551
FXUS05 KWBC 171359
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER CAMP SPRINGS MD
830 AM EDT THU APR 17 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.
COLD EPISODE (LA NINA) CONDITIONS CONTINUE ACROSS THE TROPICAL PACIFIC, THOUGH
THE EPISODE HAS WEAKENED OVER THE PAST FEW WEEKS. SEA SURFACE TEMPERATURES
(SSTS) ARE BELOW AVERAGE THROUGHOUT THE EQUATORIAL PACIFIC BETWEEN 150E AND
110W. 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. THE WEEKLY NINO 3.4 INDEX VALUE PEAKED
IN MID-FEBRUARY NEAR -2.1 DEG C, AND HAS SINCE DECREASED TO NEAR -0.9 BY THE
START OF APRIL. THIS DECREASE IN THE NINO 3.4 INDEX IS CONSISTENT WITH A
WEAKENING OF LA NINA CONDITIONS. WEAKENING LA NINA CONDITIONS WERE ALSO
OBSERVED AT THIS TIME OF YEAR DURING THE LAST STRONG LA NINA EPISODE IN BOTH
1999 AND 2000.
FORECASTS GENERALLY INDICATE WEAK LA NINA CONDITIONS FOR MJJ 2008, FOLLOWED BY
SIGNIFICANT UNCERTAINTY THEREAFTER. THE CONSENSUS OF MODEL FORECASTS FOR NINO
3.4 SSTS INDICATE THAT THE CURRENT SST ANOMALY OF -0.9 DEGREE C BELOW NORMAL
WILL DECREASE SLIGHTLY DURING MJJ 2008. THE CONSENSUS ALSO INDICATES THAT A
BORDERLINE WEAK COLD OR NEUTRAL ENSO PHASE IS EXPECTED THROUGH EARLY WINTER.
THE TEMPERATURE OUTLOOK FOR MJJ 2008 DEPICTS AN INCREASED PROBABILITY OF ABOVE
AVERAGE TEMPERATURES FOR MOST OF THE WESTERN CONUS, PENINSULAR FLORIDA, NEW
YORK, NEW ENGLAND, SOUTHWEST ALASKA, AND PARTS OF THE ALASKAN NORTH SLOPE.
BELOW AVERAGE TEMPERATURES ARE PREDICTED FOR THE ALASKA PANHANDLE AND WESTERN
WASHINGTON. EQUAL CHANCES (EC) OF ABOVE, NEAR AND BELOW AVERAGE TEMPERATURES
ARE EXPECTED ELSEWHERE. FOR ALL LONGER LEADS ENHANCED PROBABILITIES OF ABOVE
NORMAL TEMPERATURE COVER DIFFERENT REGIONS OF THE U.S. GREATER PROBABILITIES
OF ABOVE NORMAL TEMPERATURES ARE PRIMARILY IN THE WEST FROM MJJ THROUGH ASO
2008 AND PRIMARILY IN THE SOUTHWEST AND CENTRAL STATES AS WE PROGRESS INTO NEXT
WINTER. THE WIDESPREAD WARMTH PREDICTED OVER MOST OF THE CONUS DURING DJF
2008-09, JFM 2009, AND FMA 2009 IS INDICATED BY THE CONSOLIDATION TOOL, WHICH
IS LARGELY DOMINATED BY TRENDS THIS FAR INTO THE FUTURE.
THE PRECIPITATION OUTLOOK FOR MJJ 2008 INDICATES AN ENHANCED PROBABILITY OF
BELOW AVERAGE PRECIPITATION AMOUNTS OVER MUCH OF THE WESTERN CONUS (BASED ON
THE CAS, CFS, IRI AND ECCA TOOLS), AND OVER THE SOUTHERN AND CENTRAL RIO GRANDE
VALLEY (BASED ON THE CFS AND IRI TOOLS). THIS LATTER AREA OF DRYNESS IS ALSO
BASED ON THE INFLUENCE OF CURRENT AND EXPECTED SOIL MOISTURE CONDITIONS.
