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PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EDT THURSDAY OCT 18 2012
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 TOGETHER 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", WHICH ARE USED AT TIMES 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
1981-2010).
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 CONSIDERED LESS PREDICTABLE ON A SEASONAL
TIMESCALE THAN ENSO.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE
VARIABILITY AFFECTING 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 SPRING AND 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). THE UPGRADED PARALLEL VERSION OF THE CFS (CFSV2) BECAME OPERATIONAL IN
LATE MARCH OF 2011. BOTH VERSIONS OF CFS ARE CURRENTLY RUN IN PARALLEL. AN
EXPERIMENTAL MODEL FORECAST SYSTEM, THE NATIONAL MULTI-MODEL ENSEMBLE,
COMPRISED OF SEVERAL MODELS AND DESIGNATED NMME, MAY ALSO BE USED
EXPERIMENTALLY AND SUBJECTIVELY UNTIL IT IS INCLUDED INTO THE CONSOLIDATION. AN
INTERNATIONAL MODEL ENSEMBLE DESIGNATED IMME IS ALSO AVAILABLE.
9) CONSOLIDATION (CON) - AN OBJECTIVE, SKILL WEIGHTED COMBINATION 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.
BORDERLINE ENSO-NEUTRAL-WEAK EL NINO CONDITIONS PREVAILED ACROSS THE EQUATORIAL
PACIFIC OCEAN DURING SEPTEMBER. THE SEA SURFACE TEMPERATURE (SST) ANOMALY
PATTERN, WHICH ONLY A MONTH EARLIER SHOWED MOSTLY ABOVE-NORMAL ALONG THE
CENTRAL AND EASTERN EQUATORIAL PACIFIC, HAS WEAKENED CONSIDERABLY. BUOY DATA
INDICATES NEAR TO ABOVE-NORMAL SSTS FROM 140W WESTWARD ACROSS THE DATE LINE,
AND NEAR TO BELOW-NORMAL SSTS FROM 140W EASTWARD TO THE SOUTH AMERICAN COAST.
SST ANOMALIES IN THE NINO 3.4 REGION ARE HOVERING NEAR THE POSITIVE 0.5 C
THRESHOLD. DYNAMICAL AND STATISTICAL MODELS PREDICT SST ANOMALIES IN THIS
REGION TO EITHER HOLD STEADY NEAR THE POSITIVE 0.5 C THRESHOLD, OR BRIEFLY
EXCEED IT INTO WEAK EL NINO TERRITORY FOR NDJ 2012-13 AND DJF 2012-13, AFTER
WHICH MOST MODELS GRADUALLY DECREASE THE REGIONAL SST ANOMALIES TOWARDS ZERO.
THE LATEST OBSERVATIONS AND MODEL PREDICTIONS EMPHASIZE THE LARGE AMOUNT OF
UNCERTAINTY ASSOCIATED WITH THE SURFACE TEMPERATURE AND PRECIPITATION OUTLOOKS
FOR THE UNITED STATES DURING THIS UPCOMING WINTER SEASON.
THE NDJ 2012-13 TEMPERATURE OUTLOOK INDICATES ENHANCED CHANCES FOR ABOVE NORMAL
TEMPERATURES ACROSS MOST OF THE WESTERN HALF OF THE LOWER 48 STATES, AND FOR
NORTHERN AND CENTRAL ALASKA, AND ENHANCED CHANCES FOR BELOW-NORMAL TEMPERATURES
OVER THE FLORIDA PENINSULA. THIS IS SUPPORTED BY DYNAMICAL MODELS AND BY LOCAL
SSTS ALONG THE SHORE OF NORTHERN ALASKA.
THE NDJ 2012-13 PRECIPITATION OUTLOOK INDICATES AN INCREASED LIKELIHOOD FOR
BELOW-MEDIAN PRECIPITATION FOR THE PACIFIC NORTHWEST, NORTHERN SECTIONS OF BOTH
CALIFORNIA AND NEVADA, MOST OF THE ALASKA PANHANDLE, AND ACROSS MIDDLE AND
UPPER PORTIONS OF THE MISSISSIPPI VALLEY AND ADJACENT EASTERN PLAINS BASED ON
THE DYNAMICAL MODELS. THERE IS AN INCREASED LIKELIHOOD FOR ABOVE-MEDIAN
PRECIPITATION ACROSS THE CENTRAL AND EASTERN GULF COAST REGION BASED ON THE
POSSIBILITY THAT WEAK EL NINO CONDITIONS COULD HAVE AN EFFECT DURING THIS
SEASON ACROSS THE GULF COAST REGION. ODDS ALSO FAVOR ABOVE-MEDIAN PRECIPITATION
OVER NORTHWESTERN PORTIONS OF ALASKA BASED ON DYNAMICAL MODEL CONSIDERATIONS.
