PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 830 AM EDT THU OCT 18 2018 SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS THIS SECTION OF THE SEASONAL OUTLOOK MESSAGE SUMMARIZES THE FIRST FORECAST IN THE SET, THE NOVEMBER-DECEMBER-JANUARY (NDJ) 2018-2019 SEASONAL OUTLOOK. DESCRIPTION OF THE SUBSEQUENT OUTLOOKS, CLIMATE FACTORS CONSIDERED, AND SPECIFIC FORECAST RATIONALE FOR ALL OUTLOOKS ARE PROVIDED IN THE LAST TWO SECTIONS OF THE MESSAGE. THE NDJ 2018-2019 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL SEASONAL MEAN TEMPERATURES FOR MUCH OF THE FORECAST DOMAIN TO INCLUDE ALL OF ALASKA AND MOST OF THE WESTERN AND NORTHERN CONTIGUOUS U.S. THE GREATEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE INDICATED FOR WESTERN AND NORTHERN ALASKA AND TO A LESSER DEGREE THE PACIFIC NORTHWEST. FOR SEASONAL TOTAL PRECIPITATION AMOUNTS DURING NDJ 2018-2019, THERE ARE MODESTLY ELEVATED CHANCES OF ABOVE-NORMAL PRECIPITATION FOR MOST OF THE SOUTHERN TIER OF THE CONTIGUOUS U.S., THE CENTRAL EASTERN SEABOARD, AND SOUTHERN ALASKA. EQUAL CHANCES (EC) FOR ABOVE-, NEAR-, OR BELOW-NORMAL SEASONAL MEAN TEMPERATURES OR SEASONAL TOTAL PRECIPITATION AMOUNTS ARE INDICATED IN AREAS WHERE THE LIKELIHOOD OF THESE VARIABLES ARE FAVORED TO BE SIMILAR TO CLIMATOLOGICAL PROBABILITIES. THE REASONS FOR THIS CAN BE A COMBINATION OF WEAKLY DEFINED OR NON-RELIABLE CLIMATE FACTORS AS WELL AS CONSIDERABLE SPREAD IN FORECAST TOOL SOLUTIONS. 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 STARTING WITH OCEAN CONDITIONS, WE CONTINUE TO REMAIN IN ENSO-NEUTRAL CONDITIONS THROUGH EARLY OCTOBER AND THE EL NINO WATCH CONTINUES. IN RECENT WEEKS, HOWEVER, OBSERVATIONS ACROSS THE GLOBAL TROPICS HAVE TRENDED TOWARD MORE FAVORABLE CONDITIONS FOR DEVELOPMENT OF EL NINO IN THE NEXT COUPLE OF MONTHS. SEA SURFACE TEMPERATURES (SSTS) ARE ABOVE-NORMAL ACROSS MOST OF THE EQUATORIAL PACIFIC BASIN, GENERALLY RANGING FROM +0.5 - +1.0 DEGREES C. THE MOST RECENT WEEKLY VALUES OF THE NINO4 AND NINO3.4 INDICES ARE NOW +0.9 AND +0.6 DEGREES C RESPECTIVELY. THIS SOMEWHAT RAPID CHANGE WAS CONSIDERABLY AIDED BY THE DEVELOPMENT OF A WESTERLY WIND BURST (WWB) AND EVOLUTION OF AN ONGOING MJO EVENT AND THE ASSOCIATED WESTERLY LOW-LEVEL WIND ANOMALIES. A STRONG DOWNWELLING OCEANIC KELVIN WAVE WAS INITIATED AS A RESULT OF THIS SIGNIFICANT WEAKENING OF THE PACIFIC BASIN TRADE WINDS DUE TO THESE EVENTS AND CONTINUES TO SHIFT EASTWARD ACROSS THE PACIFIC BASIN AT DEPTH. ACCORDINGLY, THE EQUATORIAL UPPER-OCEAN