Skip Navigation Links www.nws.noaa.gov 
NOAA logo - Click to go to the NOAA home page National Weather Service   NWS logo - Click to go to the NWS home page
Climate Prediction Center
 
 

CPC Search
About Us
   Our Mission
   Who We Are

Contact Us
   CPC Information
   CPC Web Team

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.

Text Discussions
   90day Prognostic
   30day Prognostic
   Hawaiian
   Tools


More Outlooks
    0.5mn DJF 2017
    1.5mn JFM 2018
    2.5mn FMA 2018
    3.5mn MAM 2018
    4.5mn AMJ 2018
    5.5mn MJJ 2018
    6.5mn JJA 2018
    7.5mn JAS 2018
    8.5mn ASO 2018
    9.5mn SON 2018
   10.5mn OND 2018
   11.5mn NDJ 2018
   12.5mn DJF 2018
    0.5mn Dec 2017


Tools Used (see Discussion for explanation)
   CCA
   OCN
   CMP
   SMT
   POE
 
HOME> Outlook Maps>Seasonal Forecast Discussion
 
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK 
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST THU NOV 30 2017

30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2017

THE UPDATED TEMPERATURE AND PRECIPITATION OUTLOOKS FOR DECEMBER 2017 ARE BASED
ON THE WPC TEMPERATURE AND PRECIPITATION FORECASTS DURING THE FIRST WEEK OF
DECEMBER, THE CPC 8-14 DAY TEMPERATURE AND PRECIPITATION OUTLOOKS, THE LATEST
DYNAMICAL MODEL GUIDANCE, AND THE TYPICAL INFLUENCES ASSOCIATED WITH LA NINA.
THE MADDEN-JULIAN OSCILLATION (MJO) CONTINUES TO STRENGTHEN WITH ITS ENHANCED
(SUPPRESSED) PHASE OVER THE EASTERN INDIAN OCEAN AND MARITIME CONTINENT
(WESTERN HEMISPHERE). THE ENHANCED PHASE OF THE MJO IS FORECAST TO PROPAGATE
EAST TO THE WEST PACIFIC AND IT MAY INFLUENCE THE CIRCULATION PATTERN AND
TEMPERATURES ACROSS THE MID-LATITUDES LATER IN DECEMBER.

A MAJOR LONGWAVE PATTERN CHANGE IS LIKELY TO OCCUR DURING THE FIRST WEEK OF
DECEMBER AS A HIGHLY ANOMALOUS UPPER-LEVEL RIDGE BECOMES ANCHORED ALONG THE
WEST COAST WITH AN AMPLIFYING UPPER-LEVEL TROUGH DOWNSTREAM OVER EASTERN NORTH
AMERICA. FOLLOWING A MILD START TO DECEMBER, THIS MAJOR PATTERN CHANGE IS
LIKELY TO USHER IN OUTBREAKS OF BELOW TO MUCH BELOW-NORMAL TEMPERATURES TO THE
EASTERN THIRD OF THE CONUS THROUGH AT LEAST MID-DECEMBER. THE D+11 GFS AND
ECMWF ENSEMBLE MEANS ON NOV 30 ARE IN EXCELLENT AGREEMENT, MAINTAINING THIS
ANOMALOUS LONGWAVE PATTERN. THE 6Z GFS ENSEMBLE MEAN FEATURES A POSITIVE
500-HPA HEIGHT ANOMALY CENTER OF 300 METERS OVER THE ALASKA PANHANDLE WHICH
STRONGLY FAVORS A STABLE PATTERN OVER NORTH AMERICA AND BELOW-NORMAL
TEMPERATURES ACROSS THE EASTERN U.S. THE GFS ENSEMBLE MEMBERS INDICATE A
NEGATIVE ARCTIC OSCILLATION (AO) INDEX THROUGH THE END OF WEEK-2. THE PREDICTED
EVOLUTION OF THE MJO IS EXPECTED TO INCREASES THE CHANCES THAT THE BELOW NORMAL
TEMPERATURES PERSIST INTO THE LATTER HALF OF THE MONTH. THE CFS MODEL AT WEEKS
3-4 (ENDING ON DEC 28) INDICATES BELOW NORMAL TEMPERATURES FROM THE MISSISSIPPI
VALLEY TO THE EAST COAST. BASED ON EXCELLENT MODEL AGREEMENT AND CONTINUITY
REGARDING THIS HIGHLY ANOMALOUS PATTERN, BELOW-NORMAL TEMPERATURES ARE FAVORED
FOR THE EASTERN THIRD OF THE CONUS. THE HIGHEST ODDS FOR BELOW NORMAL
TEMPERATURES ARE FORECAST ACROSS THE UPPER OHIO VALLEY WHERE THE MOST
ANOMALOUSLY COLD AIR IS EXPECTED DURING EARLY TO MID-DECEMBER.

