90 Day Narrative

901 
FXUS05 KWBC 211231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU SEP 21 2017
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
THE OCTOBER-NOVEMBER-DECEMBER (OND) 2017 TEMPERATURE OUTLOOK INDICATES 
INCREASED CHANCES OF ABOVE-NORMAL TEMPERATURES FOR MOST OF ALASKA AND THE 
CONTIGUOUS 48 STATES. THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES 
ARE FORECAST FOR PARTS OF THE SOUTHWEST AND THE NORTH SLOPE OF ALASKA (AT OR 
ABOVE 60-PERCENT). THE OND 2017 PRECIPITATION OUTLOOK INDICATES INCREASED ODDS 
OF ABOVE-NORMAL PRECIPITATION FOR WESTERN ALASKA, FROM THE NORTH COAST TO THE 
ALASKA PENINSULA  AND THE ALEUTIANS, AS WELL AS FOR THE PACIFIC NORTHWEST AND 
NORTHERN ROCKIES. ODDS FOR BELOW-NORMAL PRECIPITATION ARE INCREASED, RELATIVE 
TO CLIMATOLOGY, ACROSS THE MIDDLE AND LOWER MISSISSIPPI VALLEYS AND ACROSS MUCH 
OF THE SOUTHEAST.
THE CURRENT NEUTRAL PHASE OF ENSO IS EXPECTED TO PERSIST THROUGH THE NORTHERN 
HEMISPHERE AUTUMN, WITH INCREASING CHANCES FOR A TRANSITION TO LA NINA 
CONDITIONS LATER IN THE AUTUMN AND WINTER 2017-2018. AS THE ENSO OUTLOOK 
BECOMES MORE CERTAIN DURING THE NEXT COUPLE OF MONTHS, CORRESPONDING 
ADJUSTMENTS WILL BE MADE TO THE SEASONAL OUTLOOKS.
EQUAL CHANCES (EC) ARE FORECAST OVER AREAS WHERE PROBABILITIES OF ABOVE-, 
BELOW-, OR NEAR-NORMAL SEASONAL MEAN TEMPERATURES AND SEASONAL ACCUMULATED 
PRECIPITATION AMOUNTS ARE EXPECTED TO BE SIMILAR TO CLIMATOLOGICAL 
PROBABILITIES.
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
OCEANIC AND ATMOSPHERIC OBSERVATIONS ACROSS THE EQUATORIAL PACIFIC INDICATE 
ENSO-NEUTRAL CONDITIONS. DURING THE LAST FOUR WEEKS, SEA-SURFACE TEMPERATURES 
(SST) HAVE GENERALLY DECREASED OVER THE CENTRAL AND EASTERN EQUATORIAL PACIFIC, 
INTENSIFYING THE NEGATIVE ANOMALIES IN THOSE REGIONS. ACROSS THE WESTERN 
PACIFIC, POSITIVE ANOMALIES HAVE SLIGHTLY DECREASED IN COVERAGE AND MAGNITUDE. 
SUBSURFACE TEMPERATURE MEASUREMENTS IN THE CENTRAL AND EASTERN EQUATORIAL 
PACIFIC REVEAL A LARGE RESERVOIR OF ANOMALOUSLY COLD WATER FROM ABOUT 50-175 
METERS BELOW THE SURFACE. THE PRESENCE AND GROWTH OF THIS FEATURE CONTRIBUTE TO 
THE ASSESSMENT FOR INCREASING ODDS FOR LA NINA DEVELOPMENT IN THE COMING 
MONTHS. DECREASING UPPER-OCEAN HEAT CONTENT VALUES REFLECT THIS CONTINUED 
COOLING. OUTGOING LONGWAVE RADIATION (OLR) ANOMALIES DURING LATER AUGUST AND 
EARLY SEPTEMBER SHOW BELOW-AVERAGE CONVECTION FROM 140E TO 150W, FROM THE 
EQUATOR TO 10N. DURING THIS SAME PERIOD, THE TRADE WINDS HAVE BEEN ABOVE 
AVERAGE WEST OF THE DATE LINE WITH REDUCED TRADES OVER THE EASTERN PACIFIC. THE 
REDUCED TRADES OVER THE EASTERN PACIFIC HAVE BEEN DISPLACED NORTHWARD, SO ARE 
LIKELY TO HAVE HAD LESS OF AN INFLUENCE ON EQUATORIAL SST VALUES. OVERALL, THE 
OCEAN AND ATMOSPHERE SYSTEM REMAINS CONSISTENT WITH ENSO-NEUTRAL CONDITIONS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE MOST RECENT PREDICTIONS FROM THE NCEP CLIMATE FORECAST SYSTEM (CFSV2) AND 
THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) INDICATE THE FORMATION OF LA 
NINA AS SOON AS THE NORTHERN HEMISPHERE FALL 2017. THE NMME MEAN INDICATES A 
NINO 3.4 VALUE (-0.6 DEG C) BELOW THE LA NINA THRESHOLD BY NOVEMBER OF 2017, 
WITH CONSTITUENT ENSEMBLE MEMBERS VARYING FROM -0.3 TO -1.1 BY DECEMBER OF 
2017. THE CONSTRUCTED ANALOG BASED ON SST PATTERNS (SST-CA), CCA, AND MARKOV 
MODEL INDICATE ENSO NEUTRAL CONDITIONS THROUGH THE NORTHERN HEMISPHERE WINTER. 
