Prognostic Meteorological Discussion
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FXUS07 KWBC 311925
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300PM EDT FRIDAY JUL 31 2015

30-DAY OUTLOOK DISCUSSION FOR AUGUST 2015

SEA SURFACE TEMPERATURES (SSTS) CONTINUE TO BE MORE THAN ONE DEGREE C ABOVE
NORMAL ALONG THE EQUATOR IN THE PACIFIC OCEAN FROM THE INTERNATIONAL DATE LINE
EASTWARD TO THE SOUTH AMERICAN COAST. SST ANOMALIES ARE GREATER THAN +2.0
DEGREES C IN THE EAST PACIFIC FROM ABOUT 135 W LONGITUDE TO THE SOUTH AMERICAN
COAST AND EXCEED +3.0 C EASTWARD OF 100 W LONGITUDE. THERE CONTINUES TO BE A
LARGE AREA OF POSITIVE SST ANOMALIES OVER MUCH OF THE NORTH PACIFIC ALONG THE
WEST COAST OF NORTH AMERICA. SUBSURFACE OCEAN TEMPERATURES NEAR THE EQUATOR
HAVE BEEN PERSISTENTLY ABOVE NORMAL TO DEPTHS EXCEEDING 100 METERS EAST OF THE
INTERNATIONAL DATE LINE, CONTRIBUTING TO SUSTAINED POSITIVE SST ANOMALIES.
NEGATIVE OLR ANOMALIES ABOVE THE EASTERN PACIFIC TO THE NORTH OF THE EQUATOR
INDICATE ANOMALOUSLY ACTIVE CONVECTION. ANOMALOUS LOW-LEVEL (850-HPA) WESTERLY
WINDS EXTENDED FROM THE WEST PACIFIC TO THE EAST-CENTRAL EQUATORIAL PACIFIC.
ANOMALOUS UPPER-LEVEL (200-HPA) EASTERLIES WERE OBSERVED OVER THE EAST-CENTRAL
EQUATORIAL PACIFIC. THESE ATMOSPHERIC AND OCEANIC CONDITIONS INDICATE STRONG
OCEAN-ATMOSPHERE COUPLING ASSOCIATED WITH EL NINO CONDITIONS.



THE MONTHLY UPDATE TO THE AUGUST 2015 U.S. CLIMATE OUTLOOK IS BASED LARGELY ON
DYNAMICAL MODEL FORECASTS, INCLUDING WEATHER PREDICTION MODELS FOR THE FIRST
WEEK IN THE MONTH, AS WELL AS THE NORTH AMERICAN ENSEMBLE FORECAST SYSTEM
(NAEFS) AND THE REFORECAST-CALIBRATED GLOBAL ENSEMBLE FORECAST SYSTEM (GEFS)
FOR THE SECOND WEEK, THE ECMWF ENSEMBLE PREDICTION SYSTEM FORECASTS FOR THE
THIRD AND FOURTH WEEK, AND THE NCEP CLIMATE FORECAST SYSTEM (CFS) FOR THE FULL
MONTH.



THE UPDATE TO THE AUGUST TEMPERATURE OUTLOOK INDICATES ONLY SMALL CHANGES TO
THE TEMPERATURE PATTERN RELATIVE TO THE HALF-MONTH LEAD OUTLOOK. ENHANCED
PROBABILITIES OF BELOW-NORMAL TEMPERATURES OVER THE SOUTHWEST EXTEND FURTHER
NORTHWARD INTO THE CENTRAL ROCKIES AND NORTHERN PLAINS FOLLOWING CHANGES IN
DYNAMICAL MODEL GUIDANCE. GUIDANCE ALSO INDICATES INCREASING LIKELIHOODS OF
ABOVE-NORMAL TEMPERATURES FOR AN EXPANDED AREA OF EAST TEXAS AND THE SOUTHEAST.



