PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300 PM EDT WED AUG 31 2016 30-DAY OUTLOOK DISCUSSION FOR SEPTEMBER 2016 THE UPDATES TO THE OUTLOOKS FOR TEMPERATURE AND PRECIPITATION FOR SEPTEMBER 2016 ARE BASED ON RECENT DYNAMICAL GUIDANCE, AS WELL AS THE LATEST OFFICIAL OUTLOOKS FROM CPC, WPC, AND NHC. SIGNIFICANT UNCERTAINTY EXISTS NOT ONLY TOWARD THE END OF THE OUTLOOK PERIOD (WEEKS 3 AND 4), BUT ALSO IN THE SHORT-TERM DUE TO THE IMPACT OF TROPICAL CYCLONE ACTIVITY NEAR AND OVER THE EASTERN CONUS. RECENT OUTPUTS FROM DYNAMICAL MODELS SUGGEST A WARM FIRST HALF OF THE MONTH FOR SEPTEMBER, WITH THE HIGHEST ODDS OVER THE NORTHEAST. DUE TO THE PROJECTED PATH OF THE TROPICAL CYCLONE CURRENTLY OVER THE GULF OF MEXICO, UNCERTAINTY IS ELEVATED OVER THE NORTHEAST, OTHERWISE THE ODDS FOR ABOVE NORMAL TEMPERATURES WOULD BE HIGHER. WEST OF THE PATH OF THE RAINS ASSOCIATED WITH THE TROPICAL CYCLONE, DRY CONDITIONS SHOULD CONTRIBUTE TO ABOVE NORMAL TEMPERATURES OVER THE INTERIOR SOUTHEAST. THROUGH WEEK-2, GUIDANCE SUGGESTS ENHANCED ODDS FOR BELOW NORMAL TEMPERATURES OVER THE NORTHERN ROCKIES, SO ENHANCED ODDS OF ABOVE NORMAL TEMPERATURES ON THE MONTHLY MAP HAVE BEEN REMOVED FROM THAT REGION. RECENT REDUCTION IN SSTS NEAR NORTHERN ALASKA REDUCE THE ODDS FOR ABOVE NORMAL TEMPERATURES FOR THE NORTHERN SLOPE, WHILE SSTS WELL ABOVE NORMAL NEAR SOUTHWESTERN ALASKA STILL FAVOR ABOVE NORMAL TEMPERATURES THERE. MODEL FORECASTS AND OFFICIAL FORECASTS FROM NHC INDICATE THE GREATEST IMPACTS FROM TROPICAL ACTIVITY ARE LIKELY FROM FLORIDA TO THE NORTHEAST, THEREFORE ODDS FOR ABOVE MEDIAN PRECIPITATION ARE ENHANCED FOR THAT REGION. THE AREA WHERE BELOW MEDIAN PRECIPITATION IS FAVORED OVER THE INTERIOR SOUTHEAST AT THE MID-MONTH OUTLOOK IS SHIFTED NORTHWESTWARD. MODEL GUIDANCE AND OFFICIAL OUTLOOKS IN THE SHORT TERM AND THROUGH WEEK-2 INDICATE ENHANCED ODDS FOR HEAVY PRECIPITATION OVER THE NORTHERN GREAT PLAINS AND MIDWEST, SO THAT AREA WAS ADDED TO THE OUTLOOK. SHORT-TERM GUIDANCE FAVORS SOME MODERATE PRECIPITATION OVER THE PACIFIC NORTHWEST, INCREASING UNCERTAINTY ABOUT MONTHLY TOTALS, SO THE AREA OF BELOW MEDIAN PRECIPITATION WAS TRIMMED OUT OF MOST OF WASHINGTON. ----------- PREVIOUS MESSAGE FROM AUGUST 18 IS BELOW ------------ THE SEPTEMBER 2016 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL MODEL GUIDANCE AND, TO A LESSER EXTENT, STATISTICAL TOOLS. THE IMPACT OF CURRENT SOIL MOISTURE CONDITIONS ON THE TEMPERATURES DURING THE FOLLOWING MONTH BEGINS TO WANE IN THE AUTUMN, BUT THERE IS STILL A RESPECTABLE CORRELATION OVER THE SOUTHERN GREAT PLAINS BETWEEN AUGUST SOIL MOISTURE AND SEPTEMBER TEMPERATURES. ENSO IS NOW IN ITS NEUTRAL PHASE ACROSS THE TROPICAL PACIFIC. LA NINA IS SLIGHTLY FAVORED TO DEVELOP DURING AUGUST - OCTOBER 2016, WITH ABOUT A 55-60% CHANCE OF LA NINA DURING THE FALL AND WINTER 2016-17. PLEASE REFER TO THE ENSO DIAGNOSTIC DISCUSSION AT: HTTP://WWW.CPC.NCEP.NOAA.GOV/PRODUCTS/ANALYSIS_MONITORING/ENSO_ADVISORY/ FOR A MORE DETAILED ANALYSIS OF ENSO CONDITIONS ACROSS THE EQUATORIAL PACIFIC. DURING THE FIRST HALF OF AUGUST, ABOVE AVERAGE CONVECTION HAS