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FXUS06 KWBC 202001
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST FRI DECEMBER 20 2024
6-10 DAY OUTLOOK FOR DEC 26 - 30 2024
BROAD RIDGING IS FORECAST ACROSS MUCH OF THE EASTERN HALF OF NORTH AMERICA
DURING THE FORECAST PERIOD, WITH A LARGE POSITIVE 500-HPA HEIGHT ANOMALY CENTER
(GREATER THAN +360 METERS) OVER EASTERN CANADA IN THE MANUAL HEIGHT BLEND.
AMPLIFIED LONGWAVE TROUGHING IS INITIALLY PREDICTED ACROSS THE NORTHEASTERN
PACIFIC. HOWEVER, THIS FEATURE IS FAVORED TO WEAKEN AND THE 0Z ECENS AND CMCE
DEPICT RIDGING DEVELOPING ALONG THE WEST COAST BY THE END OF THE PERIOD. FOR
THE PERIOD AS A WHOLE, ABOVE-NORMAL HEIGHTS ARE FORECAST FOR MOST OF THE
CENTRAL AND EASTERN CONUS, WITH REDUCED POSITIVE HEIGHT ANOMALIES ACROSS
PORTIONS OF THE INTERIOR WEST AND SOUTHERN PLAINS DUE TO PERIODIC INTRUSIONS OF
SHORTWAVE TROUGHS. NEAR-NORMAL HEIGHTS ARE FAVORED OVER SOUTH FLORIDA.
ABOVE-NORMAL HEIGHTS ARE FORECAST ACROSS THE SOUTHWEST TIED TO AN INCREASE IN
RIDGING AS THE UPSTREAM TROUGH BEGINS TO RETREAT. THE TROUGHING OVER THE
NORTHEAST PACIFIC FAVORS BELOW-NORMAL HEIGHTS ACROSS ALASKA, AND EXTENDING INTO
THE NORTHWESTERN CONUS. ANOMALOUS RIDGING OVER THE CENTRAL PACIFIC FAVORS
ABOVE-NORMAL HEIGHTS OVER HAWAII, ALTHOUGH WEAKENING OF THESE ANOMALIES IS
FORECAST LATER IN THE PERIOD AS A TROUGH DEVELOPS TO THE EAST OF THE ISLANDS.
THERE IS HIGH CONFIDENCE FOR ABOVE-NORMAL TEMPERATURES ACROSS MUCH OF THE CONUS
UNDERNEATH THE FAVORED RIDGING, WITH THE UNCALIBRATED 0Z ECENS AND GEFS
DEPICTING DAILY TEMPERATURES 15-20 DEG F ABOVE-NORMAL ACROSS PORTIONS OF THE
UPPER MIDWEST THROUGHOUT THE PERIOD WHERE THE HIGHEST PROBABILITIES (GREATER
THAN 90 PERCENT) ARE FORECAST. WHILE SOME DECREASE IN MID-LEVEL HEIGHTS IS
FORECAST ACROSS THE WEST, THE ENHANCED PACIFIC FLOW STILL FAVORS ABOVE-NORMAL
TEMPERATURES, ALTHOUGH SOME REDUCTION IN MAGNITUDE IS POSSIBLE TOWARD THE END
OF THE PERIOD. INCREASED SOUTHERLY FLOW FAVORS INCREASED CHANCES FOR
ABOVE-NORMAL TEMPERATURES OVER EASTERN ALASKA, WITH ENHANCED NEAR- TO
BELOW-NORMAL TEMPERATURE PROBABILITIES INDICATED ACROSS WESTERN PARTS OF THE
STATE CLOSER TO THE NEGATIVE HEIGHT ANOMALY CENTER. HIGH CHANCES FOR
ABOVE-NORMAL TEMPERATURES REMAIN FORECAST OVER HAWAII UNDERNEATH CENTRAL
PACIFIC RIDGING AND A LESS VARIABLE CLIMATOLOGY.
