952
FXUS05 KWBC 211231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU SEP 21 2023
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
EL NIñO CONDITIONS ARE PRESENT, AS REPRESENTED IN CURRENT OCEANIC AND
ATMOSPHERIC OBSERVATIONS. A CONTINUATION OF EL NIñO IS EXTREMELY LIKELY THIS
FALL AND WINTER, WITH OVER A 95 PERCENT CHANCE THROUGH JANUARY-FEBRUARY-MARCH
(JFM) 2024. ADDITIONALLY, A STRONG EL NIñO IS LIKELY BY LATE FALL AND EARLY
WINTER, WITH APPROXIMATELY A 70 PERCENT CHANCE OF OCCURRENCE DURING THE
NOVEMBER-DECEMBER-JANUARY (NDJ) 2023-24 SEASON.
THE OCTOBER-NOVEMBER-DECEMBER (OND) 2023 TEMPERATURE OUTLOOK FAVORS ABOVE
NORMAL TEMPERATURES FOR ALASKA, THE WESTERN THIRD OF THE CONTIGUOUS UNITED
STATES (CONUS), THE NORTHEAST, GREAT LAKES, PARTS OF THE SOUTHERN PLAINS,
FLORIDA, AND THE IMMEDIATE GULF AND EAST COASTS. THE LARGEST PROBABILITIES
(GREATER THAN 60 PERCENT) OF ABOVE NORMAL TEMPERATURES ARE FORECAST ACROSS THE
NORTH SLOPE OF ALASKA. ABOVE NORMAL TEMPERATURES ARE ALSO LIKELY (PROBABILITIES
GREATER THAN 50 PERCENT) FOR PARTS OF THE PACIFIC NORTHWEST AND NORTHERN NEW
ENGLAND. THE OND 2023 PRECIPITATION OUTLOOK DEPICTS ENHANCED PROBABILITIES OF
ABOVE NORMAL PRECIPITATION AMOUNTS ACROSS THE SOUTHEAST, SOUTHERN PLAINS, AND
PARTS OF THE MID-ATLANTIC STATES AS WELL AS NORTHERN AND WESTERN ALASKA. THE
GREATEST CHANCES OF ABOVE NORMAL PRECIPITATION (ABOVE 50 PERCENT PROBABILITY)
ARE INDICATED FOR PARTS OF NORTHERN FLORIDA AND SOUTHERN GEORGIA. EQUAL CHANCES
(EC) ARE FORECAST FOR AREAS WHERE PROBABILITIES FOR EACH CATEGORY OF 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
THE COUPLED OCEANIC AND ATMOSPHERIC OBSERVATIONS REFLECT EL NIñO CONDITIONS. IN
AUGUST, SEA SURFACE TEMPERATURES (SSTS) WERE ABOVE AVERAGE ACROSS THE
EQUATORIAL PACIFIC OCEAN WITH STRENGTHENING POSITIVE ANOMALIES NOTED IN THE
CENTRAL AND EAST-CENTRAL PACIFIC. IN THE LAST WEEK, THE NIñO INDEX VALUES
RANGED FROM +1.1°C TO +2.6°C. AREA-AVERAGED SUBSURFACE TEMPERATURE ANOMALIES
INCREASED COMPARED TO JULY IN ASSOCIATION WITH ANOMALOUS WARMTH IN THE CENTRAL
AND EASTERN EQUATORIAL PACIFIC OCEAN. TROPICAL ATMOSPHERIC ANOMALIES WERE ALSO
CONSISTENT WITH EL NIñO. OVER THE EAST-CENTRAL PACIFIC, LOW-LEVEL WINDS WERE
ANOMALOUSLY WESTERLY, WHILE UPPER-LEVEL WINDS WERE ANOMALOUSLY EASTERLY.
CONVECTION WAS SLIGHTLY ENHANCED AROUND THE INTERNATIONAL DATE LINE, STRETCHING
INTO THE EASTERN PACIFIC, JUST NORTH OF THE EQUATOR. CONVECTION WAS MOSTLY
SUPPRESSED AROUND INDONESIA. THE EQUATORIAL SOUTHERN OSCILLATION INDEX (SOI)
AND THE TRADITIONAL STATION-BASED SOI WERE BOTH SIGNIFICANTLY NEGATIVE.
