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FXUS05 KWBC 171231
PMD90D
PROGNOSTIC DISCUSSION FOR LONG-LEAD SEASONAL OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU AUG 17 2023
SUMMARY OF THE OUTLOOK FOR NON-TECHNICAL USERS
THE SEPTEMBER-OCTOBER-NOVEMBER (SON) 2023 TEMPERATURE OUTLOOK FAVORS
ABOVE-NORMAL SEASONAL MEAN TEMPERATURES ACROSS A MAJORITY OF THE U.S.,
INCLUDING ALL OF ALASKA, THE WESTERN CONUS, THE SOUTHEAST, AND THE NORTHEAST.
THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES EXCEED 50 PERCENT FOR
PARTS OF NORTHERN ALASKA, THE SOUTHWEST, AND THE NORTHEAST.
THE SON PRECIPITATION OUTLOOK FAVORS ABOVE-NORMAL PRECIPITATION FOR WESTERN AND
NORTHERN ALASKA AND A LARGE AREA OF THE SOUTHEASTERN CONUS FROM FLORIDA TO
PARTS OF THE MID-ATLANTIC REGION. BELOW-NORMAL PRECIPITATION IS FAVORED FOR THE
PACIFIC NORTHWEST, THE WESTERN GREAT LAKES REGION, AND A SMALL AREA OF THE
SOUTHWEST, INCLUDING SOUTHEASTERN ARIZONA, WESTERN NEW MEXICO, AND A SMALL PART
OF WEST TEXAS.
EL NIñO CONDITIONS ARE PRESENT AND EQUATORIAL SEA SURFACE TEMPERATURES (SSTS)
ARE ABOVE AVERAGE ACROSS THE CENTRAL AND EASTERN EQUATORIAL PACIFIC OCEAN. EL
NIñO IS EXPECTED TO STRENGTHEN AND PERSIST THROUGH THE WINTER OF 2023-24.
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 REFLECT
CONTINUING EL NIñO CONDITIONS. THE LATEST OBSERVED WEEKLY SSTS INDICATE
POSITIVE ANOMALIES ACROSS THE EQUATORIAL PACIFIC WITH ANOMALIES EXCEEDING +1
DEGREE C NEAR AND EAST OF THE DATE LINE AND EXCEEDING +2 DEGREES C IN THE EAST
PACIFIC. EQUATORIAL UPPER-OCEAN HEAT ANOMALIES (AVERAGED BETWEEN 180 TO 100 °W
AND 0-300M DEPTH) REMAIN STRONGLY POSITIVE BUT HAVE SHOWN SOME RECENT WEAKENING
AT DEPTHS OF MORE THAN 100 METERS IN THE EAST-CENTRAL PACIFIC. OUTGOING
LONGWAVE RADIATION (OLR) ANOMALIES ARE NEGATIVE NEAR THE DATE LINE, INDICATING
ENHANCED CONVECTIVE PRECIPITATION, CONSISTENT WITH EL NIñO CONDITIONS.
LOW-LEVEL WIND ANOMALIES AT THE 850-HPA LEVEL WERE WESTERLY OVER THE WESTERN
EQUATORIAL PACIFIC AND EASTERLY OVER THE EASTERN PACIFIC, WHILE UPPER-LEVEL
WIND ANOMALIES AT THE 200-HPA LEVEL WERE WESTERLY OVER THE EASTERN TROPICAL
PACIFIC.
STRONGLY POSITIVE SST ANOMALIES ARE PRESENT NEAR THE NORTHERN COAST OF ALASKA.
SST ANOMALIES REMAIN STRONGLY POSITIVE ALONG THE GULF COAST AND THE SOUTHEAST
ATLANTIC COAST AS WELL, WHILE POSITIVE SST ANOMALIES NEAR THE NORTHEAST
ATLANTIC COAST HAVE DECREASED IN THE LAST TWO WEEKS.
PROGNOSTIC DISCUSSION OF SST FORECASTS
THE CPC SST CONSOLIDATION FOR THE NIñO 3.4 REGION INDICATES AN INCREASE IN THE
MAGNITUDE OF POSITIVE ANOMALIES THROUGH AUTUMN INTO EARLY WINTER, WITH A PEAK
MEDIAN ANOMALY EXCEEDING +1 DEGREE C THROUGH THE DJF WINTER SEASON. THE MEDIAN
NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) CONSOLIDATION FORECAST EXCEEDS +1.5
DEGREES C AT ITS PEAK IN LATE AUTUMN AND EARLY WINTER BEFORE DECREASING AT
LONGER LEADS WITH GREATER UNCERTAINTY. THE CPC CONSENSUS ENSO OUTLOOK INDICATES
GREATER THAN A 90 PERCENT CHANCE THAT EL NIñO WILL CONTINUE THROUGH WINTER,
WITH GREATER THAN A 60 PERCENT CHANCE THAT THE STRENGTH OF THE NIñO 3.4 ANOMALY
WILL EXCEED +1.5 DEGREES C AT ITS PEAK.
