946
FXUS06 KWBC 182010
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 18 2018
6-10 DAY OUTLOOK FOR DEC 24 - 28 2018
GOOD MODEL AGREEMENT CONTINUES TODAY THAT AN AMPLIFIED 500-HPA HEIGHT PATTERN
WILL TAKE SHAPE OVER THE CONUS IN THE 6-10 DAY PERIOD, WITH RIDGING FAVORED IN
THE EAST, AND TROUGHING IN THE WEST. THIS WILL YIELD POSITIVE HEIGHT ANOMALIES
FOR MUCH OF THE EASTERN CONUS AND NEGATIVE HEIGHT ANOMALIES IN THE WESTERN
CONUS. TROUGHING IS FORECAST OVER THE BERING SEA WITH SOME RIDGING BUILDING
INTO EASTERN MAINLAND ALASKA.
A WARMING TREND IS FORECAST FOR THE EASTERN CONUS DURING THE 6-10 DAY PERIOD
WITH THE HIGHEST CONFIDENCE IN THE EASTERN PLAINS AND MISSISSIPPI VALLEY,
UNDERNEATH THE CENTER OF THE RIDGE AXIS. ABOVE NORMAL TEMPERATURES ARE ALSO
FAVORED FARTHER EAST INTO THE MID-ATLANTIC AND PARTS OF THE NORTHEAST. HOWEVER,
ANOMALOUS TROUGHING IN THE WESTERN ATLANTIC OCEAN MAY HOLD BACK THE EXTENT OF
THE WARMTH OVER THE EASTERN CONUS, WITH NEAR NORMAL TEMPERATURES FAVORED FOR
PARTS OF NEW ENGLAND AND THE NORTHEAST. THIS TROUGH IN THE WESTERN ATLANTIC
TELECONNECTS WITH BELOW NORMAL TEMPERATURES IN THE NORTHEAST BUT NEAR NORMAL IS
BEING FAVORED DUE TO MOST OF THE DYNAMICAL GUIDANCE SUPPORTING ABOVE NORMAL
TEMPERATURES. TROUGHING IN THE WESTERN CONUS FAVORS BELOW NORMAL TEMPERATURES
OVER THE ROCKIES AND THE GREAT BASIN. OF NOTE IS THAT THE PERIOD LOOKS TO START
ON THE WARMER SIDE, BUT IS FORECAST TO BECOME COOLER LATER IN THE THE PERIOD AS
THE TROUGH BUILDS IN. THIS RESULTS IN A DAMPENING OF PROBABILITIES SINCE WARMER
TEMPERATURES INITIALLY IN THE WEST WILL SKEW THE MEAN TOWARD NEAR NORMAL OR
ONLY SLIGHTLY BELOW NORMAL. BELOW NORMAL TEMPERATURES ARE FORECAST FOR MUCH OF
ALASKA DUE TO TROUGHING OVER THE BERING SEA AND NEGATIVE HEIGHT ANOMALIES
ACROSS THE STATE, WITH THE EXCEPTION BEING THE ALEUTIANS WHICH ARE FAVORED TO
BE SLIGHTLY ABOVE NORMAL.
THERE IS A STRONG SIGNAL FOR ABOVE NORMAL PRECIPITATION ACROSS THE CENTRAL
CONUS DURING THE 6-10 DAY PERIOD, WITH TROUGHING IN THE WESTERN CONUS FAVORING
A FRONTAL ZONE AND MEAN STORM TRACK THROUGH THE PLAINS AND MISSISSIPPI VALLEY.
