067  
FXUS07 KWBC 181231  
PMD30D  
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
830 AM EDT THU OCT 18 2018  
 
30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2018  
 
FORECASTS OF AUTUMN CLIMATE ARE ESPECIALLY DIFFICULT, AND THE NOVEMBER 2018  
OUTLOOK IS NO EXCEPTION. LOW-FREQUENCY CLIMATE FORCING FROM ENSO IS EXPECTED TO  
GRADUALLY INCREASE DURING THE NEXT SEVERAL WEEKS, THOUGH THIS HAS LIMITED  
APPLICATIONS TO THE CURRENT OUTLOOK, ESPECIALLY WITH RESPECT TO TEMPERATURE.  
THE MJO HAS BEEN ACTIVE OVER THE PAST SEVERAL WEEKS, BUT IS NOT EXPECTED TO  
PLAY A MAJOR ROLE DURING NOVEMBER - THIS IS DUE TO BOTH UNCERTAIN MJO FORCING  
ITSELF AS WELL AS ONLY MODEST EXTRATROPICAL TELECONNECTIONS AT THIS POINT IN  
THE SEASONAL CYCLE. THE FORECAST IS THEREFORE INFORMED FIRSTLY BY A BLEND OF  
CALIBRATED DYNAMICAL GUIDANCE FROM THE NMME AND STATISTICAL GUIDANCE THAT  
LARGELY UTILIZES LONG-TERM TRENDS. THIS IS AUGMENTED BY ADDITIONAL DYNAMICAL  
GUIDANCE FROM THE ECMWF, THE WEEKS 3-4 GUIDANCE, AND THE CURRENT EVOLUTION OF  
DYNAMICAL MODEL FORECASTS THROUGH THE EXTENDED RANGE (~DAYS 10-16) PERIOD.  
 
LONG-TERM TRENDS GENERALLY FAVOR ABOVE-NORMAL TEMPERATURES OVER MUCH OF THE  
CONUS DURING THIS TIME OF YEAR, STRETCHING FROM THE SOUTHWEST TO THE NORTHEAST,  
WITH RELATIVE WEAKNESSES IN THE NORTHWEST AND SOUTHEAST, RESPECTIVELY. AT THIS  
POINT, ENSO TELECONNECTIONS ARE NOT A MAJOR PLAYER IN THE TEMPERATURE FORECAST  
FOR TWO REASONS: THE CONVECTIVE RESPONSE TO THE DEVELOPING ENSO EVENT HAS BEEN  
SLOW TO EMERGE TO THIS POINT, AND EVEN IN THE PRESENCE OF A SUBSTANTIAL EVENT  
THE SIGNAL-TO-NOISE RATIO IS QUITE LOW FOR NOVEMBER (CORRELATIONS NEAR OR LESS  
THAN 0.2). THE CALIBRATED NMME MODEL OUTPUT FAVORS ABOVE-NORMAL TEMPERATURES  
OVER NEARLY ALL OF NORTH AMERICA, WITH THE LOWEST PROBABILITIES OVER THE  
SOUTHEASTERN QUARTER OF THE CONUS. THE CFS HAS CONSISTENTLY BEEN FORECASTING  
ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE CONUS AND MUCH OF ALASKA, WITH  
BELOW-NORMAL TEMPERATURES CONFINED TO MUCH OF NORTHEASTERN CANADA. THE  
AFOREMENTIONED FACTORS POINT TO AN INITIAL 'FIRST GUESS' THAT FAVORS ENHANCED  
PROBABILITIES OF ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE FORECAST DOMAIN,  
WITH THE HIGHEST PROBABILITIES OVER NORTHERN AND WESTERN ALASKA AND PARTS OF  
THE WESTERN CONUS. HOWEVER, PROBABILITIES ARE TEMPERED BY TWO MAIN FACTORS OVER  
THE CENTRAL AND EASTERN U.S. FIRST, THE ECMWF IN BOTH ITS LONG-RANGE ENSEMBLE  
SYSTEM AND EXTENDED RANGE (WEEKS 3-4) SYSTEM FAVOR NEAR- TO BELOW-NORMAL  
TEMPERATURES CENTERED OVER THE CENTRAL AND SOUTHEASTERN CONUS, AND RUN-TO-RUN  
CONTINUITY HAS BEEN GOOD IN THIS REGARD. SECONDLY, THIS APPEARS SUPPORTED BY A  
FORECAST PATTERN CHANGE OVER THE HIGH LATITUDES TOWARD A NEGATIVE PHASE OF THE  
NAO/AO DURING THE NEXT WEEK TO 10 DAYS. THE LATEST EVOLUTION OF THE GEFS FROM  
DAYS 11 TO 16 FAVORS A CONTINUATION OF POSITIVE HEIGHT ANOMALIES OVER NORTHERN  
LATITUDES AND ANOMALOUS TROUGHING SOMEWHERE OVER THE CENTRAL/EASTERN CONUS  
HEADING INTO THE VERY BEGINNING OF NOVEMBER. THESE COMPOUNDING FACTORS LEAD TO  
A REDUCTION IN PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES OVER MOST OF  
THE CENTRAL AND EASTERN CONUS. HOWEVER, GIVEN THE LARGE SCALE CLIMATE FACTORS  
AT PLAY, THEY ARE NOT SUFFICIENT TO REVERSE THE SIGN OF THE EXPECTED CLIMATE  
ANOMALIES.  
 
THE PRECIPITATION FORECAST FOR NOVEMBER 2018 HAS MUCH REDUCED COVERAGE COMPARED  
TO THE TEMPERATURE OUTLOOK, AS IS EXPECTED GIVEN THE LIMITED PREDICTABILITY FOR  
THIS TYPE OF FORECAST. THE FORECAST IS INFORMED BY THE DYNAMICAL MODEL  
CONSENSUS AND NINO 3.4 REGRESSIONS, WHICH JUST ABOUT REVEAL THE SAME GENERAL  
PATTERN. ABOVE-MEDIAN PRECIPITATION IS FAVORED OVER PARTS OF THE SOUTHERN TIER  
OF THE CONUS AS WELL AS MUCH OF ALASKA. A MODEST AREA DEPICTING BELOW-MEDIAN  
PRECIPITATION IS INDICATED OVER THE PACIFIC NORTHWEST AND NORTHERN ROCKIES.  
AREAS SHOWN IN WHITE LABELED EC DEPICT A FORECAST WHERE THE PROBABILITIES FOR  
EITHER OF THREE CATEGORIES, BELOW-, NEAR- OR ABOVE-MEDIAN MONTHLY TOTAL  
PRECIPITATION ARE NOT SIGNIFICANTLY DIFFERENT FROM CLIMATOLOGICAL PROBABILITIES.  
 
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 WED OCTOBER 31 2018  
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.  

 
 
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