PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 
300PM EDT MONDAY SEP 30 2013 
 
30-DAY OUTLOOK DISCUSSION FOR OCTOBER 2013 
 
THERE ARE SOME ADJUSTMENTS TO THE OCTOBER MONTHLY OUTLOOK IN THE UPDATE BASED 
ON THE MOST RECENT SHORT-, MEDIUM- AND EXTENDED-RANGE MODEL GUIDANCE, AS WELL 
AS MJO CONSIDERATIONS. 
 
ABOVE-NORMAL TEMPERATURES CONTINUE TO BE FAVORED FOR MUCH OF THE CONUS WITH THE 
ADDITION OF PARTS OF THE LOWER OHIO VALLEY, NORTHEAST AND MID-ATLANTIC THAT 
WERE EQUAL CHANCES (EC) IN THE PREVIOUS OUTLOOK. THERE IS CONSISTENT GUIDANCE 
FROM THE SHORT-RANGE TO THE MONTHLY TOOLS FOR THIS INCREASE IN COVERAGE. 
ELEVATED CHANCES FOR BELOW-NORMAL TEMPERATURES EARLY IN THE MONTH ACROSS MUCH 
OF THE PACIFIC NORTHWEST AND ROCKIES RESULTS IN LESS CONFIDENCE FOR 
ABOVE-NORMAL OCTOBER MEAN TEMPERATURES FOR THE WEST. A LARGER AREA OF EC IS NOW 
INDICATED IN THIS PORTION OF THE COUNTRY COMPARED TO THE PREVIOUS OUTLOOK AS 
WELL AS SOMEWHAT LOWER PROBABILITIES FOR ABOVE-NORMAL OCTOBER MEAN TEMPERATURES 
FOR PARTS OF THE SOUTHWEST AND SOUTHERN ROCKIES. THE HIGHEST PROBABILITIES FOR 
ABOVE-NORMAL TEMPERATURES ARE NOW FOR AREAS OF THE GREAT LAKES, MIDWEST AND 
NORTHEAST WHERE AGREEMENT IN MODEL GUIDANCE ACROSS TIME SCALES WAS HIGH. 
 
PROSPECTS OF A MEAN TROUGH EARLY IN THE MONTH NEAR THE BERING STRAIT EVIDENT IN 
EXTENDED RANGE AND MONTHLY (CFS) MODEL GUIDANCE FAVOR BELOW-NORMAL TEMPERATURES 
FOR PORTIONS OF SOUTHWEST ALASKA, AN ADDITION TO THE PREVIOUS OUTLOOK. 
 
FOR PRECIPITATION, THE AREA OF FAVORED BELOW-MEDIAN PRECIPITATION FORECAST FOR 
THE WESTERN HIGH PLAINS AND PARTS OF THE EASTERN ROCKIES WAS SHIFTED WESTWARD 
AND SOUTHWARD AS THERE REMAINS CONSISTENT SIGNATURES IN THE EXTENDED RANGE 
MODEL GUIDANCE FOR DRIER-THAN-AVERAGE CONDITIONS IN THESE AREAS. MODEL GUIDANCE 
ALSO HAS SHIFTED THE LOCATION OF AN ENHANCED MEAN OCTOBER PACIFIC JET SLIGHTLY 
NORTHWARD SO COVERAGE FOR ABOVE-MEDIAN PRECIPITATION ACROSS THE PACIFIC 
NORTHWEST WAS REDUCED AND EXPANDED ALONG THE SOUTH COAST OF ALASKA, AS COMPARED 
TO THE PREVIOUS OUTLOOK. 
 
THE MJO REMAINS ACTIVE AND IS PROGRESSING AS EXPECTED WITH THE ENHANCED PHASE 
NOW CENTERED ACROSS THE PACIFIC OCEAN AND IS MOVING EASTWARD. THE MJO ENHANCED 
PHASE IS FAVORED TO CONTINUE SHIFTING EASTWARD TO THE AMERICAS, THE ATLANTIC 
AND LATER AFRICA DURING THE FIRST HALF OF OCTOBER. THE MJO FAVORS ELEVATED ODDS 
FOR ABOVE-MEDIAN PRECIPITATION ACROSS THE PACIFIC NORTHWEST DURING MID-OCTOBER. 
MOREOVER, AN AREA OF ELEVATED ODDS FOR ABOVE-MEDIAN PRECIPITATION HAS BEEN 
ADDED ALONG THE GULF COAST, PARTS OF THE LOWER MISSISSIPPI VALLEY AND SOUTHEAST 
INCLUDING FLORIDA, CONSISTENT WITH MJO COMPOSITES. 
 
