PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300 PM EDT TUE OCT 31 2017 30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2017 THE UPDATED NOVEMBER OUTLOOK SHARES MANY SIMILARITIES WITH THE 0.5-MONTH LEAD OUTLOOK FROM EARLIER IN THE MONTH, SUGGESTING THAT THE BROAD LOW-FREQUENCY PATTERN FAVORED IN THE ORIGINAL OUTLOOK IS CONSISTENT WITH THE FORECAST EVOLUTION OVER THE NEXT FEW WEEKS. THE MJO HAS BEEN ACTIVE, AND THE RECENT EVOLUTION OVER THE NORTH PACIFIC AND FORECAST EVOLUTION OVER THE NEXT SEVERAL DAYS OVER NORTH AMERICA IS CONSISTENT WITH WHAT ONE WOULD EXPECT FROM MJO FORCING. HOWEVER THE MJO IS FORECAST TO BREAK DOWN AND NO LONGER PROJECT ONTO A FAVORABLE TROPICAL FORCING PATTERN DURING THE NEXT WEEK, LIMITING ITS USEFULNESS AT THIS TIME. A HIGH-AMPLITUDE PATTERN IS FORECAST EARLY IN THE PERIOD, WITH ANOMALOUS RIDGING (TROUGHING) FAVORED OVER PARTS OF THE NORTH PACIFIC (WEST-CENTRAL CANADA). THIS PATTERN FAVORS THE DEVELOPMENT OF COLD, CONTINENTAL AIR MASSES OVER WESTERN CANADA WHICH IN TURN ARE EXPECTED TO SURGE SOUTHWARD INTO THE NORTHERN ROCKIES AND NORTHERN HIGH PLAINS. THE MEAN FRONTAL ZONE IS FORECAST TO RESIDE NEAR THE GREAT LAKES, EXTENDING SOUTHWESTWARD FROM THERE. AS A RESULT A GENERAL COLD NORTHWEST-WARM SOUTHEAST PATTERN IS DEPICTED WITH FAIRLY HIGH CONFIDENCE GIVEN THE HIGH-AMPLITUDE PATTERN FORECAST DURING THE FIRST TWO WEEKS OF THE MONTH. THIS PATTERN PROJECTS STRONGLY ONTO THE WINTERTIME PNA PATTERN (NEGATIVE PHASE), AND A POSITIVE AO/NAO PATTERN IS FAVORED BY VARIOUS MODELS EARLY IN THE MONTH. THE LATEST WEEK 3-4 GUIDANCE FROM THE CFS AND ECMWF ARE IN BROAD AGREEMENT DEPICTING A CONTINUED TILT TOWARD BELOW-NORMAL TEMPERATURES OVER THE NORTHWEST, BUT DIFFER FARTHER EAST. THE ECMWF FAVORS NEAR-NORMAL TEMPERATURES OVER THE GREAT LAKES, FOR INSTANCE, MORE CONSISTENT WITH THE FORECAST NEGATIVE PHASE OF THE NPO-WP TELECONNECTION PATTERN THROUGH THE FIRST TWO-THIRDS OF THE MONTH. THE ECMWF SOLUTION IS ALSO MORE CONSISTENT WITH THE EVOLUTION OF THE GEFS THROUGH DAY 16, AND SO IS WEIGHTED MORE IN THIS UPDATED OUTLOOK. THE PRECIPITATION OUTLOOK IS UPDATED TO REFLECT THE INCREASED CONFIDENCE GAINED FROM EARLY MONTH PRECIPITATION ACROSS PARTS OF THE WEST AND, TO LESSER EXTENT, THE OHIO VALLEY AND GREAT LAKES. BELOW-NORMAL RAINFALL IS LIKELY ACROSS MUCH OF THE SOUTHEAST AND SOUTHERN PLAINS, WITH THE VARIOUS FORECAST TOOLS LINING UP IN AGREEMENT. HIGH AMPLITUDE RIDGING OVER THE BERING SEA DURING AT LEAST THE FIRST HALF OF THE MONTH FAVORS BELOW-NORMAL PRECIPITATION FOR SOUTHERN ALASKA INCLUDING THE PANHANDLE. THE ORIGINAL NOVEMBER FORECAST DISCUSSION FOLLOWS BELOW: ---------------------------------------------------------------- THE OUTLOOK FOR NOVEMBER 2017 IS DRAWN FROM A COMBINATION OF DYNAMICAL AND EMPIRICAL FORECAST TOOLS SPANNING SUBSEASONAL TO SEASONAL TIME SCALES. THE 0.5-MONTH LEAD MONTHLY OUTLOOK IS ALWAYS CHALLENGING BECAUSE OF THE UNCERTAIN INTERPLAY BETWEEN LOW-FREQUENCY VARIABILITY AND WEEK-TO-WEEK CLIMATE VARIABILITY. THIS PROBLEM IS NOW AMPLIFIED CONSIDERING THAT AUTUMN IS A PERIOD WHEN PREDICTABILITY OF SUBSEASONAL VARIABILITY IS RELATIVELY LOW