008
FXUS06 KWBC 162001
PMDMRD
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD
300 PM EST MON DECEMBER 16 2024
6-10 DAY OUTLOOK FOR DEC 22 - 26 2024
AT THE START OF THE 6-10 DAY PERIOD, DEEP TROUGHING IS FORECAST ACROSS THE
EASTERN CONTIGUOUS U.S. (CONUS), WITH BROAD RIDGING ENCOMPASSING THE WESTERN
AND CENTRAL PORTIONS OF THE CONUS. ANOTHER HIGHLY AMPLIFIED TROUGH IS PREDICTED
ACROSS THE NORTHEASTERN PACIFIC, JUST SOUTH OF THE ALEUTIANS. AS THE PERIOD
PROGRESSES, THESE FEATURES ARE FORECAST TO SHIFT EASTWARD. THIS WOULD RESULT IN
A TREND TOWARD HIGHER MID-LEVEL HEIGHTS IN THE EAST AND LOWERING HEIGHTS NEAR
THE WEST COAST. FOR THE PERIOD AS A WHOLE, ABOVE-NORMAL HEIGHTS ARE FORECAST
FOR MOST OF THE CONUS, WITH THE LARGEST POSITIVE ANOMALIES ACROSS THE UPPER
MISSISSIPPI VALLEY AND WESTERN GREAT LAKES (+150 METERS). NEAR-NORMAL HEIGHTS
ARE FAVORED ACROSS THE PACIFIC NORTHWEST AND FLORIDA PENINSULA. CONVERSELY,
BELOW-NORMAL HEIGHTS ARE PREDICTED OVER ALASKA. 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, WITH POSSIBLY SOME OF THE COLDEST TEMPERATURES
OF THE SEASON THUS FAR. 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 THE EASTERN THIRD OF THE CONUS 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.
ANOMALOUS RIDGING FAVORS ENHANCED PROBABILITIES FOR BELOW-NORMAL PRECIPITATION
ACROSS MOST OF THE CONUS DURING THE PERIOD. THE KEY EXCEPTION IS ACROSS THE
WEST COAST WHERE ENHANCED ONSHORE FLOW IS LIKELY TO LEAD TO SUCCESSIVE ROUNDS
OF HEAVY PRECIPITATION, WITH ELEVATED PROBABILITIES FOR INTEGRATED VAPOR
TRANSPORT (IVT) TO EXCEED 250 KG/M/S INDICATIVE OF INCREASED ATMOSPHERIC RIVER
POTENTIAL. CHANCES FOR ABOVE-NORMAL PRECIPITATION ARE ALSO ENHANCED ACROSS
PARTS OF THE SOUTH-CENTRAL CONUS TIED TO SOUTHERLY RETURN FLOW AROUND SURFACE
HIGH PRESSURE FORECAST OVER THE EAST, AND ALSO ACROSS THE FLORIDA PENINSULA
SUPPORTED BY THE GEFS AND ECENS REFORECAST TOOLS. ABOVE-NORMAL PRECIPITATION IS
FORECAST FOR MUCH OF ALASKA, WITH THE HIGHEST PROBABILITIES TOWARD SOUTHEAST
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 0Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 5% OF TODAY'S OPERATIONAL 0Z 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 24 - 30 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. LATER IN WEEK-2, THE STRONGEST POSITIVE MID-LEVEL HEIGHT
ANOMALIES ARE PREDICTED TO SHIFT OVER EASTERN NORTH AMERICA, AND THERE ARE SOME
SIGNS THAT THE PATTERN BEGINS TO BREAK DOWN OVER THE WESTERN AND CENTRAL CONUS,
WITH EVIDENCE OF TROUGHING AND NEAR-NORMAL HEIGHTS EMERGING. THIS WOULD BE
CONSISTENT WITH THE PREDICTED MJO PROPAGATION INTO PHASE-7 BY THE END OF THE
MONTH. FOR WEEK-2 AS A WHOLE, ABOVE-NORMAL HEIGHTS REMAIN FORECAST FOR MOST OF
THE CONUS, ALTHOUGH THE HIGHEST POSITIVE ANOMALIES ARE NOW FORECAST OVER THE
GREAT LAKES AND NORTHEAST (+120 METERS). 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 90 PERCENT). WHILE THE EAST MAY HAVE A RELATIVELY
CHILLY START TO THE PERIOD, AN UPWARD TREND IN TEMPERATURES IS PREDICTED FOR
THE REGION RESULTING IN AN EASTWARD PROGRESSION OF THE ENHANCED ABOVE-NORMAL
TEMPERATURE PROBABILITIES COMPARED TO YESTERDAY. 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. AS RIDGING MOVES FURTHER TO THE EAST, PERIODIC INTRUSIONS OF
TROUGHING ARE POSSIBLE ACROSS THE CENTRAL CONUS TOWARD THE END OF THE PERIOD.
