047
FXUS05 KWBC 201341
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EST THU DEC 20 2007
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 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). THE OCN TOOL
REPRESENTS THE TREND.
3) THE TROPICAL 30-60 DAY OSCILLATION - 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) 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.
6) STATISTICAL FORECAST TOOLS - CANONICAL CORRELATION ANALYSIS (CCA)... AND
SCREENING MULTIPLE LINEAR REGRESSION (SMLR).
7) DYNAMICAL FORECAST MODELS... INCLUDING THE NCEP CLIMATE FORECAST SYSTEM
(CFS).
8) AN OBJECTIVE CONSOLIDATION (ABBREVIATED CON IN THE TEXT) OF THE OCN...
CCA... SMLR 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.
A MODERATELY STRONG COLD EVENT (LA NINA) CONTINUES ACROSS THE PACIFIC BASIN.
SEA SURFACE TEMPERATURES (SSTS) ARE BELOW AVERAGE THROUGHOUT THE CENTRAL AND
EASTERN EQUATORIAL PACIFIC OCEAN, WITH ANOMALOUSLY COLD SSTS EXTENDING FROM THE
SOUTH AMERICAN COAST WESTWARD BEYOND THE DATE LINE TO 160E LONGITUDE. SSTS IN
THE NINO 3.4 REGION (FROM 5N TO 5S AND 170W TO 120W) ARE A GOOD INDICATOR OF
THE STRENGTH OF A LA NINA. SSTS IN THE NINO 3.4 REGION AVERAGED 1.5 DEGREES C
BELOW NORMAL DURING NOVEMBER, WHERE A VALUE OF 1.0 TO 1.5 DEGREES BELOW NORMAL
INDICATES THE EXISTENCE OF MODERATE LA NINA CONDITIONS.
THESE OBSERVATIONS AGREE WITH WHAT MOST DYNAMICAL AND STATISTICAL MODELS HAVE,
FOR SOME TIME, BEEN PREDICTING FOR THIS FALL AND WINTER. THESE FORECASTS AND
OBSERVATIONS SUPPORT A PREDICTION OF MODERATE LA NINA CONDITIONS FOR THE
JANUARY-FEBRUARY-MARCH (JFM) 2008 SEASON AND POSSIBLY FMA 2008 AS WELL,
FOLLOWED BY WEAK LA NINA CONDITIONS FOR MAM. THE CONSENSUS OF MODEL FORECASTS
FOR NINO 3.4 SSTS INDICATE THAT THE CURRENT SST ANOMALIES OF BETWEEN 1 AND 2
DEGREES C BELOW NORMAL ARE LIKELY TO PERSIST THROUGH JFM 2008 ... AND THEN
GRADUALLY DIMINISH DURING FMA AND MAM (SPRING) 2008.
THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR JANUARY-FEBRUARY-MARCH (JFM)
2008 REFLECT LA NINA IMPACTS IN COMBINATION WITH RECENT TRENDS. TEMPERATURES
FROM THE PACIFIC NORTHWEST EASTWARD ACROSS THE NORTHERN TIER OF STATES TO
NORTHERN MICHIGAN ARE EXPECTED TO BE COOLER THAN THE AVERAGE OF RECENT YEARS
AND SEASONAL MEANS SHOULD BE MORE IN LINE WITH THOSE EXPECTED IN THE 1971-2000
CLIMATE BASE PERIOD. MOST OF THE REMAINDER OF THE NATION, INCLUDING NORTHWEST
ALASKA, IS LIKELY TO EXPERIENCE ABOVE AVERAGE TEMPERATURES, BASED ON A
COMBINATION OF TREND AND LA NINA INFLUENCES. ELSEWHERE... THE FORECAST CALLS
FOR EQUAL CHANCES (EC) OF ABOVE-, NEAR-, AND BELOW AVERAGE TEMPERATURES.
THE PRECIPITATION OUTLOOK FOR JFM 2008 FAVORS ABOVE AVERAGE PRECIPITATION
AMOUNTS IN THE PACIFIC NORTHWEST AND NORTHERN ROCKIES, AND FROM THE CENTRAL
MISSISSIPPI VALLEY NORTHEASTWARD TO THE CENTRAL GREAT LAKES. BELOW AVERAGE
PRECIPITATION AMOUNTS ARE EXPECTED IN THE SOUTHWEST... THE SOUTHERN AND CENTRAL
PLAINS... ALONG THE GULF COAST AND THROUGHOUT MUCH OF THE SOUTHEASTERN U.S.
INCLUDING FLORIDA, THE MIDDLE ATLANTIC COAST STATES AND COASTAL SECTIONS FROM
THE DELMARVA PENINSULA TO FAR EASTERN SECTIONS OF MASSACHUSETTS. ELSEWHERE...
