Prognostic Meteorological Discussion
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000 FXUS07 KWBC 301900 PMD30D PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300PM EDT TUESDAY JUN 30 2015 30-DAY OUTLOOK DISCUSSION FOR JULY 2015 THIS UPDATE TO THE 30-DAY OUTLOOK FOR JULY, 2015 IS BASED SUBSTANTIALLY ON INFORMATION FROM SHORT-TERM WEATHER FORECASTS FOR THE FIRST 14 DAYS OF THE MONTH. ENSEMBLE FORECASTS FROM THE GEFS, CANADIAN, AND ECMWF MODELS SHOW GOOD CONSENSUS ON THE UPPER LEVEL CIRCULATION PATTERNS EXPECTED IN EARLY JULY. THE ASSOCIATED SURFACE TEMPERATURE AND PRECIPITATION PATTERNS AGREE WELL WITH THE JULY OUTLOOK ISSUED IN MID-JUNE. EL NINO CONDITIONS HAVE MAINTAINED AMPLITUDE IN RECENT WEEKS AND CONTINUE TO BE ON TRACK WITH PREDICTIONS MADE IN THE LAST MONTH OR TWO. MODELS PREDICT A MEAN RIDGE OVER WESTERN NORTH AMERICA WITH A DOWNSTREAM TROUGH FORECAST TO BE LOCATED NEAR THE EAST COAST OF THE CONUS DURING THE FIRST TWO WEEKS OF JULY. THE GEFS PERSISTS THESE FEATURES INTO WEEKS 3 AND 4, ALTHOUGH THE ECMWF ENSEMBLES SUGGEST THAT THE PATTERN MAY BREAK DOWN IN THE LATTER HALF OF JULY. FORECASTS FOR THE FIRST HALF OF THE MONTH STRONGLY SUPPORT ABOVE-NORMAL TEMPERATURES OVER THE PACIFIC NORTHWEST AND ALASKA, RESULTING IN INCREASED CONFIDENCE FOR ABOVE-NORMAL MONTHLY MEAN TEMPERATURES RELATIVE TO THE OUTLOOK RELEASED IN MID-JUNE. THE EXPECTED TROUGH OVER THE EASTERN CONUS SHOULD FAVOR A COOL START TO THE MONTH FROM THE UPPER MISSISSIPPI VALLEY TO PARTS OF THE NORTHEAST, RESULTING IN A NORTHEASTWARD EXTENSION OF THE AREA OF ENHANCED CHANCES FOR BELOW-NORMAL TEMPERATURES INDICATED ON THE PREVIOUS OUTLOOK FOR JULY. OTHERWISE THE REVISED TEMPERATURE OUTLOOK IS FAIRLY SIMILAR TO THE OUTLOOK ISSUED AT MID-MONTH. THE PRECIPITATION OUTLOOK IS HEAVILY INFLUENCED BY THE PRECIPITATION EXPECTED IN THE FIRST WEEK OF THE MONTH. THE FOLLOWING CHANGES HAVE BEEN MADE TO THE JULY, 2015 OUTLOOK ISSUED AT MID-MONTH. FORECASTS FOR THE FIRST FEW DAYS OF THE MONTH INDICATE GOOD CHANCES FOR WET CONDITIONS FROM THE TENNESSEE VALLEY TO PARTS OF THE NORTHEAST. THIS PROMPTED AN ADJUSTMENT OF THE AREA FAVORING ABOVE-MEDIAN MONTHLY TOTAL PRECIPITATION EASTWARD TO THOSE REGIONS. THE CHANCES FOR BELOW-MEDIAN PRECIPITATION APPEAR SOMEWHAT HIGHER FOR PARTS OF EASTERN TEXAS THAN THEY DID ON THE OUTLOOK ISSUED A FEW WEEKS AGO ACCORDING TO THE SHORT-TERM FORECASTS, EXCEPT FOR EXTREME SOUTHERN PARTS OF THE STATE WHERE SOME PRECIPITATION IS EXPECTED EARLY IN THE MONTH. SHORT-TERM FORECAST FAVOR ABOVE-MEDIAN RAINFALL THROUGHOUT MUCH OF THE WEST, EXCEPT FOR THE NORTHERN ROCKIES AND THE PACIFIC NORTHWEST. THIS LEADS TO A SLIGHT WESTWARD EXPANSION OF THE AREA FAVORING ABOVE-MEDIAN PRECIPITATION AMOUNTS INTO WESTERN NEVADA. AN EXPECTED DRY START TO THE MONTH INCREASES CHANCES FOR BELOW-MEDIAN MONTHLY PRECIPITATION TOTALS IN PARTS OF THE PACIFIC NORTHWEST. MODELS SUGGEST SOME RIDGING OVER ALASKA IN THE EARLY PART OF THE MONTH, ELEVATING CHANCES FOR BELOW-MEDIAN PRECIPITATION IN SOUTHEASTERN PART OF THE STATE. BELOW IS THE DISCUSSION ISSUED WITH THE OUTLOOK ISSUED IN MID-JUNE. SEA SURFACE TEMPERATURES (SSTS) IN EARLY JUNE ARE CURRENTLY MORE THAN ONE DEGREE C ABOVE NORMAL ALONG THE EQUATOR IN THE PACIFIC OCEAN FROM THE SOUTH AMERICAN COAST WESTWARD TO JUST EAST OF THE INTERNATIONAL DATE LINE. WITHIN THIS AREA THERE ARE SOME PLACES WERE THE SST ANOMALIES ARE OVER +2.0 DEGREES C. ABOVE NORMAL SSTS EXTEND NORTHWARD FROM THE EQUATOR TO COVER AN EXTENSIVE AREA TO THE WEST OF NORTH AMERICA. SUBSURFACE OCEAN WATER TEMPERATURES ARE ALSO 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 