THE CPC CONSOLIDATION PREDICTS ENSO NEUTRAL CONDITIONS THROUGH THE AUTUMN, WITH 
INCREASING ODDS FOR LA NINA BY WINTER 2017-18. FORECASTERS FAVOR THE NMME 
PREDICTIONS IN PART BECAUSE OF THE RECENT COOLING OF SURFACE AND SUB-SURFACE 
TEMPERATURE ANOMALIES, AND ALSO BECAUSE OF THE HIGHER DEGREE OF FORECAST SKILL 
AT THIS TIME OF YEAR. THE OFFICIAL CPC/IRI OUTLOOK INDICATES A 62 PERCENT 
CHANCE OF LA NINA DEVELOPMENT DURING NOVEMBER-DECEMBER-JANUARY 2017-18, AN 
INCREASE OF 36 PERCENTAGE POINTS FROM LAST MONTH. THE OFFICIAL OUTLOOK 
INDICATES A LIKELY RETURN TO ENSO NEUTRAL CONDITIONS BY NEXT SPRING, 
MARCH-APRIL-MAY 2018.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE OUTLOOKS ARE BASED ON DYNAMICAL MODEL GUIDANCE FROM THE NMME SUITE, 
REGRESSIONS OF TEMPERATURE AND PRECIPITATION ON THE CPC NINO 3.4 CONSOLIDATION, 
AND TRENDS. THE SST-CA TOOL WAS NOT USED IN THE CREATION OF OUTLOOKS THIS 
MONTH, AS IT WAS THE ONLY TOOL INDICATING POSITIVE NINO 3.4 VALUES THROUGH 
WINTER 2017-18.
PROGNOSTIC DISCUSSION OF OUTLOOKS - OND 2017 TO OND 2018
TEMPERATURE
ABOVE-NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF ALASKA AND FOR MOST OF THE 
CONTIGUOUS 48 STATES DURING OND 2017. THE ODDS FOR ABOVE-NORMAL TEMPERATURES 
ACROSS THE NORTHWEST, NORTHERN ROCKIES, AND NORTHERN GREAT PLAINS HAVE BEEN 
REDUCED FROM LAST MONTH'S OUTLOOK, AS THE INCREASING ODDS FOR LA NINA WOULD 
FAVOR BELOW-NORMAL TEMPERATURES DURING THE LATTER PORTIONS OF OND. ACROSS 
SOUTHEAST ALASKA AND THE ALASKA PANHANDLE, AS WELL AS PORTIONS OF THE NORTHERN 
GREAT PLAINS, ODDS FOR ABOVE-NORMAL TEMPERATURES WERE REDUCED ENOUGH THAT SOME 
AREAS TRANSITION TO EQUAL CHANCES. THE REDUCTION IN PROBABILITIES FOR 
ABOVE-NORMAL TEMPERATURES FROM THE NORTHWEST TO THE NORTHERN GREAT PLAINS AND 
OVER SOUTHEAST ALASKA CONTINUES THROUGH THE MAM 2018 OUTLOOKS, REFLECTING THE 
POSSIBILITY FOR LA NINA TO INFLUENCE THE TEMPERATURE PATTERN OVER THE FORECAST 
DOMAIN. THESE SAME SIGNALS, A COLDER FORECAST RELATIVE TO LAST MONTH ACROSS THE 
NORTHERN CONUS, ARE LARGELY REFLECTED IN THE NMME MODEL SUITE, THOUGH THE 
DYNAMICAL MODELS ARE SLIGHTLY COLDER FOR THE PACIFIC NORTHWEST AND THE ALASKA 
PANHANDLE. THE UNCERTAINTY AROUND THE ENSO OUTLOOKS PRECLUDES A COMPLETE SWITCH 
IN FORECAST CATEGORY DURING THE WINTER OF 2017-18. 
