PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS
CLIMATE PREDICTION CENTER NCEP
NATIONAL WEATHER SERVICE WASHINGTON DC
3 PM EDT THURSDAY AUG 17 2000
PROGNOSTIC DISCUSSION OF SST FORECASTS
SST ANOMALIES IN THE PACIFIC BECAME ENSO-NEUTRAL DURING MID-JULY TO MID-AUGUST.
EQUATORIAL SST ANOMALIES ARE AVERAGING SLIGHTLY BELOW NORMAL EAST OF 140W WITH
THE AVERAGE ANOMALY IN THE NINO 3.4 REGION (5N - 5S AND 120W - 170W) OF -0.2
DEG C. LOW-LEVEL EASTERLY WIND ANOMALIES WEAKENED TO NEAR-ZERO IN THE
EQUATORIAL WEST PACIFIC DURING JULY - BUT HAVE STRENGTHENED TO 4-5 METERS PER
SECOND DURING EARLY AUGUST. SUB-SURFACE TEMPERATURES REMAIN LESS THAN 1 DEG C
BELOW NORMAL TO DEPTHS OF AROUND 100 METERS ALONG THE EQUATOR IN THE PACIFIC
EAST OF THE DATE LINE. WARMER THAN NORMAL OCEAN TEMPERATURES ARE PERSISTING
UNDER THE SURFACE IN THE WESTERN AND CENTRAL PACIFIC - AND HAVE BEEN SLOWLY
MIGRATING EASTWARD OVER THE PAST SEVERAL SEASONS.
BEGINNING WITH THE FORECAST MADE IN EARLY MAY 2000 - THE NCEP COUPLED MODEL
CORRECTLY PREDICTED NEUTRAL CONDITIONS BY AUGUST - WHILE THE STATISTICAL MODELS
WERE CONSISTENTLY COLD. THIS CIRCUMSTANCE CONTINUES WITH THE CURRENT FORECAST.
CONSTRUCTED ANALOG METHOD (CA) AND THE CCA - WHICH ARE STARTED FROM 3-MONTH MEAN
CONDITIONS ENDING WITH JULY - CONTINUE TO PREDICT SUB-NORMAL SSTS WHILE THE NCEP
MODEL HOLDS TEMPERATURES AT NEAR-NEUTRAL THROUGH THE END OF THE YEAR. THE
AUTOMATED OFFICIAL FORECAST - WHICH IS A CONSOLIDATION OF THE 3 MODELS BASED ON
PAST PERFORMANCE - ALSO GIVES A FORECAST WHICH IS TOO COLD.
THE FORECAST BEYOND NEXT SPRING BECOMES HIGHLY UNCERTAIN - WITH THE CCA AND
CONSOLIDATION FORECASTS SUGGESTING A WARM EVENT BY NEXT SUMMER - WHILE CA LIMITS
THE PREDICTED SST POSITIVE ANOMALY TO ABOUT O.5 DEGREES.
PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2000 TO SON 2001
THESE OUTLOOKS REFLECT THE EXPECTED U.S. CLIMATE ANOMALIES FOR ENSO-NEUTRAL
CONDITIONS. ON AVERAGE - THIS WINTER WILL BE COLDER THAN THE LAST THREE -
WHICH WERE EXCEPTIONALLY WARM IN PART DUE TO THREE STRAIGHT YEARS OF STRONG ENSO
CONDITIONS AND IN PART TO THE INFLUENCE OF THE POSITIVE PHASE OF THE NORTH
ATLANTIC OSCILLATION TELECONNECTION PATTERN - WHICH HAS HAD A DOWNWARD TREND IN
ITS AMPLITUDE IN THE LAST 10 YEARS AND IS NOW RELATIVELY WEAK. NONETHELESS - WE
STILL EXPECT GENERALLY WARMER THAN NORMAL TEMPERATURES - COMPARED TO THE
RELATIVELY COOL 1961-90 CLIMATOLOGY - WHICH WE WILL CONTINUE TO USE TO COMPUTE
ANOMALIES FROM UNTIL EARLY NEXT YEAR.
THE PRIMARY TOOL FOR THIS SET OF FORECASTS IS THE TREND - AS RENDERED BY
THE OCN TOOL RELATIVE TO THE 1961-90 CLIMATOLOGY. THE CCA AND SMLR FORECASTS
WERE ALSO CONSULTED FOR ALL LEAD TIMES. COMPOSITES FOR NEUTRAL ENSO EVENTS FOR
1950-95 WERE ALSO CONSIDERED FOR THIS FORECAST. THE COOL TEMPERATURES INDICATED
BY THAT TOOL WERE USED TO TEMPER OUR COLD SEASON PROBABILITIES FOR ABOVE NORMAL
TEMPERATURE. THE CMP - ECHAM AND CCM3 MODELS WERE ALSO CONSULTED FOR SON AND
NDJ. ALL THREE MODELS WORKED FROM TROPICAL PACIFIC SSTS WHICH WERE WARMER THAN
NORMAL BEGINNING IN NDJ. SINCE WE EXPECT NEUTRAL CONDITIONS - THESE MODEL RUNS
WERE NOT USED IN THIS MONTHS OUTLOOKS.
