861
FXUS06 KWBC 182001
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST WED DECEMBER 18 2024
6-10 DAY OUTLOOK FOR DEC 24 - 28 2024
BROAD RIDGING IS FORECAST EAST OF THE ROCKIES DURING THE FORECAST PERIOD, WITH
A LARGE POSITIVE 500-HPA HEIGHT ANOMALY CENTER (GREATER THAN +300 METERS)
BECOMING ESTABLISHED OVER EASTERN CANADA. HIGHLY AMPLIFIED LONGWAVE TROUGHING
IS PREDICTED ACROSS THE NORTHEASTERN PACIFIC, JUST SOUTH OF THE ALEUTIANS, WITH
SEVERAL SHORTWAVE DISTURBANCES EMBEDDED WITHIN THIS TROUGH MOVING INTO THE
WESTERN CONUS. THE 0Z AND 6Z GEFS CONTINUE TO BE THE MOST ROBUST WITH THE
INCOMING SHORTWAVE ENERGY, DEPICTING NEGATIVE HEIGHT ANOMALIES INCREASING OVER
THE INTERIOR WEST AND GREAT PLAINS LATE IN THE PERIOD. FOR THE PERIOD AS A
WHOLE, ABOVE-NORMAL HEIGHTS ARE FORECAST FOR MOST OF THE CONUS, WITH THE
LARGEST POSITIVE ANOMALIES ACROSS THE GREAT LAKES. CLOSER TO NORMAL HEIGHTS ARE
FORECAST ACROSS THE FLORIDA PENINSULA. THE AFOREMENTIONED 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
WESTERN AND CENTRAL CONUS UNDERNEATH RIDGING, WITH THE UNCALIBRATED 0Z ECENS
AND GEFS DEPICTING DAILY TEMPERATURES 15-20 DEG F ABOVE-NORMAL ACROSS PORTIONS
OF THE CENTRAL CONUS THROUGHOUT THE PERIOD. WHILE SOME DECREASE IN MID-LEVEL
HEIGHTS IS FORECAST ACROSS THE WEST, THE PREDICTED INCREASE IN PACIFIC FLOW
AHEAD OF TROUGHING STILL FAVORS ABOVE-NORMAL TEMPERATURES. A RELATIVELY CHILLY
START TO THE PERIOD IS LIKELY ACROSS THE EAST TIED TO A SURGE OF ARCTIC AIR
THAT IS FORECAST TO PEAK PRIOR TO THE FORECAST PERIOD. HOWEVER, A QUICK
MODERATION IS ANTICIPATED AS THE UPSTREAM RIDGING EXPANDS EASTWARD, WITH
TEMPERATURES FLIPPING TO ABOVE-NORMAL LATER IN THE PERIOD. ONLY COASTAL AREAS
OF THE MID-ATLANTIC AND NORTHEAST ARE FORECAST TO HAVE NEAR-NORMAL TEMPERATURES
FOR THE PERIOD AS A WHOLE, WITH INCREASING PROBABILITIES FOR ABOVE-NORMAL
TEMPERATURES FURTHER INLAND. INCREASED SOUTHERLY FLOW FAVORS INCREASED CHANCES
FOR ABOVE-NORMAL TEMPERATURES OVER SOUTH-CENTRAL AND SOUTHEASTERN ALASKA, WITH
NEAR- TO BELOW-NORMAL TEMPERATURE PROBABILITIES 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 70 PERCENT)
HIGHLIGHTED OVER THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA. CHANCES FOR
ABOVE-NORMAL PRECIPITATION ALSO EXTEND ACROSS THE INTERIOR WEST GIVEN THE
POTENTIAL FOR SHORTWAVE TROUGHING TO MOVE FURTHER INLAND, AND ARE ALSO ENHANCED
ACROSS MUCH OF THE CENTRAL AND EAST-CENTRAL CONUS, TIED TO SOUTHERLY RETURN
FLOW AROUND SURFACE HIGH PRESSURE FORECAST OVER THE NORTHEAST AND SOME 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) HIGHLIGHTED OVER PORTIONS OF THE MISSISSIPPI VALLEY. THE
SURFACE HIGH OVER THE NORTHEAST FAVORS ENHANCED CHANCES FOR NEAR- TO
BELOW-NORMAL PRECIPITATION ACROSS MUCH OF THE EASTERN SEABOARD, EXCLUDING
FLORIDA WHERE ABOVE-NORMAL PRECIPITATION ODDS ARE ELEVATED BASED ON THE GEFS
AND ECENS REFORECAST TOOLS. ABOVE-NORMAL PRECIPITATION IS FORECAST FOR MUCH OF
ALASKA, WITH THE HIGHEST PROBABILITIES OVER SOUTH-CENTRAL AND SOUTHEASTERN
ALASKA UNDERNEATH THE STRONGEST ONSHORE FLOW WITH A SERIES OF SURFACE LOW
PRESSURE SYSTEMS FORECAST TO MOVE INTO THE GULF OF ALASKA. BELOW-NORMAL
PRECIPITATION PROBABILITIES ARE INCREASED ACROSS HAWAII CONSISTENT WITH THE
CONSOLIDATED REFORECAST TOOL AND RIDGING FORECAST OVER THE STATE.