THIS EVOLUTION, COMBINED WITH THE ENHANCED RETURN FLOW FORECAST ACROSS THE
MISSISSIPPI VALLEY, FAVORS A BROAD AREA OF ENHANCED ABOVE-NORMAL PRECIPITATION
PROBABILITIES EXTENDING FROM THE WEST COAST TO THE OHIO VALLEY. SOME OF THIS
MOISTURE MAY EXTEND FURTHER INTO THE EAST ALTHOUGH THE REFORECAST TOOLS DIFFER
WITH THE GEFS (ECENS) SUPPORTING ENHANCED ABOVE (BELOW) NORMAL PRECIPITATION
CHANCES. THEREFORE, NEAR-NORMAL PRECIPITATION IS FAVORED FOR MUCH OF THE
EASTERN THIRD OF THE CONUS, WITH A SLIGHT TILT TOWARD BELOW-NORMAL ACROSS THE
NORTHEAST CONSISTENT WITH YESTERDAY’S OUTLOOK. ELEVATED ODDS FOR BELOW-NORMAL
PRECIPITATION ARE FORECAST ACROSS THE SOUTHWEST AND FOUR CORNERS, FURTHER
DISPLACED FROM THE TROUGHING TO THE NORTH AND SUPPORTED BY THE REFORECAST
CONSOLIDATION TOOL. 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: 40% OF TODAY'S 0Z 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
CONTINUED GOOD TOOL AGREEMENT ESPECIALLY REGARDING TEMPERATURES, OFFSET BY SOME
SIGNS OF A TRANSITIONING PATTERN LATER IN THE PERIOD, AND DIFFERING
PRECIPITATION SIGNALS.
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 - 20031207 - 20031226 - 19661211 - 20061211
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:
20031225 - 20031207 - 19941214 - 19661212 - 20061213
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 22 - 26 2024
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 N WYOMING A A
UTAH A B ARIZONA A B COLORADO A B
NEW MEXICO A B N DAKOTA A B S DAKOTA A B
NEBRASKA A B KANSAS A B OKLAHOMA A N
N TEXAS A A S TEXAS A A W TEXAS A B
MINNESOTA A B IOWA A B MISSOURI A N
ARKANSAS A N LOUISIANA A N WISCONSIN A B
ILLINOIS A N MISSISSIPPI N B MICHIGAN A B
INDIANA N N OHIO B B KENTUCKY B B
TENNESSEE B B ALABAMA B B NEW YORK B B
VERMONT B B NEW HAMP B B MAINE B B
MASS B B CONN B B RHODE IS B B
PENN B B NEW JERSEY B B W VIRGINIA B B
MARYLAND B B DELAWARE B B VIRGINIA B B
N CAROLINA B B S CAROLINA B B GEORGIA B B
FL PNHDL B B FL PENIN B N AK N SLOPE B A
AK ALEUTIAN A N AK WESTERN A N 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 24 - 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 N WYOMING A A
UTAH A A ARIZONA A N COLORADO A A
NEW MEXICO A N N DAKOTA A N S DAKOTA A A
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 A KENTUCKY A A
TENNESSEE A N ALABAMA A N NEW YORK A N
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 N W VIRGINIA A N
MARYLAND A N DELAWARE A N VIRGINIA A N
N CAROLINA A N S CAROLINA A N GEORGIA A N
FL PNHDL A N FL PENIN A N AK N SLOPE B A
AK ALEUTIAN A N AK WESTERN N N 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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