ENSEMBLE GUIDANCE FROM THE ECMWF AND GEFS SHOWS GREATER THAN 1" OF
PRECIPITATION OVER THE 6-10 DAY PERIOD WITH SOME AREAS OF THE EASTERN PLAINS
AND MISSISSIPPI VALLEY EXCEEDING 2". ALSO OF CONSIDERATION IS THAT THE GREAT
PLAINS ARE NORMALLY DRY THIS TIME OF YEAR, SO IT WOULD NOT TAKE MUCH
PRECIPITATION TO ACHIEVE VALUES THAT ARE ABOVE NORMAL. BOTH THE TROUGH IN THE
WEST AND RIDGE TO THE EAST TELECONNECT WITH ABOVE NORMAL PRECIPITATION IN THE
CENTRAL CONUS. HIGH PROBABILITIES WERE SKEWED TO THE WEST AND CENTERED OVER THE
PLAINS. ALTHOUGH ACTUAL PRECIPITATION VALUES ARE FORECAST TO BE HIGHER FURTHER
SOUTH AND EAST, THE AFOREMENTIONED LOW PRECIPITATION CLIMATOLOGY FAVORS THE
BEST CHANCE FOR ABOVE NORMAL PRECIPITATION OVER THE PLAINS. BELOW NORMAL
PRECIPITATION IS FAVORED FOR PARTS OF THE EAST COAST, WHICH IS FORECAST TO BE
WELL DISPLACED FROM THE MEAN STORM TRACK DURING THE PERIOD.
AS TROUGHING ENTERS THE WESTERN CONUS DURING THE 6-10 DAY PERIOD, PACIFIC FLOW
IS ONCE AGAIN FORECAST TO TAKE OVER, WITH THE POTENTIAL FOR AN ATMOSPHERIC
RIVER TYPE EVENT FOCUSED MAINLY ON THE CENTRAL PACIFIC COAST AROUND DAYS 6-7.
BELOW NORMAL PRECIPITATION PROBABILITIES ARE FAVORED FOR MOST OF ALASKA AS THE
MEAN STORM TRACK LOOKS TO BE FOCUSED MAINLY SOUTH OF THE STATE, WITH ELEVATED
PRECIPITATION CHANCES POSTED FOR THE SOUTHERN MAINLAND, ALEUTIANS, AND THE
PANHANDLE.
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 40% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 8, 10% OF TODAY'S OPERATIONAL 6Z GFS CENTERED ON
DAY 8, 40% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, AND 10% OF
TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO
GOOD AGREEMENT AMONG MODEL SOLUTIONS AND STATISTICAL TOOLS
8-14 DAY OUTLOOK FOR DEC 26, 2018 - JAN 01, 2019
AN AMPLIFIED PATTERN IS FORECAST DURING WEEK-2 WHICH INCREASES FORECAST
CONFIDENCE. RIDGING AND POSITIVE HEIGHT ANOMALIES ARE FAVORED IN THE EAST WITH
TROUGHING AND NEGATIVE HEIGHT ANOMALIES IN THE WEST. THE PATTERN IS FORECAST TO
DE-AMPLIFY AND SHIFT EASTWARD TOWARD THE END OF THE PERIOD BRINGING MORE
TROUGHING INTO THE EASTERN CONUS AROUND THE START OF 2019. FOR ALASKA, THE MEAN
TROUGH IS FORECAST TO BE CLOSER TO THE WEST COAST OF THE STATE FOR WEEK-2
COMPARED TO THE 6-10 DAY PERIOD, WITH SOME DOWNSTREAM RIDGING TO THE EAST.
ABOVE NORMAL TEMPERATURES ARE FAVORED ACROSS PARTS OF THE EASTERN CONUS IN
ASSOCIATION WITH RIDGING, WITH BELOW NORMAL TEMPERATURES IN THE WEST UNDER THE
INFLUENCE OF TROUGHING. TELECONNECTIONS WITH THE TROUGH IN THE EAST SUPPORT THE
BELOW NORMAL TEMPERATURE PROBABILITIES IN THE WEST AND ABOVE NORMAL IN THE EAST
WITH SOME UNCERTAINTY REGARDING HOW QUICKLY THE PATTERN DE-AMPLIFIES (WHICH
WOULD LEAD TO AN OVERALL MODIFICATION OF TEMPERATURES ACROSS THE CONUS). ABOVE
NORMAL TEMPERATURES ARE FORECAST FOR SOUTHERN MAINLAND ALASKA AND THE PANHANDLE
WHERE RIDGING IS FORECAST, WITH BELOW NORMAL TEMPERATURES FAVORED FOR THE REST
OF THE STATE.
