059
FXUS07 KWBC 301900
PMD30D
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.
$$