IN LOCATIONS WHERE THE LIKELIHOODS OF SEASONAL MEAN TEMPERATURES AND SEASONAL
PRECIPITATION AMOUNTS ARE SIMILAR TO THE CLIMATOLOGICAL PROBABILITIES, EQUAL
CHANCES (EC) OF BELOW, NEAR, AND ABOVE-AVERAGE TEMPERATURE AND 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
PACIFIC SST ANOMALIES ALONG THE EQUATOR ARE NEAR TO SLIGHTLY ABOVE-AVERAGE WEST
OF ABOUT 140W, AND NEAR TO SLIGHTLY BELOW-AVERAGE EAST OF 140W. THE AVERAGE
HEAT CONTENT IN THE UPPER OCEAN NEAR THE EQUATOR HAS SUBSTANTIALLY DECLINED
DURING THE PAST MONTH. THE LARGE POOL OF SUBSURFACE WARMTH IN THE CENTRAL AND
EASTERN EQUATORIAL PACIFIC OCEAN JUST ONE MONTH EARLIER HAS MOSTLY DISAPPEARED.
THE SUB-SURFACE THERMAL PROFILE IN THIS REGION IS NOW ILL-DEFINED WITH WEAK
ANOMALIES. FARTHER WEST, FROM 160W WESTWARD ACROSS THE DATE LINE TO 150E
LONGITUDE, ABOVE-AVERAGE TEMPERATURES ARE OBSERVED AT A DEPTH OF 50-200 METERS,
WITH THE LARGEST ANOMALIES RANGING BETWEEN +2.0C AND +3.0C.
THE TROPICAL ATMOSPHERIC CIRCULATION IS APPARENTLY HAVING A DIFFICULT TIME IN
TRANSITIONING FROM ENSO-NEUTRAL TO WEAK EL NINO CONDITIONS. THIS IS REVEALED BY
AN INCREASE IN LOW-LEVEL WESTERLY WIND ANOMALIES IN THE FAR WESTERN PACIFIC
(TYPICAL OF A WARM EVENT), AND ENHANCED TROPICAL CONVECTION OVER BOTH THE DATE
LINE (AGAIN TYPICAL OF A WARM EVENT) AND THE MARITIME CONTINENT (NOT TYPICAL).
THESE MIXED SIGNALS ONLY COMPLICATE THIS SET OF SEASONAL TEMPERATURE AND
PRECIPITATION OUTLOOKS FOR THE UNITED STATES, ESPECIALLY FOR THE FIRST FEW
LEADS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
LATEST WEEKLY OBSERVATIONS PLACE THE NINO 3.4 INDEX AT ABOUT 0.1C. THE CPC SST
CONSOLIDATION FORECAST FOR THE NINO 3.4 REGION STARTS OFF WITH BORDERLINE
NEUTRAL-WEAK EL NINO OCEANIC NINO INDEX (ONI) VALUES NEAR +0.5C, THEN GRADUALLY
DECLINES TO NEAR ZERO BY JFM 2013, AND REMAINING NEAR ZERO THROUGHOUT THE NEXT
SEVERAL SEASONS INTO AMJ 2013. THIS SKILL-WEIGHTED SST CONSOLIDATION FORECAST
USES THE CONSTRUCTED ANALOG, CANONICAL CORRELATION ANALYSIS, MARKOV MODEL, AND
CFSV2 AS INPUTS. THE CFSV2 ENSEMBLE PLUME FORECAST FOR THE NINO 3.4 REGION
SHOWS CONSIDERABLE VARIATION OF SST ANOMALIES (AS MUCH AS ONE FULL DEGREE C ON
EITHER SIDE OF ZERO) THROUGHOUT THE WINTER AND EARLY SPRING. HOWEVER, THE
ENSEMBLE MEAN DEPICTS A VERY SLOW DECLINE FROM INITIAL CONDITIONS (NEAR +0.5C)
TO ZERO BY FEBRUARY 2013, AND THEN SLOWLY CLIMBING FOR SEVERAL MONTHS
THEREAFTER.