TOGETHER WITH LARGE SCALE WESTERLY WIND ANOMALIES AT LOW LEVELS, AND EASTERLY ANOMALIES AT UPPER LEVELS. TOGETHER THESE SUGGEST THE DEVELOPMENT OF MODERATE STRENGTH EL NINO CONDITIONS. STATISTICAL AND DYNAMIC MODELS FOR SST PREDICTION SUGGEST THAT THE EL NINO CONDITIONS WILL PERSIST OR STRENGTHEN IN THE COMING MONTHS. EL NINO APPEARS TO BE CONTRIBUTING TO CLIMATE ANOMALIES OVER PARTS OF NORTH AMERICA IN THE PAST MONTH OR TWO, AND ARE EXPECTED TO CONTINUE TO HAVE AN INFLUENCE IN JULY. DYNAMICAL MODEL FORECASTS INITIALIZED IN THE LAST FEW MONTHS HAVE SHOWN CONSIDERABLE CONSISTENCY IN THEIR PREDICTIONS FOR NORTH AMERICAN SURFACE TEMPERATURE AND PRECIPITATION. THEIR PREDICTIONS HAVE BEEN QUITE SUCCESSFUL IN SUGGESTING ELEVATED ODDS OF WET CONDITIONS IN MUCH OF WESTERN AND CENTRAL CONUS IN THE LATE SPRING. THE MODEL PREDICTIONS AGREE REASONABLY WELL WITH THE TEMPERATURE AND PRECIPITATION ANOMALIES OBSERVED IN ASSOCIATION WITH PAST EL NINOS. THUS, THE OUTLOOK FOR JULY 2015 IS BASED HEAVILY ON THE FORECAST FROM THE CFSV2, AND PROBABILITIES FROM THE MODEL CONSENSUS OF CLIMATE MODELS RUN AS PART OF THE NMME AND IMME. THE FORECAST SUGGESTS ELEVATED CHANCES OF ABOVE-NORMAL TEMPERATURES IN THE WESTERN CONUS AND ALASKA. BELOW NORMAL TEMPERATURES ARE FAVORED IN AREAS THAT HAVE EXPERIENCED RECENT SURPLUS RAINFALL IN THE CENTRAL AND SOUTHERN PORTIONS OF THE ROCKY MOUNTAINS AND GREAT PLAINS, INCLUDING MUCH OF TEXAS. THIS AREA IS LIKELY ASSOCIATED WITH THE COOLING EFFECTS OF ABOVE AVERAGE SOIL MOISTURE, TOGETHER WITH INCREASED CHANCES FOR A CONTINUATION OF RELATIVELY WET CONDITIONS IN THE NEXT MONTH. THERE IS A FAIR CONSENSUS AMONG CLIMATE MODELS FOR ABOVE NORMAL TEMPERATURES IN THE EASTERN CONUS, HOWEVER THE CONFIDENCE IS LOW CONSIDERING THAT PAST EL NINO SUMMERS GENERALLY FAVOR COOL CONDITIONS FOR MUCH OF THE EAST AND NORTH CENTRAL CONUS. THE AREA FAVORING ABOVE NORMAL TEMPERATURES WAS RESTRICTED TO AREAS EAST OF THE APPALACHAIN MOUNTAINS WHERE THE YEAR-TO-YEAR TEMPERATURE VARIABILITY IS LOWER IN RELATION TO POSSIBLE CLIMATE SIGNALS. THERE CONTINUES TO BE A STRONG CONSENSUS AMONG MODELS FOR ABOVE-MEDIAN PRECIPITATION AMOUNTS OVER A WIDE AREA OF THE CENTRAL AND WESTERN CONUS. SOME EARLY TROPICAL STORM ACTIVITY HAS ALREADY BEEN OBSERVED IN EARLY JUNE IN THE EASTERN PACIFIC OFF THE COAST OF MEXICO, AND HAS BEEN CONTRIBUTING TO ANOMALOUS MOISTURE IN PARTS OF THE WESTERN CONUS. MODEL FORECASTS SUGGEST A CONTINUATION OF ENHANCED CHANCES OF ABOVE MEDIAN PRECIPITATION THAT APPEARS AS A NORTHWARD EXTENSION OF A LARGE AREA OF FORECAST ABOVE MEDIAN RAINFALL IN THE TROPICAL EASTERN PACIFIC. ENSO COMPOSITES GENERALLY FAVOR A WEAK SOUTHWEST MONSOON IN THE WESTERN PART OF THE MONSOON REGION, SO THE MODEL FORECASTS FOR ABOVE MEDIAN PRECIPITATION AMOUNTS IN ARIZONA MAY DEPEND ON HIT-OR-MISS RESIDUAL MOISTURE FROM TROPICAL STORMS, AND AS SUCH MAY BE UNRELIABLE IN WESTERN REGIONS OF THE DESERT SOUTHWEST. THE CFSV2 MODEL INDICATES BELOW MEDIAN PRECIPITATION FOR SOUTH TEXAS EXTENDING INTO PARTS OF THE SOUTHEASTERN CONUS. THIS AREA SEEMS A REASONABLE EXTENSION OF DRY CONDITIONS EXPECTED OVER THE CARIBBEAN IN EL NINO SUMMERS, HOWEVER MODEL CONSENSUS IN THE EASTERN PART OF THE AREA AND IN FLORIDA WAS LOW. THERE IS ALSO SOME WEAK CONSENSUS AMONG THE NMME FOR BELOW MEDIAN PRECIPITATION AMOUNTS OVER PARTS OF THE ALASKA PANHANDLE. 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: 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 AUG ... WILL BE ISSUED ON THU JUL 16 2015 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$

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