THE FORECAST CALLS FOR EQUAL CHANCES (EC) OF ABOVE-, NEAR-, AND BELOW AVERAGE
PRECIPITATION. THESE PRECIPITATION SIGNALS ARE THE EXPECTED RESPONSE TO A
MODERATE LA NINA, ALONG WITH A RELATIVELY SMALL INFLUENCE FROM TRENDS.
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
SEA SURFACE TEMPERATURES (SSTS) ARE SUBSTANTIALLY BELOW AVERAGE IN THE
EQUATORIAL PACIFIC FROM THE SOUTH AMERICAN COAST TO JUST WEST OF THE DATE LINE.
SST ANOMALIES ARE BETWEEN -2 AND -3 C FROM 120W EASTWARD... WHILE TEMPERATURES
IN THE CENTRAL EQUATORIAL PACIFIC ARE MOSTLY BETWEEN 1 AND 2 DEGREES C BELOW
NORMAL. AVERAGE SSTS IN THE NINO 3.4 AND NINO 4 REGIONS IN NOVEMBER WERE -1.5
C AND -1.1 C IN THOSE REGIONS RESPECTIVELY. NINO 3 TEMPERATURE DEPARTURE IS
NEAR -1.7 C, WHILE NINO 1+2 TEMPERATURE HAS AVERAGED ABOUT -2.2 C DEGREES BELOW
AVERAGE IN NOVEMBER. OCEAN TEMPERATURES IN THE UPPERMOST 200 METERS IN THE
EAST PACIFIC HAVE REMAINED WELL BELOW NORMAL, WITH LARGEST DEPARTURES OF -4 TO
-6 C BETWEEN 130W AND 140W, AND ALSO BETWEEN 90W AND 110W. ANOMALIES IN
OUTGOING LONGWAVE RADIATION SHOW SUPRESSED CONVECTION (POSITIVE ANOMALIES) OVER
MUCH OF THE EQUATORIAL PACIFIC... ESPECIALLY NEAR AND JUST WEST OF THE DATE
LINE. LOW LEVEL EASTERLY WINDS ARE STRONGER THAN NORMAL OVER THE CENTRAL
TROPICAL PACIFIC. THESE ATMOSPHERIC CIRCULATION ANOMALIES ARE CONSISTENT WITH
LA NINA CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THERE IS CONSENSUS AMONG SST PREDICTION METHODS THAT NINO 3.4 SSTS WILL REMAIN
AT AROUND 1 DEGREE C OR MORE BELOW NORMAL THROUGH JFM 2008. THE LATEST CFS
FORECAST INDICATES JFM SST ANOMALIES IN THE NINO 3.4 REGION OF AROUND -1.8 C,
REACHING A MINIMUM OF ABOUT -1.9 C DURING FMA 2008. THE STATISTICAL TOOLS...
THE MARKOV MODEL... CCA... AND CONSTRUCTED ANALOG PREDICT SST ANOMALIES OF
BETWEEN -0.9 AND -1.6 C FOR JFM. A CONSOLIDATION FORECAST BASED ON CCA,
CONSTRUCTED ANALOG (CA), MARKOV AND CFS MODELS PREDICTS GREATEST ANOMALIES OF
ABOUT -1.4 C IN DJF 2007-08, -1.1 C IN JFM 2008, AND CONTINUES TO STEADILY RISE
TO NEAR -0.5 C BY MAM 2008. BEYOND THIS TIME, ENSO NEUTRAL CONDITIONS ARE
PREDICTED BY THE CONSOLIDATION TOOL AT LEAST THROUGH SON 2008. THE
CONSOLIDATION METHOD GIVES A 98% CONFIDENCE THAT THE NINO 3.4 SSTS WILL REMAIN
BELOW THE -0.5 C THRESHOLD ASSOCIATED WITH LA NINA CONDITIONS THROUGH JFM 2008,
AND 86% THROUGH FMA 2008 AND A 54% CHANCE BY MAM.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE TEMPERATURE OUTLOOKS FOR ALL LEAD TIMES ARE BASED ON THE CONSOLIDATION
(CON) TOOL... WHICH IS A SKILL-AND SPREAD-WEIGHTED OBJECTIVE BLEND OF THE
CFS... CCA... SMLR AND OCN FORECAST TOOLS. IN ADDITION, COMPOSITES OF MODERATE
(WEAK) LA NINA EVENTS FROM 1950-2006 WERE USED FOR JFM 2008 (FMA AND MAM 2008).