COLLECTIVELY, THE COUPLED OCEAN-ATMOSPHERE SYSTEM REFLECTED EL NIñO.
THE REAL-TIME MULTIVARIATE MADDEN JULIAN OSCILLATION (RMM) INDEX CURRENTLY
INDICATES INCOHERENT INTRASEASONAL ACTIVITY, WITH THE MADDEN JULIAN OSCILLATION
(MJO) SIGNAL RETREATING WESTWARD TO THE INDIAN OCEAN AT A LOW AMPLITUDE DURING
THE PAST WEEK. DYNAMICAL MODEL RMM FORECASTS GENERALLY FAVOR THE RESUMPTION OF
AN EASTWARD PROPAGATING MJO SIGNAL OVER THE MARITIME CONTINENT, BUT REMAIN
DIVIDED IN REGARDS TO ITS EVENTUAL AMPLITUDE WITH LARGE ENSEMBLE SPREAD.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE MOST RECENT INTERNATIONAL RESEARCH INSTITUTE FOR CLIMATE AND SOCIETY (IRI)
PLUME INDICATES EL NIñO WILL PERSIST THROUGH THE NORTHERN HEMISPHERE WINTER
2023-24. DESPITE NEARLY THE SAME ENSEMBLE MEAN AMPLITUDE AS LAST MONTH, THE
SHORTER FORECAST HORIZON MEANS THAT THE ODDS OF A "STRONG" EL NIñO (≥1.5°C FOR
THE NOVEMBER-JANUARY SEASONAL AVERAGE IN NIñO-3.4) HAVE INCREASED TO 71%. IN
SUMMARY, EL NIñO IS ANTICIPATED TO CONTINUE THROUGH THE NORTHERN HEMISPHERE
WINTER (WITH A GREATER THAN 95% CHANCE THROUGH JFM 2024).
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
DYNAMICAL MODEL FORECASTS FROM THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME),
THE COUPLED FORECAST SYSTEM MODEL VERSION 2 (CFSV2), AND THE COPERNICUS (C3S)
MULTI-MODEL ENSEMBLE SYSTEM WERE USED EXTENSIVELY FOR THE FIRST SIX LEADS WHEN
THEY ARE AVAILABLE, AS WAS THE OBJECTIVE, HISTORICAL SKILL-WEIGHTED
CONSOLIDATION AND CALIBRATION, BRIDGING, AND MERGING (CBAM) GUIDANCE, THAT
COMBINES BOTH DYNAMICAL AND STATISTICAL FORECAST INFORMATION.
ADDITIONALLY, THE OFFICIAL ENSO FORECAST DEPICTS PROBABILITIES OF EL NIñO THAT
ARE EXCEPTIONALLY HIGH THROUGH THE UPCOMING WINTER, WITH A STRONG EVENT LIKELY.
THIS ANTICIPATED EL NIñO SIGNAL PLAYED A KEY ROLE IN THE CONSTRUCTION OF THESE
OUTLOOKS. AT LATER LEADS, DECADAL TRENDS IN TEMPERATURE AND PRECIPITATION WERE
INCREASINGLY RELIED UPON IN CREATING THE SEASONAL OUTLOOKS.
PROGNOSTIC DISCUSSION OF OUTLOOKS - OND 2023 TO OND 2024
TEMPERATURE
ONE OF THE MAJOR FORECAST CHALLENGES FOR THE UPCOMING FALL AND WINTER IS
MANAGING THE COMPETING INFLUENCES BETWEEN EL NIñO AND RECENT TRENDS. ACROSS THE
SOUTHERN CONUS IN PARTICULAR, EL NIñO COMPOSITES TEND TO FAVOR COOLER THAN
NORMAL CONDITIONS WHILE RECENT TRENDS LEAN WARM. DUE TO THESE COMPETING
INFLUENCES, A LARGE SWATH OF EC IS INDICATED ACROSS MUCH OF THE INTERIOR SOUTH
FOR OND. A SLIGHT TILT TOWARD ABOVE NORMAL TEMPERATURES IS INDICATED ALONG THE
GULF AND EAST COASTS, WHERE WARM TRENDS AND ABOVE NORMAL SSTS HAVE A GREATER
CHANCE TO COUNTERACT POTENTIAL EL NIñO INFLUENCES. ABOVE NORMAL TEMPERATURES
ARE FAVORED WITH GREATER CONFIDENCE ACROSS THE NORTHEAST AND PARTS OF THE GREAT
LAKES, WHERE RECENT TRENDS AND MODEL GUIDANCE FROM THE C3S ARE WARM.
