PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300PM EST WEDNESDAY DEC 31 2014

30-DAY OUTLOOK DISCUSSION FOR JANUARY 2015

THE JANUARY 2015 OUTLOOK CONTINUES TO REFLECT A HIGH AMOUNT OF UNCERTAINTY DUE 
TO THE POSSIBLE IMPACTS OF ENSO. A PATTERN CHANGE FROM WHAT HAS BEEN OBSERVED 
FOR MUCH OF DECEMBER IS INDICATED IN MANY OF THE DYNAMICAL AND STATISTICAL 
TOOLS IN THE TEMPERATURE AND PRECIPITATION PATTERNS ACROSS THE CONUS. THE 
PATTERN CHANGE, ESPECIALLY IN TEMPERATURES, WAS INDICATED IN THE HALF-MONTH 
LEAD OUTLOOKS, SO THE UPDATED OUTLOOKS ARE NOT SIGNIFICANTLY DIFFERENT FROM 
THOSE.

THE MEDIUM RANGE FORECASTS (THROUGH DAY 14) DEPICT COLDER THAN NORMAL 
TEMPERATURES ACROSS THE NORTHERN TIER OF THE COUNTRY.  THIS IS IN CONTRAST TO 
THE TYPICAL EL-NINO RESPONSE.  GIVEN THE LACK OF CLEAR ENSO TELECONNECTIONS IN 
THE MIDLATITUDES, MUCH OF OUTLOOK IS BASED ON DYNAMICAL MODEL OUTPUT AND SOME 
STATISTICAL TOOLS. THE NAO AND AO ARE LIKELY TO BE POSITIVE FOR THE FIRST HALF 
OF THE MONTH, LIMITING THE POTENTIAL FOR COLD AIR TO PENETRATE INTO THE DEEP 
SOUTH AND HAVING SOME CORRELATION WITH DRY CONDITIONS OVER NORTHERN CALIFORNIA.

THE TEMPERATURE OUTLOOK HAS BEEN MODIFIED TO REDUCE THE COVERAGE OF AREAS WHERE 
BELOW NORMAL TEMPERATURES ARE FAVORED ACROSS THE CENTRAL GREAT PLAINS, WHILE 
EXPANDING THE COVERAGE OF WHERE BELOW NORMAL TEMPERATURES ARE FAVORED OVER THE 
GREAT LAKES AND INTO THE NORTHEAST. A POSITIVE AO AND NAO ALSO FAVORS ABOVE 
NORMAL TEMPERATURES OVER THE SOUTHEAST, AS DO MANY OF THE DYNAMICAL MODELS.

THE PRECIPITATION OUTLOOK WAS CHANGED SLIGHTLY, TO INCLUDE AN ENHANCEMENT OF 
PROBABILITIES FOR ABOVE MEDIAN PRECIPITATION OVER PORTIONS OF THE TENNESSEE AND 
LOWER MISSISSIPPI VALLEYS DUE TO HEAVY RAINS EXPECTED EARLY IN THE MONTH. ODDS 
FOR ABOVE MEDIAN PRECIPITATION OVER NORTHERN CALIFORNIA HAVE BEEN REDUCED DUE 
TO THE FORECAST FOR A POSITIVE AO, DYNAMICAL MODEL GUIDANCE FROM SUCCESSIVE 
RUNS OF THE CFS, GFS, AND EUROPEAN CENTER, AND THE CONTINUING LACK OF 
ATMOSPHERIC RESPONSE TO SST ANOMALIES OVER THE CENTRAL PACIFIC. A SMALL 
REDUCTION IN COVERAGE OF THE BELOW MEDIAN PRECIPITATION OVER THE NORTHERN 
INTERMOUNTAIN WEST IS SUPPORTED BY MEDIUM RANGE AND MONTHLY TIME SCALE OUTPUT 
FROM THE DYNAMICAL MODELS. 

