998
FXUS07 KWBC 302001
PMD30D
PROGNOSTIC DISCUSSION FOR MONTHLY OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST THU NOV 30 2023
30-DAY OUTLOOK DISCUSSION FOR DECEMBER 2023
EL NIñO CONDITIONS CONTINUE TO BE OBSERVED, WITH RECENT SSTS ACROSS THE
EQUATORIAL PACIFIC REMAINING WELL ABOVE NORMAL. THE LATEST SST ANOMALY VALUE
IN THE NINO3.4 REGION IS 2.1C. UPPER-LEVEL AND LOWER-LEVEL WINDS AS WELL AS THE
OLR PATTERN ARE ALL REFLECTIVE OF EL NIñO CONDITIONS, INDICATING THAT THE
ATMOSPHERE AND OCEAN ARE COUPLED WITH A ROBUST RESPONSE. THE MJO REMAINS
ACTIVE AS WELL WITH THE ENHANCED CONVECTION PHASE OVER THE INDIAN OCEAN. LAGGED
IMPACTS FROM AN IO BASED MJO WOULD PUT UPPER-LEVEL RIDGING OVER THE CONTIGUOUS
U.S. (CONUS) AND UPPER-LEVEL TROUGHING OVER ALASKA FOR MUCH OF THE MONTH.
COMPOSITES ALSO SUPPORT SOME TROUGHING EARLY IN THE MONTH NEAR THE WEST COAST,
WHICH THEN FADES THROUGHOUT THE MONTH. THE MJO AND ENSO RELATED SIGNALS ARE
LIKELY TO BE ONLY A PORTION OF THE REALIZED CONDITIONS.
TEMPERATURES ARE FAVORED TO BE ABOVE-NORMAL FOR MUCH OF THE CONUS FOR THE MONTH
OF DECEMBER. A WARM START IS LIKELY FOR THE SOUTHEAST WITH A STORMY PATTERN
KEEPING MINIMUM TEMPERATURE ELEVATED, WHILE THE NORTHERN GREAT PLAINS ARE
LIKELY TO HAVE OVERALL ABOVE-NORMAL TEMPERATURES. THE MAIN AREAS OF UNCERTAINTY
IN THE TEMPERATURE OUTLOOK ARE THE SOUTHWEST AND CALIFORNIA. THE POTENTIAL FOR
EARLY MONTH TROUGHING MITIGATES THE ODDS FOR ABOVE-NORMAL TEMPERATURES IN THOSE
REGIONS. ANY TROUGHING AND UNSETTLED WEATHER PATTERN WOULD BE TRANSIENT, A
NOTION SUPPORTED BY PNA FORECASTS IN THE GEFS WHICH OSCILLATE FROM POSITIVE TO
NEGATIVE AND BACK TO POSITIVE IN THE FIRST TWO WEEKS. THE INTENSITY AND
DURATION OF POTENTIAL TROUGHING OVER ALASKA RESULTS IN AN AREA OF BELOW-NORMAL
TEMPERATURES BEING FAVORED ACROSS SOUTHWEST MAINLAND ALASKA AND A SIGNIFICANT
REDUCTION IN THE PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES IN THE OFFICIAL
OUTLOOKS COMPARED TO THE MODEL GUIDANCE. REDUCED SEA-ICE NEAR THE NORTHERN
COAST OF ALASKA FAVORS ABOVE-NORMAL TEMPERATURES POTENTIALLY MITIGATING THE
ATMOSPHERIC RELATED SIGNALS, THOUGH THE UNCERTAINTY THERE IS HIGHER THAN USUAL.
MODEL MEMBERS DO SIGNAL THE POTENTIAL FOR SOME SIGNIFICANT SHORT PERIODS OF
ANOMALOUSLY COLD AIR, WHICH WOULD ALIGN WITH MJO RELATED TROUGHING, THOUGH
EXACT TROUGH AXIS PLACEMENT IS STILL TOO UNCERTAIN TO INDICATE A SIGNAL.
