067
FXUS07 KWBC 181231
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
830 AM EDT THU OCT 18 2018
30-DAY OUTLOOK DISCUSSION FOR NOVEMBER 2018
FORECASTS OF AUTUMN CLIMATE ARE ESPECIALLY DIFFICULT, AND THE NOVEMBER 2018
OUTLOOK IS NO EXCEPTION. LOW-FREQUENCY CLIMATE FORCING FROM ENSO IS EXPECTED TO
GRADUALLY INCREASE DURING THE NEXT SEVERAL WEEKS, THOUGH THIS HAS LIMITED
APPLICATIONS TO THE CURRENT OUTLOOK, ESPECIALLY WITH RESPECT TO TEMPERATURE.
THE MJO HAS BEEN ACTIVE OVER THE PAST SEVERAL WEEKS, BUT IS NOT EXPECTED TO
PLAY A MAJOR ROLE DURING NOVEMBER - THIS IS DUE TO BOTH UNCERTAIN MJO FORCING
ITSELF AS WELL AS ONLY MODEST EXTRATROPICAL TELECONNECTIONS AT THIS POINT IN
THE SEASONAL CYCLE. THE FORECAST IS THEREFORE INFORMED FIRSTLY BY A BLEND OF
CALIBRATED DYNAMICAL GUIDANCE FROM THE NMME AND STATISTICAL GUIDANCE THAT
LARGELY UTILIZES LONG-TERM TRENDS. THIS IS AUGMENTED BY ADDITIONAL DYNAMICAL
GUIDANCE FROM THE ECMWF, THE WEEKS 3-4 GUIDANCE, AND THE CURRENT EVOLUTION OF
DYNAMICAL MODEL FORECASTS THROUGH THE EXTENDED RANGE (~DAYS 10-16) PERIOD.
LONG-TERM TRENDS GENERALLY FAVOR ABOVE-NORMAL TEMPERATURES OVER MUCH OF THE
CONUS DURING THIS TIME OF YEAR, STRETCHING FROM THE SOUTHWEST TO THE NORTHEAST,
WITH RELATIVE WEAKNESSES IN THE NORTHWEST AND SOUTHEAST, RESPECTIVELY. AT THIS
POINT, ENSO TELECONNECTIONS ARE NOT A MAJOR PLAYER IN THE TEMPERATURE FORECAST
FOR TWO REASONS: THE CONVECTIVE RESPONSE TO THE DEVELOPING ENSO EVENT HAS BEEN
SLOW TO EMERGE TO THIS POINT, AND EVEN IN THE PRESENCE OF A SUBSTANTIAL EVENT
THE SIGNAL-TO-NOISE RATIO IS QUITE LOW FOR NOVEMBER (CORRELATIONS NEAR OR LESS
THAN 0.2). THE CALIBRATED NMME MODEL OUTPUT FAVORS ABOVE-NORMAL TEMPERATURES
OVER NEARLY ALL OF NORTH AMERICA, WITH THE LOWEST PROBABILITIES OVER THE
SOUTHEASTERN QUARTER OF THE CONUS. THE CFS HAS CONSISTENTLY BEEN FORECASTING
ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE CONUS AND MUCH OF ALASKA, WITH
BELOW-NORMAL TEMPERATURES CONFINED TO MUCH OF NORTHEASTERN CANADA. THE
AFOREMENTIONED FACTORS POINT TO AN INITIAL 'FIRST GUESS' THAT FAVORS ENHANCED
PROBABILITIES OF ABOVE-NORMAL TEMPERATURES OVER THE ENTIRE FORECAST DOMAIN,
WITH THE HIGHEST PROBABILITIES OVER NORTHERN AND WESTERN ALASKA AND PARTS OF
THE WESTERN CONUS. HOWEVER, PROBABILITIES ARE TEMPERED BY TWO MAIN FACTORS OVER
THE CENTRAL AND EASTERN U.S. FIRST, THE ECMWF IN BOTH ITS LONG-RANGE ENSEMBLE
SYSTEM AND EXTENDED RANGE (WEEKS 3-4) SYSTEM FAVOR NEAR- TO BELOW-NORMAL
TEMPERATURES CENTERED OVER THE CENTRAL AND SOUTHEASTERN CONUS, AND RUN-TO-RUN
CONTINUITY HAS BEEN GOOD IN THIS REGARD. SECONDLY, THIS APPEARS SUPPORTED BY A
FORECAST PATTERN CHANGE OVER THE HIGH LATITUDES TOWARD A NEGATIVE PHASE OF THE
NAO/AO DURING THE NEXT WEEK TO 10 DAYS. THE LATEST EVOLUTION OF THE GEFS FROM
DAYS 11 TO 16 FAVORS A CONTINUATION OF POSITIVE HEIGHT ANOMALIES OVER NORTHERN
LATITUDES AND ANOMALOUS TROUGHING SOMEWHERE OVER THE CENTRAL/EASTERN CONUS
HEADING INTO THE VERY BEGINNING OF NOVEMBER. THESE COMPOUNDING FACTORS LEAD TO
A REDUCTION IN PROBABILITIES FAVORING ABOVE-NORMAL TEMPERATURES OVER MOST OF
THE CENTRAL AND EASTERN CONUS. HOWEVER, GIVEN THE LARGE SCALE CLIMATE FACTORS
AT PLAY, THEY ARE NOT SUFFICIENT TO REVERSE THE SIGN OF THE EXPECTED CLIMATE
ANOMALIES.
THE PRECIPITATION FORECAST FOR NOVEMBER 2018 HAS MUCH REDUCED COVERAGE COMPARED
TO THE TEMPERATURE OUTLOOK, AS IS EXPECTED GIVEN THE LIMITED PREDICTABILITY FOR
THIS TYPE OF FORECAST. THE FORECAST IS INFORMED BY THE DYNAMICAL MODEL
CONSENSUS AND NINO 3.4 REGRESSIONS, WHICH JUST ABOUT REVEAL THE SAME GENERAL
PATTERN. ABOVE-MEDIAN PRECIPITATION IS FAVORED OVER PARTS OF THE SOUTHERN TIER
OF THE CONUS AS WELL AS MUCH OF ALASKA. A MODEST AREA DEPICTING BELOW-MEDIAN
PRECIPITATION IS INDICATED OVER THE PACIFIC NORTHWEST AND NORTHERN ROCKIES.
AREAS SHOWN IN WHITE LABELED EC DEPICT A FORECAST WHERE THE PROBABILITIES FOR
EITHER OF THREE CATEGORIES, BELOW-, NEAR- OR ABOVE-MEDIAN MONTHLY TOTAL
PRECIPITATION ARE NOT SIGNIFICANTLY DIFFERENT FROM CLIMATOLOGICAL PROBABILITIES.
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 NOV WILL BE ISSUED ON WED OCTOBER 31 2018
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1981-2010 BASE PERIOD.
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