DEVELOPED OVER THE WESTERN PACIFIC, WITH MULTIPLE TROPICAL CYCLONES FORMING. MOST MJO INDICES HAVE AMPLIFIED IN A DIRECTION INDICATING ENHANCED CONVECTION OVER THE WESTERN PACIFIC. GOING FORWARD, MOST MODELS CONTINUE TO INDICATE CONVECTION OVER THE WESTERN PACIFIC, WHICH COULD HAVE A DOWNSTREAM IMPACT ON THE CIRCULATION OVER NORTH AMERICA, ALTHOUGH THAT CONNECTION IS MORE ROBUST LATER IN THE MONTH BECAUSE OF THE DYNAMICS OF THE SEASONAL PROGRESSION OF THE EAST ASIAN JET STREAM. DYNAMICAL MODELS ARE LIKELY THE BEST TOOLS TO CAPTURE THIS POTENTIAL IMPACT. THEREFORE, THE OUTLOOKS RELY PRIMARILY UPON THE LATEST DYNAMICAL MODEL GUIDANCE FROM THE NCEP CLIMATE FORECAST SYSTEM (CFS), THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME), THE INTERNATIONAL MULTI-MODEL ENSEMBLE (IMME), AND MODEL GUIDANCE FOR WEEKS 3 AND 4 FROM THE CFS, JAPAN METEOROLOGICAL AGENCY (JMA), AND ECMWF, WITH LESSER INPUTS FROM TOOLS BASED ON CURRENT SOIL MOISTURE CONDITIONS. MOST DYNAMICAL MODELS FROM THE NMME SUITE INDICATE GENERALLY ABOVE AVERAGE TEMPERATURES FOR SEPTEMBER 2016. ANY AREAS WHERE NEAR OR BELOW AVERAGE CONDITIONS ARE INDICATED ARE OVER THE CENTRAL PORTIONS OF THE CONUS. CURRENTLY HIGH SOIL MOISTURE OVER THE SOUTHERN GREAT PLAINS WOULD FAVOR NEAR TO BELOW AVERAGE TEMPERATURES OVER THAT REGION, WHILE UNCERTAINTY AMONG THE MODELS (NMME AND IMME) PROHIBITS THE DEPICTION OF A SIGNAL FROM THE NORTHERN GREAT PLAINS TO THE GREAT LAKES REGION. MORE AGREEMENT RETURNS OVER THE NORTHEAST, WHERE TOOLS INDICATE ABOVE AVERAGE TEMPERATURES ARE FAVORED, AND OVER THE WESTERN CONUS FROM THE ROCKIES TO THE WEST COAST, WHERE MODELS AND TRENDS FAVOR ABOVE AVERAGE TEMPERATURES. SSTS 1.5-3.5 DEGREES C ABOVE AVERAGE IN THE VICINITY OF ALASKA FAVOR ABOVE AVERAGE TEMPERATURES FOR SOUTHERN AND WESTERN ALASKA, WHILE TRENDS FAVOR ABOVE AVERAGE TEMPERATURES FOR THE NORTH SLOPE. THE PRECIPITATION OUTLOOK FOR SEPTEMBER CONTAINS A HIGH AMOUNT OF UNCERTAINTY. MODEL SIGNALS ARE SPARSE IN COVERAGE, AND WEAK EVEN WHERE SIGNALS PASS THROUGH THE CALIBRATION METHODS. TRENDS FAVOR BELOW AVERAGE PRECIPITATION OVER THE SOUTHWEST WHILE MOST MODELS IN THE NMME SUITE FAVOR ABOVE AVERAGE PRECIPITATION. THE OFFICIAL OUTLOOK FAVORS ABOVE AVERAGE PRECIPITATION, BUT OVER A SMALLER AREA THAN WHAT THE DYNAMICAL MODELS INDICATE TO ACCOUNT FOR THE UNCERTAINTY RAISED BY CONFLICTING GUIDANCE. OVER THE NORTHERN GREAT PLAINS, ABOUT HALF OF THE MODELS DEPICT ABOVE AVERAGE PRECIPITATION AND TRENDS FROM THE SEASONAL OPTIMAL CLIMATE NORMALS HAVE LITTLE TO NO SIGNAL, SO NO SIGNAL IS DEPICTED. TRENDS AND MODELS DEPICT BELOW AVERAGE PRECIPITATION FOR THE NORTHWEST AND FROM THE SOUTHERN GREAT PLAINS TO THE SOUTHEAST. MODEL FORECASTS SUPPORT ABOVE AVERAGE PRECIPITATION FOR SOUTHERN ALASKA, ALTHOUGH THEY VARY IN WHERE THE HIGHEST AMOUNTS ARE LIKELY TO OCCUR, SO THE OFFICIAL FORECAST COVERS ALL OF THE AREAS WHERE THE NMME MODELS FAVOR ABOVE AVERAGE PRECIPITATION. FORECASTER: MATTHEW ROSENCRANS 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 OCT ... WILL BE ISSUED ON THU SEP 15 2016 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$