ENHANCED ONSHORE FLOW IS LIKELY TO LEAD TO ROUNDS OF HEAVY PRECIPITATION ALONG
MUCH OF THE WEST COAST OF THE CONUS, WITH ELEVATED PROBABILITIES FOR INTEGRATED
VAPOR TRANSPORT (IVT) TO EXCEED 250 KG/M/S INDICATIVE OF INCREASED ATMOSPHERIC
RIVER POTENTIAL. THIS RESULTS IN HIGH PROBABILITIES FOR ABOVE-NORMAL
PRECIPITATION, WITH THE HIGHEST ODDS (GREATER THAN 60 PERCENT) HIGHLIGHTED OVER
PARTS OF THE PACIFIC NORTHWEST, NORTHERN CALIFORNIA, AND THE NORTHERN AND
CENTRAL GREAT BASIN. A DRYING TREND IS PREDICTED BY THE END OF THE PERIOD DUE
TO THE WEAKENING INFLUENCE FROM TROUGHING AND POTENTIAL FOR MORE RIDGING ALONG
THE WEST COAST. CHANCES FOR ABOVE-NORMAL PRECIPITATION ALSO EXTEND ACROSS MUCH
OF THE REMAINDER OF THE CONUS, TIED TO PERIODIC SHORTWAVE TROUGHS AND ELEVATED
POTENTIAL FOR LEE CYCLOGENESIS. PRECIPITABLE WATER IS FORECAST TO BE
ABOVE-NORMAL GIVEN THE WARM AIR MASS PREDICTED TO BE IN PLACE AND THIS COULD
FURTHER ENHANCE PRECIPITATION TOTALS RESULTING IN HIGHER PROBABILITIES (GREATER
THAN 50 PERCENT) OVER PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY AND ADJACENT
AREAS OF THE CENTRAL AND SOUTHERN PLAINS. SURFACE HIGH PRESSURE OVER THE
NORTHEAST FAVORS ENHANCED CHANCES FOR NEAR- TO BELOW-NORMAL PRECIPITATION. THE
GEFS AND ECENS REFORECAST TOOLS SUPPORT ELEVATED PROBABILITIES FOR BELOW-NORMAL
PRECIPITATION ACROSS SOUTHERN CALIFORNIA AND MUCH OF THE SOUTHWEST, FURTHER
DISPLACED FROM THE MEAN STORM TRACK TO THE NORTH. ABOVE-NORMAL PRECIPITATION IS
FORECAST FOR MUCH OF ALASKA, WITH THE HIGHEST PROBABILITIES OVER SOUTHEASTERN
MAINLAND ALASKA UNDERNEATH THE STRONGEST ONSHORE FLOW WITH A SERIES OF SURFACE
LOW PRESSURE SYSTEMS FORECAST TO MOVE INTO THE GULF OF ALASKA. NEAR-NORMAL
PRECIPITATION IS FAVORED ACROSS HAWAII CONSISTENT WITH THE CONSOLIDATED
REFORECAST TOOL.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 35% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 5% OF TODAY'S OPERATIONAL 6Z GFS CENTERED ON
DAY 8, 35% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, 5% OF
TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND 20% OF TODAY'S 0Z CANADIAN
ENSEMBLE MEAN CENTERED ON DAY 8
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: WELL ABOVE AVERAGE, 5 OUT OF 5,
DUE TO GOOD TOOL AGREEMENT AND A HIGHLY AMPLIFIED MID-LEVEL HEIGHT PATTERN
PREDICTED OVER THE FORECAST DOMAIN.
8-14 DAY OUTLOOK FOR DEC 28, 2024 - JAN 03, 2025
MODELS ARE COMING INTO BETTER AGREEMENT REGARDING A REALIGNMENT OF THE
MID-LEVEL HEIGHT PATTERN DURING WEEK-2. TROUGHING INITIALLY OVER THE NORTHEAST
PACIFIC IS FORECAST TO QUICKLY RETREAT, WITH THE 0Z GEFS, ECENS, AND CMCE
DEPICTING RIDGING DEVELOPING ALONG THE WEST COAST OF NORTH AMERICA BY THE END
OF WEEK-2, AND EVIDENCE OF MORE BROAD LONGWAVE TROUGHING BECOMING ESTABLISHED
OVER THE CENTRAL CONUS. THE WEEK-2 MANUAL 500-HPA HEIGHT BLEND DEPICTS
ABOVE-NORMAL HEIGHTS OVER MUCH OF EASTERN NORTH AMERICA, WITH A +330 METER
POSITIVE HEIGHT ANOMALY CENTER ACROSS EASTERN CANADA. REDUCED POSITIVE HEIGHT
ANOMALIES ARE PREDICTED ACROSS THE INTERIOR WEST, EXTENDING THROUGH THE CENTRAL
AND SOUTHERN PLAINS AND SOUTHEAST TIED TO PERIODIC SHORTWAVE DISTURBANCES.
