PROGNOSTIC DISCUSSIONS FOR LONG-LEAD OUTLOOKS 
CLIMATE PREDICTION CENTER NCEP 
NATIONAL WEATHER SERVICE  WASHINGTON DC             
3 PM EDT THURSDAY AUGUST 13 1998


PROGNOSTIC DISCUSSION OF SST FORECASTS

THE OFFICIAL SST FORECAST FOR THE EAST-CENTRAL EQUATORIAL 
PACIFIC (120-170W LONGITUDE - ALSO CALLED NINO 3.4) IS FOR 
CONTINUED STRENGTHENING OF NEGATIVE ANOMALIES IN THE COMING 
SEASON.  BELOW NORMAL SSTS SHOULD CONTINUE THROUGH THE 
REMAINDER OF THE YEAR.  THE CURRENT SSTS ALONG THE EQUATOR ARE 
MORE THAN 2 DEGREES C BELOW NORMAL FROM ABOUT 120W TO 160W - 
DOWN TO MINUS 3 IN A SMALL AREA - WITH TEMPERATURES ABOUT .5 
DEGREES C BELOW NORMAL EXTENDING WESTWARD TO ABOUT 160 E.  SSTS 
EAST OF ABOUT 100 W REMAIN 1 TO 2 DEGREES ABOVE NORMAL - 
ESPECIALLY SOUTH OF THE EQUATOR. HOWEVER - SUB-SURFACE NEGATIVE 
TEMPERATURE ANOMALIES THERE HAVE BEEN STEADILY STRENGTHENING 
AND THE ABOVE NORMAL TEMPERATURES ARE NOW RESTRICTED TO ONLY  
A VERY SHALLOW LAYER NEAR THE SURFACE.  IT IS ANTICIPATED THAT 
BELOW NORMAL SSTS WILL BE FIRMLY IN PLACE IN THE EASTERN 
EQUATORIAL PACIFIC AS WELL WITHIN THE NEXT COUPLE OR MONTHS. 
THE TROPICAL ATMOSPHERE HAS ADJUSTED TO THE EMERGING COLD EVENT 
CONDITIONS WITH TRADE WINDS AT LEAST AS STRONG AS NORMAL - A 
POSITIVE SOI AND SOMEWHAT SUPPRESSED CONVECTION EAST OF THE 
DATE LINE. A POINT TO KEEP IN MIND IS THAT THE NEGATIVE SST 
ANOMALIES APPEARED EXTREMELY RAPIDLY IN LATE MAY AND EARLY JUNE 
BUT THE DEVELOPMENT SINCE HAS BEEN MUCH SLOWER.

MOST MAJOR ENSO PREDICTON MODELS - BOTH THOSE RUN HERE AT NCEP 
AND THOSE FROM OTHER MODELING GROUPS NOW INDICATE THAT MODERATE 
TO STRONG LA NINA CONDITIONS WILL LIKELY BE IN PLACE THIS FALL 
AND WINTER.  THE TWO STATISTICAL MODELS USED AT CPC FOR NINO 
3.4 GUIDANCE - CCA AND CONSTRUCTED ANALOG - PREDICT THE NINO 
3.4 SSTS TO REMAIN SUBSTANTIALLY BELOW NORMAL INTO NEXT 
SPRING.  TEMPERATURES ARE FORECAST TO BE FROM 1.5 TO 2 DEGREES 
C BELOW NORMAL THROUGH EARLY 1999 AND THEN MODERATE TO AROUND 
1.0 DEGREE C BELOW NORMAL BY LATE SPRING.  THE NCEP COUPLED 
MODEL ALSO FORECASTS NEGATIVE ANOMALIES THROUGHOUT THIS SAME 
PERIOD - ALTHOUGH  ITS FORECAST IS THE MOST CONSERVATIVE OF THE 
ENSO SST TOOLS USED AT CPC - WITH MAXIMUM NEGATIVE ANOMALIES OF 
ONLY ABOUT -.90 DEGREES C IN JANUARY 99.  THE NCEP MODEL IS 
MOST LIKELY TOO WARM IN OUR JUDGEMENT AND HAS BEEN SLOW TO 
CATCH UP WITH THIS COLD EVENT ONSET AND EVOLUTION. NEVERTHELESS 
THE THREE NCEP MODELS SHOW GREATER AGREEMENT THAN BEFORE AS THE 
STATISTICAL TOOLS ARE BACKING OFF FROM THEIR MORE EXTREME 
FORECASTS ONLY A FEW MONTHS AGO - WHILE THE COUPLED MODEL IS 
GAINING AMPLITUDE. 

