30 Day Narrative

541 
FXUS07 KWBC 311900
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300PM EDT WEDNESDAY JUL 31 2013
30-DAY OUTLOOK DISCUSSION FOR AUGUST 2013
THE OUTLOOK FOR AUGUST, 2013 IS UPDATED WITH INFORMATION FROM THE LATEST MODEL 
GUIDANCE FROM THE NCEP GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS), AND RECENT 
FORECASTS FROM THE NORTH AMERICAN ENSEMBLE FORECAST SYSTEM (NAEFS). THE UPDATED 
OUTLOOK REFLECTS THE INFLUENCE OF FORECAST WEATHER CONDITIONS DURING THE FIRST 
HALF OF THE MONTH ON EXPECTED MONTHLY MEAN TEMPERATURE ANOMALIES AND MONTHLY 
TOTAL PRECIPITATION FOR AUGUST.
ANOMALIES IN THE SEA SURFACE TEMPERATURE (SST) AND SOIL MOISTURE CONDITIONS 
THAT WERE EXPECTED TO INFLUENCE THE U.S. CLIMATIC CONDITIONS REMAINED LARGELY 
UNCHANGED SINCE MID-JULY. OCEANIC CONDITIONS IN THE EQUATORIAL PACIFIC REMAIN 
CONSISTENT WITH ENSO-NEUTRAL CONDITIONS, AS WAS ANTICIPATED EARLIER THIS MONTH. 
THE MADDEN-JULIAN OSCILLATION (MJO) REMAINS WEAK AS OF LATE JULY.  SST'S ALONG 
THE WEST COAST OF THE CONUS HAVE BECOME INCREASINGLY BELOW AVERAGE IN THE PAST 
FEW WEEKS, WHILE SST'S SURROUNDING ALASKA REMAIN ABOVE NORMAL, WITH SLIGHT 
INCREASES IN ANOMALIES ALONG THE SOUTH COAST. SOIL MOISTURE CONTINUES TO BE 
BELOW NORMAL IN MANY AREAS OF THE WEST, WITH SOME IMPROVEMENT IN THE CENTRAL 
AND SOUTHERN ROCKY MOUNTAINS AND THE SOUTHWEST. WET SOIL MOISTURE CONDITIONS 
CONTINUE TO BE OBSERVED IN MUCH OF THE SOUTHEASTERN CONUS.
THE TEMPERATURE OUTLOOK FOR AUGUST 2013 CALLS FOR ENHANCED CHANCES FOR ABOVE 
NORMAL TEMPERATURES THROUGHOUT MUCH OF ALASKA, AND ALSO FOR MUCH OF THE WESTERN 
CONUS. THIS AREA IS QUITE SIMILAR TO THE ONE ISSUED IN MID-JULY AND IS NEAR THE 
MEAN UPPER LEVEL RIDGE POSITIONS EXPECTED DURING THE FIRST TWO WEEKS OF AUGUST. 
EXPECTED ABOVE NORMAL TEMPERATURES IN ALASKA DURING THE FIRST HALF OF THE MONTH 
SUBSTANTIALLY INCREASES CONFIDENCE IN ABOVE NORMAL MONTHLY MEAN TEMPERATURES 
FOR THAT STATE COMPARED TO THE PREVIOUS OUTLOOK. THE CHANCES FOR BELOW NORMAL 
TEMPERATURES ARE INCREASED FOR PARTS OF THE UPPER MIDWEST DUE TO EXPECTED BELOW 
NORMAL TEMPERATURES FOR EARLY AUGUST.  BELOW NORMAL TEMPERATURES EXPECTED 
DURING THE FIRST HALF OF AUGUST IN THE NORTHEASTERN CONUS REDUCES THE CHANCES 
FOR ABOVE NORMAL MEAN TEMPERATURES, RESULTING IN A FORECAST REVISION TO EQUAL 
CHANCES FOR BELOW, NEAR OR ABOVE NORMAL TEMPERATURES.
