191  
FXUS07 KWBC 312000  
PMD30D  
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD300 PM EST SUN DEC 31 2017  
 
30-DAY OUTLOOK DISCUSSION FOR JANUARY 2018  
 
LA NINA CONDITIONS REMAIN IN PLACE OVER THE PACIFIC OCEAN, WITH A CORRESPONDING  
ATMOSPHERIC RESPONSE THAT IS LARGELY CONSISTENT WITH CANONICAL LA NINA IMPACTS  
OVER MUCH OF THE PACIFIC. DOWNSTREAM IMPACTS, OVER NORTH AMERICA, ARE BEING  
INFLUENCED BY EXTRATROPICAL MODES AS WELL, SO THE LA NINA RESPONSE IS NOT AS  
CLEAR. THE MJO HAS STRENGTHENED AND THE CONVECTIVELY ACTIVE PHASE IS NOW  
LOCATED OVER THE INDIAN OCEAN, PHASE 2 IN THE WHEELER-HENDON PHASE SPACE MODEL.  
THE MJO INTRODUCES A SIGNIFICANT SOURCE OF UNCERTAINTY IN THE OUTLOOK.  
 
CHANGES TO THE PRIOR OUTLOOK ARE BASED ON RECENT MODEL GUIDANCE AND THE  
EMERGENCE OF THE MJO OVER THE INDIAN OCEAN. SHORT-TERM MODEL GUIDANCE AND  
OFFICIAL OUTLOOKS PREDICT COLDER THAN NORMAL CONDITIONS OVER THE EASTERN CONUS,  
WITH THE FIRST WEEK SIGNIFICANTLY BELOW AVERAGE FROM THE MISSISSIPPI VALLEY TO  
THE EAST COAST. SOME MODERATION IS PREDICTED IN THE WEEK-2 TIME PERIOD, MOSTLY  
OVER THE SOUTHEAST. THIS PREDICTED MODERATION WOULD BE CONSISTENT WITH LAGGED  
IMPACTS FROM A PHASE-2 MJO. OVER THE SOUTHERN PLAINS, THE REVISED OUTLOOK IS  
COLDER THAN THE MID-MONTH OUTLOOK, RELATED TO THE VERY EARLY COLD, THE WEEK-2  
OUTLOOKS FAVORING BELOW NORMAL TEMPERATURES, AND SOME POTENTIAL IMPACT FROM MJO  
ACTIVITY WITH TROUGHING OVER THE WESTERN CONUS. ODDS FOR ABOVE NORMAL  
TEMPERATURES WERE INCREASED ACROSS THE GREAT BASIN AND SOUTHERN OREGON,  
SUPPORTED BY SHORT-TERM WARMTH AND MODEL GUIDANCE FOR THE FULL MONTH. LATER IN  
THE MONTH, UNCERTAINTY INCREASES AS LAGGED IMPACTS FROM THE MJO WOULD FAVOR  
COOLER TEMPERATURE AND TROUGHING ALONG THE WEST COAST, SO PROBABILITIES ARE  
STILL MODEST. OVER FLORIDA, SOME MODERATION IN TEMPERATURES WITH A SLIGHT TILT  
TOWARD ABOVE NORMAL TEMPERATURES IS INDICATED IN THE LAST FEW DAYS OF CFS RUNS,  
AND WOULD BE CONSISTENT WITH LA NINA CONDITIONS.  
 
THE UPDATED PRECIPITATION OUTLOOK IS MORE UNCERTAIN THAN THE ACCOMPANYING  
TEMPERATURE OUTLOOK. RUN-TO-RUN CONSISTENCY IN THE CFS IS QUITE LOW. THE CFS  
OUTPUT FOR THE MONTHLY TOTALS AND WEEK3-4, AS WELL AS SOME SHORTER-TERM  
OFFICIAL OUTLOOKS, SHOW INCREASED ODDS FOR PRECIPITATION OVER THE CENTRAL  
PLAINS TO THE OHIO VALLEY. NORTH OF THAT, THERE ARE CONSISTENT SIGNALS FOR  
DRYNESS OVER THE UPPER MIDWEST IN MONTHLY MODEL RUNS. A BRIEF WET PERIOD IN THE  
MIDDLE OF THE MONTH, AS DEPICTED IN WEEK-2 OUTLOOKS IS POSSIBLE FOR THE  
MIDWEST. DRYER THAN NORMAL CONDITIONS ARE STILL FAVORED OVER THE SOUTHERN  
PLAINS, WITH AN AREA OF BELOW NORMAL PRECIPITATION NOW ADDED TO FLORIDA, BOTH  
CONSISTENT WITH LA NINA AND MONTHLY GUIDANCE FROM THE CFS. LAGGED COMPOSITES ON  
MJO ACTIVITY INCLUDE TROUGHING FROM THE PACIFIC NORTHWEST TO THE FOUR CORNERS  
REGION, FOR THE EARLY PORTION OF THE MONTH, WITH MORE TROUGHING OVER THE  
SOUTHWEST THROUGH MID MONTH, WHICH RESULTED IN THE REDUCTION IN COVERAGE FOR  
BELOW NORMAL PRECIPITATION OVER ARIZONA AND SOUTHERN CALIFORNIA. FOR NORTHERN  
CALIFORNIA, SOME TROUGHING AND PRECIPITATION ARE PREDICTED EARLY IN THE MONTH,  
THOUGH SOME OF THOSE PREDICTED WEEKLY QPF TOTALS ARE CLOSE TO OR JUST BELOW  
NORMAL FOR WEEKLY NORMALS. LATER LAGS ON MJO COMPOSITES WOULD FAVOR SOME  
RIDGING OVER THE PACIFIC NORTHWEST LATER IN THE MONTH, WHICH IMPLIES BELOW  
NORMAL STORM ACTIVITY AND BELOW NORMAL PRECIPITATION FOR CALIFORNIA, WHICH  
WOULD BE CONSISTENT WITH LA NINA CONDITIONS AS WELL.  
 
----------- PREVIOUS MESSAGE FROM DEC 21TH IS BELOW ------------------  
 
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.  
 
THE NEXT MONTHLY OUTLOOK...FOR FEB ... WILL BE ISSUED ON THU JAN 18 2018  
 
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.  

 
 
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