PREVIOUS DISCUSSION FROM 9/19 
 
OCEANIC CONDITIONS ACROSS THE EQUATORIAL CENTRAL PACIFIC OCEAN CONTINUE TO 
REFLECT AN ENSO NEUTRAL STATE. SEA SURFACE TEMPERATURE (SST) ANOMALIES ARE 
CLOSE TO ZERO FOR MUCH OF THE EQUATORIAL PACIFIC WITH POSITIVE ANOMALIES OF 
GREATER THAN +0.5 DEGREES C NEAR 160E AND NEGATIVE ANOMALIES OF LESS THAN -1.0 
DEGREES C IN SMALL AREAS BETWEEN 110W AND THE SOUTH AMERICAN COAST. THE MJO 
STRENGTHENED IN LATE AUGUST AND SEPTEMBER WITH THE ENHANCED CONVECTIVE PHASE 
NOW CENTERED ACROSS THE EASTERN MARITIME CONTINENT AND FAR WESTERN PACIFIC 
OCEAN AND NEEDS TO BE CONSIDERED FOR THE OCTOBER FORECAST. 
 
THERE HAS BEEN A RAPID EXPANSION OF DRY SOIL MOISTURE CONDITIONS ACROSS PARTS 
OF THE NORTHERN PLAINS, THE UPPER MISSISSIPPI VALLEY AND WESTERN GREAT LAKES 
STATES IN RECENT WEEKS. SOIL MOISTURE CONDITIONS HAVE IMPROVED ACROSS PORTIONS 
OF THE WESTERN U.S. PRIMARILY OVER AREAS OF THE SOUTHWEST U.S. AND SOUTHERN 
ROCKIES, ALTHOUGH MUCH OF THE WEST REMAINS IN SEVERE DROUGHT (D2 OR GREATER). 
 
THE OCTOBER TEMPERATURE OUTLOOK INDICATES ELEVATED ODDS FOR ABOVE-NORMAL 
MONTHLY MEAN TEMPERATURES FOR MUCH OF THE WESTERN CONUS, THE GREAT PLAINS, THE 
WESTERN GREAT LAKES STATES, NEW ENGLAND AND NORTHERN ALASKA. THERE IS GOOD 
AGREEMENT AMONGST BOTH TRADITIONAL STATISTICAL TOOLS (CCA, OCN, SMLR) AS WELL 
AS FROM DYNAMICAL MODEL GUIDANCE (CFS, NMME, IMME) FOR ABOVE NORMAL 
TEMPERATURES ACROSS THE SOUTHWEST, CALIFORNIA AND AREAS IN THE INTERMOUNTAIN 
WEST. SOME INDICATORS, NAMELY THE CFS, INDICATE SOMEWHAT LESS CONFIDENCE IN 
ABOVE-NORMAL TEMPERATURES ACROSS SOME AREAS OF THE SOUTHWEST AND SOUTHERN 
ROCKIES SO FORECAST PROBABILITIES ARE LOWER IN THESE AREAS. 
 
THE HIGHLIGHTED AREA OF ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES IS EXTENDED 
EASTWARD ACROSS MUCH OF THE CENTRAL CONUS PRIMARILY DUE TO FORECAST MEAN 
OCTOBER POSITIVE HEIGHT ANOMALIES DEPICTED BY THE CFS, NMME, AND IMME. LOW SOIL 
MOISTURE CONDITIONS MAY ALSO PLAY A VERY MINOR ROLE. BOTH STATISTICAL AND 
DYNAMICAL MODEL FORECAST TOOLS FAVOR ABOVE-NORMAL TEMPERATURES FOR NEW ENGLAND. 
LONG TERM TRENDS ASSOCIATED WITH LATER RETURN OF SEA ICE EXTENT DURING AUTUMN 
FAVOR ABOVE NORMAL TEMPERATURES FOR THE NORTH SLOPE OF ALASKA. 
 
THE INFLUENCE OF THE MJO ON MONTHLY MEAN TEMPERATURES IS DIFFICULT TO ASSESS 
GIVEN THAT TEMPERATURE SIGNATURES VARY WIDELY AS A FUNCTION OF MJO PHASE, AS 
INDICATED BY MJO COMPOSITES, ESPECIALLY WITH THE NORMAL UNCERTAINTY OF WHETHER 
THE MJO REMAINS ROBUST IN BOTH AMPLITUDE AND PROPAGATION. 
 
IN AREAS WHERE THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES ARE SIMILAR TO 
CLIMATOLOGICAL PROBABILITIES, EQUAL CHANCES (EC) IS SHOWN. 
 
THE PRECIPITATION OUTLOOK FOR OCTOBER 2013 INDICATES INCREASED PROBABILITIES OF 
ABOVE MEDIAN PRECIPITATION STRETCHING FROM THE ALASKA PANHANDLE TO THE PACIFIC 
NORTHWEST WITH BELOW MEDIAN PRECIPITATION FAVORED FOR AN AREA IN THE CENTRAL 
ROCKIES AND GREAT PLAINS. AS IS TYPICAL DURING THE AUTUMN MONTHS, EMPIRICAL 
FORECAST TOOLS OFFER LITTLE RELIABLE INFORMATION AND DYNAMICAL MODEL FORECAST 
GUIDANCE IS THE PRIMARY DRIVER FOR THE PRECIPITATION FORECAST, ALONG WITH 
CONSIDERATIONS FROM THE MJO. 
 