ABOVE-NORMAL HEIGHTS ARE FAVORED ALONG THE WEST COAST OF THE CONUS AND EASTERN
ALASKA TIED TO THE AFOREMENTIONED RIDGING PREDICTED TO DEVELOP, WITH
BELOW-NORMAL HEIGHTS REMAINING FORECAST ACROSS WESTERN ALASKA. NEAR TO
BELOW-NORMAL HEIGHTS ARE FORECAST ACROSS HAWAII TIED TO TROUGHING DEVELOPING TO
THE EAST OF THE ISLANDS.
ALL FORECAST GUIDANCE FAVORS AN UNSEASONABLY WARM END TO 2024 ACROSS MUCH OF
THE CONUS WITH DAILY TEMPERATURE ANOMALIES EXCEEDING +15 DEG F OVER PORTIONS OF
THE NORTHERN PLAINS AND UPPER MIDWEST WHERE CONFIDENCE IS HIGHEST DURING WEEK-2
(GREATER THAN 80 PERCENT). THE UNCALIBRATED 0Z GEFS, ECENS, AND CMCE DEPICT
DECREASING POSITIVE TEMPERATURE ANOMALIES TOWARD THE END OF WEEK-2, BUT LIKELY
REMAINING ABOVE-NORMAL. RIDGING DEVELOPING NEAR THE WEST COAST FAVORS A MORE
NORTHERLY COMPONENT TO THE MID-LEVEL FLOW PATTERN ACROSS THE NORTHWEST AND
GREAT BASIN LATER IN WEEK-2 WHICH MAY LEAD TO DECREASING TEMPERATURES, WITH
UNCALIBRATED MODEL GUIDANCE INDICATING BELOW-NORMAL TEMPERATURES BY THE END OF
THE PERIOD. WEAK PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES ARE FORECAST
ACROSS THESE AREAS FOR WEEK-2 AS A WHOLE GIVEN CONTINUED SUPPORT FROM THE GEFS
AND ECENS REFORECAST TOOLS. PROBABILITIES FOR NEAR- TO ABOVE-NORMAL
TEMPERATURES ARE INCREASED ACROSS MUCH OF ALASKA GIVEN THE TREND TOWARD MORE
RIDGING AND WEAKER TROUGHING RELATIVE TO THE 6-10 DAY PERIOD. THE NORTHWESTERN
PORTION OF MAINLAND ALASKA STILL TILTS TOWARD ENHANCED BELOW-NORMAL TEMPERATURE
PROBABILITIES. ABOVE-NORMAL TEMPERATURES REMAIN LIKELY ACROSS HAWAII.
ENHANCED ONSHORE FLOW ALONG WITH ELEVATED ATMOSPHERIC RIVER POTENTIAL IS
FORECAST TO CONTINUE ACROSS MUCH OF THE WEST COAST AT THE BEGINNING OF WEEK-2
FAVORING ELEVATED PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION. HOWEVER, THE
AFOREMENTIONED RIDGING DEVELOPING ACROSS THE WEST COAST FAVORS A DRYING TREND
BEYOND DAY-9, AND A RESULTANT DECREASE IN PROBABILITIES FOR ABOVE-NORMAL
PRECIPITATION COMPARED TO THE 6-10 DAY PERIOD. PERIODIC INTRUSIONS OF SHORTWAVE
TROUGHING FAVOR A BROAD AREA OF ENHANCED ABOVE-NORMAL PRECIPITATION
PROBABILITIES EXTENDING THROUGHOUT MUCH OF THE CONUS, ALSO TIED TO ENHANCED
SOUTHERLY RETURN FLOW, ELEVATED POTENTIAL FOR LEE CYCLOGENESIS, AND
ABOVE-NORMAL PRECIPITABLE WATER VALUES DUE TO THE PREDICTED ABOVE-NORMAL
TEMPERATURES. ENHANCED CHANCES FOR BELOW-NORMAL PRECIPITATION ARE FAVORED
ACROSS SOUTHERN CALIFORNIA AND THE SOUTHWEST, SUPPORTED BY THE GEFS AND ECENS
REFORECAST TOOLS AND FURTHER DISPLACED FROM THE MEAN STORM TRACK TO THE NORTH.
