860
FXUS06 KWBC 132001
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 13 2024
6-10 DAY OUTLOOK FOR DEC 19 - 23 2024
AN AREA OF STRONGLY BELOW-NORMAL MID-LEVEL HEIGHTS IS FORECAST ACROSS THE NORTH
PACIFIC UPSTREAM OF A STRONG RIDGE AND POSITIVE MID-LEVEL HEIGHT ANOMALIES
ACROSS THE WESTERN CONTIGUOUS UNITED STATES (CONUS) DURING THE 6-10 DAY PERIOD.
THE STRONGEST POSITIVE 500-HPA HEIGHT ANOMALIES ARE FORECAST OVER THE NORTHERN
ROCKIES WITH AN ASSOCIATED STRONG MID-LEVEL RIDGE. THE AXIS OF THIS RIDGE IS
FORECAST TO BE JUST INLAND OF THE WEST COAST RESULTING IN ONSHORE MID-LEVEL
FLOW TO MUCH OF ALASKA. IN THE EAST, MID-LEVEL HEIGHTS CONTINUE TO DECLINE
RELATIVE TO PRIOR FORECASTS AND ARE TODAY FORECAST TO BE BELOW-NORMAL. POSITIVE
500-HPA HEIGHTS ARE FORECAST FOR HAWAII.
ABOVE-NORMAL TEMPERATURES ARE FAVORED ACROSS THE WESTERN HALF OF THE CONUS
BENEATH A STRONG MID-LEVEL RIDGE WITH PROBABILITIES EXCEEDING 70% ACROSS THE
SOUTHWEST. A SHORTWAVE TROUGH PROGRESSING INTO THE EASTERN CONUS EARLY IN THE
PERIOD DEVELOPS INTO A FULL LATITUDE TROUGH DURING THE 6-10 DAY FORECAST. THE
RAPID PROGRESSION OF THE PATTERN BRINGS CHANCES FOR BELOW-NORMAL TEMPERATURES
CONSISTENT WITH THE DYNAMICAL AND STATISTICAL MODEL GUIDANCE. IN ALASKA,
SOUTHERLY FLOW BRINGS STRONG CHANCES FOR ABOVE-NORMAL TEMPERATURES WITH
PROBABILITIES EXCEEDING 80% IN SOUTHEAST ALASKA IN GOOD AGREEMENT WITH MOST
MODEL GUIDANCE. THERE ARE STRONG CHANCES FOR ABOVE-NORMAL TEMPERATURES IN
HAWAII WHERE PROBABILITIES EXCEED 70% WITH STRONG AGREEMENT AMONG REFORECAST
AND SHORT-TERM BIAS-CORRECTED TOOLS BENEATH POSITIVE MID-LEVEL HEIGHT ANOMALIES.
THE AMPLIFIED RIDGE ACROSS THE WESTERN CONUS REDUCES CHANCES FOR PRECIPITATION
FOR MOST OF THE WESTERN CONUS. THE GREATEST UNCERTAINTY IS ALONG THE IMMEDIATE
WEST COAST WHERE NEAR TO SLIGHTLY ABOVE-NORMAL IS FAVORED WITH WEAK ONSHORE
FLOW AHEAD OF THE MID-LEVEL RIDGE AXIS AND DOWNSTREAM OF THE STRONG TROUGH OVER
THE NORTH PACIFIC. THE EXACT LOCATION OF THE RIDGE AXIS WILL BE IMPORTANT IN
DETERMINING PRECIPITATION AMOUNTS. EAST OF THE CASCADES AND SIERRA NEVADA,
STRONG CHANCES FOR BELOW-NORMAL PRECIPITATION IS FAVORED EXPANDING EAST INTO
THE PLAINS AND MISSISSIPPI VALLEY BENEATH THE EXPANDING RIDGE. ABOVE-NORMAL IS
FAVORED ALONG THE IMMEDIATE EAST COAST AHEAD OF THE DEVELOPING MID-LEVEL
TROUGH. IN ALASKA, ABOVE-NORMAL PRECIPITATION IS FAVORED ACROSS THE SOUTHERN
HALF OF THE STATE WITH STRONG AGREEMENT AMONG THE GUIDANCE AND WITH THE OVERALL
MID-LEVEL PATTERN. IN HAWAII, NEAR-NORMAL PRECIPITATION IS FORECAST FOR MUCH OF
HAWAII WITH BELOW-NORMAL FAVORED FOR THE BIG ISLAND CONSISTENT WITH DYNAMICAL
TOOLS.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 35% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 35% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 8, AND 30% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON DAY
8
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE-AVERAGE, 4 OUT OF 5. GOOD
AGREEMENT AMONG THE DYNAMICAL AND STATISTICAL TOOLS IS OFFSET BY A PROGRESSIVE
AND SHIFTING PATTERN AND WEAK PRECIPITATION SIGNALS.