THE PERSISTENCE OF A HIGHLY ANOMALOUS RIDGE ALOFT AND EXCELLENT AGREEMENT AMONG
TEMPERATURE TOOLS SUPPORT INCREASED CHANCES FOR ABOVE NORMAL TEMPERATURES
ACROSS MUCH OF THE WESTERN U.S. PROBABILITIES AND COVERAGE FOR ABOVE NORMAL
TEMPERATURES ARE REDUCED ACROSS THE NORTHERN ROCKIES AND NORTHERN GREAT PLAINS
COMPARED TO THE DYNAMICAL MODEL GUIDANCE. THIS MODIFICATION IS RELATED TO AN
INCREASING CHANCE OF BELOW NORMAL TEMPERATURES AFFECTING THESE AREAS LATER IN
THE MONTH, IF THE ENHANCED PHASE OF THE MJO PROPAGATES INTO THE WEST PACIFIC
AND INFLUENCES THE MID-LATITUDE CIRCULATION PATTERN.  ALTHOUGH PERIODS OF
ANOMALOUS COLD ARE EXPECTED TO AFFECT THE GREAT PLAINS DURING DECEMBER, LARGE
POSITIVE ANOMALIES AT THE BEGINNING OF THE MONTH AND AN EXPECTED VARIABLE
TEMPERATURE PATTERN RESULT IN EQUAL CHANCES (EC) OF BELOW, NEAR, OR ABOVE
NORMAL TEMPERATURES FOR THIS REGION.

BELOW-NORMAL PRECIPITATION IS FAVORED ACROSS THE WESTERN U.S. DUE TO THE
LIKELIHOOD OF A PERSISTENT UPPER-LEVEL RIDGE THROUGH AT LEAST MID-DECEMBER.
LITTLE TO NO PRECIPITATION IS LIKELY FOR CALIFORNIA DURING THE FIRST TWO WEEKS
OF THE MONTH. HIGHER PROBABILITIES OF BELOW NORMAL PRECIPITATION WOULD BE
FORECAST ACROSS CALIFORNIA, BUT THE CFS MODEL INDICATES AN UPPER-LEVEL TROUGH
APPROACHING THE WEST COAST DURING THE WEEKS 3-4 PERIOD. A COLD FRONT,
ASSOCIATED WITH THE ONSET OF THE MAJOR PATTERN CHANGE, IS EXPECTED TO RESULT IN
PRECIPITATION AMOUNTS OF 0.5 TO 2 INCHES ACROSS THE EASTERN U.S. DURING THE
FIRST WEEK OF DECEMBER. FOLLOWING THIS FRONTAL PASSAGE, A PROLONGED PERIOD OF
ANOMALOUS NORTHERLY FLOW ENHANCES ODDS FOR BELOW NORMAL PRECIPITATION FROM THE
CENTRAL AND SOUTHERN GREAT PLAINS NORTHEAST TO THE MIDDLE MISSISSIPPI VALLEY.
THE FAVORED AREA OF BELOW NORMAL PRECIPITATION ACROSS THE SOUTHERN GREAT PLAINS
IS CONSISTENT WITH THE ONGOING LA NINA. A LARGER COVERAGE OF INCREASED CHANCES
OF BELOW NORMAL PRECIPITATION WOULD BE FORECAST FOR THE EASTERN U.S., BUT
PRECIPITATION AT THE BEGINNING OF DECEMBER AND POTENTIAL FOR WAVES OF SURFACE
LOW PRESSURE TO DEVELOP WITH THE AMPLIFIED TROUGH LIMIT FORECAST CONFIDENCE ON
BELOW NORMAL PRECIPITATION VERIFYING.