THE PREVIOUS DISCUSSION, ISSUED DECEMBER 18, FOLLOWS:

THE JANUARY 2015 OUTLOOK REFLECTS A GENERALLY HIGH AMOUNT OF UNCERTAINTY AS 
COMPARED TO OTHER MONTHLY OUTLOOKS. SEVERAL FACTORS ARE LIKELY TO IMPACT THE 
TEMPERATURES AND PRECIPITATION DURING THE MONTH. SOME OF THE INPUTS SUGGEST A 
LIKELY TO FLIP IN SIGN OF TEMPERATURES AND PRECIPITATION ANOMALIES DURING THE 
MIDDLE OF THE MONTH, SPECIFICALLY INDICATED IN THE DYNAMICAL MODEL GUIDANCE 
PRODUCTS.

DYNAMICAL MODEL GUIDANCE FOR THE WEEKS 3 AND 4 PERIOD FROM THE CFS AND EUROPEAN 
CENTER DEPICT SIMILAR PATTERNS THROUGH THE MIDDLE JANUARY. BOTH MODELS SHOW A 
COLD START TO JANUARY FOR THE CONUS, EAST OF THE ROCKIES, WITH ABOVE NORMAL 
TEMPERATURES FAVORED ACROSS THE WEST AND FOR ALASKA. MODEL OUTLOOKS FROM THE 
CFS, NMME, AND IMME FOR THE ENTIRE MONTH DEPICT A MILD PATTERN ACROSS MOST OF 
THE CONUS AND ALASKA, IMPLYING THE POTENTIAL FOR A PATTERN SHIFT DURING THE 
MIDDLE OF THE MONTH.  

A ROBUST ATMSOPHERIC RESPONSE TO THE ABOVE AVERAGE EQUATORIAL PACIFIC SSTS 
REMAINS LACKING. THE PDO REMAINS POSITIVE, AND REGRESSIONS OF JANUARY 
TEMPERATURE ON NOVEMBER PDO VALUES SUPPORT A COOLER PATTERN, ESPECIALLY EAST OF 
THE ROCKIES. IN CONTRAST, THE MJO IS FORECAST TO INCREASE INTENSITY OVER THE 
INDIAN OCEAN LATER IN DECEMBER, AND LAGGED COMPOSITES BASED ON THAT MJO 
FORECAST FAVOR WARMING OVER THE NORTHERN AND EASTERN CONUS.  

THE JANUARY 2015 OUTLOOK INCORPORATES A WEAK ENSO WARM PHASE SIGNAL, SOME 
INFLUENCE OF THE POSITIVE PDO, AND SOME OF THE SIGNAL FOR COLDER CONDITIONS 
EAST OF THE ROCKIES IN THE DYNAMICAL GUIDANCE. THE MJO PLAYED LITTLE ROLE IN 
THE MONTHLY OUTLOOK AT THIS TIME SINCE THERE IS HIGH UNCERTAINTY WHETHER THE 
MJO WILL ACT TO ENHANCE CONVECTION OVER THE INDIAN OCEAN/MARITIME CONTINENT 
LATER THIS MONTH. GIVEN THOSE INPUTS, ABOVE NORMAL TEMPERATURES ARE FAVORED FOR 
ALASKA AND OVER THE CONUS FROM THE WEST COAST TO THE ROCKIES.  BELOW NORMAL 
TEMPERATURES ARE FAVORED OVER THE CENTRAL AND SOUTHERN GREAT PLAINS, AS WELL AS 
PORTIONS OF THE OHIO VALLEY. SOME DYNAMICAL MODEL GUIDANCE SUPPORTS COOLER THAN 
NORMAL CONDITIONS FOR THE CENTRAL GREAT PLAINS, WHILE ENSO AND PDO COMPOSITES, 
AS WELL AS SOME DYNAMICAL GUIDANCE SUPPORT BELOW NORMAL TEMPERATURES ACROSS THE 
SOUTHERN GREAT PLAINS.

GUIDANCE FROM SOME OF THE NMME CONSTITUENTS ALIGN WITH WARM ENSO COMPOSITES AND 
POSITIVE PDO REGRESSIONS TO SUPPORT ABOVE AVERAGE RAINFALL OVER PORTIONS OF 
CALIFORNIA.  MODEL GUIDANCE AND ENSO WARM PHASE COMPOSITES SUPPORT WETTER THAN 
AVERAGE CONDITIONS ACROSS THE SOUTHWEST AND PORTIONS OF THE SOUTHERN GREAT 
PLAINS, WHILE FAVORING BELOW AVERAGE PRECIPITATION ACROSS PORTIONS OF THE 
NORTHWEST.  NO RELIABLE SIGNALS ARE EVIDENT FOR PRECIPITATION ACROSS ALASKA.
 