WITHIN THIS OUTLOOK IS INCLUDED POTENTIAL FOR A WET START TO THE MONTH IN THE
SOUTHEAST DURING THE FIRST WEEK, THEN A SHORT-DRY PERIOD, WITH THE OVERALL
BACKGROUND INFLUENCED BY THE EL NIñO WHICH FAVORS A TILT TOWARD WET. THE EARLY
WET PERIOD IS LIKELY TO PROVIDE PRECIPITATION AMOUNTS THAT EFFECTIVELY RULE OUT
THE POTENTIAL FOR BELOW-NORMAL TOTAL PRECIPITATION FOR THE MONTH. THAT SAME
OSCILLATION FROM WET TO DRY TO WET IS LIKELY TO ALSO FAVOR AN OVERALL WET
PERIOD FOR PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, AS THE DECEMBER
CLIMATOLOGY OF PRECIPITATION IS RELATIVELY LOW ACROSS PORTIONS OF KANSAS AND
NORTHERN MISSOURI. A VERY WET PERIOD AS AN IMPACT FROM AN ATMOSPHERIC RIVER IS
LIKELY TO START THE MONTH FOR THE PACIFIC NORTHWEST, THOUGH THE EXACT AREA OF
HIGHEST PRECIPITATIONL IS UNCERTAIN. THE OVERALL FLOW FOR THE MONTH IS LIKELY
TO SUPPORT CONTINUED WET CONDITIONS ACROSS THE PACIFIC NORTHWEST AS BOTH MODELS
AND MJO COMPOSITES INDICATE AN ACTIVE STORM TRACK ACROSS THAT REGION.
BELOW-NORMAL PRECIPITATION IS FAVORED ACROSS THE NORTHERN GREAT PLAINS AND
UPPER GREAT LAKES, THOUGH PRECIPITATION TOTALS THERE ARE LOW DURING THE WINTER,
SO THE UNCERTAINTY IN THAT FORECAST IS HIGHER THAN FOR THE AREAS IN THE
SOUTHEAST AND NORTHWEST.
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--------------- PREVIOUS DISCUSSION FROM MID-NOVEMBER FOLLOWS -----------------
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EL NIñO CONDITIONS ARE CURRENTLY OBSERVED, AND EQUATORIAL SEA SURFACE
TEMPERATURES (SSTS) ARE ABOVE AVERAGE ACROSS THE CENTRAL AND EASTERN EQUATORIAL
PACIFIC OCEAN. THE TROPICAL PACIFIC ATMOSPHERE IS CONSISTENT WITH EL NIñO, AND
AS SUCH WE EXPECT EL NIñO TO BE THE DOMINANT TROPICAL-BASED TELECONNECTION FOR
DECEMBER. THE MADDEN JULIAN OSCILLATION (MJO) RECENTLY WEAKENED ACCORDING TO
THE REAL-TIME MULTIVARIATE (RMM) INDEX AND CPC'S 200-HPA VELOCITY POTENTIAL
INDEX, BUT IS FORECAST TO STRENGTHEN LATER IN NOVEMBER. A STRENGTHENING MJO
COULD RESULT IN MORE VARIABILITY OVER THE WESTERN CONUS DURING THROUGH
MID-DECEMBER. IN ADDITION TO THESE INFLUENCING FACTORS, THE DECEMBER
TEMPERATURE AND PRECIPITATION OUTLOOKS CONSIDER LOCAL SST ANOMALIES, DYNAMICAL
MODEL GUIDANCE FROM THE NORTH AMERICAN MULTI-MODEL ENSEMBLE (NMME), COPERNICUS
MODEL SUITE (C3S), AND THE CLIMATE FORECAST SYSTEM VERSION 2 (CFSV2), AS WELL
AS STATISTICAL MODELS THAT INCLUDE THE INFLUENCE OF TREND AND ENSO. WEEK 3-4
OUTPUTS FROM CFSV2, ECMWF, AND GEFSV12 FROM MID-NOVEMBER FOR THE EARLY PART OF
DECEMBER WERE ALSO CONSIDERED.