PROBABILITIES OF ABOVE NORMAL TEMPERATURES EXCEED 50 PERCENT ACROSS PARTS OF
NORTHERN NEW ENGLAND WHERE RECENT TRENDS ARE THE STRONGEST AND SSTS IN THE
ADJACENT ATLANTIC OCEAN ARE WARMER THAN NORMAL. RECENT TRENDS AND DYNAMICAL
MODELS GUIDANCE ALSO FAVOR WARMTH ACROSS THE WESTERN THIRD OF THE CONUS. THE
GREATEST PROBABILITIES OF ABOVE NORMAL TEMPERATURES (ABOVE 50 PERCENT CHANCE)
ARE INDICATED FOR THE PACIFIC NORTHWEST, WHERE DYNAMICAL AND STATISTICAL INPUTS
ARE IN GENERALLY GOOD AGREEMENT AND ADJACENT SSTS ARE ABOVE NORMAL. RELATIVELY
WEAKER PROBABILITIES OF ABOVE NORMAL TEMPERATURES (LESS THAN 40 PERCENT CHANCE)
ARE INDICATED OVER THE SOUTHWESTERN CONUS, WHERE EL NIñO INFLUENCES MAY
COUNTERACT RECENT WARM TRENDS. FARTHER TO THE NORTH AND EAST, EC IS INDICATED
FOR THE NORTH-CENTRAL CONUS WHERE GUIDANCE FROM THE NMME AND RECENT TRENDS
YIELD WEAK SIGNALS. ABOVE NORMAL TEMPERATURES ARE FAVORED THROUGHOUT ALASKA AS
EL NIñO, TREND, AND DYNAMICAL MODEL GUIDANCE ALL FAVOR MILDER THAN NORMAL
CONDITIONS ACROSS MUCH OF THE STATE. THE STRONGEST PROBABILITIES OF ABOVE
NORMAL TEMPERATURES (GREATER THAN 60 PERCENT CHANCE) ARE INDICATED ACROSS THE
NORTH SLOPE AS SEA ICE EXTENT IS CURRENTLY MUCH BELOW NORMAL ACROSS THE
ADJACENT ARCTIC OCEAN.
FROM NOVEMBER-DECEMBER-JANUARY (NDJ) THROUGH MARCH-APRIL-MAY (MAM), IMPACTS
FROM THE ONGOING EL NIñO STRENGTHEN AS ABOVE NORMAL TEMPERATURES ARE FAVORED
ACROSS THE NORTHERN CONUS AND PERSIST ACROSS ALASKA. EC IS INDICATED ACROSS THE
SOUTHERN CONUS AS EL NIñO FAVORS COOLER THAN NORMAL CONDITIONS FOR MOST OF THE
REGION WHILE RECENT TRENDS FAVOR WARM. A SMALL AREA OF ENHANCED BELOW NORMAL
TEMPERATURE PROBABILITIES ARE INDICATED FOR PARTS OF THE SOUTHWEST AND SOUTHERN
HIGH PLAINS DURING JFM AND FMA WHERE EL NIñO COMPOSITES YIELD A COLD SIGNAL AND
RECENT TRENDS ARE RELATIVELY WEAK. AFTER MAM, THE FORECAST PATTERN INCREASINGLY
REFLECTS TRENDS WITH ABOVE NORMAL TEMPERATURES GENERALLY FAVORED ACROSS THE
NORTHEAST DURING SPRING AND THEN EXPANDING ACROSS THE ENTIRE EASTERN THIRD OF
THE CONUS BY THE EARLY SUMMER. SIMILARLY, AN AREA OF ELEVATED ABOVE NORMAL
TEMPERATURE PROBABILITIES ACROSS THE NORTHWEST DURING THE SPRING EXPANDS ACROSS
MOST OF THE REMAINDER OF THE WESTERN THIRD OF THE CONUS DURING THE SUMMER
MONTHS. ALASKA IS GENERALLY FAVORED TO EXPERIENCE MILDER THAN NORMAL CONDITIONS
THROUGHOUT THE SPRING AND SUMMER MONTHS. DURING THE LATE SUMMER AND EARLY FALL,
TRENDS FAVOR WARMTH ACROSS ALL OF THE FORECAST DOMAIN SO ABOVE NORMAL
TEMPERATURE PROBABILITIES ARE ELEVATED ACROSS THE ENTIRE NATION FROM JAS
THROUGH SON. TRENDS WEAKEN LATER IN THE FALL ACROSS SOUTHEASTERN ALASKA AND THE
NORTHWESTERN CONUS WHERE EC IS INDICATED DURING THE OND 2024 SEASON.
