415  
FXUS07 KWBC 311902  
PMD30D  
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:  
 
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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.  
 

 
 
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