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.
$$