NEAR- TO ABOVE-NORMAL PRECIPITATION IS FAVORED ACROSS ALASKA GIVEN THE
CONTINUED ACTIVE STORM TRACK ACROSS THE STATE, ESPECIALLY EARLY IN THE PERIOD.
ENHANCED CHANCES FOR NEAR- TO ABOVE-NORMAL PRECIPITATION ARE FORECAST OVER
HAWAII.
THE 500-HPA HEIGHT PATTERN REALIGNMENT ACROSS NORTH AMERICA DISCUSSED DURING
WEEK-2 IS FORECAST TO CONTINUE INTO WEEK-3, TIED TO THE MJO PROPAGATION INTO
PHASES 7 AND 8. THIS COULD RESULT IN A COLDER PATTERN ACROSS THE CENTRAL AND
EASTERN CONUS BY THE SECOND WEEK OF JANUARY. PLEASE REFER TO THE LATEST CPC
WEEK 3-4 OUTLOOK FOR MORE INFORMATION.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 40% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 40% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 11, AND 20% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON
DAY 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO
GENERALLY CONTINUED GOOD TOOL AGREEMENT, OFFSET BY SOME UNCERTAINTY RELATED TO
THE REALIGNMENT OF THE MID-LEVEL PATTERN, AND WEAK SIGNALS IN THE PRECIPITATION
GUIDANCE.
FORECASTER: THOMAS COLLOW
NOTES:
AUTOMATED FORECASTS ARE ISSUED ON SATURDAY AND SUNDAY. OCCASIONALLY MANUAL
INTERVENTION IS NECESSARY TO ADDRESS QUALITY CONTROL AND CONSISTENCY ISSUES. IN
THESE CASES, FORECASTS ARE MANUALLY DRAWN BUT A FULL DISCUSSION IS NOT ISSUED.
THE NOTATION FOR THE CATEGORICAL FORECAST INDICATED ON THE MAPS IS THE SAME AS
THAT IN THE TABLES: A-ABOVE N-NEAR NORMAL B-BELOW
THE TEMPERATURE MAP SHOWS REGIONS WITH > 33% CHANCE OF BEING WARMER (ORANGE,
"A"), COLDER (BLUE, "B"), OR CLOSE TO (UNSHADED, "N"). HISTORICAL AVERAGE
VALUES FOR THE CALENDAR PERIOD OF THE FORECAST (DASHES, "F"). LABELS ON THE
SHADED LINES GIVE THE PROBABILITY (> 33%) OF THE MORE LIKELY CATEGORY (B OR A).
PROBABILITY OF N IS ALWAYS < 40%.
THE PRECIPITATION MAP SHOWS REGIONS WITH > 33% CHANCE OF BEING WETTER (GREEN,
"A"), DRIER (TAN, "B"), OR CLOSE TO (UNSHADED, "N"). HISTORICAL MEDIAN VALUES
FOR THE CALENDAR PERIOD OF THE FORECAST (DASHES, "INCHES"). LABELS ON THE
SHADED LINES GIVE THE PROBABILITY (> 33%) OF THE MORE LIKELY CATEGORY (B OR A).
PROBABILITY OF N IS ALWAYS < 40%.
IN THE SOUTHWEST AND OTHER CLIMATOLOGICALLY DRY REGIONS - THERE WILL BE A
GREATER THAN 33.3% CHANCE OF NO PRECIPITATION AND OCCASIONALLY EVEN A NORMAL
(I.E. MEDIAN) VALUE OF ZERO - ESPECIALLY DURING THE DRY SEASONS. IN SUCH CASES
A FORECAST OF NEAR NORMAL IS EFFECTIVELY A FORECAST OF LITTLE OR NO
PRECIPITATION.