THE LATEST PRECIPITATION FORECASTS FROM THE CFS CONTINUE TO BE CONSISTENT WITH 
THE FORECASTS ISSUED EARLIER IN THE MONTH. THE SOUTHWEST MONSOON IS EXPECTED TO 
BE LESS ACTIVE IN THE FIRST HALF OF AUGUST THAN IT WAS IN JULY.  THIS RESULTED 
IN A REVISION IN THE FORECAST FOR SOME PARTS OF THE SOUTHWEST AND SOUTHERN 
ROCKIES TO EC REFLECTING DECREASING CONFIDENCE IN THE SIGNAL FOR ABOVE MEDIAN 
PRECIPITATION AMOUNTS. THE LATEST FORECASTS FROM THE CFS CONTINUE TO INDICATE 
ABOVE MEDIAN PRECIPITATION AMOUNTS FOR THE SOUTHEASTERN CONUS, WHICH IS IN 
GENERAL AGREEMENT WITH AN ANTICIPATED MEAN TROUGH OVER THE EASTERN PART OF THE 
COUNTRY DURING THE FIRST HALF OF AUGUST. PRECIPITATION ASSOCIATED WITH AN 
EXPECTED MEAN FRONTAL BOUNDARY DURING THE FIRST PART OF AUGUST MAY BRING ENOUGH 
PRECIPITATION TO ELEVATE THE CHANCES FOR ABOVE MEDIAN PRECIPITATION MONTHLY 
TOTALS NEAR THE MIDDLE MISSISSIPPI VALLEY AND ALSO FOR PARTS OF THE NORTHERN 
ROCKY MOUNTAINS.
THE DISCUSSION FROM THE HALF-MONTH LEAD AUGUST OUTLOOK RELEASED ON JULY 18TH IS 
GIVEN BELOW.
 
ENSO NEUTRAL CONDITIONS CONTINUED DURING JUNE AND INTO THE FIRST HALF OF JULY.  
EQUATORIAL SEA SURFACE TEMPERATURES (SSTS) REMAIN BELOW NORMAL FROM THE SOUTH 
AMERICAN COAST TO ABOUT 130 W LONGITUDE AND ARE NEAR LONG-TERM CLIMATOLOGICAL 
NORMALS FROM 130 W TO ABOUT 170 E. PACIFIC SSTS ALONG THE EQUATOR WEST OF 170 E 
ARE BETWEEN 0.5 AND 1.0 DEGREES C ABOVE NORMAL. SUB-SURFACE OCEAN TEMPERATURES 
ALONG THE EQUATOR IN THE EAST-CENTRAL PACIFIC HAVE WARMED SIGNIFICANTLY DURING 
THE LAST 30 DAYS AND ARE NOW OVER 1 DEGREE C ABOVE NORMAL FROM ABOUT 100 TO 200 
METERS DEPTH. THESE OCEANIC OBSERVATIONS ARE CONSISTENT WITH ENSO NEUTRAL 
CONDITIONS.  
ATMOSPHERIC ANOMALIES OVER THE TROPICAL PACIFIC OCEAN SIMILARLY SUGGEST ENSO 
NEUTRAL CONDITIONS, WITH EQUATORIAL PACIFIC LOW LEVEL WINDS NEAR AVERAGE AND 
WEAK UPPER LEVEL WESTERLY WIND ANOMALIES.  CONVECTION NEAR THE EQUATOR REMAINED 
ENHANCED OVER INDONESIA AND WAS SLIGHTLY SUPPRESSED OVER THE CENTRAL PACIFIC 
OCEAN DURING JUNE.  THE MADDEN-JULIAN OSCILLATION (MJO) WAS QUITE PRONOUNCED IN 
LATE JUNE AND EARLY JULY, AND MAY HAVE INFLUENCED BOTH THE MEAN LARGE SCALE 
WIND AND CONVECTIVE ANOMALIES DURING THE LAST MONTH, ALTHOUGH SOME INDICATORS 
SHOW THAT THE MJO HAS WEAKENED RECENTLY. TAKEN TOGETHER, THESE ATMOSPHERIC AND 
OCEANIC OBSERVATIONS INDICATE ENSO NEUTRAL CONDITIONS WITH NO CLEAR SUGGESTION 
OF THE POSSIBLE EMERGENCE OF WARM OR COOL ENSO CONDITIONS IN THE NEXT FEW 
MONTHS.  THIS IS CONSISTENT WITH THE LATEST SST FORECASTS FROM DYNAMICAL AND 
STATISTICAL TOOLS THAT FAVOR CONTINUED ENSO NEUTRAL CONDITIONS THROUGH THE END 
OF AUGUST.
