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90-Day Index



Official 90-day outlooks are issued once each month near mid-month at 3pm Eastern Time. Please consult the schedule of 30 & 90-day outlooks for exact release dates.


PROGNOSTIC DISCUSSION FOR LONG-LEAD OUTLOOKS
CLIMATE PREDICTION CENTER NCEP
NATIONAL WEATHER SERVICE  WASHINGTON DC
3 PM EDT THURSDAY OCTOBER 18 2001

     BASIS AND SUMMARY OF THE CURRENT LONG-LEAD OUTLOOK
         .         .         .         .         .         .         .         .
THESE OUTLOOKS REFLECT THE EXPECTED U.S. CLIMATE ANOMALIES FOR ENSO-NEUTRAL 
CONDITIONS ... THE LONG-TERM TREND AS ESTIMATED BY OCN AND FORECASTS OF OCEANIC 
AND ATMOSPHERIC CONDITIONS FROM DYNAMICAL MODELS.  EQUATORIAL PACIFIC SSTS ARE 
NOW SLIGHTLY ABOVE NORMAL IN THE WEST AND CENTRAL PACIFIC AND BELOW 
NORMAL NEAR SOUTH AMERICA.  MOST STATISTICAL AND DYNAMIC PREDICTIONS OF NINO 
3.4 SSTS INDICATE ANOMALIES VERY NEAR ZERO THROUGHOUT THE UPCOMING COOL SEASON 
WITH SLIGHT WARM EPISODE (EL NINO) CONDITIONS BY LATE IN THE SPRING OR EARLY IN 
THE SUMMER OF 2002.  WHILE IT IS LIKELY THAT EQUATORIAL PACIFIC SSTS NEAR AND 
JUST WEST OF THE DATELINE WILL BE ABOVE AVERAGE ... THE ANOMALIES ARE EXPECTED
TO BE WEAK AND NOT LIKELY TO PRODUCE THE LARGE-SCALE ATMOSPHERIC EFFECTS 
ASSOCIATED WITH STRONG EL NINO EVENTS THIS COOL SEASON. THE ABSENCE OF 
SIGNIFICANT ENSO-RELATED INFLUENCES SUGGESTS THE UPCOMING COOL SEASON MAY BE 
MARKED BY SIGNIFICANT MONTH-TO-MONTH VARIABILITY...WHICH MAY BE ENHANCED IF THE
CURRENTLY STRONG SERIES OF MADDEN AND JULIAN OSCILLATION (MJO) WAVES CONTINUES
OVER THE PACIFIC.
 
     CURRENT ATMOSPHERIC AND OCEANIC CONDITIONS

NEAR-NORMAL ATMOSPHERIC AND OCEANIC CONDITIONS CONTINUE TO PREVAIL IN THE
TROPICAL PACIFIC IN SEPTEMBER.  SST ANOMALIES ALONG THE EQUATOR CURRENTLY ARE
NEAR +1.0 DEG C WEST OF THE DATELINE AND ARE AROUND -1.O DEG IN THE
EASTERN PACIFIC - EAST OF ABOUT 130W.  ABOVE NORMAL OCEAN TEMPERATURES EXTEND 
FROM THE SURFACE OR NEAR THE SURFACE TO OVER 200 M DEPTH OVER MOST OF THE 
CENTRAL PACIFIC OCEAN AND TO 100 M DEPTH AS FAR EAST AS 130 W.  ENHANCED MJO
ACTIVITY HAS BEEN NOTED DURING THE LAST SIX MONTHS.  THIS IS EXPECTED TO 
CONTINUE AND WILL HAVE AN IMPACT ON SSTS IN THE CENTRAL EQUATORIAL PACIFIC.
WITH WARM SSTS FARTHER EAST THAN LAST WINTER THERE IS A BETTER CHANCE STRONG
MJO WILL MAKE IT TO THE DATELINE AND HAVE AN OPPORTUNITY TO IMPACT PRECIPITATION
IN THE WESTERN UNITED STATES.  
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     PROGNOSTIC DISCUSSION OF SST FORECASTS