THE UPDATE TO THE AUGUST PRECIPITATION OUTLOOK SHOWS ONLY SMALL CHANGES IN THE
PREDICTED PRECIPITATION PATTERN COMPARED TO THE HALF-MONTH LEAD OUTLOOK. A
LARGE AREA WITH ENHANCED PROBABILITIES OF ABOVE-MEDIAN PRECIPITATION FROM THE
SOUTHWEST NORTHWARD INTO THE CENTRAL ROCKIES AND EASTWARD ACROSS THE CENTRAL
PLAINS TO THE MISSISSIPPI RIVER EXTENDS FARTHER TO THE NORTH IN THE UPDATED
OUTLOOK AS INDICATED BY MOST DYNAMICAL MODEL GUIDANCE, INCLUDING THE CFS. AN
AREA OF ENHANCED PROBABILITIES OF BELOW-MEDIAN PRECIPITATION WAS REMOVED FROM
THE PACIFIC NORTHWEST IN THE UPDATED OUTLOOK, AS MODEL GUIDANCE FOR THE FIRST
TWO WEEKS OF AUGUST FORECASTS INCREASED PRECIPITATION AMOUNTS. AN AREA OF
ENHANCED PROBABILITIES OF BELOW-MEDIAN PRECIPITATION FOR SOUTH FLORIDA WAS
REMOVED FOLLOWING MODEL GUIDANCE FOR THE MONTH.



BELOW IS THE DISCUSSION FROM THE HALF-MONTH LEAD, AUGUST, MONTHLY FORECAST
ISSUED JULY 16, 2015.



SEA SURFACE TEMPERATURES (SSTS) ARE CURRENTLY MORE THAN ONE DEGREE C ABOVE
NORMAL ALONG THE EQUATOR IN THE PACIFIC OCEAN FROM THE SOUTH AMERICAN COAST
WESTWARD TO JUST WEST OF THE INTERNATIONAL DATE LINE. SST ANOMALIES ARE GREATER
THAN +2.0 DEGREES C IN THE EAST PACIFIC FROM ABOUT 130 W LONGITUDE TO THE SOUTH
AMERICAN COAST. ABOVE NORMAL SSTS EXTEND NORTHWARD FROM THE EQUATOR TO COVER AN
EXTENSIVE AREA OF THE NORTH PACIFIC TO THE WEST OF NORTH AMERICA. SUBSURFACE
OCEAN WATER TEMPERATURES TO A DEPTH OF ABOUT 100 METERS ARE CONSIDERABLY ABOVE
NORMAL THROUGHOUT THE EASTERN EQUATORIAL PACIFIC OCEAN.  RECENT ATMOSPHERIC
OBSERVATIONS OVER THE EASTERN AND CENTRAL TROPICAL PACIFIC OCEAN SUGGEST STRONG
OCEAN-ATMOSPHERE COUPLING, WITH UNUSUALLY ACTIVE CONVECTION ACROSS THE CENTRAL
AND EAST-CENTRAL EQUATORIAL PACIFIC TOGETHER WITH LARGE SCALE WESTERLY WIND
ANOMALIES AT LOW LEVELS OVER THE WEST AND CENTRAL PACIFIC. ATMOSPHERIC AND
OCEANIC CONDITIONS SUGGEST CONTINUED STRENGTHENING OF EL NINO CONDITIONS.
STATISTICAL AND DYNAMICAL SST FORECASTS INDICATE EL NINO CONDITIONS WILL
PERSIST THROUGH WINTER, AND ANOMALIES IN SST ARE LIKELY TO GROW INTO THE
BEGINNING OF WINTER AS THE CLIMATOLOGY OF SST COOLS. EL NINO IS LIKELY
CONTRIBUTING TO RECENT CLIMATE ANOMALIES OVER NORTH AMERICA AND IS EXPECTED TO
HAVE AN INFLUENCE ON CLIMATE ANOMALIES IN AUGUST.



