877
FXUS05 KWBC 211337
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EST THU FEB 21 2008
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) 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 RATHER STRONG COLD EVENT (LA NINA) CONTINUES ACROSS THE PACIFIC BASIN. SEA
SURFACE TEMPERATURES (SSTS) ARE BELOW AVERAGE THROUGHOUT THE ENTIRE EQUATORIAL
PACIFIC OCEAN EAST OF ABOUT 160E LONGITUDE, WITH THE EXCEPTION OF THE IMMEDIATE
COAST OF SOUTH AMERICA. 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 NINO 3.4,
WHICH AVERAGED 1.5 DEGREES C BELOW NORMAL DURING NOVEMBER AND DECEMBER,
AVERAGED 1.8 DEGREES C BELOW NORMAL FOR THE MONTH OF JANUARY, WHERE A VALUE
GREATER THAN 1.5 DEGREES C BELOW NORMAL IS USUALLY ASSOCIATED WITH STRONG LA
NINA CONDITIONS. LA NINA CONDITIONS ARE NOT EXPECTED TO WEAKEN SUBSTANTIALLY
FOR THE NEXT SEVERAL WEEKS.
FORECASTS GENERALLY INDICATE MODERATE LA NINA CONDITIONS FOR MAM 2008, FOLLOWED
BY WEAKER LA NINA CONDITIONS THEREAFTER. THE CONSENSUS OF MODEL FORECASTS FOR
NINO 3.4 SSTS INDICATE THAT THE CURRENT SST ANOMALY OF MORE THAN 1.5 DEGREES C
BELOW NORMAL WILL GRADUALLY DECREASE DURING MAM AND AMJ (SPRING) 2008. MANY
MODELS PREDICT A CONTINUATION OF THE CURRENT LA NINA THROUGH NEXT AUTUMN,
ALTHOUGH THERE IS A LARGE AMOUNT OF UNCERTAINTY AFTER AMJ 2008.
THE TEMPERATURE OUTLOOK FOR MAM 2008 INDICATES GREATER THAN NORMAL CHANCES OF
ABOVE NORMAL TEMPERATURES FOR MOST OF THE WESTERN AND SOUTHERN U.S., BASED ON
THE COMBINED INFLUENCES OF LA NINA AND THE TREND. BELOW NORMAL TEMPERATURES
ARE MOST PROBABLE ALONG THE PACIFIC COAST IN THE LOWER ALASKAN PANHANDLE, THE
PACIFIC NORTHWEST AND SOUTHERN CALIFORNIA. ELSEWHERE, THE FORECAST CALLS FOR
EQUAL CHANCES (EC) OF ABOVE, NEAR AND BELOW AVERAGE TEMPERATURES.
THE PRECIPITATION OUTLOOK FOR MAM 2008 INDICATES AN ENHANCED PROBABILITY OF
BELOW AVERAGE PRECIPITATION AMOUNTS IN THE SOUTHWEST, THE SOUTHERN AND CENTRAL
PLAINS, THE LOWER MISSISSIPPI VALLEY AND ALONG THE GULF COAST, AND MUCH OF THE
SOUTHEAST INCLUDING FLORIDA AND THE ATLANTIC COASTAL STATES AS FAR NORTH AS THE
CHESAPEAKE BAY. THESE PRECIPITATION ANOMALIES ARE THE EXPECTED RESPONSE TO A
STRONG LA NINA IN ADDITION TO THE LESSER INFLUENCE OF PRECIPITATION TRENDS.
ELSEWHERE, THE FORECAST CALLS FOR EQUAL CHANCES (EC) OF ABOVE, NEAR AND BELOW
AVERAGE PRECIPITATION.
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 SOMEWHAT BELOW AVERAGE IN THE EQUATORIAL
PACIFIC FROM JUST WEST OF THE SOUTH AMERICAN COAST TO ABOUT 160E LONGITUDE.