A STABLE PATTERN WITH AN ANOMALOUS TROUGH (RIDGE) OVER THE ALEUTIANS (EASTERN
ALASKA) AND PERSISTENT SOUTHERLY FLOW AT THE SURFACE ENHANCES ODDS FOR ABOVE
NORMAL TEMPERATURES THROUGHOUT ALASKA. PRECIPITATION TOOLS AT ALL TIME LEADS
DURING DECEMBER AND THE LONGWAVE PATTERN FAVOR ELEVATED ODDS FOR ABOVE NORMAL
PRECIPITATION ACROSS THE ALEUTIANS, SOUTHWEST ALASKA, AND ALONG THE SOUTHERN
COAST OF MAINLAND ALASKA.  DOWNSLOPING SLOW, ASSOCIATED WITH PERSISTENT
SOUTHERLY FLOW OFF THE ALASKA RANGE, TILTS THE ODDS TO BELOW NORMAL
PRECIPITATION FOR PARTS OF EASTERN MAINLAND ALASKA.

----------- PREVIOUS MESSAGE (FROM NOVEMBER 16) IS SHOWN BELOW ------------

THE DECEMBER 2017 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL
MODEL GUIDANCE, THE TYPICAL INFLUENCE ASSOCIATED WITH LA NINA, AND LONG-TERM
TRENDS. DURING THE PAST MONTH, LA NINA CONDITIONS DEVELOPED AS NEGATIVE SEA
SURFACE TEMPERATURE ANOMALIES CONTINUED ACROSS THE EASTERN AND CENTRAL
EQUATORIAL PACIFIC ALONG WITH SUPPRESSED (ENHANCED) CONVECTION ACROSS THE
CENTRAL TROPICAL PACIFIC (MARITIME CONTINENT AND PHILIPPINES). CLIMATE SIGNALS
TYPICALLY ASSOCIATED WITH LA NINA WERE CONSIDERED IN MAKING THE DECEMBER 2017
OUTLOOK, GIVEN THESE CURRENT ATMOSPHERIC AND OCEANIC STATES.

A ROBUST MJO OCCURRED DURING OCTOBER, BUT IT WEAKENED SINCE THE BEGINNING OF
NOVEMBER.  THE DYNAMICAL MODELS INDICATE A CONTINUED WEAK OR INCOHERENT SIGNAL
DURING THE NEXT TWO WEEKS. THEREFORE, THE MJO IS NOT EXPECTED TO PROVIDE ANY
FORCING TO THE EXTRATROPICS. ALTHOUGH THE MJO DID NOT FACTOR INTO THE DECEMBER
OUTLOOK, ITS EVOLUTION WILL BE CLOSELY MONITORED FOR THE REVISED OUTLOOK AT THE
END OF THE MONTH.

