453
FXUS06 KWBC 192002
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST THU DECEMBER 19 2024
6-10 DAY OUTLOOK FOR DEC 25 - 29 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.
HIGHLY AMPLIFIED LONGWAVE TROUGHING IS PREDICTED ACROSS THE NORTHEASTERN
PACIFIC, JUST SOUTH OF ALASKA, WITH SEVERAL SHORTWAVE DISTURBANCES EMBEDDED
WITHIN THIS TROUGH PREDICTED TO MOVE INTO THE WESTERN AND CENTRAL CONUS. FOR
THE PERIOD AS A WHOLE, ABOVE-NORMAL HEIGHTS ARE FORECAST FOR MOST OF THE
CENTRAL AND EASTERN CONUS, WITH NEAR-NORMAL HEIGHTS FAVORED ACROSS PORTIONS OF
THE INTERIOR WEST, SOUTHERN PLAINS, AND SOUTH FLORIDA. ABOVE-NORMAL HEIGHTS ARE
FORECAST ACROSS PORTIONS OF CALIFORNIA AND ADJACENT AREAS OF 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.
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
GREAT PLAINS AND 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 PREDICTED INCREASE IN PACIFIC FLOW
STILL FAVORS ABOVE-NORMAL TEMPERATURES. ACROSS THE EAST, TEMPERATURES ARE
FORECAST TO TREND FROM NEAR-NORMAL ON CHRISTMAS DAY TO ABOVE-NORMAL LATER IN
THE PERIOD. INCREASED SOUTHERLY FLOW FAVORS INCREASED CHANCES FOR ABOVE-NORMAL
TEMPERATURES OVER SOUTH-CENTRAL AND EASTERN ALASKA, WITH NEAR- TO BELOW-NORMAL
TEMPERATURE PROBABILITIES THAT ARE ENHANCED ACROSS NORTHERN AND 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 SUCCESSIVE ROUNDS OF HEAVY
PRECIPITATION ALONG 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 THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA. CHANCES FOR
ABOVE-NORMAL PRECIPITATION ALSO EXTEND ACROSS MUCH 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 MISSISSIPPI VALLEY AND EASTERN PLAINS. THE SURFACE HIGH 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 THE SOUTHERN FOUR CORNERS, 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 FORECAST 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 27, 2024 - JAN 02, 2025
MODELS ARE COMING INTO BETTER AGREEMENT REGARDING A REALIGNMENT OF THE
MID-LEVEL HEIGHT PATTERN ACROSS THE WEST 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 A SERIES OF SHORTWAVE TROUGHS PROGRESSING
INTO PARTS OF THE WESTERN AND 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. NEAR-NORMAL
HEIGHTS ARE PREDICTED ACROSS THE INTERIOR WEST, EXTENDING THROUGH THE CENTRAL
AND SOUTHERN PLAINS AND SOUTHEAST. 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-NORMAL HEIGHTS ARE FORECAST ACROSS HAWAII TIED TO
WEAKENING CENTRAL PACIFIC RIDGING.
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. THEREFORE, ONLY WEAK PROBABILITIES FOR ABOVE-NORMAL TEMPERATURES
ARE FORECAST ACROSS THESE AREAS FOR WEEK-2 AS A WHOLE. 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
FORECAST ACROSS HAWAII.
ENHANCED ONSHORE FLOW ALONG WITH ELEVATED ATMOSPHERIC RIVER POTENTIAL IS
FORECAST TO CONTINUE ACROSS THE WEST COAST DURING THE EARLY PORTION OF WEEK-2
FAVORING ELEVATED PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION, WITH THE
HIGHEST PROBABILITIES (GREATER THAN 50 PERCENT) ACROSS PARTS OF NORTHERN
CALIFORNIA AND WESTERN OREGON. THE AFOREMENTIONED RIDGING DEVELOPING ACROSS THE
WEST COAST LATER IN THE PERIOD FAVORS A DRYING TREND 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 SOUTHERN FOUR
CORNERS, 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
FORECAST 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 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:
20001217 - 20051219 - 20051224 - 19631223 - 19861222
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 - 20001217 - 20061207 - 20041213 - 19841231
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 25 - 29 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 N
VERMONT A B NEW HAMP A B MAINE A B
MASS A B CONN A N RHODE IS A N
PENN A A NEW JERSEY A N W VIRGINIA A A
MARYLAND A A DELAWARE A A VIRGINIA A A
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 A A
AK S INT A A AK SO COAST A A AK PNHDL A A
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 27, 2024 - JAN 02, 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 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 B
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 A MAINE A A
MASS A A 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 A S CAROLINA A A GEORGIA A A
FL PNHDL A A FL PENIN A A AK N SLOPE N N
AK ALEUTIAN N A AK WESTERN N A AK INT BSN A A
AK S INT A A AK SO COAST A A AK PNHDL A N
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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