IMPACT OF EL NINO BEGINNING WITH OND 2009, PEAKING IN JFM 2010. THE
ENHANCED PROBABILITY OF ABOVE MEDIAN PRECIPITATION DUE TO EL NINO EXTENDS INTO
THE SOUTHERN PLAINS IN OND 2010 AND ACROSS THE ENTIRE SOUTHERN US DURING THE
WINTER SEASONS.
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 FROM JJA TO SON 2010 DUE TO A DECADAL TREND IN TROPICAL
PRECIPITATION.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: DAN COLLINS
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 SEP 17 2009
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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