6-10 Day Narrative

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.
$$