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.