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) ACROSS THE EQUATORIAL PACIFIC REMAIN BELOW
AVERAGE BETWEEN 110W AND 150E. BY THE START OF APRIL, SSTS OVER MUCH OF THIS
REGION AVERAGED 1 TO 2 DEG C BELOW AVERAGE. OCEAN TEMPERATURES WITHIN 75
METERS OF THE SURFACE OVER THE CENTRAL EQUATORIAL PACIFIC (155E TO 130W) RANGED
BETWEEN 1.0 AND 2.0 DEG C BELOW AVERAGE... WITH THE LARGER NEGATIVE ANOMALIES
(BETWEEN -2 C AND -4 C) LOCATED BETWEEN 155W AND 135W. IN THE WESTERN PACIFIC,
SUBSURFACE OCEAN TEMPERATURES ARE GENERALLY FROM 2 C TO PERHAPS AS MUCH AS 6 C
ABOVE AVERAGE BETWEEN 100 AND 250 METERS DEPTH... IMPLYING AN ANOMALOUSLY DEEP
THERMOCLINE. IN THE EASTERN PACIFIC, A VERY SHALLOW LAYER OF RELATIVELY WARM
WATER IS UNDERLAIN BY ANOMALOUSLY COLD WATER BETWEEN 25 AND 150 METER DEPTH.
OVER THE PAST 30 DAYS, TROPICAL CONVECTION HAS BEEN FOCUSED OVER THE WESTERN
PACIFIC, INCLUDING INDONESIA, WITH SUPPRESSED CONVECTION PERSISTING OVER THE
EQUATORIAL REGION NEAR THE DATE LINE. IN ADDITION... LOW LEVEL (850-HPA)
EASTERLY WIND ANOMALIES WERE OBSERVED BETWEEN 140E AND 160W... AND UPPER LEVEL
(200-HPA) WESTERLY WIND ANOMALIES WERE OBSERVED OVER THE CENTRAL PACIFIC IN
ASSOCIATION WITH CYCLONIC ANOMALIES IN THE SUBTROPICS OF BOTH HEMISPHERES.
THESE ATMOSPHERIC CIRCULATION ANOMALIES ARE ALL CONSISTENT WITH MODERATE LA
NINA CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE STATISTICAL TOOLS (CCA, MARKOV MODEL AND CONSTRUCTED ANALOG) PREDICT SSTS
REMAINING BELOW AVERAGE THROUGH MJJ 2008... PREDICTING A NINO 3.4 SST INDEX
VALUE BETWEEN -0.4 C AND -1.0 C. WEAK LA NINA CONDITIONS ARE PREDICTED TO
CONTINUE BY THE CFS, CONSTRUCTED ANALOG (CA) AND THE CCA UNTIL NEXT WINTER.
THEREAFTER ALL TECHNIQUES FEATURE SOME DEGREE OF WARMING. IN COMPARISON, THE
MARKOV MODEL MAINTAINS A MODERATE STRENGTH COLD EVENT UNTIL DJF 2008-09... WITH
SUBSEQUENT WARMING. THIS SOLUTION IS THE COLDEST OF ALL THESE MODELS. A
CONSOLIDATION (CON) FORECAST BASED ON THE CCA, CONSTRUCTED ANALOG (CA), MARKOV
AND CFS MODELS PREDICTS WEAK LA NINA CONDITIONS FOR MJJ 2008, AND POSSIBLY
THROUGHOUT THE SUMMER, WITH A SLIGHT STRENGTHENING DURING AUTUMN AND EARLY
WINTER BEFORE FINALLY WEAKENING TO A NEUTRAL EVENT BY LATE WINTER. IT IS TOO
EARLY TO MAKE A CONFIDENT FORECAST FOR NEXT WINTER, ALTHOUGH IT IS CLEAR FROM
THESE MODEL RUNS THAT WEAK LA NINA OR BORDERLINE ENSO-NEUTRAL CONDITIONS MAY
DOMINATE FOR THE REMAINDER OF THIS YEAR.