PROGNOSTIC TOOLS USED FOR U.S. TEMPERATURE AND PRECIPITATION OUTLOOKS
THE SEASONAL OUTLOOKS RELIED ON DYNAMICAL MODEL GUIDANCE FROM THE NMME,
INCLUDING HYBRID STATISTICAL-DYNAMICAL GUIDANCE FROM THE CALIBRATION, BRIDGING,
AND MERGING (CBAM) POST-PROCESSING OF THE NMME, AND A VERSION OF THE NMME THAT
POST-PROCESSES AND WEIGHTS THE MODELS USING PROBABILITY ANOMALY CORRELATION
(PAC). STATISTICAL TOOLS ARE ALSO USED, SUCH AS CONSTRUCTED ANALOG, CANONICAL
CORRELATION ANALYSIS (CCA), AND A REGRESSION FORECAST BASED ON THE PREDICTED
MEDIAN NIñO 3.4 SST ANOMALY FROM THE CPC SST FORECAST CONSOLIDATION WITH THE
ADDITION OF OPTIMUM CLIMATE NORMALS (OCN) TO REPRESENT DECADAL TRENDS. A FINAL
CONSOLIDATION TOOL COMBINES THE CONSOLIDATION OF NMME MODEL FORECASTS WITH A
CONSOLIDATION OF STATISTICAL TOOLS.
EL NIñO TEMPERATURE AND PRECIPITATION CORRELATIONS TO SURFACE TEMPERATURES AND
PRECIPITATION WERE RELIED UPON FROM SON 2023 THROUGH FMA 2024. DECADAL TRENDS
IN TEMPERATURE AND PRECIPITATION WERE A FACTOR AT ALL TIME LEADS BUT RELIED
UPON THE MOST AT THE LONGER LEADS FROM MAM 2024 ONWARD, WHEN SIGNALS DUE TO EL
NIñO DECREASE. CURRENT SOIL MOISTURE CONDITIONS WERE A CONSIDERATION IN THE
UPPER MIDWEST AND SOUTHERN PLAINS IN THE SON TEMPERATURE OUTLOOK.
PROGNOSTIC DISCUSSION OF OUTLOOKS - SON 2023 TO SON 2024
TEMPERATURE
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS ALASKA AND THE WESTERN CONUS IN
THE SON AND OND 2024 TEMPERATURE OUTLOOKS, CONSISTENT WITH DYNAMICAL AND
STATISTICAL MODEL GUIDANCE AND THE CONSOLIDATION OF BOTH. THE GREATEST
PROBABILITIES EXCEED 50 PERCENT FOR NORTHERN ALASKA AND PARTS OF THE SOUTHWEST,
DUE TO DECADAL TRENDS. ABOVE-NORMAL TEMPERATURES ARE ALSO FAVORED EASTWARD
ACROSS THE SOUTHERN CONTIGUOUS UNITED STATES (CONUS) INTO THE SOUTHEAST AND
NORTHWARD THROUGH THE EASTERN CONUS INTO THE EASTERN GREAT LAKES REGION,
CONSISTENT WITH THE CONSOLIDATION OF TOOLS. DECADAL TRENDS LEAD TO HIGHER
PROBABILITIES OF ABOVE-NORMAL TEMPERATURES OVER THE NORTHEAST. POTENTIAL EL
NIñO IMPACTS FOR THE SON AND OND SEASONS INCLUDE COOLER TEMPERATURES OVER MUCH
OF THE CENTRAL CONUS, LEADING TO WEAKER PROBABILITIES FOR ABOVE-NORMAL
TEMPERATURES IN TOOLS THAT EXPLICITLY CONSIDER ENSO, SUCH AS CBAM. A FORECAST
OF EQUAL CHANCES (EC) OF ABOVE-, NEAR-, AND BELOW-NORMAL TEMPERATURES IS
INDICATED OVER THIS REGION FOR THE FIRST TWO LEADS.