THE CLIMATE PREDICTION CENTER USES 1991-2020 BASE PERIOD MEANS AS REFERENCE IN
THE CLIMATE OUTLOOKS.
THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON
JANUARY 16.
ANALOGS TO THE 5 DAY MEAN OBSERVED PATTERN CENTERED 3 DAYS AGO (D-3)
FOR THE REGION FROM 20N TO 70N LATITUDE AND 175E TO 60W LONGITUDE
INCLUDE THE 5 DAY PERIODS CENTERED ON THE FOLLOWING DATES:
20051220 - 20061206 - 19631223 - 19931230 - 20051225
ANALOGS TO THE 7 DAY MEAN OBSERVED PATTERN CENTERED 4 DAYS AGO (D-4)
FOR THE REGION FROM 20N TO 70N LATITUDE AND 175E TO 60W LONGITUDE
INCLUDE THE 7 DAY PERIODS CENTERED ON THE FOLLOWING DATES:
20051221 - 20061206 - 19821212 - 19631226 - 19601222
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 26 - 30 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A A OREGON A A NRN CALIF A A
SRN CALIF A A IDAHO A A NEVADA A A
W MONTANA A A E MONTANA A A WYOMING A A
UTAH A A ARIZONA A B COLORADO A A
NEW MEXICO A A N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A A OKLAHOMA A A
N TEXAS A A S TEXAS A A W TEXAS A A
MINNESOTA A A IOWA A A MISSOURI A A
ARKANSAS A A LOUISIANA A A WISCONSIN A A
ILLINOIS A A MISSISSIPPI A A MICHIGAN A A
INDIANA A A OHIO A A KENTUCKY A A
TENNESSEE A A ALABAMA A A NEW YORK A B
VERMONT A B NEW HAMP A B MAINE A B
MASS A B CONN A B RHODE IS A B
PENN A N NEW JERSEY A B W VIRGINIA A A
MARYLAND A N DELAWARE A N VIRGINIA A N
N CAROLINA A A S CAROLINA A A GEORGIA A A
FL PNHDL A A FL PENIN A A AK N SLOPE B A
AK ALEUTIAN B A AK WESTERN B A AK INT BSN B A
AK S INT A A AK SO COAST A A AK PNHDL A A
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 28, 2024 - JAN 03, 2025
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A A OREGON A A NRN CALIF A A
SRN CALIF A B IDAHO A A NEVADA A A
W MONTANA A A E MONTANA A A WYOMING A A
UTAH A A ARIZONA A B COLORADO A A
NEW MEXICO A N N DAKOTA A A S DAKOTA A A
NEBRASKA A A KANSAS A A OKLAHOMA A A
N TEXAS A A S TEXAS A A W TEXAS A A
MINNESOTA A A IOWA A A MISSOURI A A
ARKANSAS A A LOUISIANA A A WISCONSIN A A
ILLINOIS A A MISSISSIPPI A A MICHIGAN A A
INDIANA A A OHIO A A KENTUCKY A A
TENNESSEE A A ALABAMA A A NEW YORK A A
VERMONT A A NEW HAMP A N MAINE A N
MASS A N CONN A A RHODE IS A N
PENN A A NEW JERSEY A A W VIRGINIA A A
MARYLAND A A DELAWARE A A VIRGINIA A A
N CAROLINA A N S CAROLINA A N GEORGIA A N
FL PNHDL A N FL PENIN A N AK N SLOPE N N
AK ALEUTIAN N A AK WESTERN N A AK INT BSN A N
AK S INT A A AK SO COAST A A AK PNHDL A A
LEGEND
TEMPS WITH RESPECT TO NORMAL PCPN WITH RESPECT TO MEDIAN
A - ABOVE N - NEAR NORMAL A - ABOVE N - NEAR MEDIAN
B - BELOW B - BELOW
THE FORECAST CLASSES REPRESENT AVERAGES FOR EACH STATE. NORMAL
VALUES - WHICH MAY VARY WIDELY ACROSS SOME STATES - ARE
AVAILABLE FROM YOUR LOCAL WEATHER SERVICE FORECAST OFFICE.
FOR ADDITIONAL INFORMATION SEE MESSAGE FXUS06 KWBC - ON AWIPS AS
PMDMRD.
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