ENHANCED PRECIPITATION PROBABILITIES ARE FORECAST FOR THE PLAINS AND INTO THE
SOUTHEAST FOR THE WEEK-2 PERIOD. AS OUTLINED IN THE 6-10 DAY OUTLOOK, THE
HIGHEST PROBABILITIES ARE ACROSS THE EASTERN PLAINS WHERE HIGH MODELED
PRECIPITATION TOTALS COMBINED WITH LOW PRECIPITATION CLIMATOLOGIES YIELD THE
HIGHEST CONFIDENCE FOR ABOVE NORMAL PRECIPITATION. DYNAMICAL GUIDANCE FORECASTS
THE HIGHEST TOTALS ACROSS THE LOWER MISSISSIPPI VALLEY AND DEEP SOUTH DURING
THIS PERIOD WITH ENSEMBLE SOLUTIONS FROM THE ECMWF AND GEFS SHOWING 2"-3" FOR
THE PERIOD. AS THE TROUGH AXIS SHIFTS MORE EASTWARD LATE IN THE PERIOD,
ELEVATED PRECIPITATION CHANCES WILL BECOME MORE FAVORED INTO THE MID-ATLANTIC
AND NORTHEAST. COMPARED TO YESTERDAY, GUIDANCE IS IN BETTER AGREEMENT IN TERMS
OF FAVORING NEAR NORMAL PRECIPITATION FOR MOST OF THE PACIFIC NORTHWEST, WITH
THE EXCEPTION BEING COASTAL PARTS OF WASHINGTON WHERE THE GEFS AND ECMWF
REFORECAST TOOLS SUPPORT SLIGHT CHANCES OF ABOVE NORMAL PRECIPITATION. THE
NORTHWARD SHIFT OF THE PACIFIC STORM TRACK AND INCREASING SOUTHERLY FLOW FAVORS
ABOVE NORMAL PRECIPITATION PROBABILITIES FOR THE ALEUTIANS AND THE SOUTHERN
HALF OF MAINLAND ALASKA.
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 50% OF TODAY'S 6Z GFS
ENSEMBLE MEAN CENTERED ON DAY 11, AND 50% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN
CENTERED ON DAY 11
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: ABOVE AVERAGE, 4 OUT OF 5, DUE TO
CONTINUED GOOD AGREEMENT AMONG THE FORECAST TOOLS
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 1981-2010 BASE PERIOD MEANS FOR
TEMPERATURE...PRECIPITATION...AND 500-HPA HEIGHTS AS REFERENCE IN THE CLIMATE
OUTLOOKS.
THE NEXT SET OF LONG-LEAD MONTHLY AND SEASONAL OUTLOOKS WILL BE RELEASED ON
DECEMBER 20.
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:
19941219 - 20061222 - 20021213 - 20051225 - 20061227
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:
20061211 - 19941220 - 20061223 - 20021213 - 20021231
6-10 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 24 - 28 2018
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON N A OREGON B A NRN CALIF B A
SRN CALIF N A IDAHO B A NEVADA B A
W MONTANA N A E MONTANA N A WYOMING N A
UTAH N A ARIZONA N A 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 N N NEW HAMP N N MAINE N B
MASS N N CONN N N RHODE IS N N
PENN A A NEW JERSEY A N W VIRGINIA A A
MARYLAND A A DELAWARE A N VIRGINIA A A
N CAROLINA A N S CAROLINA A A GEORGIA A A
FL PNHDL A N FL PENIN A N AK N SLOPE B B
AK ALEUTIAN N A AK WESTERN B B AK INT BSN B B
AK S INT N N AK SO COAST N A AK PNHDL B A
8-14 DAY OUTLOOK TABLE
OUTLOOK FOR DEC 26, 2018 - JAN 01, 2019
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN
WASHINGTON B N OREGON B N NRN CALIF B N
SRN CALIF B A IDAHO B N NEVADA B A
W MONTANA B N E MONTANA N A WYOMING B A
UTAH B A ARIZONA B A COLORADO B A
NEW MEXICO B A N DAKOTA N A S DAKOTA N A
NEBRASKA N A KANSAS A A OKLAHOMA A A
N TEXAS A A S TEXAS A A W TEXAS N 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 A
VERMONT A A NEW HAMP A A MAINE N A
MASS A A CONN A A RHODE IS A A
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 B N
AK ALEUTIAN N A AK WESTERN B A AK INT BSN B 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.
$$