NEAR-NEUTRAL ENSO CONDITIONS ARE PREDICTED FOR MUCH OF THE WINTER.  MOST  
DYNAMICAL MODELS (NCEP - SCRIPPS) GRADUALLY INCREASE NINO 3.4 SSTS  
BEGINNING IN THE SPRING.  THE CONSTRUCTED ANALOG AND INVERSE MODEL PREDICT 
NEUTRAL OR COOL NINO 3.4 SSTS FOR THIS COOL SEASON WHILE CCA PREDICTS MODESTLY
ABOVE NORMAL SSTS.   A MARKOV SST MODEL INDICATES PERSISTENCE OF CURRENT SSTS
THROUGH THE SPRING WITH WARM ENSO CONDITIONS DEVELOPING DURING APRIL THROUGH
JUNE 2002.   A CONSOLIDATION OF THREE NCEP TOOLS BASED ON THEIR PAST PERFORMANCE 
INDICATES NEAR NORMAL CONDITIONS WILL PREVAIL THROUGH THE WINTER WITH GRADUALLY 
INCREASING ANOMALIES THAT REACH AROUND +0.5 DEGREES C BY LATE NEXT SPRING.  

     PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOK

THE STATISTICAL TOOLS ... CCA ... OCN AND SMLR ... WERE CONSULTED AT ALL LEAD
TIMES.  ENSO-NEUTRAL COMPOSITES WERE ALSO CONSULTED.  THESE WERE SUBJECTED TO A 
HIGH-PASS FILTER PRIOR TO ISOLATE INTERANNUAL SIGNALS FROM LONGER TIME SCALES.  
FINALLY DYNAMICAL MODEL FORECASTS FROM NCEP - EC HAMBURG - NASA AND NCAR - 
INITIATED FROM ATMOSPHERIC AND OCEANIC CONDITIONS FROM LATE SEPTEMBER - WERE 
ALL CONSULTED.  ALTHOUGH THE INITIAL ENSO STATE IS NEAR ZERO - THERE WAS  
AGREEMENT AMONG 3 OF THE 4 DYNAMICAL MODELS ON A WAVE-TRAIN EMANATING FROM THE 
ABNORMALLY WARM POOL OF WATER IN THE WESTERN TROPICAL PACIFIC WHICH APPEARS TO 
CAUSE A PERSISTENT PATTERN OVER NORTH AMERICA.  THIS PATTERN FAVORS 
POSITIVE UPPER AIR HEIGHT ANOMALIES OVER THE GULF OF ALASKA AND NEGATIVE 
ANOMALIES OVER EASTERN NORTH AMERICA.  THE TEMPERATURE FORECASTS FROM THESE 
DYNAMICAL MODELS ARE IN OVERALL AGREEMENT WITH MANY OF THE STATISTICAL TOOLS - 
INCLUDING THE ENSO-NEUTRAL COMPOSITES AND CCA - BOTH OF WHICH PREDICT BELOW 
NORMAL TEMPERATURES IN THE NORTHEASTERN US AND ABOVE NORMAL IN THE SOUTHWEST 
DURING THE COLD SEASON.   IN PARTS OF THE EAST WE GAVE GREATER WEIGHT TO THESE 
TOOLS THAN TO THE TREND (OCN) - LEADING TO FORECASTS OF CL IN THE SOUTHEAST AND 
BELOW NORMAL IN THE NORTH-CENTRAL AND NORTHEASTERN U.S.
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     PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2001-2 TO NDJ 2002-3

TEMPERATURE:

MOST FORECAST TOOLS INDICATE WARMER-THAN-NORMAL TEMPERATURES FOR NDJ 2001-2
THROUGH NDJ 2002-3 IN THE SOUTHWEST U.S.  THIS SIGNAL IS THE STRONGEST TREND
SIGNAL ON THE MAP AND THE PROBABILITIES ARE ACCORDINGLY HIGH.  MIXED SIGNALS 
APPEAR OVER ALASKA AND CLIMATOLOGICAL PROBABILITIES ARE OFTEN PREDICTED THERE.  
ONE MAJOR FACTOR INFLUENCING THE SEASONAL CLIMATE ANOMALIES OVER THE EASTERN 
U.S.  THIS WINTER WILL BE THE PHASE OF THE NAO- WHICH IS NOT YET PREDICTABLE 
BEYOND ABOUT 1-2 WEEKS IN ADVANCE.  ENSO-NEUTRAL COMPOSITES INDICATE COOLER 
THAN NORMAL TEMPERATURES OVER MUCH OF THE CENTRAL AND EASTERN U.S. - WHICH 
OPPOSES RECENT WARM TRENDS. BELOW-NORMAL TEMPERATURE WHICH CCA PREDICTED
FOR ALASKA IN NDJ AND DJF IN LAST MONTHS FORECAST HAVE BEEN REMOVED -
SINCE OCN AND CMP BOTH PREDICT WARM.

BEYOND FMA 2002 CCA AND OCN ARE THE PRIMARY TOOLS.  THESE SHOW THE WARM TREND
IN THE WESTERN AND SOUTHERN U.S. DURING THE WARM SEASON AND A COOL TREND IN
THE NORTH-CENTRAL U.S. DURING THE LATE SUMMER.
.        .         .         .         .         .         .         .         .
PRECIPITATION:

CCA AND OCN PREDICT ABOVE-MEDIAN PRECIPITATION OVER TEXAS FOR NDJ THROUGH JFM
AND SUB-NORMAL RAINFALL OVER FLORIDA AND PARTS OF THE SOUTHEAST FOR NDJ THROUGH
DJF.  WHILE MJO ACTIVITY IS EXPECTED TO BE STRONG DURING THE COLD SEASON AND SUCH
ACTIVITY CAN BE ASSOCIATED WITH HEAVY PRECIPITATION EVENTS ALONG THE WEST COAST  
- THE TOOLS CURRENTLY GIVE MIXED INDICATIONS IN THAT REGION AND CL IS PREDICTED
THERE.  ODDS FOR ABOVE-MEDIAN PRECIPITATION INCREASE IN THE NORTHWEST IN AMJ
AND MJJ DUE TO LONG-TERM TRENDS.  BEYOND MJJ PREDICTABILITY OF PRECIPITATION IS
LIMITED TO SCATTERED SMALL REGIONS ASSOCIATED WITH LONG-TERM TRENDS.

THE BIGGEST CHANGES FROM LAST MONTHS OUTLOOK ARE REMOVING ABOVE-MEDIAN
PRECIPITATION FROM THE NDJ THROUGH JFM FORECASTS FOR THE PANHANDLE OF FLORIDA 
AND FORECASTING SUB-MEDIAN PRECIPITATION FOR NDJ AND DJF FOR FLORIDA AND PARTS 
OF THE SOUTHEAST.  THIS SIGNAL COMES FROM CCA AND THE DYNAMICAL MODELS - WHICH
INDICATE THAT THE SIGNAL FADES RAPIDLY AFTER DJF.  

LAST MONTHS FORECAST OF BELOW-MEDIAN IN THE SOUTHWEST FOR NDJ AND DJF 
HAS BEEN MODIFIED TO CL IN LIGHT OF DYNAMICAL MODEL FORECASTS OF
ABOVE-MEDIAN RAINFALL.  ABOVE MEDIAN PRECIPITATION PREDICTED FOR ALASKA
IN DJF THIS MONTH COMES FROM THE DYNAMICAL MODEL FORECASTS.

FORECASTERS:  ED OLENIC AND HUUG VAN DEN DOOL
  
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  (USE LOWER CASE LETTERS)

INFORMATION ON THE FORMULATION AND SKILL OF THE CAS FORECASTS MAY BE FOUND AT:
HTTP://WWW.CPC.NCEP.NOAA.GOV/SOILMST/FORECASTS.HTML  (USE LOWER CASE LETTERS)

NOTES - 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.  

THIS SET OF OUTLOOKS WILL BE SUPERSEDED BY THE ISSUANCE OF THE NEW SET NEXT
MONTH ON THURSDAY NOVEMBER 15 2001.

1971-2000 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 17 2001
FORECAST RELEASE.

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