FROM THE NDJ 2023-24 TO THE FMA 2024 SEASONS, AS THE LEADS EXTEND THROUGH
AUTUMN INTO WINTER, INCREASING PROBABILITIES OF ABOVE-NORMAL TEMPERATURES ARE
FORECAST FROM THE PACIFIC NORTHWEST ACROSS THE NORTHERN TIER OF THE CONUS INTO
THE MIDWEST AND NORTHEAST, CONSISTENT WITH INCREASING IMPACTS OF A
STRENGTHENING EL NIñO. EQUAL CHANCES OF ABOVE, NEAR, AND BELOW NORMAL
TEMPERATURES (EC) IS FORECAST ACROSS THE SOUTHERN TIER OF THE CONUS WITH A
TENDENCY TOWARDS COOLER TEMPERATURES ARISING FROM EL NIñO IMPACTS. FOR MAM 2024
AND LONGER LEADS THROUGH SON 2024, THE OUTLOOKS RELIED HEAVILY ON THE ENSO-OCN
TOOL, AND DECADAL TRENDS PROVIDE MOST OF THE AVAILABLE CLIMATE SIGNALS. THE
SEASONAL TEMPERATURE OUTLOOKS EVOLVE TOWARD A SIMILAR PATTERN AT THE LONGEST
LEADS (MAM 2024 THROUGH SON 2024), AND THE FORECASTS GENERALLY DEPICT A
U-SHAPED PATTERN OF ENHANCED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES OVER
THE CONUS, AND EC IN THE NORTHERN CENTRAL CONUS INTO THE CENTRAL MISSISSIPPI
VALLEY.
PRECIPITATION
DURING SON 2023, ABOVE-NORMAL PRECIPITATION IS FAVORED FOR WESTERN AND NORTHERN
ALASKA AND THE SOUTHEASTERN CONUS, WHILE BELOW-NORMAL PRECIPITATION IS FAVORED
FOR THE PACIFIC NORTHWEST, A SMALL AREA OF THE SOUTHWEST, AND THE WESTERN GREAT
LAKES REGION. ENHANCED PROBABILITIES OF ABOVE-NORMAL PRECIPITATION FOR PARTS OF
ALASKA ARE SUPPORTED BY THE CONSOLIDATION OF DYNAMICAL AND STATISTICAL TOOLS.
BELOW-NORMAL PRECIPITATION FOR THE PACIFIC NORTHWEST AND GREAT LAKES AND
ABOVE-NORMAL PRECIPITATION FOR THE SOUTHEAST ARE CONSISTENT WITH EL NIñO
IMPACTS, AND LARGELY PERSIST THROUGH THE NEXT SEVERAL LEADS. BELOW-NORMAL
PRECIPITATION FOR PARTS OF THE SOUTHWEST IN THE SON SEASON IS CONSISTENT WITH
THE PERSISTENCE OF A WEAKER THAN NORMAL SOUTHWEST MONSOON, WHILE THE OUTLOOK
FOR THE MONTH OF SEPTEMBER FAVORS ABOVE-NORMAL PRECIPITATION IN AREAS OF
SOUTHERN CALIFORNIA, NEVADA AND ARIZONA TO THE WEST DUE TO SHORTER TERM
MOISTURE FLOW FROM THE EAST PACIFIC.
BELOW-NORMAL PRECIPITATION IS FORECAST ACROSS MUCH OF THE NORTHERN TIER OF THE
CONUS FROM PARTS OF THE PACIFIC NORTHWEST TO THE GREAT LAKES REGION FROM NDJ
2023-24 TO FMA 2024, DUE TO THE EXPECTED STRENGTHENING EL NIñO. THE ENHANCED
PROBABILITIES OF ABOVE-NORMAL PRECIPITATION FOR THE SOUTHEAST INCREASE AND
EXTEND WESTWARD INCREMENTALLY ACROSS THE SOUTHERN PLAINS INTO THE SOUTHWEST FOR
THESE LEADS, ALSO CONSISTENT WITH A STRENGTHENING EL NIñO. FOR THE MAM 2024
SEASON AND LONGER LEADS, AREAS OF ABOVE- AND BELOW-NORMAL PRECIPITATION
COINCIDE WITH SIGNALS DUE TO DECADAL TRENDS, INCLUDING ENHANCED PROBABILITIES
FOR BELOW-NORMAL PRECIPITATION IN AREAS OF THE NORTHWESTERN CONUS AND ENHANCED
PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION IN THE LOWER MISSISSIPPI VALLEY
AND MID-ATLANTIC REGION.
FORECASTER: DAN COLLINS
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 SEP 21 2023
1991-2020 BASE PERIOD MEANS WERE IMPLEMENTED EFFECTIVE WITH THE MAY 20, 2021
FORECAST RELEASE.
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