PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD 300 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. $$