904  
FXUS07 KWBC 191231  
PMD30D  
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU OCT 19 2017  
 
30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2017  
 
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.  
 
AN UPDATED MONTHLY OUTLOOK... FOR NOV WILL BE ISSUED ON TUE OCTOBER 31 2017  
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.  
 

 
 
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