PRECIPITATION OUTLOOKS FOR JFM 2008 THROUGH MAM 2008 ARE DERIVED ALMOST
ENTIRELY FROM COMPOSITES OF LA NINAS... WITH PROBABILITIES ADJUSTED TO REFLECT
THE EXPECTED INTENSITY OF THE CURRENT LA NINA CONDITIONS. THE CON IS NOT
AVAILABLE FOR ALASKA... SO THE FORECAST THERE IS BASED LARGELY ON ANALYSIS OF
THE CFS WITH CONSIDERATION OF THE OCN... CCA AND SMLR. PRECIPITATION OUTLOOKS
FOR AMJ 2008 AND BEYOND REFLECT WEAK SIGNALS FROM LONG TERM TRENDS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - JFM 2008 TO JFM 2009
TEMPERATURE:
THE TEMPERATURE OUTLOOK FOR JFM 2008 CALLS FOR ENHANCED CHANCES OF ABOVE
AVERAGE TEMPERATURES FOR MOST OF THE SOUTHERN AND CENTRAL CONUS AS WELL AS
NORTHWEST ALASKA, WITH NEAR AVERAGE TEMPERATURES FORECAST FROM THE PACIFIC
NORTHWEST EASTWARD ACROSS THE NORTHERN TIER OF STATES TO NORTHERN MICHIGAN.
EQUAL CHANCES (EC) OF ABOVE-, NEAR- AND BELOW AVERAGE TEMPERATURES ARE EXPECTED
ELSEWHERE. THE JFM 2008 TEMPERATURE FORECAST IS BASED LARGELY ON
TREND-ADJUSTED LA NINA COMPOSITES (FOR MODERATE EVENTS), AND CONSIDERATION OF
THE CONSOLIDATION TOOL, THE CFS AND IRI TOOLS, AND CURRENT AND ANTICIPATED
LOCATIONS OF SIGNIFICANT SNOW/ICE COVER. THE SEASONAL OUTLOOKS FOR FMA AND MAM
2008 LARGELY REFLECT THESE SAME TOOLS THOUGH THE TREND-ADJUSTED LA NINA
COMPOSITES THAT WERE USED WERE FOR WEAK COLD EVENTS. THE TREND DOMINATES THE
TEMPERATURE CONSOLIDATION FORECAST OUTLOOKS BEYOND MAM.
PRECIPITATION:
THE PRECIPITATION OUTLOOK FOR JFM 2008 CALLS FOR ELEVATED CHANCES OF ABOVE
AVERAGE PRECIPITATION AMOUNTS IN THE PACIFIC NORTHWEST AND FROM THE CENTRAL
MISSISSIPPI VALLEY, THROUGH SECTIONS OF THE OHIO VALLEY AND TENNESSEE, TO THE
CENTRAL GREAT LAKES. ELEVATED CHANCES FOR BELOW AVERAGE PRECIPITATION ARE
FORECAST FOR THE SOUTHWEST, THE SOUTHERN ROCKIES, THE SOUTHERN AND CENTRAL
PLAINS, THE SOUTHEAST, AND FROM VIRGINIA AND DELAWARE UP THE IMMEDIATE EAST
COAST TO FAR EASTERN MASSACHUSETTS. FOR FMA AND MAM 2008... THE PREDICTED
ANOMALY PATTERNS ARE FAIRLY SIMILAR TO THAT FOR JFM, THOUGH LA NINA BASED
SUPPORT FOR THE ABOVE AVERAGE PRECIPITATION AREAS DISAPPEARS BY MAM 2008.
THESE FORECASTS ARE BASED PRIMARILY ON TREND-ADJUSTED LA NINA COMPOSITES
(MODERATE EVENTS FOR JFM, WEAK EVENTS FOR FMA AND MAM 2008), AND TO A LESSER
EXTENT ON THE CONSOLIDATION TOOL. FORECASTS FOR AMJ 2008 AND BEYOND ARE BASED
ON LONG-TERM TRENDS AND THE CONSOLIDATION TOOL. THE LIKELIHOOD OF ABOVE
AVERAGE PRECIPITATION IS INCREASED ACROSS FLORIDA FROM JAS-SON 2008, WHICH
COINCIDES WITH THE EXPECTED BULK OF SEASONAL TROPICAL CYCLONE ACTIVITY. BELOW
AVERAGE PRECIPITATION AMOUNTS ARE EXPECTED FOR SECTIONS OF THE PACIFIC
NORTHWEST FROM MJJ THROUGH ASO 2008, AND FOR SECTIONS OF THE SOUTHEAST IN DJF
2008-09 AND JFM 2009.
NOTE - AREAS OF UNCERTAINTY THAT FORMERLY WERE LABELED CL (CLIMATOLOGICAL
PROBABILITIES) ARE NOW LABELED EC (EQUAL CHANCES).
FORECASTER: ANTHONY ARTUSA
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 JAN 17 2008
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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