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.
$$