738
FXUS07 KWBC 301900
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT SEP 30 2023
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2023
THE UPDATED OCTOBER MONTHLY TEMPERATURE AND PRECIPITATION OUTLOOK IS LARGELY
ADJUSTED BY DYNAMICAL MODEL GUIDANCE FROM THE SHORT AND MEDIUM, EXTENDED AND
SUBSEASONAL FORECAST RANGES. THE MJO HAS NOT BECOME ANY MORE ORGANIZED SINCE
THE MIDDLE OF THE MONTH AND FORECASTS OF ITS SUBSEQUENT EVOLUTION DO NOT
INDICATE THAT THIS IS LIKELY TO CHANGE IN THE NEAR FUTURE. ABOVE-NORMAL SEA
SURFACE TEMPERATURES (SSTS) FOR WATERS IN PROXIMITY TO ALASKA AND ACROSS MUCH
OF THE NORTHERN PACIFIC CONTINUE TO CONTRIBUTE TO THE FORECAST.
THE FIRST 1-2 WEEKS OF THE MONTH LOOK TO SEE GENERALLY PROGRESSIVE FLOW WITH
TRANSIENT TROUGHING IMPACTING THE CONUS FROM THE WESTERN U.S AT THE START OF
THE MONTH TO THE EASTERN SEABOARD DURING THE SECOND WEEK. BELOW-NORMAL
TEMPERATURES ARE FAVORED DURING THESE PERIODS IN THESE REGIONAL AREAS, BUT ARE
LIKELY TO HAVE GENERALLY MINOR IMPACT ON THE OVERALL MONTHLY AVERAGE ANOMALOUS
TEMPERATURE. NEVERTHELESS, FORECAST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES
ARE REDUCED FROM THE MID-MONTH OUTLOOK FOR AREAS IN THE CENTRAL AND SOUTHERN
ROCKIES, SOUTHWEST, SOUTHERN PLAINS AND SOUTHEAST CONUS.
THE GREATEST ODDS FOR ABOVE-NORMAL TEMPERATURES ARE NOW PRIMARILY CENTERED OVER
THE NORTHERN PLAINS. DYNAMICAL MODEL GUIDANCE FOR THE WEEK 3-4 PERIOD IS
GENERALLY IN GOOD AGREEMENT FOR ELEVATED ODDS OF ABOVE-NORMAL TEMPERATURES FOR
MUCH OF THE FORECAST DOMAIN SUPPORTING AN OUTLOOK PRIMARILY OF FAVORED
ABOVE-NORMAL TEMPERATURES, TEMPERED BY TYPICAL HIGH UNCERTAINTY DURING THE
MONTH OF OCTOBER. ONLY MINOR CHANGES TO THE ALASKA FORECAST ARE MADE IN THE
UPDATE.
THE FORECAST PATTERN EVOLUTION NOTED ABOVE DURING THE FIRST HALF OF OCTOBER
PRIMARILY DROVE THE FORECAST CHANGES IN THE OCTOBER PRECIPITATION OUTLOOK
UPDATE FROM MID-MONTH. TROUGHING AND ANOMALOUS MERIDIONAL FLOW DURING EARLY
OCTOBER FAVORS BELOW-NORMAL PRECIPITATION FOR MUCH OF THE EASTERN U.S. FROM THE
EASTERN GREAT LAKES AND NORTHEAST SOUTHWARD TO THE OHIO VALLEY AND SOUTHEAST. A
DRY START TO THE MONTH IN THE PACIFIC NORTHWEST IS TEMPERED BY THE POTENTIAL
FOR EASTWARD EXTENSION OF THE PACIFIC JET AND STORMINESS IMPACTING THE PACIFIC
NORTHWEST BEGINNING THE SECOND WEEK OF OCTOBER. BELOW-NORMAL PRECIPITATION
REMAINS FAVORED FOR PARTS OF THE FAR PACIFIC NORTHWEST FROM THE INITIAL OUTLOOK
DUE TO HIGH CLIMATOLOGICAL PRECIPITATION AMOUNTS IN COASTAL AREAS DURING
OCTOBER.
ELEVATED ODDS FOR ABOVE-NORMAL PRECIPITATION REMAINS FORECAST FOR MUCH OF THE
WESTERN CONUS, BUT IS ALSO EXTENDED NORTHWARD AT LOW ODDS TO PARTS OF THE
NORTHERN PLAINS. THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL MONTHLY
PRECIPITATION AMOUNTS IS HIGHLIGHTED FOR TEXAS (ANTICIPATED HEAVY RAINFALL
DURING THE FIRST WEEK OF OCTOBER) AND FOR PARTS OF THE INTERIOR WEST - ALSO FOR
SHORT TERM FAVORED PRECIPITATION. ONLY MINOR CHANGES ARE MADE TO THE FORECAST
FOR ALASKA WITH ABOVE-NORMAL PRECIPITATION NOW FAVORED FOR MORE OF THE STATE.
