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FXUS05 KWBC 191331
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EST THU NOV 19 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.
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 MODERATE EL NINO CONDITIONS EXIST IN THE TROPICAL PACIFIC. THEY MAY
HAVE BE AT MAXIMUM STRENGTH RIGHT NOW AND ARE EXPECTED TO PERSIST INTO THE
2009-10 NORTHERN HEMISPHERE WINTER. THE LIKELIHOOD OF A CONTINUING EL NINO
EVENT INFLUENCES THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR DJF 2009-10
THROUGH MAM 2010, MAINLY VIA EL NINO COMPOSITES. THE IMPACT OF EL NINO ON THE
CLIMATE OVER NORTH AMERICA HAS HISTORICALLY BEEN THE GREATEST DURING THE WINTER
SEASONS. 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 DJF 2009-10 INDICATES AN ENHANCED LIKELIHOOD OF
ABOVE AVERAGE TEMPERATURES FOR MUCH OF THE WESTERN HALF OF THE CONUS AND
ALASKA, AND ESPECIALLY SO IN THE NORTHERN ROCKIES ALONG THE CANADIAN BORDER.
BELOW NORMAL TEMPERATURES ARE LIKELY FROM CENTRAL TEXAS ALONG THE GULF COAST TO
THE MID-ATLANTIC. IN LOCATIONS 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 PRECIPITATION IS MOST LIKELY DURING DJF 2009-10 FOR PARTS OF THE
PACIFIC NORTHWEST AND THE OHIO VALLEY. ABOVE MEDIAN PRECIPITATION AMOUNTS ARE
MOST LIKELY IN TEXAS, FLORIDA, AND IN CALIFORNIA, AND NORTHERN SECTIONS OF
ALASKA. IN LOCATIONS WHERE THE LIKELIHOOD OF ABOVE OR BELOW MEDIAN SEASONAL
PRECIPITATION IS SIMILAR TO THE CLIMATOLOGICAL PROBABILITIES, 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
WEEKLY SEA SURFACE TEMPERATURE (SST) ANOMALIES HAVE RAPIDLY WARMED IN LATE
OCTOBER AND EARLY NOVEMBER, AND EXCEED +1.5 CELSIUS ACROSS MUCH OF THE
EQUATORIAL PACIFIC OCEAN AND ARE LOCALLY OVER +2C CELSIUS FROM THE DATE LINE
EAST TO 130W. OUTGOING LONGWAVE RADIATION ANOMALIES ARE NOT YET IN SYNC WITH AN
EL NINO EVENT. TRADE WINDS WERE VERY WEAK IN MID TO LATE OCTOBER BUT ARE CLOSE
TO NORMAL AT PRESENT. SUBSURFACE HEAT CONTENT IS GENERALLY ABOVE NORMAL IN THE
UPPER 200 METERS OF THE TROPICAL PACIFIC OCEAN WITH WATER TEMPERATURE ANOMALIES
EXCEEDING +5 CELSIUS AT THERMOCLINE DEPTH NEAR 130W, MUCH MORE THAN A MONTH
AGO. 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 SPRING
2010.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE CURRENT MEAN PDF CORRECTED ENSEMBLE CFS FORECAST INDICATES SST ANOMALIES IN
THE NINO 3.4 REGION PRESENTLY AT PEAK NEAR +1.5 CELSIUS, THUS CALLING FOR
MODERATE TO STRONG EL NINO CONDITIONS BUT NO FURTHER STRENGTHENING. 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 CPC
CONSOLIDATION OF NINO 3.4 SST TEMPERATURE ANOMALY FORECASTS INDICATES THAT THE
CURRENT EL NINO WILL LIKELY WEAKEN AND END BY MAM OR AMJ 2010. THE CFS FORECAST
IS NO LONGER AMONG THE WARMEST ONES IN THE IRI MULTI-MODEL ENSEMBLE PLUME AND
CONSENSUS BY EYE OF THE IRI PLUME AGREES WELL WITH CPC'S CONSOLIDATION FORECAST.
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 DJF 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
EARLY ON.
PROGNOSTIC DISCUSSION OF OUTLOOKS - DJF 2009 TO DJF 2010
TEMPERATURE:
THE TEMPERATURE OUTLOOKS FOR DJF 2009-10 THROUGH DJF 2010-11 INDICATE THAT
THREE-MONTH MEAN TEMPERATURES ARE MOST LIKELY TO BE IN THE ABOVE NORMAL
CATEGORY FOR MUCH OF THE WESTERN U.S. 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 DJF THROUGH MAM. 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 DJF 2009 TO FMA 2010 AS A RESULT OF EL NINO.
THE LIKELIHOOD OF ABOVE AVERAGE TEMPERATURES IN THE NORTH-CENTRAL US PEAKS IN
JFM. 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 AMJ 2010 THROUGH DJF 2010 ARE BASED ON THE CONSOLIDATION
FORECAST AND ATTRIBUTABLE TO TEMPERATURE TRENDS AND WEAK INTERANNUAL SIGNALS.
PRECIPITATION:
THE PRECIPITATION OUTLOOKS FOR DJF 2009-10 THROUGH MAM 2010 ARE MAINLY BASED ON
THE EXPECTED IMPACTS OF AN EL NINO EVENT, INCLUDING THOSE DEPICTED BY EL NINO
COMPOSITES, WHILE THE LONGER LEAD FORECASTS FROM AMJ TO DJF 2010-11 ARE MAINLY
BASED ON THE CONSOLIDATION, WHICH USES ONLY STATISTICAL TOOLS AS INPUT AFTER
MJJ 2010.
THE AREA OF ENHANCED PROBABILITY OF BELOW MEDIAN PRECIPITATION FORECAST FOR THE
PACIFIC NORTHWEST FROM DJF 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 EXPECTED IMPACT
OF EL NINO BEGINNING WITH DJF 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 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 DJF 2010-11 BELOW MEDIAN PRECIPITATION DUE TO TRENDS RETURNS IN THE
SOUTHEAST.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: HUUG VAN DEN DOOL
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 DEC 17 2009
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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