SST ANOMALIES ARE BELOW -2 C FROM THE DATE LINE TO ABOUT 120W. OCEAN
TEMPERATURES IN THE UPPER 200 METERS IN THE EASTERN EQUATORIAL PACIFIC CONTINUE
TO BE WELL BELOW NORMAL, WITH THE LARGEST MAGNITUDE OF NEGATIVE ANOMALIES
BETWEEN -4 AND -5 C BETWEEN 140W AND 100W. IN THE WESTERN PACIFIC, SUBSURFACE
OCEAN TEMPERATURES SHOW AN EXTENSIVE POSITIVE ANOMALY OF 2 C TO 4 C IMPLYING AN
ANOMALOUSLY DEEP THERMOCLINE. POSITIVE ANOMALIES IN OUTGOING LONGWAVE
RADIATION (OLR) INDICATE SUPPRESSED CONVECTION OVER THE EQUATORIAL PACIFIC NEAR
THE DATE LINE FROM AROUND 150E TO 130W LONGITUDE. THE AVERAGE OLR ANOMALY
(FROM 5N TO 5S AND 160E TO 160W) WEAKENED DURING JANUARY DUE TO MJO ACTIVITY
BUT HAS REBOUNDED IN FEBRUARY AND APPEARS NEAR A MAXIMUM RELATIVE TO THE LAST
SEVERAL MONTHS. ENHANCED CONVECTION OVER THE WESTERN PACIFIC NOW APPEARS
STATIONARY AND CONSISTENT WITH LA NINA CONDITIONS. LOW LEVEL EASTERLY WINDS
ARE STRONGER THAN NORMAL OVER THE CENTRAL TROPICAL PACIFIC THOUGH SLIGHTLY
WEAKER NOW THAN A COUPLE WEEKS AGO. THESE ATMOSPHERIC CIRCULATION ANOMALIES
ARE CONSISTENT WITH LA NINA CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE STATISTICAL TOOLS (CCA, MARKOV MODEL AND CONSTRUCTED ANALOG) PREDICT A NINO
3.4 SST ANOMALY BETWEEN -0.3 AND -1.3 C FOR MAM 2008 AND WARMING THEREAFTER.
WEAK LA NINA CONDITIONS ARE PREDICTED TO CONTINUE IN THE CASE OF THE MARKOV
MODEL, WHILE EL NINO CONDITIONS ARE PREDICTED BY NEXT WINTER BY THE CCA. IN
COMPARISON, THE CFS FORECASTS A -1.7 C ANOMALY IN MAM 2008 AND ONLY A SLIGHT
WARMING THROUGH JAS 2008 BEFORE LEVELING OFF NEAR -1 C. A CONSOLIDATION
FORECAST BASED ON CCA, CONSTRUCTED ANALOG (CA), MARKOV AND CFS MODELS PREDICTS
WEAK LA NINA CONDITIONS FOR MAM 2008 RISING TO APPROXIMATELY A ZERO TEMPERATURE
ANOMALY BY JAS 2008. HOWEVER, THE CCA FORECAST OF ABOVE NORMAL NINO 3.4
TEMPERATURES BY MJJ 2008 AND A STRONG EL NINO BY ASO IS AN OUTLIER RELATIVE TO
THE OTHER MODELS AND HAS BEEN DISCOUNTED IN THE SEASONAL OUTLOOK. WITHOUT THE
CCA PREDICTION, AT LEAST WEAK LA NINA CONDITIONS ARE EXPECTED TO PERSIST INTO
THE AUTUMN. IT IS TOO EARLY TO MAKE A CONFIDENT FORECAST FOR NEXT WINTER,
ALTHOUGH IT IS NOTED THAT SOME MODEL FORECASTS DO INDICATE AT LEAST THE
POSSIBILITY OF CONTINUATION OF A BELOW NORMAL AVERAGE NINO 3.4 SST.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE TEMPERATURE AND PRECIPITATION OUTLOOKS FOR ALL LEAD TIMES ARE BASED ON THE
CONSOLIDATION (CON), A SKILL-WEIGHTED AND CALIBRATED OBJECTIVE BLEND OF THE
CFS, CCA, SMLR AND OCN FORECAST TOOLS. THE TREND DOMINATES THE TEMPERATURE
CONSOLIDATION FORECAST ESPECIALLY BEYOND THE AMJ SEASON. IN ADDITION,
COMPOSITES OF MODERATE OR WEAK LA NINA EVENTS WERE USED FOR THE MAM THROUGH MJJ
2008 TEMPERATURE OUTLOOKS, CONSIDERING THE EXPECTED WEAKENING OF THE CURRENT LA
NINA CONDITIONS OVER THE PERIOD. THE CON IS NOT AVAILABLE FOR ALASKA, SO THE
FORECAST THERE IS BASED MOSTLY ON THE TRENDS FROM OCN AND THE CFS. THE
PRECIPITATION OUTLOOKS FOR MAM THOUGH ASO 2008 ARE BASED IN PART ON LA NINA
COMPOSITES AND WEAK TRENDS AS INDICATED BY OCN.