****** PREVIOUS INITIAL OUTLOOK DISCUSSION FROM THE MID-MONTH ******
EL NINO CONDITIONS REMAIN STRONGLY IN PLACE ACROSS THE EQUATORIAL PACIFIC OCEAN
BOTH IN THE OCEAN AS WELL AS THE ATMOSPHERE AND SO IS CONSIDERED IN THE
PREPARATION OF THE OCTOBER OUTLOOK. POTENTIAL IMPACTS, HOWEVER, ARE LESS LIKELY
AND GENERALLY WEAKER THAN THAT SOMETIMES OBSERVED DURING WINTER AND EARLY
SPRING. RECENT MJO ACTIVITY HAS NOT BEEN STRONG IN RECENT WEEKS AS COMPARED TO
EARLIER IN 2023. SOME MODEL FORECASTS OF THE RMM INDEX AND OTHER MJO FORECAST
TOOLS INDICATE POTENTIAL STRENGTHENING IN THE WESTERN PACIFIC (WPAC), BUT THERE
IS CONSIDERABLE UNCERTAINTY OVERALL IN THIS OUTCOME ESPECIALLY GIVEN ONGOING
ROBUST EL NINO CONDITIONS.
EVENTUAL EVOLUTION OF THE MJO AMPLITUDE AND PHASE NOTWITHSTANDING, CONDITIONS
IN THE WPAC REMAIN QUITE CONDUCIVE FOR TROPICAL CYCLONE DEVELOPMENT OVER THE
NEXT FEW WEEKS IN THE WPAC AS FORECAST IN THE LATEST CPC GLOBAL TROPICS HAZARDS
OUTLOOK (GTH). SINCE LATE SEPTEMBER AND OCTOBER IS NEAR THE PEAK FOR
EXTRATROPICAL CIRCULATION INFLUENCING WPAC RE-CURVING TYPHOONS, PREDICTABILITY
AND OVERALL FORECAST CONFIDENCE IS GENERALLY AT A MINIMUM FOR OCTOBER WITHIN
THE SEASONAL CYCLE. THE OCTOBER OUTLOOK WILL BE UPDATED ON THE LAST DAY OF
SEPTEMBER UTILIZING THE LATEST INFORMATION INCLUDING THAT RELATED TO THE ABOVE
UNCERTAINTIES.
THE OCTOBER 2023 TEMPERATURE OUTLOOK FAVORS ABOVE-NORMAL MONTHLY MEAN
TEMPERATURES FOR THE MAJORITY OF THE FORECAST DOMAIN WITH THE ONLY EXCEPTIONS
BEING SOUTHEAST ALASKA AND THE ALASKA PANHANDLE AS WELL AS A REGION FROM THE
CENTRAL ROCKIES TO THE CENTRAL PLAINS WHERE EQUAL-CHANCES (EC) OF EITHER OF THE
THREE CATEGORIES ARE EQUALLY LIKELY. THE GREATEST PROBABILITIES FOR
ABOVE-NORMAL TEMPERATURES ARE FORECAST FOR AREAS IN NORTHERN AND WESTERN ALASKA
AND FOR THE GREAT LAKES, NORTHEAST, MID-ATLANTIC AND PARTS OF THE SOUTHEAST AND
GULF COAST.
FOR ALASKA, REDUCED SEA ICE COVERAGE AND ABOVE-NORMAL SEA SURFACE TEMPERATURES
(SSTS) IN SURROUNDING WATERS ELEVATE ODDS FOR WARMER THAN NORMAL CONDITIONS AS
WELL AS EL NINO CONSIDERATIONS AND DYNAMICAL MODEL GUIDANCE FROM THE NMME AND
C3S CONTRIBUTING ENSEMBLE SYSTEMS. CHANCES FOR ABOVE-NORMAL TEMPERATURES
DECREASE MOVING SOUTH AND EAST ACROSS ALASKA.