HEAT CONTENT HAS INCREASED CONSIDERABLY DURING SEPTEMBER AND EARLY OCTOBER MAKING THE DEVELOPMENT OF EL NINO SOMEWHAT MORE LIKELY. SPECIFIC NINO3.4 SST FORECASTS ARE REVIEWED IN THE SECTION BELOW. THE ATMOSPHERIC CONDITIONS ASSOCIATED WITH A DEVELOPING EL NINO EVENT REMAIN MODEST AT BEST. ALTHOUGH WESTERLY LOW-LEVEL WIND ANOMALIES ARE NOW PRESENT, ANY ORGANIZED AREAS OF ENHANCED CONVECTION ARE NOT YET PRESENT. THIS IS MOST LIKELY, HOWEVER, IN PART DUE TO THE COUNTER-ACTING EFFECT FROM LARGE SCALE SUBSIDENCE ASSOCIATED WITH THE SUPPRESSED CONVECTIVE PHASE OF THE MJO. TURNING TO CURRENT TERRESTRIAL CONDITIONS, WE NOTE MUCH ABOVE-NORMAL SOIL MOISTURE ANOMALIES FROM TEXAS TO THE MIDWEST, EASTWARD TO THE GREAT LAKES, MID-ATLANTIC AND PARTS OF THE NORTHEAST, WHILE DROUGHT CONDITIONS PERSIST ACROSS MANY AREAS OF THE WEST. AS WE ARE ENTERING THE LATE AUTUMN AND WINTER MONTHS, SOIL MOISTURE CONDITIONS, ALTHOUGH NEAR THE 99TH PERCENTILE IN MANY AREAS, IS NOT EXPECTED TO CONTRIBUTE ANY SIGNIFICANT IMPACT TO THE CLIMATE CONDITIONS OVER THE NEXT SEVERAL MONTHS. SNOW COVER ANOMALIES (BOTH NEGATIVE AND POSITIVE) FOR SEPTEMBER AND THE FIRST HALF OF OCTOBER ARE IMPORTANT TO NOTE. SNOWFALL OVER AREAS OF EURASIA AND ALASKA ARE CURRENTLY BELOW-NORMAL IN MANY AREAS, BUT SNOWFALL HAS BEEN SUBSTANTIALLY ABOVE-NORMAL FOR PORTIONS OF CENTRAL AND EASTERN CANADA. PROGNOSTIC DISCUSSION OF SST FORECASTS FORECASTS OF THE NINO3.4 SST ANOMALY HAVE NOT CHANGED VERY MUCH OVER THE PAST FEW MONTHS TO FIRST ORDER. THE CPC CONSOLIDATION NINO3.4 SST ANOMALY FORECAST MAINTAINS ITS RECENT PREDICTIONS OVER THE PAST SEVERAL MONTHS WITH A PEAK IN POSITIVE ANOMALY DURING NDJ 2018-2019 OF JUST UNDER +1.0 DEGREE C AND THEN SLOWLY DECREASES OVER THE COURSE OF THE WINTER AND SPRING MONTHS OF 2019, ALTHOUGH THE FORECAST IS TEMPERED BY AN OUTLIER FORECAST FROM THE CCA STATISTICAL MODEL. THIS MODEL FORECAST REMAINS IN ENSO-NEUTRAL TERRITORY THROUGH THE WINTER AND INCREASES THEREAFTER. THE NMME NINO3.4 SST ANOMALY MODEL GUIDANCE ALSO HAS REMAINED CONSISTENT OVER THE PAST FEW MONTHS AND CONTINUES TO INDICATE A SLIGHTLY STRONGER EVENT (ENSEMBLE MEAN PEAKING AND PERSISTING BETWEEN +1.0 - +1.2 DEGREES C) DURING THE WINTER AND SPRING MONTHS. THE OFFICIAL CPC-IRI ENSO OUTLOOK FAVORS EL NINO THIS WINTER AND SPRING AT A GREATER THAN 70% PROBABILITY THROUGH JFM 2019 AND THEN DECREASING TO NEAR 50% BY AMJ 2019. PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS THIS SET OF OUTLOOKS UTILIZED TYPICAL IMPACTS