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 26, 2024 - JAN 01, 2025
AS DISCUSSED IN THE 6-10 DAY OUTLOOK, ENHANCED MID-LEVEL RIDGING IS FORECAST
OVER MUCH OF THE CENTRAL AND EASTERN CONUS AT THE START OF WEEK-2, WITH
LONGWAVE TROUGHING SITUATED OFF THE WEST COAST AND OVER ALASKA. THE LARGEST
POSITIVE 500-HPA HEIGHT ANOMALIES ARE PREDICTED TO SHIFT INTO EASTERN NORTH
AMERICA (+330 METERS OVER EASTERN CANADA IN THE MANUAL BLEND), WITH DECREASING
POSITIVE HEIGHT ANOMALIES ACROSS THE WESTERN CONUS DUE TO THE POTENTIAL FOR
SHORTWAVE TROUGHING TO MOVE INTO THE REGION. WHILE THE 0Z ECENS AND CMCE ALSO
INDICATE A WEAKNESS IN THE MID-LEVEL HEIGHT FIELD ACROSS THE INTERIOR WEST AND
CENTRAL CONUS DURING THE EARLY AND MIDDLE PART OF WEEK-2, BOTH ENSEMBLES
INDICATE A TREND TOWARD MORE RIDGING OVER THE WEST BY THE END OF THE PERIOD.
FOR WEEK-2 AS A WHOLE, ABOVE-NORMAL HEIGHTS REMAIN FORECAST FOR MOST OF THE
CONUS. NEAR-NORMAL HEIGHTS ARE PREDICTED OVER THE PACIFIC NORTHWEST AND SOUTH
FLORIDA, WITH BELOW-NORMAL HEIGHTS FAVORED OVER ALASKA. ANOMALOUS RIDGING OVER
THE CENTRAL PACIFIC CONTINUES TO FAVOR ABOVE-NORMAL HEIGHTS ACROSS HAWAII.
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). AN UPWARD TREND IN TEMPERATURES IS PREDICTED FOR THE
EAST TIED TO THE UPSTREAM RIDGING, WITH MUCH OF THE ANTECEDENT ARCTIC AIR MASS
EXITING LATE IN WEEK-1. ACROSS THE WEST, THERE ARE SOME INDICATIONS OF
TEMPERATURES COOLING LATER IN THE PERIOD, PARTICULARLY IN THE GEFS, AND AS A
RESULT, ABOVE-NORMAL TEMPERATURE PROBABILITIES ARE REDUCED COMPARED TO FURTHER
EAST BUT STILL REMAIN ABOVE-NORMAL. ALASKA REMAINS GENERALLY UNCHANGED FROM THE
6-10 DAY OUTLOOK, WITH INCREASED ONSHORE FLOW FAVORING ELEVATED ABOVE-NORMAL
TEMPERATURE PROBABILITIES ACROSS EASTERN AND SOUTHERN PORTIONS OF THE STATE AND
INCREASED BELOW-NORMAL TEMPERATURE CHANCES ACROSS THE NORTHWESTERN MAINLAND AND
THE ALEUTIANS CLOSER TO THE TROUGH AXIS. ABOVE-NORMAL TEMPERATURES REMAIN
FORECAST ACROSS HAWAII.
ENHANCED ONSHORE FLOW ALONG WITH ELEVATED ATMOSPHERIC RIVER POTENTIAL IS
FORECAST TO CONTINUE ACROSS THE WEST COAST, ESPECIALLY DURING THE EARLY PORTION
OF WEEK-2, FAVORING ELEVATED PROBABILITIES FOR ABOVE-NORMAL PRECIPITATION. THE
0Z ECENS AND CMCE DEPICT RIDGING DEVELOPING ACROSS THE WEST BY THE END OF THE
PERIOD, WHICH MAY PROMOTE A DRYING TREND. PERIODIC INTRUSIONS OF TROUGHING ARE
POSSIBLE ACROSS THE CENTRAL CONUS WHICH FAVORS 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. NEAR- TO ABOVE-NORMAL PRECIPITATION IS FORECAST
ACROSS ALASKA GIVEN THE PERSISTENT PATTERN AND ACTIVE STORM TRACK ACROSS THE
STATE. ENHANCED CHANCES FOR NEAR- TO BELOW-NORMAL PRECIPITATION ARE FORECAST
OVER HAWAII.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 30% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 50% 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 DIFFERENCES IN THE
MID-LEVEL PATTERN EVOLUTION ACROSS THE WEST.
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
DECEMBER 19.
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:
19951214 - 19861222 - 20051226 - 19931130 - 19661211
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:
20001217 - 19861221 - 20051226 - 20051218 - 19661212
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 24 - 28 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 B 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 N
VERMONT A N NEW HAMP A N MAINE A B
MASS N N CONN N N RHODE IS N N
PENN A N NEW JERSEY N N W VIRGINIA A A
MARYLAND A N DELAWARE N N VIRGINIA A N
N CAROLINA A N S CAROLINA A N GEORGIA A N
FL PNHDL A N 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 26, 2024 - JAN 01, 2025
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 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 N
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 N GEORGIA A N
FL PNHDL A N FL PENIN A N AK N SLOPE B A
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 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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