THE DECEMBER 2023 TEMPERATURE OUTLOOK FAVORS A BROAD AREA OF ABOVE NORMAL
TEMPERATURES FOR THE EASTERN CONUS, FROM THE NORTHERN GREAT PLAINS TO THE LOWER
MISSISSIPPI VALLEY AND EASTWARD TO THE COAST. THE HIGHEST PROBABILITIES FOR
ABOVE-NORMAL TEMPERATURES ARE OVER THE UPPER MISSISSIPPI VALLEY AND GREAT
LAKES, WHERE THE IMPACTS OF TREND AND ENSO ARE MAXIMIZED. NMME OUTPUTS SUPPORT
THE AREA OF ABOVE-NORMAL TEMPERATURES EAST OF THE MISSISSIPPI RIVER, BUT WITH
LOWER PROBABILITIES THAN THE STATISTICAL TOOLS (CCA, CA, OCN). ACROSS THE GREAT
PLAINS TO THE ROCKIES, TRENDS ARE WEAK AND THE DYNAMICAL MODEL SIGNALS ARE
MIXED, SO EQUAL CHANCES (EC) IS INDICATED. OCN INDICATES WARMTH ACROSS THE
SOUTHWEST WHILE ENSO-OCN FAVORS BELOW-NORMAL TEMPERATURES IN THE FOUR CORNERS
REGION. LAGGED COMPOSITES OF PREDICTED MJO ACTIVITY WOULD FAVOR A HIGHLY
VARIABLE PATTERN ACROSS THE ROCKIES, FURTHER CONTRIBUTING TO THE EC OUTLOOK
THERE. ACROSS NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST, THE STATISTICAL
TOOLS AND DYNAMICAL MODELS BOTH INDICATE ABOVE-NORMAL TEMPERATURES, BUT THE
SPATIAL PATTERNS IN THE TOOLS ARE NOT ALIGNED, INDICATING UNCERTAINTY IN THE
OUTPUT AND LIKELY UNCERTAINTY IN THE FORCING, SO EC IS INDICATED THERE. ACROSS
ALASKA, RECENT SST OBSERVATIONS ARE SHOWING ABOVE-NORMAL SSTS AND LOWER SEA ICE
COVERAGE, BOTH OF WHICH WOULD FAVOR ABOVE-NORMAL TEMPERATURES FOR WESTERN AND
NORTHERN ALASKA. NMME AND WEEK3/4 MODEL GUIDANCE ALSO SUPPORT BROAD SCALE
ABOVE-NORMAL TEMPERATURES ACROSS MOST OF ALASKA, THOUGH TEMPERED BY MEAN
TROUGHING ASSOCIATED WITH THE PREDICTED PHASES OF MJO EARLY IN THE MONTH.
THE STRONGEST SIGNAL FOR ABOVE-NORMAL PRECIPITATION IS ACROSS THE SOUTHEAST,
CONSISTENT WITH NMME AND STATISTICAL TOOL GUIDANCE, AS WELL AS WEEK-3/4
GUIDANCE. A STORM TRACK ACROSS THE SOUTHEAST IS CONSISTENT WITH THE WINTER TIME
RESPONSE TO EL NIñO. THE ENSO-OCN TOOL INDICATED A WET START TO THE MONTH FROM
TEXAS TO SOUTH DAKOTA, AND THE OCN INDICATES A STRONG WET TREND IN THE NORTHERN
PLAINS. MJO COMPOSITES INDICATE VARIABILITY IN STORM TRACK DURING THE MONTH,
WITH EARLY MONTH TROUGHING ACROSS THE WESTERN CONUS THAT EVOLVES INTO AN
ENHANCED JET BY MID MONTH. THAT TRANSITION AND PROGRESSIVE PATTERN RESULTS IN
EC OVER MOST OF THE WESTERN CONUS, THOUGH NORTH OF THE MEAN TROUGH LIKELY EARLY
IN THE MONTH IS AN AREA ACROSS THE NORTHERN GREAT PLAINS WHERE BELOW-NORMAL
PRECIPITATION IS LIKELY FOR THE MONTH AS A WHOLE. MEAN TROUGHING TO THE WEST OF
ALASKA FROM MJO COMPOSITES, TRENDS, AND SST PATTERNS INDICATE ABOVE-NORMAL
PRECIPITATION FOR WESTERN AND NORTHERN MAINLAND ALASKA IS THE MOST LIKELY
OUTCOME.
FORECASTER: MATTHEW ROSENCRANS
THE CLIMATIC NORMALS ARE BASED ON CONDITIONS BETWEEN 1991 AND 2020, 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 2023
THESE OUTLOOKS ARE BASED ON DEPARTURES FROM THE 1991-2020 BASE PERIOD.
CLICK HERE TO GO TO PREVIOUS BULLETINS.
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