PROGNOSTIC DISCUSSION OF OUTLOOKS - MAM 2008 TO MAM 2009
TEMPERATURE:
THE TEMPERATURE OUTLOOK FOR MAM 2008 DEPICTS AN INCREASED PROBABILITY OF ABOVE
AVERAGE TEMPERATURES FOR MOST OF THE WESTERN U.S. INTO THE SOUTHEAST. LA NINA
CONDITIONS INCREASE THE CHANCES OF BELOW NORMAL TEMPERATURES FOR PARTS OF THE
LOWER ALASKAN PANHANDLE AND THE COASTS OF WASHINGTON AND OREGON. THERE IS AN
ENHANCED PROBABILITY FOR BELOW NORMAL TEMPERATURES ALONG THE SOUTHERN
CALIFORNIA COAST DUE TO BELOW NORMAL SEA SURFACE TEMPERATURES. EQUAL CHANCES
(EC) OF ABOVE, NEAR AND BELOW AVERAGE TEMPERATURES ARE EXPECTED ELSEWHERE. FOR
ALL LONGER LEADS ENHANCED PROBABILITIES OF ABOVE NORMAL TEMPERATURE COVER MUCH
OF THE U.S. GREATER PROBABILITIES OF ABOVE NORMAL TEMPERATURES ARE PRIMARILY
IN THE WEST FROM MJJ THROUGH JAS AND PRIMARILY IN THE SOUTHWEST, THE GREAT
PLAINS AND UPPER MISSISSIPPI VALLEY AS WE PROGRESS INTO NEXT WINTER. GENERALLY
SMALL CHANGES HAVE BEEN MADE IN THE FORECASTS RELEASED LAST MONTH.
PRECIPITATION:
THE PRECIPITATION OUTLOOK FOR MAM 2008 INDICATES GREATER PROBABILITY OF BELOW
MEDIAN PRECIPITATION FOR MUCH OF THE SOUTHERN U.S., INCLUDING PARTS OF THE
SOUTHWEST, THE SOUTHERN ROCKIES, THE SOUTHERN AND CENTRAL PLAINS, MOST OF THE
SOUTHEAST, AND THE ATLANTIC COASTAL STATES AS FAR NORTH AS VIRGINIA AND
SOUTHERN MARYLAND. FORECASTS FOR ALL LEADS ARE BASED ON THE CONSOLIDATION AND
LONG-TERM TRENDS, WITH CONSIDERATION OF LA NINA COMPOSITES OUT TO JAS 2008.
THE CHANCES OF BELOW MEDIAN PRECIPITATION ARE INCREASED FOR PARTS OF THE
PACIFIC NORTHWEST FROM MJJ THROUGH ASO 2008 AND AGAIN DURING NEXT WINTER, AS
INDICATED BY THE CONSOLIDATION. AN ENHANCED PROBABILITY OF BELOW MEDIAN
PRECIPITATION IS INDICATED FOR PARTS OF THE MIDWEST DURING THE SUMMER,
CORRESPONDING TO POSSIBLE WEAK TO MODERATE LA NINA CONDITIONS AND THE TREND.
THE LIKELIHOOD OF ABOVE MEDIAN PRECIPITATION IS INCREASED FOR MOST OF THE
FLORIDA PENINSULA FROM JAS TO SON 2008, AS INDICATED BY THE TRENDS WHICH ARE
LARGELY RELATED TO AN INCREASE IN SEASONAL TROPICAL ACTIVITY. ABOVE MEDIAN
PRECIPITATION AMOUNTS ARE EXPECTED FOR SECTIONS OF THE CENTRAL SOUTHERN STATES
NEXT WINTER, BASED ON THE TREND. BEGINNING IN WINTER (DJF) THROUGH MAM 2009,
ABOVE MEDIAN PRECIPITATION AMOUNTS IS PREDICTED FOR PARTS OF THE MIDWEST AND
BELOW MEDIAN PRECIPITATION IS PREDICTED FOR PARTS OF THE SOUTHEAST, RESULTING
FROM THE TRENDS.
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 MAR 20 2008
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
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