Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1
000
FXUS07 KWBC 211232
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EDT THURSDAY AUG 21 2014

30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2014

RECENT ATMOSPHERIC AND OCEANIC CONDITIONS ACROSS THE TROPICAL PACIFIC INDICATE
CURRENT ENSO-NEUTRAL CONDITIONS. CLIMATE MODEL FORECASTS AND THE CPC/IRI ENSO
OUTLOOK INDICATE THE EXPECTED DEVELOPMENT OF EL NINO IN LATE SUMMER OR EARLY
AUTUMN. MOST FORECASTS INDICATE EL NINO TO PEAK AT WEAK OR MODERATE STRENGTH IN
LATE AUTUMN INTO EARLY WINTER.



DURING THE PAST FEW WEEKS, POSITIVE SST ANOMALIES PERSISTED IN THE EASTERN
EQUATORIAL PACIFIC AND WEST OF THE DATE LINE, WHILE ANOMALIES ARE NEAR ZERO IN
THE EAST-CENTRAL PACIFIC. THE LATEST WEEKLY SST ANOMALY IN THE NINO 3.4 REGION
IS +0.0C. POSITIVE ANOMALIES IN AVERAGE OCEANIC HEAT CONTENT BASED ON
SUBSURFACE TEMPERATURE ANOMALIES IN THE UPPER 300-METERS OF THE EASTERN AND
CENTRAL EQUATORIAL PACIFIC (180W TO 100W) DECREASED IN THE LAST FEW MONTHS,
BECOMING SLIGHTLY NEGATIVE IN RECENT WEEKS, BEFORE RETURNING TO AN AVERAGE
ANOMALY NEAR ZERO. IN RECENT WEEKS A POSITIVE SUBSURFACE TEMPERATURE ANOMALY
EMERGED IN THE WESTERN PACIFIC AT ABOUT 100 TO 200 METERS DEPTH, WHILE A LARGE
AREA OF POSITIVE TEMPERATURE ANOMALIES AT DEPTH IN THE CENTRAL AND EASTERN
EQUATORIAL PACIFIC DECREASED IN SIZE AND MAGNITUDE AND IS NOW LOCATED FROM
ABOUT 145W TO 85W EXTENDING ONLY TO A DEPTH OF ABOUT 75 METERS. DURING THE PAST
30-DAYS, POSITIVE OLR ANOMALIES, INDICATING SUPPRESSED CONVECTION AND
PRECIPITATION, WERE OBSERVED OVER INDONESIA AND NEAR THE DATE LINE. LOW-LEVEL
850-HPA WINDS WERE NEAR AVERAGE ACROSS THE EQUATORIAL PACIFIC, AND EASTERLY
UPPER-LEVEL 200-HPA WIND ANOMALIES WERE OBSERVED OVER THE EAST-CENTRAL PACIFIC.
THE SEPTEMBER 2014 TEMPERATURE AND PRECIPITATION OUTLOOKS RELY MAINLY ON
CLIMATE MODEL FORECASTS WITHOUT AN EXPECTATION OF SIGNIFICANT IMPACTS ON THE
CLIMATE OF NORTH AMERICA BY NEXT MONTH FROM POTENTIAL EL NINO DEVELOPMENT.



A GREATER LIKELIHOOD OF ABOVE-NORMAL MONTHLY MEAN TEMPERATURES FOR SEPTEMBER
2014 IS PREDICTED FOR THE GULF COAST AND PARTS OF THE SOUTHEAST FROM THE TEXAS
COAST TO EASTERN NORTH CAROLINA. THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES IS
GREATEST FOR SOUTHERN AND EASTERN PARTS OF THE REGION. THE LIKELIHOOD OF
ABOVE-NORMAL TEMPERATURES IS ALSO ENHANCED FOR NEW ENGLAND. ABOVE-NORMAL
TEMPERATURES ARE ALSO MOST LIKELY FOR ALASKA AND MUCH OF THE WEST INCLUDING THE
NORTHERN ROCKIES, GREAT BASIN AND PACIFIC COASTAL STATES, WITH THE GREATEST
PROBABILITIES ALONG THE WEST COAST AND THE SOUTHERN COAST OF ALASKA. THE
TEMPERATURE OUTLOOK IS SUPPORTED BY RECENT CLIMATE MODEL FORECASTS FROM THE
CFS, NMME AND IMME. POSITIVE SEA SURFACE TEMPERATURE ANOMALIES OVER THE NORTH
PACIFIC AND ALONG THE SOUTHERN CALIFORNIA, EASTERN GULF AND NEW ENGLAND COASTS
MAY INCREASE THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES NEAR THE COAST.
CLIMATE MODELS AS SHOWN IN CFSV2 FORECASTS INDICATE ABOVE-NORMAL MID-LEVEL
700-HPA HEIGHTS OVER ALASKA, THE PACIFIC COAST AND THE EAST, SUPPORTING AN
ENHANCED LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES.



THE MONTHLY OUTLOOK FOR SEPTEMBER 2014 INDICATES A GREATER THAN NORMAL
LIKELIHOOD OF ABOVE-MEDIAN PRECIPITATION FOR A LARGE AREA OF THE SOUTHWEST FROM
SOUTHERN CALIFORNIA TO WESTERN TEXAS AND OKLAHOMA AND NORTHEASTWARD TO UTAH,
SOUTHERN WYOMING, NEBRASKA AND KANSAS. THE PRECIPITATION OUTLOOK FOR SEPTEMBER
2014 IS SUPPORTED BY CLIMATE MODEL FORECASTS FROM THE NMME AND IMME.
ABOVE-NORMAL EASTERN PACIFIC SEA SURFACE TEMPERATURES AND THE PREDICTED
ATMOSPHERIC CIRCULATION INDICATE AN INCREASED FLOW OF ATMOSPHERIC MOISTURE FROM
THE TROPICS INTO THE SOUTHWEST.



IN AREAS WHERE CLIMATE SIGNALS ARE WEAK SUCH THAT THE LIKELIHOODS OF MONTHLY
MEAN TEMPERATURES OR MONTHLY ACCUMULATED PRECIPITATION AMOUNTS ARE SIMILAR TO
CLIMATOLOGICAL PROBABILITIES, EQUAL CHANCES (EC) IS INDICATED.



THE MAIN FACTORS THAT 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 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN 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: DAN COLLINS


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.



AN UPDATED MONTHLY OUTLOOK... FOR SEP WILL BE ISSUED ON SUN AUGUST 31 2014


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.

$$


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.