AN SST PLUME DIAGRAM FOR THE NINO 3.4 REGION SHOWING THE AVERAGE OF 17
DYNAMICAL MODELS AND 8 STATISTICAL MODELS DEPICTS THE DYNAMICAL AVERAGE BRIEFLY
EXCEEDING +0.5C FOR BOTH NDJ 2012-13 AND DJF 2012-13 WHICH VERY SLOWLY TAPERS
OFF TO ABOUT +0.25C BY SUMMER, WITH THE STATISTICAL AVERAGE PARALLELING THE
DYNAMICAL MODEL CURVE BUT REMAINING SEVERAL TENTHS OF A DEGREE C COOLER.
BASED ON THESE FORECAST TOOLS, IT IS POSSIBLE THAT AN EL NINO EVENT OF WEAK
AMPLITUDE WILL OCCUR LATER THIS FALL AND INTO WINTER. FOR THE PHYSICAL IMPACT,
THE THRESHOLD DEFINITION OF HALF A DEGREE IS SOMEWHAT ARBITRARY. SO A NON-EVENT
OF 0.49 C MAY BE AS IMPORTANT FOR THE NORTH AMERICAN CLIMATE AS A WEAK EVENT OF
0.51.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
WITH THE ADVANCE OF COUPLED ATMOSPHERE OCEAN MODELS WE NOW HAVE A SET OF ABOUT
10 MODELS, EACH WITH MANY RUNS, THAT IN GENERAL REFLECT SST ANOMALIES THAT ARE
WEAKER THAN EXPECTED A MONTH AGO. WE DO MAINTAIN CONTINUITY AS MUCH AS IS
REASONABLE WITH FORECASTS RELEASED LAST MONTH. ENSO COMPOSITES HAVE BEEN
CONSIDERED BUT DOWNPLAYED. THE FORECAST WAS ADJUSTED TO REFLECT THE NMME AND
IMME, AS WELL AS THE CONSOLIDATION WHERE AND WHEN DEEMED HELPFUL. A SIGNIFICANT
WILDCARD IN THE UPCOMING WINTER OUTLOOK IS THE UNCERTAINTY ASSOCIATED WITH THE
PHASE OF THE ARCTIC OSCILLATION (AO). UNFORTUNATELY, IT IS VERY DIFFICULT TO
PREDICT THE PHASE OF THE AO MORE THAN A FEW WEEKS INTO THE FUTURE. THE OUTLOOKS
FOR NDJ 2012-13 THUS PRIMARILY REFLECT DYNAMICAL MODEL FORECASTS INCLUDING THE
CFSV2 AND IMME AND NMME FORECASTS, AS WELL AS DECADAL TIMESCALE TRENDS. THE
CONSOLIDATION OF (MOSTLY) STATISTICAL TOOLS IS THE ONLY BASIS FOR FORECASTS
FROM AMJ 2013 ONWARD.
PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2012 TO NDJ 2013
TEMPERATURE
THE NDJ 2012-13 TEMPERATURE OUTLOOK INDICATES ENHANCED CHANCES FOR ABOVE-NORMAL
TEMPERATURES ACROSS MOST OF THE WESTERN HALF OF THE LOWER 48 STATES, AND FOR
NORTHERN AND CENTRAL ALASKA, AND ENHANCED CHANCES FOR BELOW-NORMAL TEMPERATURES
OVER THE FLORIDA PENINSULA. THIS IS SUPPORTED BY DYNAMICAL MODELS AND BY LOCAL
SSTS ALONG THE SHORE OF NORTHERN ALASKA.
TEMPERATURE OUTLOOKS FROM DJF 2012-13 THROUGH FMA 2013 SHOW INCREASED CHANCES
OF ABOVE-NORMAL TEMPERATURES ACROSS MUCH OF THE WESTERN AND CENTRAL CONUS AND
NORTHERN PORTIONS OF ALASKA, MOSTLY DUE TO DYNAMICAL MODEL INPUT (CFSV2, NMME,
IMME) AND THE CON TOOL. PROBABILITIES ARE HIGHEST IN NORTHERN ALASKA, REACHING
50 PERCENT IN NDJ AND DJF. THE ELEVATED ODDS FOR BELOW-NORMAL TEMPERATURES IN
FLORIDA IN NDJ AND DJF ARE DUE TO THE POSSIBLE EARLY-SEASON INFLUENCE OF WEAK
EL NINO CONDITIONS, AS SEEN IN EMPIRICAL COMPOSITES AND THE CON. THE OUTLOOKS
FROM MAM AND AMJ 2013 ONWARD ARE BASED ON DECADAL TRENDS AS INDICATED BY THE
CONSOLIDATION TOOL.