THE ARCTIC OSCILLATION (AO) INDEX IS FORECAST TO BECOME LARGELY NEGATIVE DURING
MID-NOVEMBER AS A BLOCKING RIDGE PERSISTS OVER THE BERING SEA WITH ANOTHER
UPPER-LEVEL RIDGE BUILDING OVER THE DAVIS STRAIT. THE DURATION OF THIS NEGATIVE
AO INDEX IS UNCERTAIN AND COULD BE TRANSIENT WITH MANY GFS ENSEMBLE MEMBERS
INDICATING THAT THE AO INDEX BECOMES MORE NEUTRAL BY THE END OF NOVEMBER. MOST
INPUTS TO THE NMME AGREE ON ENHANCED ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS
THE EASTERN CONUS. SINCE THE ECMWF MODEL AT WEEKS 3-4 (WHICH INCLUDES DEC
1-12)INDICATES INCREASED CHANCES FOR BELOW-NORMAL TEMPERATURES ACROSS MUCH OF
THE EASTERN CONUS AND GREAT LAKES, EQUAL CHANCES OF BELOW, NEAR, OR ABOVE
NORMAL TEMPERATURES ARE NECESSARY FOR THESE AREAS AT THIS TIME LEAD. THE
SPATIAL PATTERN OF THE TEMPERATURE FORECAST ACROSS THE WESTERN AND
SOUTH-CENTRAL CONUS IS SIMILAR TO THE SEASONAL OUTLOOK SINCE LA NINA WAS A
MAJOR FACTOR IN CREATING THE DECEMBER OUTLOOK, BUT THE COVERAGE OF AREAS WHERE
BELOW- AND ABOVE-NORMAL TEMPERATURES ARE FAVORED IS SMALLER DUE TO UNCERTAINTY.
DYNAMICAL MODELS, INCLUDING WEEKS 3-4, AND LONG-TERM TRENDS SUPPORT THE
RELATIVELY HIGH ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS THE SOUTHWESTERN
CONUS.

THE PRECIPITATION OUTLOOK FOR DECEMBER IS BASED PRIMARILY ON THE CALIBRATED
NMME AND IS CONSISTENT WITH LA NINA CONDITIONS AND THE DJF OUTLOOK. THE HIGHEST
PROBABILITIES FOR BELOW-NORMAL PRECIPITATION ARE FORECAST ACROSS PARTS OF THE
GULF COAST AND SOUTHEAST WHERE A DRY SIGNAL IS STRONG IN LA NINA COMPOSITES FOR
NDJ AND PROBABILITIES ARE RELATIVELY HIGH IN THE CALIBRATED NMME. THE BROAD
AREA OF ENHANCED ODDS FOR ABOVE-NORMAL PRECIPITATION FROM THE PACIFIC NORTHWEST
EAST TO THE GREAT LAKES IS EITHER SUPPORTED BY LA NINA COMPOSITES OR THE
CALIBRATED NMME.  PROBABILITIES FOR BELOW- AND ABOVE-NORMAL PRECIPITATION ARE
MODEST DUE TO LIMITED SKILL INHERENT IN A MONTHLY OUTLOOK AT THIS TIME LEAD.

THE HIGHEST ODDS FOR ABOVE-NORMAL TEMPERATURES ACROSS ALASKA ARE FORECAST FOR
AREAS OF THE STATE ADJACENT TO THE BERING AND CHUKCHI SEAS WHERE SEA SURFACE
TEMPERATURE ANOMALIES ARE AVERAGING AS MUCH AS 1.5 DEGREES C ABOVE NORMAL.
ENHANCED ODDS FOR BELOW-NORMAL TEMPERATURES FORECAST ACROSS PARTS OF SOUTHEAST
MAINLAND ALASKA AND THE ALASKA PANHANDLE ARE BASED ON THE MONTHLY CFS
TEMPERATURE FORECAST. THE FAVORED AREAS OF BELOW- AND ABOVE-NORMAL
PRECIPITATION ACROSS ALASKA ARE CONSISTENT WITH THE TEMPERATURE OUTLOOK AND
SUPPORTED BY THE WEEKS 3-4 CFS AND ECMWF PRECIPITATION FORECASTS ALONG WITH THE
MONTHLY CFS PRECIPITATION FORECAST.


FORECASTER: BRAD PUGH


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 JAN ... WILL BE ISSUED ON THU DEC 21 2017


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

$$

NOAA/ National Weather Service
National Centers for Environmental Prediction
Climate Prediction Center
5200 Auth Road
Camp Springs, Maryland 20746
Climate Prediction Center Web Team
Page last modified: January 17, 2006
Disclaimer
Information Quality
Credits
Glossary
Privacy Policy
Freedom of Information Act
About Us
Career Opportunities