AND THE EXTRATROPICAL RESPONSE TO ENSO IS NOT YET FULLY MATURE. A FIRST PASS AT THE NOVEMBER TEMPERATURE OUTLOOK MUST CONSIDER THE COMBINED EFFECTS OF ENSO AND LONG-TERM TRENDS. THIS MONTH THERE IS CONSTRUCTIVE INTERFERENCE OVER THE SOUTHWESTERN CONUS BETWEEN WARMING TRENDS AND THE LA NINA CLIMATE FOOTPRINT. CALIBRATED DYNAMICAL GUIDANCE ALSO YIELDS THE HIGHEST PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES OVER THAT REGION, AND SO THE OFFICIAL FORECAST FAVORS ABOVE-NORMAL TEMPERATURES OVER MUCH OF THE SOUTHWESTERN CONUS. LONG-TERM TRENDS AND CALIBRATED MODEL GUIDANCE AGREE ON A SLIGHT TILT TOWARD ABOVE-NORMAL TEMPERATURES FOR PARTS OF THE NORTHEAST. OVER MUCH OF ALASKA, ESPECIALLY THE NORTH SLOPE, LONG-TERM TRENDS CONTINUE TO DOMINATE AND LEAD TO A FAIRLY CONFIDENT FORECAST IN FAVOR OF ABOVE-NORMAL TEMPERATURES. OVER A LARGE SWATH OF THE COUNTRY, HOWEVER, SPANNING FROM THE ALASKA PANHANDLE TO THE NORTHWEST TO THE MIDWEST TO THE SOUTHEAST, EQUAL CHANCES OF ABOVE-, NEAR-, AND BELOW-NORMAL TEMPERATURES ARE FORECAST. THIS IS DUE TO CONFLICTING FORECAST SIGNALS AMONG VARIOUS TOOLS. IN THE VERY SHORT TERM, A HIGH AMPLITUDE PATTERN CHANGE IS FORECAST OVER NORTH AMERICA WITH A WEST-EAST RIDGE/TROUGH PATTERN FORECAST DURING THE 6 TO 10 DAY PERIOD. THIS PATTERN CHANGE MIGHT BE AMPLIFIED BY THE FORECAST RECURVATURE AND EXTRATROPICAL TRANSITION OF TYPHOON LAN OVER THE WEST PACIFIC. THIS IS LIKELY TO LEAD TO BELOW-NORMAL TEMPERATURES FOR A TIME OVER PARTS OF THE EASTERN HALF OF THE CONUS. HOWEVER, THE LATEST EXTENDED RANGE GUIDANCE FROM THE GLOBAL ENSEMBLE SYSTEMS SUGGESTS THAT THIS PATTERN IS MORE OR LESS TRANSIENT. THE LATEST FORECASTS FROM THE CFS FAVOR ABOVE-NORMAL TEMPERATURES ACROSS MOST OF THE CONUS, INCLUDING OVER AREAS OF THE CENTRAL CONUS WHERE THE MODEL HAS CONSIDERABLE HINDCAST SKILL. ADDITIONALLY, THE LATEST WEEKS 3-4 DYNAMICAL MODEL GUIDANCE FAVORS ABOVE-NORMAL TEMPERATURES FOR THE FIRST HALF OF THE MONTH OVER MOST OF THE NORTHERN TIER OF THE CONUS, BUT SLIGHTLY FAVORS BELOW-NORMAL TEMPERATURES OVER THE SOUTHEAST. COMPLICATING MATTERS IS AN ONGOING STRONG MJO EVENT THAT IS FORECAST TO PROPAGATE OVER THE FAR WESTERN PACIFIC DURING THE COMING TWO WEEKS. AN EMPIRICAL FORECAST MODEL THAT INCORPORATES THE MJO, ENSO, AND LONG-TERM TRENDS DEPICTS BELOW-NORMAL TEMPERATURES CENTERED OVER THE UPPER MIDWEST DURING THE FIRST HALF OF NOVEMBER. THIS DISCUSSION IS PROVIDED HERE TO GIVE SOME INSIGHTS INTO THE VARIOUS CONSIDERATIONS AND CONFLICTING CLIMATE SIGNALS THAT GO INTO A EC FORECAST. THE PRECIPITATION OUTLOOK FOR NOVEMBER 2017 HAS LESS COVERAGE THAN THE TEMPERATURE FORECAST AND DRAWS MOSTLY ON THE LOW-FREQUENCY ENSO FOOTPRINT. GIVEN LARGE DISAGREEMENTS BETWEEN STATISTICAL AND DYNAMICAL GUIDANCE OVER MUCH OF THE CONUS, MODEST PROBABILITIES REFLECTING THE BACKGROUND CLIMATE STATE ARE MOST APPROPRIATE. ABOVE-NORMAL PRECIPITATION IS FAVORED OVER NORTHERN ALASKA WHICH IS CONSISTENT WITH LONG-TERM TRENDS. FORECASTER: STEPHEN BAXTER 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 DEC ... WILL BE ISSUED ON THU NOV 16 2017 THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD. $$