322  
FXUS07 KWBC 211330  
PMD30D  
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD830 AM EST THU DEC 21 2017  
 
30-DAY OUTLOOK DISCUSSION FOR JANUARY 2018  
 
THE JANUARY 2018 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON MODEL  
GUIDANCE, TYPICAL INFLUENCES OF LA NINA, LONG-TERM TRENDS, MID-LATITUDE  
VARIABILITY, AND THE POTENTIAL FOR SHORTER-TERM TROPICAL VARIABILITY (MJO), TO  
INFLUENCE THE PATTERN. LA NINA CONDITIONS CONTINUED DURING NOVEMBER 2017 AND  
ARE PREDICTED TO CONTINUE THROUGH THE OUTLOOK PERIOD. LONG-TERM TRENDS CENTERED  
ON JANUARY (DJF) SUPPORT ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHERN  
PLAINS, SOUTHWEST, CALIFORNIA, AND THE GREAT BASIN. WEAKLY NEGATIVE TRENDS FOR  
THE LAST 15 YEARS ARE EVIDENT OVER THE NORTHERN PLAINS, GREAT LAKES AND OHIO  
VALLEY. THE CURRENT STATE OF LA NINA AND SEASONAL TRENDS PROVIDE A BACKDROP FOR  
THE MONTHLY OUTLOOK.  
 
THE MJO WAS RELATIVELY INACTIVE IN NOVEMBER BEFORE BECOMING MORE ACTIVE DURING  
DECEMBER OVER THE WESTERN PACIFIC. MJO FORECASTS INDICATE A SIGNAL MOVING  
ACROSS THE AMERICAS AND EMERGING OVER THE INDIAN OCEAN BY EARLY JANUARY 2018.  
LAGGED COMPOSITES BASED ON AN MJO OVER THE INDIAN OCEAN WOULD FAVOR RIDGING AND  
WARMTH OVER THE EASTERN CONUS WITH TROUGHING AND COLDER TEMPERATURES OVER THE  
WESTERN CONUS, AT ODDS WITH TRENDS AND MOST MODEL OUTLOOKS FOR JANUARY, SO THE  
MJO IS A POTENTIAL SOURCE OF UNCERTAINTY DURING THE OUTLOOK PERIOD.  
 
THE ARCTIC OSCILLATION (AO) IS FORECAST TO BE NEGATIVE AT THE BEGINNING OF  
JANUARY. THAT WOULD IMPLY A COLDER SOLUTION FROM THE NORTHERN PLAINS TO THE  
GREAT LAKES AND SOUTHEAST. THE STATUS OF THE AO BEYOND 15 DAYS IS UNCERTAIN, SO  
THE AO WILL LIKELY BE MORE OF A FACTOR IN THE END-OF-MONTH UPDATE TO THIS  
OUTLOOK.  
 
THE TEMPERATURE OUTLOOK FOR JANUARY REFLECTS TRENDS, MODEL OUTLOOKS, AND LIKELY  
IMPACTS FROM THE ONGOING LA NINA FROM CALIFORNIA TO THE CENTRAL ROCKIES,  
SOUTHWEST, AND SOUTHERN PLAINS, WHERE ABOVE NORMAL TEMPERATURES ARE FAVORED. LA  
NINA AND A PREDICTED COLD START TO THE MONTH FAVOR BELOW NORMAL TEMPERATURES  
FROM THE NORTHERN GREAT PLAINS TO THE GREAT LAKES AND PORTIONS OF THE OHIO  
VALLEY AND MIDWEST. UNCERTAINTY IS HIGHER OVER THE EASTERN CONUS DUE TO  
POTENTIAL MJO ACTIVITY BRINGING WARMER CONDITIONS LATER IN THE MONTH. ACROSS  
EASTERN ALASKA AND THE PANHANDLE, LA NINA, MODEL OUTLOOKS, AND SEASONALLY BASED  
STATISTICAL TOOLS FAVOR BELOW NORMAL TEMPERATURES. THE SAME TOOLS FAVOR ABOVE  
NORMAL TEMPERATURES OVER WESTERN ALASKA, ALTHOUGH THAT SIGNAL HAS RETREATED  
WESTWARD THROUGHOUT THE MONTH IN DAILY CFS RUNS.  
 
LA NINA AND TRENDS GENERALLY FAVOR A MORE ACTIVE PATTERN ACROSS THE NORTHERN  
TIER OF THE CONUS WITH BELOW NORMAL PRECIPITATION ACROSS THE SOUTHERN TIER.  
MODEL OUTPUTS GENERALLY AGREE WITH THAT PATTERN, AND THEREFORE THE OFFICIAL  
OUTLOOK REFLECTS THOSE INPUTS. UNCERTAINTY IS INCREASED OVER THE EASTERN CONUS  
DUE TO POTENTIAL MJO ACTIVITY, SO COVERAGE IN THE OUTLOOK IS REDUCED EAST OF  
THE MISSISSIPPI RIVER. ACROSS WESTERN ALASKA, THE PREDICTED RIDGING, WHICH  
WOULD SUPPORT ABOVE NORMAL TEMPERATURES, IS ALSO LIKELY TO SUPPORT BELOW NORMAL  
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.  
 
AN UPDATED MONTHLY OUTLOOK... FOR JAN WILL BE ISSUED ON SUN DECEMBER 31 2017  
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.  

 
 
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