THERE HAS BEEN A CONSISTENT SIGNATURE FROM CFS GUIDANCE FOR ELEVATED ODDS OF 
ABOVE-MEDIAN PRECIPITATION FROM THE SOUTHEAST CORNER OF ALASKA TO THE PACIFIC 
NORTHWEST ASSOCIATED WITH A STRONG PACIFIC JET PREDICTED IN THE OCTOBER MEAN. 
ENHANCED PRECIPITATION FOR THE PACIFIC NORTHWEST IS ALSO CONSISTENT WITH 
POTENTIAL UPCOMING PHASES OF THE MJO EARLY IN THE MONTH, IF IT REMAINS ACTIVE. 
POSITIVE OCTOBER MEAN UPPER-LEVEL HEIGHT ANOMALIES ACROSS CENTRAL NORTH AMERICA 
IMPLY RIDGING AND A NORTHWARD SHIFTED STORM TRACK FAVORING BELOW-MEDIAN 
PRECIPITATION ACROSS AN AREA OF THE EAST-CENTRAL ROCKIES INTO THE WEST-CENTRAL 
GREAT PLAINS. 
 
THERE ARE LITTLE CONSISTENT OR RELIABLE SIGNALS BETWEEN THE DYNAMICAL MODEL 
GUIDANCE AND OTHER TOOLS FOR MUCH OF THE CONUS SO EQUAL CHANCES (EC) OF ABOVE-, 
NEAR- AND BELOW-AVERAGE MONTHLY TOTAL PRECIPITATION ARE INDICATED IN THESE 
AREAS. ALTHOUGH GUIDANCE FROM THE CFS, NMME AND THE IMME SHOW INDICATIONS OF 
BELOW-MEDIAN PRECIPITATION FOR AREAS ALONG THE GULF COAST AND IN THE INTERIOR 
SOUTHEAST, THIS IS AT ODDS WITH POTENTIAL UPCOMING PHASES OF THE MJO, WHICH 
GENERALLY TILT TOWARDS WETTER-THAN-AVERAGE CONDITIONS IN THESE AREAS DURING THE 
AUTUMN. 
 
THE MAIN FACTORS WHICH USUALLY INFLUENCE THE MONTHLY CLIMATE OUTLOOK INCLUDE: 
1) EL NINO AND LA NINA - WHICH COMPRISE ENSO. IMPACTS OF THESE EVENTS ARE 
SUMMARIZED BY SEPARATING 3-MONTH OBSERVATIONS FROM THREE OR MORE DECADES INTO 
EL NINO, NEUTRAL AND LA NINA SETS, AVERAGING EACH SEPARATELY, AND THEN 
COMPUTING ANOMALIES. THESE ARE CALLED "COMPOSITES" AND USED AT TIMES TO 
SUBJECTIVELY MODIFY THE FORECAST. 
2) TRENDS - APPROXIMATED BY THE OCN TOOL AS THE DIFFERENCE BETWEEN THE MOST 
RECENT 15-YEAR MEAN OF TEMPERATURE OR OF PRECIPITATION FOR A GIVEN LOCATION AND 
TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY 1981-2010). 
3) THE TROPICAL 30-60 DAY OSCILLATION - CALLED THE MADDEN JULIAN OSCILLATION 
(MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS. 
4) THE ARCTIC OSCILLATION (AO), THE SIMILAR NORTH ATLANTIC OSCILLATION (NAO), 
AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE 
ANOMALY PATTERN ESPECIALLY DURING BOREAL WINTER AND ARE GENERALLY CONSIDERED TO 
HAVE LOW PREDICTABILITY. 
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE 
VARIABILITY AFFECTING THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN 
REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO. 
6) PERSISTENTLY DRY OR WET SOILS IN THE SPRING AND SUMMER AND SNOW AND ICE 
COVER ANOMALIES IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS 
AND ACT AS A KIND OF MEMORY IN THE CLIMATE SYSTEM. 
7) STATISTICAL FORECAST MODELS - CANONICAL CORRELATION ANALYSIS (CCA), 
SCREENING MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOG (CA), AND 
ENSEMBLE CCA (ECCA). 
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM 
VERSION 2 (CFS) AND FOR THE ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE 
FORECAST SYSTEM (GEFS).  AN EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL 
MULTI-MODEL ENSEMBLE (NMME), COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED. 
 
 
FORECASTER: JON GOTTSCHALCK 
 
 
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1981 AND 2010, 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 17 2013 
 
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. 
 
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