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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
300 PM EST WED NOV 30 2016

30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2016

THE UPDATED MONTHLY TEMPERATURE AND PRECIPITATION OUTLOOKS FOR DECEMBER 2016
ARE BASED ON THE LATEST DYNAMICAL MODEL GUIDANCE, WPC TEMPERATURE AND
PRECIPITATION FORECASTS DURING THE FIRST WEEK OF DECEMBER, THE CPC 6-10/8-14
DAY TEMPERATURE AND PRECIPITATION OUTLOOKS, AND CPC'S EXPERIMENTAL WEEKS 3-4
TEMPERATURE AND PRECIPITATION OUTLOOKS. SINCE THE FUTURE MJO EVOLUTION AND ITS
POTENTIAL INFLUENCE ON THE EXTRATROPICAL CIRCULATION PATTERN ARE NOT CERTAIN
DURING THE NEXT MONTH, THE MJO WAS NOT CONSIDERED A MAJOR FACTOR IN THE REVISED
OUTLOOKS.

LARGE CHANGES WERE NECESSARY IN THE TEMPERATURE OUTLOOK, DUE TO A HIGHLY
AMPLIFIED RIDGE FORECAST OVER THE BERING SEA WITH A DOWNSTREAM AMPLIFIED TROUGH
ACROSS THE CONTINENTAL U.S. LIKELY PERSISTING THROUGH THE FIRST HALF OF
DECEMBER. THIS LONGWAVE PATTERN YIELDS A MUCH COLDER OUTLOOK ACROSS THE
CONTINENTAL U.S. AND ALASKA THAN WHAT THE DYNAMICAL MODEL GUIDANCE INDICATED AT
MID-MONTH. TEMPERATURES ARE EXPECTED TO AVERAGE 5 TO 10 DEGREES F, OR MORE,
BELOW NORMAL ACROSS MUCH OF THE WESTERN U.S. DURING THE FIRST WEEK OF DECEMBER.
ALSO, POSITIVE ANOMALIES IN SNOW COVERAGE CURRENTLY EXIST ACROSS THE GREAT
BASIN AND INTERMOUNTAIN WEST, RAISING CONFIDENCE IN BELOW-NORMAL TEMPERATURES
FOR THESE AREAS. THEREFORE, BELOW-NORMAL TEMPERATURES ARE FAVORED FOR MUCH OF
THE WESTERN U.S. IN THE REVISED OUTLOOK. THE HIGHEST PROBABILITIES FOR
BELOW-NORMAL TEMPERATURES ARE FORECAST FOR THE NORTHERN ROCKIES AND NORTHERN
HIGH PLAINS WHERE ARCTIC HIGH PRESSURE IS EXPECTED TO RESULT IN THE LARGEST
NEGATIVE TEMPERATURE ANOMALIES DURING EARLY DECEMBER AND BELOW-NORMAL
TEMPERATURES ARE MOST LIKELY TO PERSIST INTO THE SECOND WEEK OF DECEMBER.
INCREASED CHANCES FOR BELOW-NORMAL TEMPERATURES EXTEND EAST TO THE GREAT PLAINS
WHERE THE CPC 6-10/8-14 DAY OUTLOOKS FAVOR BELOW-NORMAL TEMPERATURES AS
MODIFIED ARCTIC AIR IS FORECAST TO AFFECT THIS REGION AT LEAST EARLY IN THE
MONTH. FORECAST CONFIDENCE IS LOWEST ALONG THE EAST COAST DUE TO VARIABLE
TEMPERATURES FORECAST DURING EARLY DECEMBER, FOLLOWED BY MORE UNCERTAINTY IN
THE LONGWAVE PATTERN ACROSS EASTERN NORTH AMERICA LATER IN THE MONTH. SINCE THE
EAST COAST IS EXPECTED TO RESIDE ON THE RELATIVELY WARM SIDE OF MULTIPLE LOW
PRESSURE SYSTEMS TRACKING ACROSS THE EAST-CENTRAL U.S. EARLY IN THE MONTH, A
SLIGHT TILT IN THE ODDS FOR ABOVE-NORMAL TEMPERATURES IS FORECAST FOR THE
NORTHEAST AND PARTS OF FLORIDA.