ASSOCIATED WITH EL NINO EVENTS, ALBEIT WITH THE UNDERSTANDING THAT THIS MOST LIKELY WILL BE A WEAK EVENT AND NOTING THE CONFIDENCE IN THIS IMPACTS IN INTENSITY AND LOCATION IS SOMEWHAT LOW. MOREOVER, IT IS NOTED THAT DUE TO ITS LIKELY WEAK NATURE, THE VARIANCE EXPLAINED IN THE MID-LATITUDES OVER THE EARLY PORTION OF THIS SET OF OUTLOOKS FROM THE TROPICAL PACIFIC COULD VERY WELL BE LOW. OTHER FACTORS FROM BOTH THE TROPICS (E.G., MJO) AND HIGH/POLAR LATITUDES (E.G., AO/NAO, NPO, ETC.) ARE LIKELY TO FAVOR HIGH VARIABILITY OVER THE WINTER AND EARLY SPRING SEASONS AND LIKELY WILL EXPLAIN CONSIDERABLY MORE VARIANCE IN THE UPCOMING SEASONAL MEANS IN TEMPERATURE AND PRECIPITATION. LOCAL COASTAL SSTS AND CONSIDERATIONS OF AREAS OF ANOMALOUS SNOWFALL WERE CONSIDERED IN MAKING THE OUTLOOKS. CONTRIBUTIONS TO THE OUTLOOKS ALSO INCLUDED BIAS-CORRECTED AND CALIBRATED DYNAMICAL MODEL GUIDANCE FROM THE NMME AND IMME ENSEMBLE SUITES (BOTH ENSEMBLE MEAN AND THEIR PARTICIPANT MODELS) THROUGH MAM 2019. EMPIRICAL AND STATISTICAL FORECAST MODELS ALSO PLAYED A LARGE ROLE THROUGHOUT ALL FORECAST LEADS. THESE INCLUDED GUIDANCE FROM A COMBINED ENSO-OCN TOOL, THE CCA, THE CA, AND "BRIDGING" TECHNIQUES. MOREOVER, CONSOLIDATION FORECAST GUIDANCE PRODUCTS FROM STATISTICAL ONLY, DYNAMICAL MODEL ONLY, AND COMBINED STATISTICAL AND DYNAMICAL FORECAST TOOLS WAS HEAVILY UTILIZED. OCN ALSO WAS UTILIZED OFTEN THROUGHOUT THE OUTLOOK LEADS FOR BOTH TEMPERATURE AND PRECIPITATION. PROGNOSTIC DISCUSSION OF OUTLOOKS - NDJ 2018 TO NDJ 2019 TEMPERATURE IN REVIEWING THE FIRST FOUR FORECAST LEADS THROUGH THE WINTER 2018-2019 AND EARLY SPRING MONTHS IN 2019, THE NDJ AND DJF 2018-2019 TEMPERATURE OUTLOOKS ARE SIMILAR AND DEPICT ELEVATED ODDS OF ABOVE-NORMAL TEMPERATURES FOR ALASKA AND MUCH OF THE WESTERN AND NORTHERN CONUS WITH EC NOTED FOR THE SOUTHEAST. AS WE PROGRESS THROUGH THE WINTER INTO THE EARLY SPRING, THE FORECAST SEQUENCE DEPICTS A TENDENCY FOR THE ODDS OF ABOVE-NORMAL TEMPERATURES TO DECREASE ALONG WITH FORECAST COVERAGE FIRST FOR THE OHIO VALLEY AND MID-ATLANTIC AND THEN LATER IN THE GREAT LAKES AND NORTHEAST BY FMA 2019 WHERE EC IS FORECAST. IN ADDITION, OVER THE SAME TIME, THERE IS AN EASTERN EXPANSION OF ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS THE SOUTHERN PLAINS INTO THE SOUTHEAST CONUS. FOR THESE LEADS, OTHER THAN AREAS IN ALASKA AND THE PACIFIC NORTHWEST, THE PROBABILITIES ARE QUITE MODEST. THIS DEPICTED EVOLUTION (VARIATION OF AREAS DENOTED AS EC) IN THE FORECAST OF SEASONAL