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FXUS06 KWBC 172002
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST TUE DECEMBER 17 2024
6-10 DAY OUTLOOK FOR DEC 23 - 27 2024
BROAD RIDGING IS FORECAST ACROSS THE CONUS DURING THE FORECAST PERIOD, WITH A
GRADUAL EASTWARD PROGRESSION OF THE LARGEST POSITIVE 500-HPA HEIGHT ANOMALIES.
HIGHLY AMPLIFIED LONGWAVE TROUGHING IS PREDICTED ACROSS THE NORTHEASTERN
PACIFIC, JUST SOUTH OF THE ALEUTIANS, WITH SEVERAL SHORTWAVE DISTURBANCES
EMBEDDED WITHIN THIS TROUGH ROTATING TOWARD THE WEST COAST OF THE CONUS.
TROUGHING MAY PROGRESS INLAND ACROSS THE WESTERN CONUS BY DAY-10 LEADING TO
DECREASING HEIGHTS RELATIVE TO EARLIER 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 (+150 METERS). 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 PACIFIC NORTHWEST. 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 ON CHRISTMAS EVE AND CONTINUING THROUGH THE END OF THE
PERIOD. WHILE SOME DECREASE IN MID-LEVEL HEIGHTS IS FORECAST ACROSS THE WEST,
THE PREDICTED INCREASE IN ONSHORE FLOW AHEAD OF TROUGHING STILL FAVORS
ABOVE-NORMAL TEMPERATURES. FOR THE EAST, THE PERIOD IS FORECAST TO BEGIN WITH
AN ONGOING SURGE OF ARCTIC AIR. HOWEVER, A QUICK MODERATION IS ANTICIPATED AS
THE UPSTREAM RIDGING EXPANDS EASTWARD, WITH TEMPERATURES FLIPPING TO
ABOVE-NORMAL LATER IN THE PERIOD. ENHANCED PROBABILITIES FOR BELOW-NORMAL
TEMPERATURES CONTINUE TO BE FAVORED ACROSS PARTS OF THE EASTERN SEABOARD FOR
THE ENTIRE PERIOD GIVEN THE STRONG COLD SIGNALS AT THE OUTSET OF THE PERIOD.
HOWEVER, PROBABILITIES ARE REDUCED COMPARED TO YESTERDAY DUE TO THE ANTICIPATED
WARMING TREND. INCREASED SOUTHERLY FLOW FAVORS INCREASED CHANCES FOR
ABOVE-NORMAL TEMPERATURES OVER MOST OF ALASKA, WITH THE EXCEPTION OF THE
NORTHWESTERN MAINLAND WHERE NEAR- TO BELOW-NORMAL TEMPERATURE PROBABILITIES ARE
SLIGHTLY ENHANCED. STRONG 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. 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 EAST. THIS SURFACE HIGH FAVORS ENHANCED CHANCES
FOR BELOW-NORMAL PRECIPITATION FROM THE APPALACHIANS EAST TO THE ATLANTIC, WITH
THE EXCEPTION BEING ACROSS FLORIDA WHERE ABOVE-NORMAL PRECIPITATION CHANCES 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 25 - 31 2024
AS DISCUSSED IN THE 6-10 DAY OUTLOOK, ENHANCED RIDGING IS FORECAST OVER MUCH OF
THE CONUS AT THE START OF WEEK-2, WITH LONGWAVE TROUGHING SITUATED OFF THE WEST
COAST AND OVER ALASKA. THE LARGEST POSITIVE HEIGHT ANOMALIES ARE PREDICTED TO
SHIFT INTO EASTERN NORTH AMERICA WITH DECREASING POSITIVE HEIGHT ANOMALIES
ACROSS THE WESTERN CONUS DUE TO THE POTENTIAL FOR SHORTWAVE TROUGHING TO MOVE
INTO THE REGION, MOST EVIDENCED IN THE GEFS. 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 FINAL WEEK OF 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). WHILE THE EAST MAY HAVE NEAR-NORMAL
TEMPERATURES AT THE START OF THE PERIOD, AN UPWARD TREND IN TEMPERATURES IS
PREDICTED FOR THE REGION AS THE UPSTREAM RIDGING SHIFTS FURTHER TO THE EAST.
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 YESTERDAY 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 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 BUILDING 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
CENTRAL AND EAST-CENTRAL CONUS, ALSO TIED TO ENHANCED SOUTHERLY RETURN FLOW.
ELEVATED ODDS FOR NEAR- TO BELOW-NORMAL PRECIPITATION ARE FORECAST ACROSS THE
MID-ATLANTIC AND NORTHEAST SUPPORTED BY THE GEFS AND ECENS REFORECAST TOOLS.
NEAR- TO ABOVE-NORMAL PRECIPITATION IS FORECAST ACROSS ALASKA GIVEN THE
PERSISTENT PATTERN AND ACTIVE STORM TRACK ACROSS THE STATE. ENHANCED CHANCES
FOR 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:
19941215 - 19661211 - 19951215 - 20061211 - 20011127
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:
20011126 - 19661210 - 19941228 - 19841127 - 19931129
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 23 - 27 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 N WYOMING A A
UTAH A A ARIZONA A B COLORADO A A
NEW MEXICO A B N DAKOTA A N S DAKOTA A N
NEBRASKA A A KANSAS A A OKLAHOMA A A
N TEXAS A A S TEXAS A A W TEXAS A N
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 N KENTUCKY A N
TENNESSEE A N ALABAMA A N NEW YORK N B
VERMONT N B NEW HAMP B B MAINE B B
MASS B B CONN B B RHODE IS B B
PENN N B NEW JERSEY B B W VIRGINIA N B
MARYLAND B B DELAWARE B B VIRGINIA B B
N CAROLINA B N S CAROLINA B N GEORGIA N N
FL PNHDL N N FL PENIN N A AK N SLOPE B A
AK ALEUTIAN A A AK WESTERN A 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 25 - 31 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A A OREGON A A NRN CALIF A A
SRN CALIF A N 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 N NEW HAMP A N MAINE A B
MASS A N CONN A N RHODE IS A N
PENN A A NEW JERSEY A N W VIRGINIA A A
MARYLAND A N DELAWARE A N VIRGINIA A A
N CAROLINA A A S CAROLINA A A GEORGIA A N
FL PNHDL A N FL PENIN A A AK N SLOPE B A
AK ALEUTIAN N N AK WESTERN B 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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