8-14 DAY OUTLOOK FOR DEC 21 - 27 2024
MID-LEVEL RIDGING AND STRONG POSITIVE 500-HPA HEIGHT ANOMALIES REMAIN FORECAST
ACROSS MUCH OF THE WESTERN CONUS WITH A DEEP TROUGH UPSTREAM OVER THE NORTH
PACIFIC. THE RIDGE ACROSS THE WEST HAS DEAMPLIFIED SLIGHTLY RELATIVE TO
YESTERDAY AND THE AXIS OF THE RIDGE HAS PROGRESSED EAST. ACROSS THE EASTERN
CONUS, ABOVE-NORMAL HEIGHTS ARE EXPANDING FROM THE RIDGE ACROSS THE WEST INTO
THE EAST. HOWEVER, NEAR- TO BELOW-NORMAL 500-HPA HEIGHTS ARE FORECAST ACROSS
PORTIONS OF THE SOUTHEAST AND FLORIDA. POSITIVE 500-HPA HEIGHT ANOMALIES ARE
FORECAST FOR HAWAII.
ABOVE-NORMAL TEMPERATURES REMAIN FAVORED ACROSS MOST OF THE WESTERN CONUS
DURING THE WEEK-2 PERIOD. THE STRONGEST PROBABILITIES ARE FORECAST ACROSS THE
WEST INTO THE PLAINS WITH PROBABILITIES EXCEEDING 70% ACROSS MOST OF THE
REGION. NEAR-NORMAL TEMPERATURES ARE FAVORED IN THE NORTHEAST WITH A QUICK
TRANSITION BETWEEN FORECAST BELOW-NORMAL TEMPERATURES, ASSOCIATED WITH A
MID-LEVEL TROUGH, EARLY IN THE PERIOD GIVING WAY TO ABOVE-NORMAL TEMPERATURES
IN THE SECOND HALF OF WEEK-2 AS POSITIVE MID-LEVEL HEIGHT ANOMALIES DEVELOP. IN
THE SOUTHEAST, THE MID-LEVEL TROUGH AT THE ONSET OF THE PERIOD LINGERS THROUGH
MUCH OF THE PERIOD MAINTAINING INCREASED CHANCES FOR BELOW-NORMAL TEMPERATURES
THROUGH THE END OF WEEK-2. IN ALASKA, ABOVE-NORMAL TEMPERATURES REMAIN STRONGLY
FAVORED THROUGH MUCH OF THE STATE, HOWEVER, THE STRENGTH OF THE SOUTHERLY FLOW
HAS REDUCED IN STRENGTH RELATIVE TO PRIOR FORECASTS, AND TEMPERATURE CHANCES
HAVE DECLINED SLIGHTLY RELATIVE TO YESTERDAY. ABOVE-NORMAL TEMPERATURES ARE
ALSO STRONGLY FAVORED IN HAWAII, AS IN THE 6-10 DAY PERIOD.