BASED ON SHORT-TERM AND CPC'S 6-10/8-14 DAY PRECIPITATION OUTLOOKS, INCREASED
CHANCES FOR ABOVE-MEDIAN PRECIPITATION ARE FORECAST ACROSS THE PACIFIC
NORTHWEST, NORTHERN GREAT BASIN, AND NORTH-CENTRAL ROCKIES/HIGH PLAINS. ARCTIC
HIGH PRESSURE SHIFTING SOUTH FROM WESTERN CANADA EARLY IN THE MONTH IS EXPECTED
TO ENHANCE UPSLOPE FLOW AND PRECIPITATION ACROSS THE NORTHERN AND CENTRAL HIGH
PLAINS. DOWNSTREAM OF THE AMPLIFIED UPPER-LEVEL TROUGH EARLY IN THE MONTH,
ABOVE-MEDIAN PRECIPITATION IS FAVORED ALONG THIS PREDICTED STORM TRACK. THE
HIGHEST ODDS FOR ABOVE-MEDIAN PRECIPITATION ARE FORECAST ACROSS SOUTHEAST TEXAS
AND LOUISIANA WHERE THE PRECIPITATION TOTALS PREDICTED DURING THE FIRST WEEK OF
DECEMBER ARE NEAR OR ABOVE THE DECEMBER NORMAL. THE MOST LIKELY AREA FOR
BELOW-MEDIAN PRECIPITATION EXISTS ACROSS THE FLORIDA PENINSULA DUE TO RIDGING
ALOFT DURING EARLY DECEMBER AND IT IS CONSISTENT WITH THE LOW-FREQUENCY BASE
STATE.

ARCTIC HIGH PRESSURE WITH ANOMALOUS NORTHERLY FLOW IS EXPECTED TO RESULT IN
LARGE NEGATIVE TEMPERATURE ANOMALIES ACROSS MOST OF MAINLAND ALASKA AND THE
ALASKA PANHANDLE DURING EARLY DECEMBER. BASED ON THESE LARGE NEGATIVE
TEMPERATURE ANOMALIES, BELOW-NORMAL TEMPERATURES ARE FAVORED IN THE REVISED
TEMPERATURE OUTLOOK. ABOVE-NORMAL SSTS CONTINUE TO FAVOR ABOVE-NORMAL
TEMPERATURES ACROSS THE ALEUTIANS AND COASTAL SOUTHWEST ALASKA. ENHANCED ODDS
FOR BELOW-MEDIAN PRECIPITATION PREDICTED FOR COASTAL SOUTHERN ALASKA ARE
CONSISTENT WITH RECENT DAILY RUNS OF THE CFS MODEL AND ANOMALOUS OFFSHORE FLOW
EARLY DURING DECEMBER.

----------- PREVIOUS MESSAGE (FROM NOVEMBER 17 ) IS SHOWN BELOW ------------

THE DECEMBER 2016 TEMPERATURE AND PRECIPITATION OUTLOOKS ARE BASED ON DYNAMICAL
MODEL GUIDANCE, STATISTICAL TOOLS, AND THE TYPICAL INFLUENCE FROM LA NINA.
DURING THE PAST COUPLE OF MONTHS, LA NINA CONDITIONS DEVELOPED AS OBSERVED WITH
NEGATIVE SEA SURFACE TEMPERATURES ACROSS THE EASTERN AND CENTRAL EQUATORIAL
PACIFIC OCEAN ALONG WITH SUPPRESSED (ENHANCED) CONVECTION ACROSS THE CENTRAL
TROPICAL PACIFIC (INDONESIA). CLIMATE SIGNALS TYPICALLY ASSOCIATED WITH LA NINA
WERE CONSIDERED IN MAKING THE DECEMBER 2016 OUTLOOK, GIVEN THESE CURRENT
ATMOSPHERIC AND OCEANIC STATES.

ALTHOUGH THE MJO STRENGTHENED DURING EARLY NOVEMBER, ITS EFFECTS ON THE
EXTRATROPICS ARE UNCLEAR DUE TO INTERFERENCE WITH THE LOW FREQUENCY BASE STATE.
THE DYNAMICAL MODELS INDICATE A DECREASE IN THE AMPLITUDE OF THE MJO SIGNAL
DURING THE NEXT WEEK. THEREFORE, THE MJO DID NOT FACTOR INTO THE DECEMBER
OUTLOOK. ITS EVOLUTION WILL BE CLOSELY MONITORED FOR THE REVISED OUTLOOK AT THE
END OF NOVEMBER.

