240
FXUS05 KWBC 151231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU OCT 15 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.
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.
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.
CURRENTLY WEAK EL NINO CONDITIONS ARE EXPECTED TO STRENGTHEN AND PERSIST INTO
THE 2009-10 NORTHERN HEMISPHERE WINTER. THE LIKELIHOOD OF A CONTINUING EL NINO
EVENT INFLUENCES THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR OND 2009
THROUGH MAM 2010, MAINLY VIA COMPOSITES FOR WEAK-TO-MODERATE EVENTS. 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. A STRONG EVENT IS LESS LIKELY, BUT STILL 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 NDJ 2009-10 INDICATES AN ENHANCED LIKELIHOOD OF
ABOVE AVERAGE TEMPERATURES FOR MUCH OF THE WESTERN HALF OF THE CONUS AND
ALASKA. WHERE THE CHANCE OF ABOVE OR BELOW AVERAGE SEASONAL MEAN TEMPERATURES
ARE SIMILAR TO A RANDOM DRAW FROM THE HISTORICAL RECORD (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, AND IN CALIFORNIA, AND NORTHERN
SECTIONS OF ALASKA. 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
FIVE-DAY MEAN SEA SURFACE TEMPERATURE (SST) ANOMALIES HAVE SLOWLY WARMED OVER
THE FIRST HALF OF OCTOBER, AND 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. OUTGOING LONGWAVE RADIATION
ANOMALIES INDICATE THAT CONVECTION IS SUPPRESSED OVER THE MARITIME CONTINENT
AND SLIGHTLY ENHANCED ACROSS THE WESTERN PACIFIC. TRADE WINDS IN THE EASTERN
PART OF THE BASIN WEAKENED DURING THIS PERIOD. 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 150W. 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.
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 CFS SST FORECAST HAS
RECENTLY BEGUN TO PREDICT A SLIGHTLY STRONGER EVENT THAN IT HAS IN RECENT
WEEKS. 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
LIKELY 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. THE CFS
WAS RELIED UPON TO A CONSIDERABLE DEGREE. ITS FORECASTS HAVE BEEN CONSISTENT
WITH DEVELOPING EL NINO CONDITIONS, THOUGH POSSIBLY ON THE TOO-INTENSE SIDE.
THE CFS FORECAST ALSO INDICATES MORE COLD TEMPERATURES IN THE CENTRAL AND
EASTERN CONUS EARLY IN THE FORECAST PERIOD. THE TEMPERATURE OCN, OR TREND, HAS
BEEN CHANGING OVER THE PAST DECADE. IN THE 90S, THE OCN'S STRONGEST SIGNAL
(FOR WARMTH) WAS DURING JFM. THIS HAS SHIFTED TO THE LATE FALL, AND HAS
WEAKENED IN THE WINTER. THE LARGEST PART OF THE TREND SIGNAL FOR WARMTH
CONTINUES TO RESIDE IN THE SOUTHWEST CONUS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2009 TO NDJ 2010
TEMPERATURE:
THE TEMPERATURE OUTLOOKS FOR NDJ 2009 THROUGH NDJ 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 COMPOSITES, AND THE
CONSOLIDATION. ALL OUTLOOKS USE THE CPC CONSOLIDATION FORECAST AS A STARTING
POINT WITH MODIFICATIONS DUE TO THE INFLUENCE OF THE EXPECTED IMPACT OF EL NINO
FROM NDJ THROUGH MAM. THE STATISTICAL CONSOLIDATION DOES NOT ACCOUNT FOR
INCREASES IN THE SKILL OF FORECASTS THAT INCLUDE AN ENSO SIGNAL. BEGINNING IN
NDJ 2009 AND ONTINUING TO SOME DEGREE THROUGHOUT THE NEXT 12 MONTHS, ABOVE
NORMAL MEAN TEMPERATURES ARE MOST LIKELY IN THE SECTIONS OF THE US SOUTHWEST,
MAINLY AS A RESULT OF THE LOCAL TEMPERATURE TREND. SEASONAL MEAN TEMPERATURES
ARE MOST LIKELY TO BE IN THE BELOW AVERAGE CATEGORY FOR THE SOUTHEAST, SECTIONS
OF THE MID-ATLANTIC AND ALONG THE GULF COAST REGIONS 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 NDJ 2009 THROUGH FMA 2010. 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 NDJ 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 ARE MAINLY BASED ON
THE EXPECTED IMPACTS OF A PROBABLE EL NINO EVENT, INCLUDING THOSE DEPICTED BY
EL NINO COMPOSITES, WHILE THE LONGER LEAD FORECASTS FROM AMJ TO NDJ 2010 ARE
MAINLY BASED ON THE CONSOLIDATION, WHICH USES ONLY STATISTICAL TOOLS AS INPUT
AFTER AMJ 2010.
THE AREA OF ENHANCED PROBABILITY OF BELOW MEDIAN PRECIPITATION FORECAST FOR THE
PACIFIC NORTHWEST FROM NDJ 2009 THROUGH MAM 2010 IS A RESULT OF COMPOSITES OF
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 NDJ 2009, PEAKING IN JFM 2010 AND LIKELY
EXTENDING INTO MAM. 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, AND THE INHERENT NATURALY
VARIABILITY AMONG DIFFERENT EL NINO EVENTS, 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: ED O'LENIC
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 NOV 19 2009
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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