CLIMATE MODEL FORECASTS FROM THE LAST FEW MONTHS HAVE SHOWN CONSISTENT NORTH
AMERICAN SURFACE TEMPERATURE AND PRECIPITATION ANOMALY PATTERNS. MODEL
PREDICTIONS AGREE REASONABLY WELL WITH THE TEMPERATURE AND PRECIPITATION
ANOMALIES ASSOCIATED WITH PAST EL NINO EVENTS, ALTHOUGH THE AVERAGE OF CLIMATE
MODELS CONTRIBUTING TO THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) IS
SUBSTANTIALLY WARMER ACROSS THE NORTHERN U.S. FROM THE NORTHERN ROCKIES INTO
THE NORTHEAST. THE CLIMATE FORECAST SYSTEM (CFS) FORECAST FOR AUGUST APPEARS IN
CLOSER AGREEMENT WITH ANOMALIES ASSOCIATED WITH EL NINO IMPACTS. THE CLIMATE
OUTLOOK FOR AUGUST 2015 IS BASED PRIMARILY ON FORECASTS FROM CLIMATE MODELS OF
THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME) AND REGRESSIONS OF NORTH
AMERICAN SURFACE TEMPERATURE AND PRECIPITATION TO THE NINO 3.4 INDEX.



THE FORECAST PREDICTS ELEVATED PROBABILITIES OF ABOVE-NORMAL TEMPERATURES FOR
THE U.S. WEST AND ALASKA. BELOW NORMAL TEMPERATURES ARE MORE LIKELY IN AREAS
THAT HAVE OBSERVED RECENT ABOVE AVERAGE RAINFALL SUCH AS THE SOUTHERN ROCKY
MOUNTAINS AND CENTRAL PLAINS. THIS SIGNAL IS LIKELY IN PART ASSOCIATED WITH
ABOVE AVERAGE SOIL MOISTURE AND INCREASED CHANCES OF CONTINUING ANOMALOUSLY WET
SOILS IN THE NEXT MONTH. THERE IS CONSENSUS AMONG CLIMATE ENSEMBLE MODELS FOR
ABOVE NORMAL TEMPERATURES ALONG THE GULF COAST, THE SOUTH ATLANTIC COAST AND
NORTHERN NEW ENGLAND.



THERE CONTINUES TO BE CONSENSUS AMONG CLIMATE ENSEMBLE MODELS FOR ABOVE-MEDIAN
PRECIPITATION AMOUNTS OVER A LARGE AREA OF THE SOUTHWEST EXTENDING INTO THE
CENTRAL PLAINS. ENHANCED TROPICAL STORM ACTIVITY IN THE EASTERN PACIFIC IS
LIKELY TO CONTINUE TO PROVIDE ANOMALOUS ATMOSPHERIC MOISTURE TO THE U.S.
SOUTHWEST. CLIMATE MODELS PREDICT ENHANCED PROBABILITIES OF ABOVE MEDIAN
PRECIPITATION AS A NORTHWARD EXTENSION OF A LARGE AREA OF ABOVE MEDIAN RAINFALL
OVER THE TROPICAL EASTERN PACIFIC OCEAN. REGRESSIONS OF PRECIPITATION AGAINST
THE NINO 3.4 INDEX INDICATE ABOVE-MEDIAN PRECIPITATION OVER A LARGE AREA OF THE
CENTRAL CONUS AND BELOW-MEDIAN PRECIPITATION OVER A LARGE AREA OF THE CARIBBEAN
EXTENDING INTO PARTS OF THE SOUTHERN FLORIDA PENINSULA AND THE GULF COAST OF
TEXAS AND LOUISIANA. THIS PATTERN OF PRECIPITATION ANOMALIES IS CONSISTENT IN
THE CONSENSUS OF CLIMATE MODELS FROM THE NMME. THERE IS ALSO CONSENSUS AMONG
THE NMME MODELS FOR BELOW MEDIAN PRECIPITATION OVER PARTS OF THE PACIFIC
NORTHWEST.



IN AREAS WHERE THERE ARE NO STATISTICALLY SIGNIFICANT CLIMATE SIGNALS, SUCH
THAT THE LIKELIHOODS OF MONTHLY MEAN TEMPERATURES OR MONTHLY ACCUMULATED
PRECIPITATION AMOUNTS ARE EQUAL 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.



THE NEXT MONTHLY OUTLOOK...FOR SEP ... WILL BE ISSUED ON THU AUG 20 2015


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

$$


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