PRECIPITATION
MODEL GUIDANCE AND EL NIñO COMPOSITES ARE IN GOOD AGREEMENT IN FAVORING ABOVE
NORMAL PRECIPITATION ACROSS THE SOUTHEASTERN CONUS AND ALONG MUCH OF THE EAST
COAST DURING THE OND 2023 SEASON. THUS, ABOVE NORMAL PRECIPITATION IS FAVORED
FOR THESE REGIONS. PROBABILITIES OF ABOVE NORMAL PRECIPITATION EXCEED 50
PERCENT ACROSS PARTS OF NORTHERN FLORIDA AND SOUTHERN GEORGIA, WHERE ENSEMBLE
GUIDANCE FROM THE NMME AND C3S YIELD THE STRONGEST WET SIGNALS. ELEVATED
PROBABILITIES OF ABOVE NORMAL PRECIPITATION ALSO EXPAND WEST TO THE SOUTHERN
PLAINS, CONSISTENT WITH COMBINED EL NIñO/OPTIMAL CLIMATE NORMALS (OCN)
COMPOSITES. CONVERSELY, BELOW NORMAL PRECIPITATION IS MORE LIKELY ACROSS THE
NORTHWESTERN CONUS AND THE GREAT LAKES REGION, BASED PRIMARILY ON A COMBINATION
OF EL NIñO COMPOSITES AND DYNAMICAL MODEL GUIDANCE. ABOVE NORMAL PRECIPITATION
IS FAVORED ACROSS NORTHERN AND WESTERN ALASKA DUE TO ANTICIPATED EL NIñO
INFLUENCES, RECENT TRENDS, AND DYNAMICAL MODEL GUIDANCE. BELOW NORMAL SEA ICE
EXTENT IN THE ADJACENT ARCTIC OCEAN MAY ALSO CONTRIBUTE TO INCREASED
PRECIPITATION CHANCES ACROSS THE NORTH SLOPE.