A CONSOLIDATION FORECAST BASED ON PAST PERFORMANCE OF THE TWO 
STATISTICAL TOOLS AND THE COUPLED MODEL SUGGEST A SOLUTION 
CLOSEST TO THE STATISTICAL TOOLS - WITH THE COUPLED MODEL 
SOLUTION BEING WITHIN THE STANDARD ERROR BARS.  OVERALL 
CONFIDENCE IN THIS FORECAST IS THEREFORE HIGH. THUS - COLD ENSO 
CONDITIONS ARE ASSUMED IN FORMULATING THE SON THRU FMA U.S. 
TEMP AND PRECIP FORECASTS. WE ARE MORE UNCERTAIN ABOUT COLD 
ENSO CONDITIONS BEYOND THE END OF NEXT WINTER.  

PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 1998 TO SON 1999

THE SERIES OF LONG-LEAD FORECASTS FROM SON 98 THROUGH FMA 99 
REFLECT THE HISTORICAL DISTRIBUTIONS OF SEASONAL MEAN 
TEMPERATURES AND PRECIPITATION ASSOCIATED WITH PREVIOUS LA 
NINAS. THE DEGREE OF CONFIDENCE IN THESE LA NINA CONSISTENT 
PREDICTIONS - BASED ON THE PAST PERFORMANCE OF THE ENSO SST 
PREDICTIONS - IS GREATER THAN 90 PERCENT. STILL THERE ARE 
CHANGES FROM THE SET OF FORECASTS PRODUCED A MONTH AGO - AS 
WELL AS TWO MONTHS AGO - FOR THE CORRESPONDING SEASONS EVEN 
THOUGH LA NINA COMPOSITES WERE ALSO RELIED UPON HEAVILY FOR THE 
FORECASTS RELEASED IN JULY AND JUNE. THIS IS THE CONSEQUENCE OF 
A CPC WIDE EFFORT TO BETTER DEFINE HISTORICAL COLD EVENTS AND 
CREATE A LARGER AND LESS NOISY SAMPLE - INCLUDING MODERATE AND 
EVEN WEAK EVENTS - TO BASE THE COMPOSITES ON. THESE NEW 
COMPOSITES WILL SOON REPLACE THE PRELIMINARY ESTIMATES THAT ARE 
CURRENTLY ON THE CPC HOMEPAGE. IN GENERAL THE PROBABILITY 
ANOMALIES ARE SOMEWHAT WEAKER THAN BEFORE BUT PATTERNS ARE 
ESSENTIALLY THE SAME. THE MOST SRIKING FORECASTS WITH VALUES 
LARGER OR EQUAL TO A 30% PROBABILITY ANOMALY ARE FOR BELOW 
MEDIAN PRECIPITATION IN ARIZONA IN SON AND IN FLORIDA IN DJF 
AND JFM AND ABOVE NORMAL TEMPERATURE IN DJF AND JFM IN PORTIONS 
OF THE SOUTHEAST. 

THE FORECASTS FOR SON THRU FMA ARE DERIVED MAINLY FROM LA NINA 
COMPOSITES WITH DUE CONSIDERATION OF THE CCA AND OCN. CCA 
PLAYED A BIG ROLE IN EXTENDING THE AREA FOR BELOW NORMAL 
TEMPERATURE IN THE NORTHERN STATES IN DJF THRU MAM OR IN 
INTRODUCING THESE ANOMALIES A MONTH SOONER THAN IN THE 
FORECASTS ISSUED IN JULY TO GUARANTEE GREATER TEMPORAL 
CONSISTENCY. IN SOME AREAS - OCN WAS INVOKED TO STRENGTHEN THE 
FORECAST - I.E. BOOST THE PROBABILITY ANOMALIES - WHERE 
COMPOSITES AGREED WITH OCN. AN EXAMPLE IS THE FORECAST FOR 
ABOVE NORMAL TEMPERATURE OVER THE SOUTHEAST IN DJF AND JFM.  ON 
THE OTHER HAND - OCN ALSO PLAYED A ROLE IN REDUCING THE 
PROBABILITY ANOMALIES IN AREAS WHERE THE COMPOSITE WENT AGAINST 
LONG TERM TEMPERATURE TRENDS. AN EXAMPLE OF THE LATTER IS THE 
COLD INDICATED BY LA NINA COMPOSITES FOR CALIFORNIA IN JFM 
WHICH IS UNLIKELY IN VIEW OF STRONG LONG TERM WARMING TRENDS - 
HENCE THE OFFICIAL FORECAST IS CL. OTHER ASPECTS OF OCN WERE 
COMPLETELY IGNORED BECAUSE ABOVE MEDIAN PRECIP IN PARTS OF THE 
SOUTH DUE TO LONG TERM TRENDS WOULD SEEM TO BE INAPPROPRIATE 
DURING A CONFIDENTLY FORECAST LA NINA WINTER.