MEAN TEMPERATURES IS A RESULT OF CHANGING AREAS WITH THE GREATEST UNCERTAINTY AND SO LOWER FORECAST CONFIDENCE. UNDERSTANDING THE WEAK NATURE OF EL NINO ANTICIPATED THIS WINTER AND CONFRONTED BY CONSIDERABLE CONFLICTING FORECAST TOOL INFORMATION IN THESE AREAS, EC IS FORECAST AT THIS TIME. DURING NDJ AND DJF 2018-2019, DYNAMICAL MODEL GUIDANCE FROM THE NMME DEPICTS CALIBRATED PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES NEARLY UNANIMOUSLY ACROSS MUCH OF THE NORTH IN AGREEMENT WITH THE AFOREMENTIONED STATISTICAL FORECAST TOOLS AND OBJECTIVE, SKILL WEIGHTED CONSOLIDATION GUIDANCE PRODUCTS. AS WE PROGRESS THROUGH THE WINTER, POSITIVE TEMPERATURE TRENDS IN MANY AREAS NO LONGER EXIST AND CALIBRATED DYNAMICAL MODEL GUIDANCE PROBABILITIES DECREASE SUBSTANTIALLY, ALONG WITH LITTLE HISTORICAL FORECAST SKILL INDICATED. AN ADDITIONAL FACTOR IS THAT THE ECMWF SEASONAL PREDICTION FAVORS BELOW-NORMAL TEMPERATURES FOR A CONSIDERABLE AREA THAT STRETCHES FROM THE SOUTHERN PLAINS AND PARTS OF THE SOUTHEAST CONUS IN NDJ 2018-2019 TO AN EXPANDED AREA THAT INCLUDES THE CENTRAL PLAINS, CENTRAL MISSISSIPPI VALLEY, OHIO VALLEY, AND MID-ATLANTIC. MOREOVER, THE ENSO-OCN TOOL AND OBJECTIVE, SKILL WEIGHTED CONSOLIDATION FORECAST TOOLS INDICATE A VARYING MIXTURE OF QUITE MODEST PROBABILITIES FOR EITHER OF THE THREE FORECAST CATEGORIES. IN ADDITION, UNCERTAINTIES IN THE PREDOMINATE PHASE OF THE AO/NAO AND MJO ACTIVITY ESPECIALLY FROM MID-WINTER INTO EARLY SPRING MAKE A FORECAST OF EC NOT AN UNREASONABLE CHOICE AS VARIABILITY OVERALL IS LIKELY TO BE HIGH AND DEPEND ON CONSIDERABLE IMPACTS ASSOCIATED WITH BOTH TROPICAL AND HIGH LATITUDE SUBSEASONAL VARIABILITY WHICH IS DIFFICULT TO PREDICT AT THESE FORECAST LEADS. FOR ALASKA AND THE WESTERN CONUS, THERE IS LITTLE SUPPORT FOR ANY OTHER FORECAST BESIDES ELEVATED ODDS FOR ABOVE-NORMAL TEMPERATURES FOR THIS PORTION OF THE SET OF OUTLOOKS AS WELL AS THE REMAINING OUTLOOKS THROUGH NDJ 2019-2020. THE PRIMARY DRIVER FOR THE OUTLOOKS FROM MJJ 2019 THROUGH NDJ 2019-2020 WERE OCN, ENSO-OCN, AND STATISTICAL OBJECTIVE, SKILL WEIGHTED CONSOLIDATION FORECAST TOOLS. PRECIPITATION THE OUTLOOKS FOR SEASONAL TOTAL PRECIPITATION AMOUNTS UTILIZED INFORMATION CONSISTENT WITH AN ANTICIPATED (ALBEIT WEAK) EL NINO EVENT FROM NDJ 2018-2019 THROUGH MAM 2019. DYNAMICAL MODEL GUIDANCE FROM THE NMME AND IMME CONTRIBUTED TO THE OUTLOOKS AS WELL THROUGH MAM 2019. GIVEN THE RANGE OF SOLUTIONS AND GENERALLY WEAK INDICATORS FROM MANY OF THE FORECAST TOOLS, PROBABILITIES