THROUGH A CONSIDERABLE PERIOD OF THE FIRST HALF OF THE MONTH OF OCTOBER, MODEL
FORECASTS FROM EXTENDED-RANGE AND SUBSEASONAL SYSTEMS (ECMWF, GEFSV12, JMA, CFS
AND OTHERS) INDICATE THE LIKELIHOOD OF SUBSTANTIAL POSITIVE 500-HPA HEIGHT
ANOMALIES ASSOCIATED WITH BOTH RIDGING AS WELL AS A GENERAL NORTHWARD SHIFT IN
THE MEAN WESTERLIES OVER CENTRAL NORTH AMERICA INCLUDING THE NORTHERN CONUS. AS
A RESULT, ABOVE-NORMAL TEMPERATURES ARE MOST LIKELY FOR THE NORTHERN TIER OF
THE U.S., THE EASTERN CONUS AND SOUTHERN PLAINS. CONSIDERABLY ABOVE-NORMAL SSTS
IN THE GULF OF MEXICO AND ALONG THE ATLANTIC SEABOARD ALSO SUPPORT FAVORED
ABOVE-NORMAL TEMPERATURES IN THESE AREAS. SHORT-TERM CLIMATE PREDICTION MODELS
AS PART OF THE NMME AND C3S ENSEMBLE SYSTEMS INDICATE THIS FORECAST OUTCOME IS
MAINTAINED IN THE MONTHLY MEAN TEMPERATURE FORECAST.
ELEVATED PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES FOR MUCH OF THE WESTERN
CONUS ARE LOW DUE TO UNCERTAINTY IN MODEL GUIDANCE AND OTHER FORECAST TOOLS AT
THE START OF OCTOBER. CONFLICTING FORECAST TOOLS AND EL NINO CONSIDERATIONS
(I.E., POTENTIAL BELOW-NORMAL TEMPERATURES) LED TO A FORECAST OF EC FOR A
REGION IN THE INTERIOR CONUS.
FOR PRECIPITATION, ELEVATED ODDS OF ABOVE-NORMAL OCTOBER MONTHLY TOTAL
PRECIPITATION AMOUNTS ARE FORECAST FROM THE SOUTHWEST EASTWARD TO INCLUDE PARTS
OF THE CENTRAL ROCKIES, CENTRAL AND SOUTHERN PLAINS, OHIO VALLEY AND
MID-ATLANTIC. THE FORECAST FOR THE CENTER OF THIS REGION IS MAINLY SUPPORTED BY
THE LIKELIHOOD OF MORE UNSETTLED CONDITIONS UNDERNEATH FORECAST RIDGING TO THE
NORTH AS NOTED ABOVE AND THIS IS CONSISTENT WITH MUCH OF THE EXTENDED-RANGE AND
SHORT-TERM CLIMATE PREDICTION MODEL GUIDANCE. ALTHOUGH ONLY SLIGHTLY ELEVATED,
ABOVE-NORMAL PRECIPITATION IS FORECAST FOR SOME AREAS IN THE SOUTHWEST DUE TO
POTENTIAL TROPICAL INFLUENCES OF OVERALL ENHANCED MOISTURE, TROPICAL CYCLONE
IMPACTS AND EL NINO CONSIDERATIONS. POTENTIAL UNSETTLED CONDITIONS UNDERNEATH
RIDGING, PARTIAL MODEL GUIDANCE SUPPORT AND POSITIVE PRECIPITATION LONG TERM
TRENDS SLIGHTLY FAVOR ABOVE-NORMAL PRECIPITATION FOR THE OHIO VALLEY AND
MID-ATLANTIC.
ABOVE-NORMAL PRECIPITATION IS ALSO FAVORED FOR WESTERN AND NORTHERN ALASKA
SUPPORTED BY MORE OPEN AND WARMER WATERS BOTH OVER A LARGER AREA IN THE
NORTHEAST PACIFIC AS WELL AS MORE NEARBY WATERS OF THE BERING SEA, CHUKCHI SEA
AND BEAUFORT SEA.
NORTHWARD SHIFTED WESTERLIES AND RIDGING AS INDICATED BY EXTENDED-RANGE AND
SUBSEASONAL MODEL GUIDANCE IN EARLY OCTOBER AND SHORT-TERM CLIMATE PREDICTION
MODELS (NMME AND C3S) ELEVATE ODDS FOR BELOW-NORMAL PRECIPITATION FOR PARTS OF
THE PACIFIC NORTHWEST AND AN AREA FROM THE NORTHERN GREAT LAKES TO NEW ENGLAND.
EL NINO CONSIDERATIONS (I.E., POTENTIAL BELOW-NORMAL PRECIPITATION) ALSO
SUPPORTS THE FORECAST FOR THE AREA HIGHLIGHTED IN THE PACIFIC NORTHWEST.
FORECASTER: JON GOTTSCHALCK
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1991 AND 2020, FOLLOWING
THE WORLD METEOROLOGICAL ORGANIZATION CONVENTION OF USING THE MOST RECENT 3
COMPLETE DECADES AS THE CLIMATE 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.
THE NEXT MONTHLY OUTLOOK...FOR NOV ... WILL BE ISSUED ON THU OCT 19 2023
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1991-2020 BASE PERIOD.
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