DURING THE WINTER MONTHS, IMPACTS FROM EL NINO ARE EXPECTED TO INCREASE, AND
ABOVE NORMAL PRECIPITATION IS FAVORED FOR MOST OF THE SOUTHERN TIER OF THE
CONUS FROM NDJ TO FEBRUARY-MARCH-APRIL (FMA). ADDITIONALLY, ABOVE NORMAL
PRECIPITATION IS FAVORED ALONG MUCH OF THE EASTERN SEABOARD DURING THE CORE OF
THE WINTER AS AN EAST COAST STORM TRACK IS GENERALLY FAVORED DURING EL NIñO
WINTERS. CONVERSELY, BELOW NORMAL PRECIPITATION IS MORE LIKELY ACROSS MUCH OF
THE NORTHERN TIER, PARTICULARLY FOR THE NORTHWESTERN CONUS AND THE GREAT LAKES
REGION. UNCERTAINTY IS HIGH ACROSS THE WEST COAST AS EL NIñO TENDS TO FAVOR WET
ALONG MUCH OF THE CALIFORNIA COAST WHILE TRENDS FAVOR DRY. GIVEN THE INCREASED
POSSIBILITY OF A STRONG EL NIñO EVENT, A TILT TOWARD ABOVE NORMAL PRECIPITATION
IS INDICATED FOR SOUTHERN CALIFORNIA. A TILT TOWARD ABOVE NORMAL PRECIPITATION
IS ALSO INDICATED ACROSS THE NORTH SLOPE OF ALASKA THROUGH FMA, CONSISTENT WITH
RECENT TRENDS. CONFIDENCE IN POTENTIAL ENSO IMPACTS DECREASES SUBSTANTIALLY AS
WE HEAD TO NEXT SPRING AND SUMMER, RESULTING IN INCREASED UNCERTAINTY AND
COVERAGE OF EC ACROSS MUCH OF THE NATION. HOWEVER, DURING LATE WINTER AND EARLY
SPRING (FMA), GUIDANCE FROM THE CFSV2 AND OTHER MODELS YIELDS A WET SIGNAL
ACROSS THE SOUTHERN AND CENTRAL PLAINS. THE WET SIGNAL GENERALLY PROGRESSES
EASTWARD ACROSS THE SOUTHEAST BY EARLY SUMMER (APRIL-MAY-JUNE (AMJ)) AND THEN
TO THE MID-ATLANTIC AND NORTHEAST BY THE MIDDLE OF THE SUMMER (JUNE-JULY-AUGUST
(JJA)), CONSISTENT WITH TRENDS. AS THIS WET SIGNAL PROGRESSES EASTWARD AND
NORTHWARD, THE STATISTICAL CONSOLIDATION AND TRENDS BECOME INCREASINGLY DRY
OVER PARTS OF THE CENTRAL AND SOUTHERN PLAINS BY LATE SPRING AND EARLY SUMMER.
AS A RESULT, BELOW NORMAL PRECIPITATION IS SLIGHTLY FAVORED ACROSS THESE
REGIONS DURING MAY-JUNE-JULY (MJJ) AND JJA. A SLIGHT TILT TOWARD BELOW NORMAL
PRECIPITATION IS ALSO INDICATED FOR PARTS OF THE NORTHERN HIGH PLAINS AND
NORTHERN ROCKIES THROUGH AUGUST-SEPTEMBER-OCTOBER (ASO), CONSISTENT WITH
TRENDS. FARTHER TO THE NORTH, UNCERTAINTY IS HIGH FOR MOST OF ALASKA, AND EC IS
INDICATED FOR MOST OF THE STATE FROM LATE SPRING THROUGH THE SUMMER. AS WE
ENTER THE LATE SUMMER AND EARLY FALL, A WET TREND SIGNAL IS REFLECTED ACROSS
PARTS OF THE TENNESSEE VALLEY DURING JULY-AUGUST-SEPTEMBER (JAS), TRANSLATING
FARTHER TO THE SOUTH AND WEST ACROSS THE WESTERN GULF COAST IN ASO AND RIO
GRANDE VALLEY DEEPER INTO NEXT FALL IN SEPTEMBER-OCTOBER-NOVEMBER (SON). ABOVE
NORMAL PRECIPITATION IS FAVORED FOR THE NORTH SLOPE OF ALASKA NEXT FALL DUE TO
RECENT TRENDS AND THE STATISTICAL CONSOLIDATION ALSO FAVORS ABOVE NORMAL
PRECIPITATION FOR SOUTHWESTERN PARTS OF THE STATE DURING THE SAME TIME PERIOD.
LATER NEXT FALL AND EARLY NEXT WINTER (OND), RECENT TRENDS DEPICT A TILT TOWARD
DRY FOR PARTS OF SOUTHEAST ALASKA AND THE EASTERN GREAT LAKES, AND A WET SIGNAL
FOR PARTS OF THE UPPER AND MIDDLE MISSISSIPPI VALLEY AND THE TENNESSEE VALLEY.
FORECASTER: SCOTT HANDEL
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1991 AND 2020, 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 2023
1991-2020 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 20, 2021
FORECAST RELEASE.
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