IN AREAS WHERE CLIMATE SIGNALS ARE WEAK SUCH THAT THE LIKELIHOODS OF MONTHLY 
MEAN TEMPERATURES OR MONTHLY ACCUMULATED PRECIPITATION AMOUNTS ARE SIMILAR TO 
CLIMATOLOGICAL PROBABILITIES, EQUAL CHANCES (EC) IS INDICATED.

THE MAIN FACTORS THAT USUALLY INFLUENCE THE MONTHLY CLIMATE OUTLOOK INCLUDE:
1) EL NINO AND LA NINA - WHICH COMPRISE ENSO. IMPACTS OF THESE EVENTS ARE 
SUMMARIZED BY SEPARATING 3-MONTH OBSERVATIONS FROM THREE OR MORE DECADES INTO 
EL NINO, NEUTRAL AND LA NINA SETS, AVERAGING EACH SEPARATELY, AND THEN 
COMPUTING ANOMALIES. THESE ARE CALLED "COMPOSITES" AND USED AT TIMES TO 
SUBJECTIVELY MODIFY THE FORECAST.
2) TRENDS - APPROXIMATED BY THE OCN TOOL AS THE DIFFERENCE BETWEEN THE MOST 
RECENT 10-YEAR MEAN OF TEMPERATURE OR 15-YEAR MEAN OF PRECIPITATION FOR A GIVEN 
LOCATION AND TIME OF YEAR AND THE 30-YEAR CLIMATOLOGY PERIOD (CURRENTLY 
1981-2010).
3) THE TROPICAL 30-60 DAY OSCILLATION - CALLED THE MADDEN JULIAN OSCILLATION 
(MJO) - AFFECTS CLIMATE VARIABILITY WITHIN SEASONS.
4) THE ARCTIC OSCILLATION (AO), THE SIMILAR NORTH ATLANTIC OSCILLATION (NAO), 
AND THE PACIFIC NORTH AMERICAN (PNA) PATTERNS - WHICH AFFECT THE TEMPERATURE 
ANOMALY PATTERN ESPECIALLY DURING BOREAL WINTER AND ARE GENERALLY CONSIDERED TO 
HAVE LOW PREDICTABILITY.
5) THE PACIFIC DECADAL OSCILLATION (PDO) - AN ENSO-LIKE PATTERN OF CLIMATE 
VARIABILITY AFFECTING THE TROPICS AND THE NORTH PACIFIC AND NORTH AMERICAN 
REGIONS, BUT WHICH VARIES ON A MUCH LONGER TIME-SCALE THAN ENSO.
6) PERSISTENTLY DRY OR WET SOILS IN THE SPRING AND SUMMER AND SNOW AND ICE 
COVER ANOMALIES IN THE WINTER. THESE FACTORS TEND TO PERSIST FOR LONG PERIODS 
AND ACT AS A KIND OF MEMORY IN THE CLIMATE SYSTEM.
7) STATISTICAL FORECAST MODELS - CANONICAL CORRELATION ANALYSIS (CCA), 
SCREENING MULTIPLE LINEAR REGRESSION (SMLR), CONSTRUCTED ANALOG (CA), AND 
ENSEMBLE CCA (ECCA).
8) DYNAMICAL FORECAST MODELS - INCLUDING THE NCEP CLIMATE FORECAST SYSTEM 
VERSION 2 (CFS) AND FOR THE ZERO-LEAD UPDATE FORECASTS THE NCEP GLOBAL ENSEMBLE 
FORECAST SYSTEM (GEFS).  AN EXPERIMENTAL FORECAST SYSTEM, THE NATIONAL 
MULTI-MODEL ENSEMBLE (NMME), COMPRISED OF SEVERAL DYNAMICAL MODELS IS ALSO USED.


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 15 2015


THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.

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