THROUGH FMA 2018, ODDS FOR ABOVE-NORMAL TEMPERATURES REMAIN INCREASED RELATIVE 
TO CLIMATOLOGY ACROSS THE SOUTHERN TIER OF THE CONUS, SUPPORTED BY TRENDS AND 
NMME MODEL OUTPUT. MODEL OUTPUT AND TRENDS DISAGREE OVER THE PACIFIC NORTHWEST 
(NO TREND BUT BELOW-AVERAGE TEMPERATURES IN THE OUTLOOKS) AND NORTHERN CONUS 
(COLD TREND BUT EC OR WARM IN MODELS), SO EC IS INDICATED IN THOSE REGIONS, 
UNTIL WE GET CLOSER IN TIME AND FORECAST CONFIDENCE INCREASES.  AS THE LEADS 
PROGRESS THROUGH 2018, TRENDS ARE LIKELY TO BE THE DOMINANT FACTOR AS ENSO IS 
LIKELY TO RETURN TO A NEUTRAL STATE. TRENDS FAVOR ABOVE-NORMAL TEMPERATURES FOR 
ALL OF ALASKA AND MUCH OF THE CONUS, WITH A WEAKNESS NEAR THE GREAT LAKES AND 
OHIO VALLEY DURING SUMMER, WHICH SHIFTS TOWARD THE SOUTHEAST DURING AUTUMN. 
PRECIPITATION
SIGNIFICANT CHANGES HAVE BEEN MADE TO THE OND 2017 OUTLOOK FOR PRECIPITATION, 
WHEN COMPARED TO LAST MONTH. THESE CHANGES REFLECT THE RELATIVELY DRAMATIC 
SWITCH IN MODEL OUTPUTS AS WELL AS THE DECISION TO DISCOUNT THE SST-CA DURING 
THIS CYCLE. IN GENERAL, PROBABILITIES ARE LOW, DUE TO THE UNCERTAINTY REGARDING 
THE STATE OF ENSO. THE OND OUTLOOK INDICATES INCREASED ODDS FOR ABOVE-NORMAL 
PRECIPITATION OVER WESTERN ALASKA, CONSISTENT WITH NMME OUTPUTS AND CONDITIONS 
ASSOCIATED WITH LA NINA, THOUGH PROBABILITIES ARE LOW. TRENDS, ESPECIALLY AS 
EXPRESSED DURING THE LATER AUTUMN AND WINTER SEASONS, AND A SLIGHT TILT TOWARD 
LA NINA, FAVOR BELOW-NORMAL PRECIPITATION FOR THE SOUTHEAST AND PORTIONS OF THE 
MIDDLE AND LOWER MISSISSIPPI VALLEY.  
TRENDS FOR DRIER-THAN-AVERAGE CONDITIONS ALONG THE SOUTHERN TIER OF THE CONUS 
WITH WETTER-THAN-AVERAGE CONDITIONS ACROSS THE NORTHERN TIER, AS WELL AS A TILT 
TOWARD LA NINA INFLUENCE THE OUTLOOK THROUGH FMA 2018. TRENDS FOR ABOVE-NORMAL 
PRECIPITATION ARE WEAKEST IN JFM, BUT THAT IS ALSO WHEN ANY LA NINA FOOTPRINT 
WOULD BE MOST INTENSE. FOR MAM 2018 THROUGH ASO 2018, TRENDS, AS CALCULATED IN 
THE 15-YEAR OPTIMAL CLIMATE NORMALS (OCN) WERE USED AS THE PRIMARY INPUT. 
FORECASTER: MATTHEW ROSENCRANS
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 OCT 19 2017
1981-2010 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 19, 2011 
FORECAST RELEASE.
$$