AS TO THE OTHER TOOLS PLEASE NOTE THE FOLLOWING: (1) THE CAS 
SOIL MOISTURE TOOL WAS NOT CONSIDERED FOR THIS SET OF FORECASTS 
BECAUSE ITS SKILL IS SEASONAL AND IS RELIABLY GOOD IN SUMMER 
ONLY. (2) THE MULTIPLE LINEAR REGRESSION WAS USED ONLY AS A 
SANITY CHECK FOR THE OTHER TOOLS. (3) THE COUPLED MODEL 
FORECASTS FOR US TEMP AND PRECIP PLAYED ONLY A MODEST ROLE IN 
SHAPING THE OFFICAL FORECAST SINCE ITS FORCING IN TERMS OF SST 
ANOMALY WAS ONLY MODEST AND ITS MIDLATITUDE AND U.S. PATTERNS 
DO NOT SEEM CONNECTED TO OVERRIDING TROPICAL FORCING. 

THE SON FORECAST CALLS FOR ABOVE NORMAL TEMPERATURES IN 
PORTIONS OF THE INTERIOR SOUTHWEST U.S.  RECENT TRENDS AND WARM 
UPSTREAM SSTS SHOULD ALSO FAVOR ABOVE NORMAL TEMPERATURES IN 
SOUTHERN FLORIDA. THE NEW LA NINA COMPOSITES SUPPORT THE SON 
FORECAST FOR BELOW MEDIAN PRECIPITATION IN THE SOUTHWEST AND - 
A NEW AREA - ALSO IN TEXAS - AND ABOVE MEDIAN PRECIPITATION IN 
THE NORTHWEST. A NEW AREA OF ABOVE MEDIAN PRECIPITATION IS ALSO 
INDICATED FOR THE UPPER MIDWEST AND GREAT LAKES DUE TO OCN AND 
COMPOSITES. 

FOR OND THRU FMA ALL FORECASTS ARE OF THE FLAVOR DRY AND WARM 
IN THE SOUTH AND WET AND COLD IN THE NORTH - HOWEVER WITH SOME 
IMPORTANT DIFFERENCES IN DETAIL. EARLY ON THE CENTER OF GRAVITY 
FOR BELOW MEDIAN PRECIP AND ABOVE NORMAL TEMPS IS IN THE 
SOUTHWEST - ONLY TO SHIFT TOWARDS THE SOUTHEAST FROM NDJ 
ONWARD. GENERALLY PROBABILITY ANOMALIES IN THE SOUTH ARE MUCH 
HIGHER THAN IN THE NORTH AND COVER LARGER AREAS AS WELL. THE 
WET AND COLD AREAS ALONG THE NORTHERN TIER HAVE THEIR HIGHEST 
PROBABILITY ANOMALIES EITHER IN WISCONSIN - GREAT LAKES OR IN 
THE NORTHWEST - WITH A BREAK IN BETWEEN IN SOME SEASONS. THE 
NORTHEAST IS THE MOST UNCERTAIN - HENCE CL IS SHOWN FOR MANY 
SEASONS. 

AN IMPORTANT POINT TO KEEP IN MIND REGARDING LA NINA WINTERS IS 
THE STRONG INTRA SEASONAL FLUCTUATIONS DUE TO BLOCKING EPISODES 
ALTERNATING WITH ENHANCED ZONAL FLOW. WHILE EL NINO WINTER 
FLOWS ARE STABLE - VERY LITTLE BLOCKING - LA NINA WINTERS ARE 
MUCH MORE VARIABLE AND THE WINTER MEAN CONDITIONS CPC IS TRYING 
TO FORECAST MAY MASK THE FACT THAT PERIODS OF STRIKINGLY COLD 
WINTER WEATHER AND MUCH MILDER WEATHER MAY AVERAGE OUT CLOSE TO 
NORMAL ESPECIALLY IN THE NORTHERN HALF OF THE NATION.  
 
FORECASTS PAST MAM AND AMJ 99 PREDOMINATELY REFLECT TEMPERATURE 
AND PRECIPITATION TRENDS AS INDICATED BY OCN.  

ALASKAN FORECASTS SHOW MUCH CL FOR THE INITIAL SEASONS BECAUSE 
THE LONG TERM TREND TOWARDS HIGHER TEMPS IS CONTRADICTED BY LA 
NINA COMPOSITES BEING COLD. ONLY IN THE SPRING - WHEN LA NINA 
BECOMES UNCERTAIN - DO WE FORECAST ABOVE NORMAL TEMPERATURES. 
THE EXPECTATION OF REDUCED ONSHORE FLOW LEADS US TO FORECAST 
BELOW MEDIAN PRECIPITATION IN A FEW SEASONS IN SOUTHERN 
ALASKA.  

FOR A DESCRIPTION OF THE STANDARD FORECAST TOOLS - THEIR SKILL 
- AND THE FORECAST FORMAT PLEASE SEE OUR WEB PAGE AT:  
HTTP://NIC.FB4.NOAA.GOV:80/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 17 
1998.