DESPITE EXCELLENT AGREEMENT AMONG THE DYNAMICAL MODELS THAT FAVOR ABOVE-NORMAL
TEMPERATURES THROUGHOUT THE FORECAST DOMAIN, FORECAST CONFIDENCE IN THE
TEMPERATURE OUTLOOK IS LOWER THAN WOULD BE EXPECTED. THE ARCTIC OSCILLATION
(AO) INDEX HAD ONE ITS MOST NEGATIVE VALUES FOR OCTOBER. A NEGATIVE AO INDEX IS
ASSOCIATED WITH ABOVE (BELOW) NORMAL 500-HPA HEIGHTS AT THE HIGHER (MIDDLE)
LATITUDES OF THE NORTHERN HEMISPHERE. THIS PATTERN RESULTED IN BELOW-NORMAL
TEMPERATURES ACROSS PARTS OF EURASIA. HOWEVER, ABOVE-NORMAL TEMPERATURES WERE
OBSERVED ACROSS MOST OF THE LOWER 48 DURING OCTOBER. AFTER A BRIEF PERIOD WITH
A POSITIVE AO INDEX, THE GFS MODEL REMAINS CONSISTENT THAT THE AO INDEX BECOMES
SHARPLY NEGATIVE ONCE AGAIN DURING LATE NOVEMBER. BELOW-NORMAL TEMPERATURES ARE
TYPICALLY ASSOCIATED WITH A NEGATIVE AO INDEX FROM THE NORTHERN GREAT PLAINS
SOUTHEAST TO THE SOUTHERN ATLANTIC COASTAL STATES DURING DECEMBER. GIVEN THE
LARGE DISAGREEMENT BETWEEN TEMPERATURE COMPOSITES OF A NEGATIVE AO INDEX (BELOW
NORMAL) AND DYNAMICAL MODEL GUIDANCE (ABOVE NORMAL), EQUAL CHANCES FOR BELOW,
NEAR, OR ABOVE-NORMAL TEMPERATURES ARE FORECAST FROM THE NORTHERN GREAT PLAINS
EXTENDING INTO THE SOUTHEAST. ELSEWHERE, ABOVE-NORMAL TEMPERATURES ARE FAVORED
ACROSS NEW ENGLAND AND THE WESTERN CONUS ALTHOUGH PROBABILITIES ARE TEMPERED
DUE TO THE BLOCKY 500-HPA PATTERN OVER THE NORTHERN HEMISPHERE EXPECTED AT THE
BEGINNING OF DECEMBER.

THE PRECIPITATION OUTLOOK FOR DECEMBER IS BASED PRIMARILY ON THE CALIBRATED
NMME AND IS CONSISTENT WITH LA NINA AND THE DJF PRECIPITATION OUTLOOK. HOWEVER,
THE FAVORED AREA FOR BELOW-MEDIAN PRECIPITATION OVER THE SOUTHEAST DOES NOT
EXTEND INTO THE SOUTHWESTERN CONUS SINCE THE LATEST RUNS OF THE CFS INDICATE AN
UPPER-LEVEL TROUGH OVER THIS REGION DURING EARLY DECEMBER. A SLIGHT TILT IN THE
ODDS FOR ABOVE-MEDIAN PRECIPITATION DOWNWIND OF THE GREAT LAKES IS BASED ON
ELEVATED CHANCES OF LAKE-ENHANCED PRECIPITATION WITH THE ABOVE-NORMAL LAKE
TEMPERATURES. THE PROBABILITIES FOR BELOW (ABOVE)-MEDIAN PRECIPITATION FORECAST
ACROSS THE SOUTHEASTERN (NORTHWESTERN) CONUS ARE MODEST DUE TO LIMITED SKILL
INHERENT IN A MONTHLY OUTLOOK AT THIS TIME LEAD. THIS PRECIPITATION OUTLOOK
WILL LIKELY BE REVISED AT THE END OF NOVEMBER.

THE HIGHEST ODDS FOR ABOVE-NORMAL TEMPERATURES THROUGHOUT THE FORECAST DOMAIN
ARE FORECAST ACROSS THE ALEUTIANS WHERE SEA SURFACE TEMPERATURE ANOMALIES ARE
AVERAGING AS MUCH AS 1.5 DEGREES C ABOVE NORMAL. EQUAL CHANCES FOR BELOW, NEAR,
OR ABOVE-NORMAL TEMPERATURES FORECAST ACROSS INTERIOR EASTERN ALASKA IS DUE TO
DIFFERENCES AMONG DYNAMICAL MODEL GUIDANCE AND STATISTICAL TOOLS BASED ON LA
NINA. THE DYNAMICAL MODELS OFFER WEAK PRECIPITATION SIGNALS ACROSS ALASKA WITH
THE CALIBRATED NMME INDICATING INCREASED CHANCES FOR ABOVE-MEDIAN PRECIPITATION
ACROSS THE ALEUTIANS AND WESTERN ALASKA.


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 15 2016


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

$$

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