THE AUGUST 2013 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED MAINLY ON THE 
LATEST GUIDANCE FROM THE NCEP CLIMATE FORECAST SYSTEM, VERSION 2 (CFS) AND 
OTHER CLIMATE MODELS USED IN THE NATIONAL MULTI-MODEL ENSEMBLE (NMME). 
STATISTICAL TOOLS WERE CONSULTED FOR ADDITIONAL SUPPORT FOR CLIMATE ANOMALIES.  
THE TEMPERATURE OUTLOOK FOR AUGUST 2013 INDICATES ENHANCED PROBABILITIES FOR 
ABOVE NORMAL MEAN TEMPERATURES FOR MOST OF THE WESTERN U.S., THE CENTRAL AND 
SOUTHERN PLAINS, AND FOR PARTS OF THE NORTHEAST.  ABOVE NORMAL TEMPERATURES ARE 
ALSO FAVORED FOR MOST OF ALASKA, EXCEPT FOR NEAR THE SOUTHWESTERN COAST. THESE 
FORECASTS ARE LARGELY SUPPORTED BY RECENT DYNAMICAL MODEL GUIDANCE FROM THE 
NMME, AND ARE CONSISTENT WITH DECADAL CLIMATE TRENDS AS WELL. DRY INITIAL SOIL 
MOISTURE CONDITIONS THROUGHOUT MUCH OF THE WESTERN CONUS MAY PLAY A ROLE IN 
ENHANCING CHANCES FOR ABOVE MEDIAN TEMPERATURES. SOIL MOISTURE IS ABOVE NORMAL 
IN THE EASTERN CONUS AND IS EXPECTED TO COUNTERACT RECENT TRENDS TOWARD ABOVE 
NORMAL TEMPERATURES IN PARTS OF THE SOUTHEAST, BRINGING EXPECTED TEMPERATURES 
MORE IN LINE WITH LONG TERM CLIMATOLOGICAL DISTRIBUTIONS.  THE ABOVE NORMAL 
TEMPERATURE FORECAST FOR ALASKA IS SUPPORTED BY THE NMME AND STATISTICAL TOOLS. 
SEA SURFACE TEMPERATURES NEAR THE SOUTHWESTERN COAST OF ALASKA CONTINUE TO BE 
NEAR TO BELOW NORMAL AND ARE EXPECTED TO MODERATE AIR TEMPERATURES IN THE 
SOUTHWESTERN PART OF THE STATE. ABOVE NORMAL TEMPERATURES FAVORED FOR THE 
NORTHEAST ARE PRIMARILY DUE TO RECENT TEMPERATURE TRENDS. 
THE PRECIPITATION OUTLOOK FOR AUGUST 2013 INDICATES INCREASED PROBABILITIES OF 
ABOVE MEDIAN PRECIPITATION OVER THE SOUTHWEST. THIS FORECAST IS SUPPORTED BY 
THE CFS AND NMME. THE CHANCES OF ABOVE MEDIAN PRECIPITATION AMOUNTS ARE 
ELEVATED FOR MUCH OF THE SOUTHEASTERN CONUS DUE TO CONSISTENT INDICATIONS FROM 
THE CFS AND NMME.  THERE ARE SOME HINTS FROM STATISTICAL TOOLS THAT SUGGEST 
THAT THE WET SOIL MOISTURE CONDITIONS MAY PLAY A ROLE IN INCREASING ODDS OF 
ABOVE MEDIAN PRECIPITATION IN THE SOUTHEAST AS WELL.  
IN AREAS WHERE THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES AND MONTHLY 
ACCUMULATED PRECIPITATION AMOUNTS ARE SIMILAR TO CLIMATOLOGICAL PROBABILITIES, 
EQUAL CHANCES (EC) IS SHOWN.
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: DAVID UNGER
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 SEP ... WILL BE ISSUED ON THU AUG 15 2013
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.
$$