FOR EITHER FORECAST CATEGORY (ABOVE- OR BELOW-NORMAL PRECIPITATION) ARE QUITE MODEST, NOT REACHING 50% PROBABILITY FROM THE CLIMATOLOGICAL PROBABILITY OF 33% UNTIL DJF 2018-2019 AND JFM 2019 WHEN A SMALL AREA FAVORING ABOVE-NORMAL PRECIPITATION IS INDICATED FOR AN AREA IN SOUTHERN GEORGIA AND NORTHERN FLORIDA. THIS AREA IS A PART OF A LARGER REGION OF FAVORED ABOVE-NORMAL PRECIPITATION ACROSS THE SOUTHERN TIER OF THE CONUS THROUGH MAM 2019. PRIMARILY SUPPORTED BY DYNAMICAL MODEL GUIDANCE, AN INCREASE IN COVERAGE OF THIS REGION IN THE CENTRAL ROCKIES AND CENTRAL PLAINS DURING JFM AND FMA 2019 IS FORECAST. BELOW-NORMAL PRECIPITATION IS FAVORED FOR PARTS OF PACIFIC NORTHWEST AND NORTHERN ROCKIES IN NDJ 2018-2019 AND THEN PRIMARILY CENTERED ACROSS MONTANA DURING JFM AND FMA 2019. SIMILARLY, BELOW NORMAL PRECIPITATION IS FAVORED FOR PARTS OF THE GREAT LAKES AND LATER THE OHIO VALLEY OVER THE SEASONS FROM DJF 2018-2019 TO FMA 2019. EL NINO CONSIDERATIONS AND CONSISTENT DYNAMICAL MODEL GUIDANCE FAVORED ELEVATED ODDS OF ABOVE-NORMAL PRECIPITATION FOR SOUTHERN ALASKA THROUGH FMA 2019. THERE WAS CONSIDERABLE CONFLICTING FORECAST TOOL INFORMATION (SEVERAL SOURCES) FOR THE EARLY LEADS ACROSS CALIFORNIA SO EC WAS INDICATED AT THIS TIME FOR THIS REGION EXCEPT FOR A SMALL AREA IN SOUTHERN CALIFORNIA. FROM AMJ 2019 THROUGH NDJ 2019-2020, THE OUTLOOKS ARE BASED PREDOMINATELY ON LONG TERM TRENDS AS DIAGNOSED BY OCN FOR EACH FORECAST SEASON. TO THIS END, THE MOST BROAD AND CONSISTENT SIGNALS FOR THIS ARE ELEVATED ODDS FOR BELOW-NORMAL PRECIPITATION IN THE NORTHERN ROCKIES FROM MJJ 2019 THROUGH JAS 2019 AND A LARGER AREA FOR FAVORED ABOVE-NORMAL PRECIPITATION FOR PARTS OF THE GREAT LAKES, NORTHEAST, OHIO VALLEY, AND MID-ATLANTIC FROM MJJ 2019 THROUGH OND 2019. FORECASTER: JON GOTTSCHALCK THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, FOLLOWING THE WORLD METEROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3 COMPLETE DECADES AS THE CLIMATIC REFERENCE PERIOD. THE PROBABILITY ANOMALIES FOR TEMPERATURE AND PRECIPITATION BASED ON THESE NEW NORMALS BETTER REPRESENT SHORTER TERM CLIMATIC ANOMALIES THAN THE FORECASTS BASED ON OLDER NORMALS. 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/LONG_RANGE/TOOLS.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/PRODUCTS/SOILMST_MONITORING/US/OUTLOOK/OUTLOOK.SHTM L (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 NOV 15 2018 1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011 FORECAST RELEASE. $$