THE WEEK-2 PRECIPITATION FORECAST FAVORS BELOW-NORMAL PRECIPITATION ACROSS MUCH
OF THE CONUS. SURFACE HIGH PRESSURE IS FORECAST ACROSS MUCH OF THE PLAINS,
MISSISSIPPI VALLEY, AND SOUTHEAST, REDUCING CHANCES FOR PRECIPITATION ACROSS
THESE REGIONS. TOOLS CONTINUE TO HAVE MIXED SIGNALS ALONG THE WEST COAST AND
NEAR- TO ABOVE-NORMAL PRECIPITATION IS FORECAST. AS THE RIDGE HAS DEAMPLIFIED
AND SHIFTED EAST, PRECIPITATION CHANCES HAVE INCREASED SLIGHTLY RELATIVE TO
YESTERDAY. THE ECENS BASED FORECASTS CONTINUE TO INDICATE MORE PRECIPITATION
RELATIVE TO THE DRIER GEFS BASED TOOLS. WE ARE NEAR THE CLIMATOLOGICAL PEAK OF
PRECIPITATION ALONG THE WEST COAST SO NEAR-NORMAL PRECIPITATION MAY STILL BRING
CHANCES FOR ROUNDS OF PRECIPITATION INTO THE REGION. IN ALASKA, ENHANCED
CHANCES FOR ABOVE-NORMAL PRECIPITATION REMAINS FORECAST ACROSS THE SOUTHERN
PORTIONS OF ALASKA, WITH NEAR TO ABOVE-NORMAL PRECIPITATION FAVORED ACROSS
NORTHERN ALASKA CONSISTENT WITH MODEL GUIDANCE. BELOW-NORMAL PRECIPITATION IS
FAVORED IN THE EASTERN HALF OF HAWAII AND NEAR-NORMAL FAVORED FURTHER WEST.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 35% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, 35% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 11, AND 30% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON
DAY 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: AVERAGE, 3 OUT OF 5, WITH
DIVERGENT SOLUTIONS AMONG THE MODEL GUIDANCE FOR PRECIPITATION REDUCING
CONFIDENCE OFFSET BY VERY GOOD AGREEMENT AMONG TEMPERATURE SOLUTIONS.
FORECASTER: RYAN BOLT
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:
19521126 - 20001220 - 19781208 - 20061202 - 19851226
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:
20001220 - 19521126 - 19781210 - 19851226 - 20001214
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 19 - 23 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A N OREGON A N NRN CALIF A N
SRN CALIF A B IDAHO A B NEVADA A B
W MONTANA A B E MONTANA A B WYOMING A B
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 N B
N TEXAS N B S TEXAS N B W TEXAS A B
MINNESOTA N B IOWA N B MISSOURI B B
ARKANSAS B B LOUISIANA B B WISCONSIN B B
ILLINOIS B B MISSISSIPPI B B MICHIGAN B N
INDIANA B B OHIO B N KENTUCKY B B
TENNESSEE B B ALABAMA B B NEW YORK B A
VERMONT B A NEW HAMP N A MAINE N A
MASS N A CONN B A RHODE IS B A
PENN B N NEW JERSEY B A W VIRGINIA B N
MARYLAND B A DELAWARE B A VIRGINIA B A
N CAROLINA B A S CAROLINA B N GEORGIA B B
FL PNHDL B B FL PENIN B A AK N SLOPE A N
AK ALEUTIAN A N AK WESTERN A A AK INT BSN A N
AK S INT A A AK SO COAST A A AK PNHDL A A
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 21 - 27 2024
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON A A OREGON A N NRN CALIF A N
SRN CALIF A B IDAHO A B NEVADA A B
W MONTANA A B E MONTANA A B WYOMING A B
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 B
N TEXAS A N S TEXAS A N W TEXAS A B
MINNESOTA A B IOWA A B MISSOURI A B
ARKANSAS N B LOUISIANA N B WISCONSIN A B
ILLINOIS A B MISSISSIPPI B B MICHIGAN A B
INDIANA N B OHIO N B KENTUCKY B B
TENNESSEE B B ALABAMA B B NEW YORK N B
VERMONT N B NEW HAMP N B MAINE N N
MASS N B CONN N B RHODE IS N 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 A N
AK ALEUTIAN A N AK WESTERN A 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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