THE TEMPERATURE FORECAST FOR SON 2000 CALLS FOR WARM IN THE WEST AND SOUTH -
PARTICULARLY IN THE DESERT SOUTHWEST AND IN FLORIDA WHICH SHOW SUBSTANTIAL
WARMING TRENDS THROUGHOUT MUCH OF THE YEAR. BECAUSE LA NINA CONDITIONS LASTED
INTO THE SUMMER WE EXPECT ANOTHER ACTIVE ATLANTIC TROPICAL STORM SEASON. THIS
RAISES THE LIKELIHOOD OF ABOVE MEDIAN PRECIPITATION ALONG THE EAST COAST FOR SON
AND EXTENDING THROUGH OND IN FLORIDA. PRECIPITATION HAS BEEN TRENDING TOWARDS
DRIER CONDITIONS IN PARTS OF THE WEST AND CCA PREDICTS DRY CONDITIONS FORECAST
FOR THE OHIO VALLEY.
THE FORECAST FOR OND 2000 THROUGH FMA 2001 REFLECTS THE LONG TERM TRENDS.
TEMPERATURE TRENDS ARE SMALL IN THE FALL - BUT INCREASE AS THE SEASONS PROGRESS
UNTIL THEY FAVOR ABOVE MEDIAN TEMPERATURES THROUGHOUT THE ENTIRE LOWER 48 STATES
- EXCEPT FOR THE GREAT BASIN AND NORTHWEST - BY DJF AND JFM. PROBABILITIES FOR
ABOVE NORMAL TEMPERATURES ARE HIGHEST IN THE SOUTH AND SOUTHWEST WHERE YEAR-TO-
YEAR VARIABILITY IS SMALL IN RELATION TO THE TRENDS. PROBABILITIES FOR ABOVE
NORMAL TEMPERATURES HAVE BEEN REDUCED SLIGHTLY FROM WHAT TRENDS ALONE WOULD
INDICATE IN THE CENTRAL AND NORTHERN U.S. ON THE BASIS OF NEUTRAL ENSO
COMPOSITES. CCA INDICATES BELOW NORMAL TEMPERATURES FOR MUCH OF ALASKA IN THE
FALL. THE CCA - SMLR - CMP - AND COMPOSITE TOOLS ALL FAVOR BELOW MEDIAN
PRECIPITATION ALONG PORTIONS OF THE WEST COAST. CCA INDICATES BELOW MEDIAN
PRECIPITATION IN ALASKA. ABOVE MEDIAN PRECIPITATION FORECAST FOR THE SOUTH-
CENTRAL PORTION OF THE COUNTRY IS MOSTLY FROM OCN.
THE FORECAST FOR MAM-MJJ 2001 MOSTLY REFLECT TEMPERATURE AND PRECIPITATION
TRENDS. THE WINTER TIME WARMING TREND CONTINUES INTO SPRING ONLY IN THE
WESTERN U.S. SO FORECAST PROBABILITIES FOR ABOVE NORMAL TEMPERATURES IN THE
EAST AND CENTRAL U.S. DIMINISH RAPIDLY FROM WINTER TO SPRING. PROBABILITIES
FOR ABOVE NORMAL TEMPERATURES HAVE BEEN REDUCED SOMEWHAT FROM WHAT TRENDS
ALONE INDICATE ALONG THE WEST COAST - BECAUSE WARMING TRENDS THERE APPEAR TO
HAVE DIMINISHED SOMEWHAT IN THE LAST FEW YEARS. OCN INDICATES STRONG WARMING
TRENDS IN ALASKA IN THE SPRING AND SUMMER. PRECIPITATION TRENDS ARE TOWARD
WETTER SPRINGTIME CONDITIONS IN THE PACIFIC NORTHWEST - AND ALSO IN PORTIONS OF
THE CENTRAL AND SOUTHERN ROCKIES IN SOME SPRINGTIME MONTHS. OCN INDICATES DRY
CONDITIONS ALONG THE SOUTH ATLANTIC COAST. THE FORECAST FOR BELOW MEDIAN
PRECIPITATION IN ALASKA IS FROM CCA.
THE FORECAST FOR JJA 2001-SON 2001 SHOWS WARMING TRENDS FOR MUCH OF THE WEST -
ALONG THE EAST COAST AND IN ALASKA FOR JJA - DIMINISHING FROM JAS - SON.
TRENDS INCREASE THE LIKELIHOOD OF SUB-NORMAL TEMPERATURES IN THE CENTER OF THE
LOWER 48 STATES DURING MJJ-JAS. CCA INDICATES BELOW MEDIAN PRECIPITATION IN
JJA FOR ALASKA - WITH OCN INDICATING TRENDS TOWARD LESS PRECIPITATION FOR THE
GREAT BASIN REGION IN JAS AND ASO - AND IN THE NORTHWEST - THE WEST COAST AND
MUCH OF THE FAR SOUTHWEST IN SON - AND TOWARD INCREASING PRECIPITATION AMOUNTS
IN THE CENTRAL HIGH PLAINS IN ASO AND THE CENTRAL PLAINS AND THE SOUTHEAST IN
SON.
FOR A DESCRIPTION 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/MULTI-SEASON/
13_SEASONAL_OUTLOOKS/TOOLS
NOTE - THESE CLIMATE OUTLOOKS ARE INTENDED FOR USE PRIOR TO THE START OF THEIR
VALID PERIODS. WITHIN ANY GIVEN VALID PERIOD OBSERVATIONS AND SHORT AND MEDIUM
RANGE FORECASTS SHOULD BE CONSULTED. ALSO - THIS SET OF OUTLOOKS WILL BE
SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT MONTH ON THURSDAY SEPTEMBER 14
2000.
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