IN AREAS WITHOUT STRONG CLIMATE SIGNALS, EQUAL CHANCES FOR BELOW-NORMAL, NEAR-
NORMAL, OR ABOVE-NORMAL SEASONAL MEAN TEMPERATURES IS PREDICTED.
PRECIPITATION
THE NDJ 2012-13 PRECIPITATION OUTLOOK INDICATES AN INCREASED LIKELIHOOD FOR
BELOW-MEDIAN PRECIPITATION FOR THE PACIFIC NORTHWEST, NORTHERN SECTIONS OF BOTH
CALIFORNIA AND NEVADA, MOST OF THE ALASKA PANHANDLE, AND ACROSS MIDDLE AND
UPPER PORTIONS OF THE MISSISSIPPI VALLEY AND ADJACENT EASTERN PLAINS BASED ON
THE DYNAMICAL MODELS. THERE IS AN INCREASED LIKELIHOOD FOR ABOVE-MEDIAN
PRECIPITATION ACROSS THE CENTRAL AND EASTERN GULF COAST REGION BASED ON THE
POSSIBILITY THAT WEAK EL NINO CONDITIONS COULD HAVE AN EFFECT DURING THIS
SEASON ACROSS THE GULF COAST REGION. ODDS ALSO FAVOR ABOVE-MEDIAN PRECIPITATION
OVER NORTHWESTERN PORTIONS OF ALASKA BASED ON DYNAMICAL MODEL CONSIDERATIONS.
IT IS UNCLEAR AT THIS TIME WHETHER OR NOT WEAK EL NINO CONDITIONS WILL BECOME
ESTABLISHED THIS WINTER ACROSS THE U.S., AND TO WHAT DEGREE AN EXTENDED
SUBTROPICAL JET STREAM MAY INFLUENCE PRECIPITATION PATTERNS ACROSS THE
SOUTHEAST. THEREFORE, LAST MONTH'S PREDICTED AREA OF ABOVE-MEDIAN PRECIPITATION
HAS BEEN SIGNIFICANTLY REDUCED IN COVERAGE THIS MONTH ACROSS THE SOUTH. IN
ADDITION, THE PREDICTED AREA OF BELOW-MEDIAN PRECIPITATION OVER THE OHIO VALLEY
(A FEATURE CONSISTENT WITH EL NINO WINTERS) FOR THE DJF, JFM AND FMA SEASONS
LAST MONTH HAS BEEN REPLACED WITH EC. SOME CLIMATE MODELS TILT THE ODDS TOWARDS
THE INTRODUCTION OF A NEW AREA OF BELOW-MEDIAN PRECIPITATION OVER THE UPPER AND
MIDDLE MISSISSIPPI VALLEY FOR BOTH NDJ AND DJF. THE PREDICTED BELOW-MEDIAN
PRECIPITATION AMOUNTS OVER THE PACIFIC NORTHWEST ARE STRONGLY INDICATED BY
VARIOUS DYNAMICAL MODELS. IN NORTHERN ALASKA, THE ENHANCED ODDS OF ABOVE-MEDIAN
PRECIPITATION IN NDJ 2012-13 ARE BASED ON NMME PROBABILISTIC FORECASTS, AND TO
SOME EXTENT THE CFSV2 MODEL. FOR DJF 2012-13 THROUGH MAM 2013, DYNAMICAL MODELS
SUPPORT ELEVATED ODDS OF ABOVE-MEDIAN PRECIPITATION AMOUNTS ACROSS PORTIONS OF
THE GULF COAST REGION. BEYOND MAM, THERE ARE PRACTICALLY NO SIGNALS FROM
DECADAL TRENDS, EXCEPT FOR BELOW-MEDIAN PRECIPITATION IN THE PACIFIC NORTHWEST
FOR JJA AND JAS 2013.
IN AREAS WITHOUT STRONG CLIMATE SIGNALS, EQUAL CHANCES FOR BELOW, NEAR, OR
ABOVE-MEDIAN SEASONAL PRECIPITATION AMOUNTS IS PREDICTED.
FORECASTER: ANTHONY ARTUSA
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING
THE WORLD METEROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3
COMPLETE DECADES AS THE CLIMATIC REFERENCE PERIOD. THE PROBABILITY ANOMALIES
FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT
SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS.
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 NOV 15 2012
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011
FORECAST RELEASE.
$$ 
