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Official 90-day Outlooks are issued once each month near mid-month at 8:30am Eastern Time. Please consult the schedule of 30 & 90-day outlooks for exact release dates.

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HOME> Outlook Maps>Seasonal Forecast Discussion
 
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830AM EST THURSDAY NOV 20 2014

30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2014

THE OUTLOOK FOR DECEMBER 2014 IS DECIDEDLY UNCERTAIN AT THIS POINT. THERE ARE
SEVERAL COMPETING INFLUENCES THAT ARE YET TO BE CLEARLY RESOLVED IN EITHER THE
STATISTICAL OR DYNAMICAL TOOLS.

LET'S FIRST BEGIN WITH THE DYNAMICAL MODEL GUIDANCE. MONTHLY FORECASTS FROM THE
NMME AND IMME ARE FAIRLY MILD ACROSS MUCH OF THE CONUS, ESPECIALLY THE NORTHERN
AND WESTERN PORTIONS. THIS IS A REASONABLE SOLUTION GIVEN THE GENERAL WARM ENSO
SIGNAL. HOWEVER, THERE IS LITTLE INDICATION THAT A ROBUST ENSO RESPONSE IN THE
EXTRATROPICS CAN BE SUSTAINED ABSENT SOME REASONABLY CANONICAL EQUATORIAL
CONVECTIVE ANOMALIES CONSISTENT WITH AN EL NINO. CURRENTLY, THE CONVECTIVE
STATE OF THE EQUATORIAL PACIFIC IS SOMEWHAT INCONSISTENT WITH WHAT WOULD
OTHERWISE BE EXPECTED. SO IN THIS SENSE, MODEL GUIDANCE INITIALIZED WEEKS AGO
THAT INDICATE AN ENSO-LIKE FOOTPRINT OVER NORTH AMERICA ARE SOMEWHAT SUSPECT.
ADDING TO THE UNCERTAINTY IS THE FACT THAT MORE RECENT GUIDANCE FROM THE CFS
AND ECMWF THAT EXTENDS AT LEAST THROUGH THE MIDDLE OF DECEMBER INDICATES A
DIFFERENT PATTERN FOR THE FIRST TWO WEEKS OF THE MONTH, WITH ABOVE-NORMAL
TEMPERATURES CENTERED IN THE EASTERN CONUS (WITH THE CFS WARMER THAN THE
ECMWF), AND NEAR- TO BELOW-NORMAL TEMPERATURES CENTERED OVER PARTS OF THE WEST.
THIS LATER GUIDANCE IS SLIGHTLY PREFERRED, BUT THE TYPICAL LOW FORECAST SKILL
IS UNDERSTOOD.

THE CURRENT AND FORECAST STATE OF THE MJO MAY HAVE SOME IMPLICATIONS FOR THE
MONTHLY FORECAST. THIS, TOO, IS UNCERTAIN SINCE THERE DOES NOT SEEM TO BE A
STRONG ATMOSPHERIC RESPONSE IN THE SUBTROPICS YET, CASTING DOUBT ON WHETHER THE
ONGOING EVENT WILL SUBSTANTIALLY MODULATE NORTH AMERICAN CLIMATE. SHOULD A
ROBUST MJO PROPAGATE FROM THE INDIAN OCEAN TO THE PACIFIC, THE RESPONSE LATER
IN THE MONTH COULD BALANCE OUT A WARMER SIGNAL INDICATED EARLY BY THE FORECAST
EVOLUTION OVER THE NEXT WEEK OR TWO.

FINALLY, THERE ARE SIGNS IN THE CURRENT MEDIUM RANGE GUIDANCE THAT RELOADING OF
ANOMALOUSLY COLD AIR IN WESTERN CANADA COULD OCCUR BY LATE NOVEMBER. THIS IS
BEST SUPPORTED BY THE LATEST CANADIAN AND ECMWF ENSEMBLE AND DETERMINISTIC
GUIDANCE. SUCH A SCENARIO CASTS MORE DOUBT ON THE WARM ENSO RESPONSE OVER
SOUTHERN CANADA AND THE NORTHERN CONUS.

IN LIGHT OF THE AFOREMENTIONED DISCUSSION, THERE IS RELATIVELY LITTLE COVERAGE
ON THE 0.5 LEAD MONTHLY TEMPERATURE MAP. ABOVE-NORMAL TEMPERATURES ARE FAVORED
FOR THE IMMEDIATE WEST COAST BASED ON GOOD MODEL CONSENSUS AND STATISTICAL
GUIDANCE BASED ON PACIFIC SSTS. UNCERTAINTY INCREASES IN THE PACIFIC NORTHWEST
SOMEWHAT. ABOVE-NORMAL TEMPERATURES ARE FAVORED IN THE NORTHEASTERN CONUS AT
THE INTERSECTION OF SIGNALS FROM ENSO, MJO, AND RECENT MODEL GUIDANCE.
CONFIDENCE HERE IS STILL FAIRLY LOW AS INDICATED BY MEAGER PROBABILITIES.
BELOW-NORMAL TEMPERATURES ARE WEAKLY FAVORED FOR THE SOUTH-CENTRAL CONUS WHERE
THE ENSO SIGNAL IS STRONGEST AND THERE IS MORE SUPPORT FROM MODEL GUIDANCE. THE
NORTHWARD EXTENSION IS BASED ON THE DISTINCT POSSIBILITY THAT ANOTHER ARCTIC
AIRMASS MOVES SOUTHWARD EAST OF THE ROCKIES EARLY IN THE MONTH. IF THIS OCCURS,
EVEN AN EMERGENCE OF A STATIONARY ENSO SIGNAL LATER IN THE MONTH WOULD STILL
NOT UNDO THE ODDS FOR BELOW-NORMAL TEMPERATURES OVER THE INDICATED REGION.

FOR PRECIPITATION, A GENERAL CONSENSUS OF ENSO IMPACTS AND MODEL GUIDANCE IS
USED, WITH LOW PROBABILITIES INDICATING THE LOW CONFIDENCE IN LIGHT OF THE
ABOVE FACTORS. IF ROBUST MJO IMPACTS ARE REALIZED EARLY IN THE MONTH,
ABOVE-MEDIAN PRECIPITATION MIGHT EXTEND FARTHER NORTH INTO PARTS OF THE OHIO
VALLEY AT THE EXPENSE OF RAINFALL NEAR THE GULF COAST. UNCERTAINTY IS ALSO
ESPECIALLY HIGH OVER THE PACIFIC NORTHWEST, WHERE THERE ARE MULTIPLE
CONFLICTING SIGNALS.

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: STEPHEN BAXTER


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 DEC WILL BE ISSUED ON SUN NOVEMBER 30 2014


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

$$

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