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 CON TOOL IS NOT AVAILABLE FOR
ALASKA, SO THE FORECAST THERE IS BASED MOSTLY ON THE TRENDS FROM OCN. THE CFS
AND IRI TOOLS WERE USED FOR ALASKA ONLY FOR THE MJJ 2008 SEASON. LA NINA
COMPOSITES WERE CONSIDERED FOR THE CONUS FOR THE FIRST LEAD FORECAST. THE
PRECIPITATION OUTLOOK FOR MJJ 2008 IS BASED ON THE CFS, IRI, ECCA AND CAS
TOOLS. THE REMAINDER OF THE SUITE OF PRECIPITATION FORECASTS IS BASED LARGELY
ON ANY AVAILABLE WEAK TRENDS, AS WELL AS THE CON TOOL.
PROGNOSTIC DISCUSSION OF OUTLOOKS - MJJ 2008 TO MJJ 2009
TEMPERATURE:
THE TEMPERATURE OUTLOOK FOR MJJ 2008 INDICATES GREATER THAN NORMAL CHANCES OF
ABOVE AVERAGE TEMPERATURES FOR MOST OF THE WESTERN CONUS, THE FLORIDA
PENINSULA, NEW YORK, NEW ENGLAND, SOUTHWESTERN ALASKA, AND MUCH OF THE ARCTIC
COAST OF ALASKA. FOR THE LOWER 48 STATES, THIS IS LARGELY BASED ON THE
CONSOLIDATION (CON) TOOL, ECCA, IRI AND CAS TOOLS... WITH CONSIDERATION GIVEN
TO MJJ LA NINA COMPOSITES. THE ALASKA MJJ 2008 TEMPERATURE FORECAST IS MOSTLY
ATTRIBUTED TO LONG-TERM TRENDS, AND TO A LESSER EXTENT THE CCA TOOL. BELOW
AVERAGE TEMPERATURES ARE PREDICTED FOR THE ALASKA PANHANDLE AND WESTERN
WASHINGTON. THIS IS ATTRIBUTED TO THE CAS, CFS AND IRI TOOLS. ELSEWHERE, THE
FORECAST CALLS FOR EQUAL CHANCES (EC) OF ABOVE, NEAR AND BELOW AVERAGE
TEMPERATURES.
PRECIPITATION:
THE PRECIPITATION OUTLOOK FOR MJJ 2008 INDICATES AN ELEVATED PROBABILITY OF
BELOW MEDIAN PRECIPITATION FOR MOST OF THE WEST, AND ALSO FOR THE SOUTHERN AND
CENTRAL RIO GRANDE VALLEY. FORECASTS FOR ALL LEADS ARE BASED TO A LARGE DEGREE
ON THE CONSOLIDATION AND LONG-TERM TRENDS... WITH CONSIDERATION GIVEN TO LA
NINA COMPOSITES FOR THE FIRST LEAD FORECAST. THE CHANCES OF BELOW MEDIAN
PRECIPITATION ARE INCREASED FOR THE PACIFIC NORTHWEST FROM MJJ THROUGH ASO
2008. AN ENHANCED PROBABILITY OF ABOVE MEDIAN PRECIPITATION IS INDICATED FOR
FLORIDA FROM JAS THROUGH SON 2008, ASSOCIATED WITH LONG TERM TRENDS IN
PRECIPITATION POSSIBLY RELATED TO INCREASED TROPICAL ACTIVITY SINCE 1995. FOR
SON AND OND 2008, AN AREA OF BELOW MEDIAN PRECIPITATION IS ANTICIPATED OVER THE
CENTRAL MISSISSIPPI VALLEY, DUE TO THE OCN - CFS - AND ECCA (SON 2008 ONLY)
TOOLS.
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 MAY 15 2008
1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17, 2001
FORECAST RELEASE.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page