124  
FXUS06 KWBC 182049  
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 18 2017  
 
6-10 DAY OUTLOOK FOR DEC 24 - 28 2017  
 
TODAY'S MODEL FORECASTS ARE IN GOOD AGREEMENT ON A PREDICTED AMPLIFIED 500-HPA  
CIRCULATION PATTERN FOR THE 6-10 DAY PERIOD. ENSEMBLE PREDICTION SYSTEMS FROM  
THE NCEP GEFS, ECMWF, AND ENVIRONMENT CANADA PREDICT A STRONG RIDGE OVER THE  
NORTH PACIFIC AND EASTERN ALASKA, A DOWNSTREAM TROUGH EXTENDING FROM HUDSON BAY  
INTO THE CONUS, AND ABOVE NORMAL 500-HPA HEIGHTS OVER THE SOUTHEASTERN CONUS  
AND NORTH ATLANTIC. THE ECMWF ENSEMBLE PREDICTS ORIENTATION OF THE PREDICTED  
TROUGH AXIS OVER NORTH AMERICA TO EXTEND FROM THE NORTH-CENTRAL CONUS TO THE  
SOUTHWEST. THE ENVIRONMENT CANADA ENSEMBLE PREDICTS A SIMILAR BUT LESS  
AMPLIFIED TROUGH, WHILE THE GEFS INDICATES A LESS AMPLIFIED TROUGH CENTERED  
OVER THE U.S. MIDWEST. THE 500-HPA FLOW PATTERN OF THE ECMWF ENSEMBLE  
PREDICTION SYSTEM IS WEIGHTED MORE HEAVILY IN THE OFFICIAL FORECAST.  
 
ABOVE NORMAL TEMPERATURES ARE LIKELY FOR MOST OF ALASKA, EXCEPT FOR THE  
SOUTHERN ALASKA PANHANDLE, UNDER LARGE POSITIVE 500-HPA HEIGHT ANOMALIES AND  
ANOMALOUS SOUTHERLY FLOW, WITH PROBABILITIES EXCEEDING 70 PERCENT FOR NORTHWEST  
REGIONS. BELOW NORMAL TEMPERATURES ARE LIKELY FOR A LARGE AREA OF THE CONUS,  
UNDER A PREDICTED AMPLIFIED TROUGH AND AN INFLUX OF ARCTIC AIR. PROBABILITIES  
EXCEED 70 PERCENT OVER A LARGE AREA OF THE NORTHERN CONUS, AS WELL AS THE  
CENTRAL AND SOUTHERN GREAT PLAINS STATES. UNDER PREDICTED ANOMALOUS SOUTHERLY  
FLOW AND ABOVE NORMAL 500-HPA HEIGHTS, ABOVE NORMAL TEMPERATURES ARE LIKELY FOR  
ATLANTIC COASTAL STATES IN THE SOUTHEAST, INCLUDING FLORIDA.  
 
TROUGHING TO THE WEST AND PREDICTED SOUTHERLY FLOW OVER ALASKA LEADS TO LIKELY  
ABOVE NORMAL PRECIPITATION OVER PARTS OF WESTERN AND INTERIOR REGIONS OF THE  
STATE. THE PREDICTED TROUGH OVER THE WEST-CENTRAL CONUS ENHANCES THE  
PROBABILITY OF ABOVE NORMAL PRECIPITATION FOR EASTERN AREAS OF COLORADO AND  
ARIZONA, PARTS OF THE SOUTHERN PLAINS, AS WELL AS ALONG A LINE FROM LOUISIANA  
ACROSS THE SOUTHEAST INTO THE MID-ATLANTIC AND NEW ENGLAND COASTS, ALONG THE  
PREDICTED MEAN FRONTAL BOUNDARY. BELOW NORMAL PRECIPITATION IS LIKELY FOR THE  
NORTHWEST UNDER PREDICTED ANOMALOUS NORTHERLY 500-HPA FLOW. BELOW NORMAL  
PRECIPITATION IS LIKELY FROM THE NORTHERN PLAINS INTO THE CENTRAL MISSISSIPPI  
VALLEY WITH AN INFLUX OF DRY ARCTIC AIR.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 15% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 8, 40% 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: ABOVE AVERAGE, 4 OUT OF 5, DUE TO  
GOOD MODEL AGREEMENT ON A HIGHLY AMPLIFIED FLOW PATTERN.  
 
8-14 DAY OUTLOOK FOR DEC 26, 2017 - JAN 01, 2018  
 
MODEL FORECASTS PREDICT A LESS AMPLIFIED TROUGH WITH SOME EASTWARD PROGRESSION  
OVER THE CONUS IN THE WEEK 2 PERIOD, AND NEGATIVE 500-HPA HEIGHT ANOMALIES  
PRIMARILY LOCATED FROM THE NORTHERN PLAINS AND GREAT LAKES REGION INTO THE  
NORTHEAST. ENSEMBLE PREDICTION SYSTEMS FROM THE NCEP GEFS, ECMWF, AND  
ENVIRONMENT CANADA ENSEMBLES ARE IN GENERAL AGREEMENT ON THE DEAMPLIFICATION  
AND EASTWARD PROGRESSION OF THE CIRCULATION PATTERN. ENSEMBLE SPREAD AND  
UNCERTAINTY, HOWEVER, INCREASE IN THE WEEK 2 PERIOD FORECASTS.  
 
ABOVE NORMAL TEMPERATURES REMAIN VERY LIKELY FOR MOST OF ALASKA, EXCEPT FOR  
SOUTHEASTERN REGIONS OF THE STATE, UNDER THE PREDICTED RIDGE. BELOW NORMAL  
TEMPERATURES ARE MOST LIKELY FOR THE ALASKA PANHANDLE, UNDER ANOMALOUS  
NORTHERLY FLOW. BELOW NORMAL TEMPERATURES CONTINUE TO BE LIKELY FOR A LARGE  
AREA OF THE CONUS, UNDER THE PREDICTED TROUGH. ABOVE NORMAL TEMPERATURES ARE  
LIKELY OVER PARTS OF SOUTHERN CALIFORNIA AND THE SOUTHWEST REGION WITH MORE  
ZONAL FLOW PREDICTED OVER THE REGION, RELATIVE TO THE MODEL 6-10 DAY PERIOD  
FORECASTS. THE GEFS ENSEMBLE FORECAST INDICATES GREATER POSITIVE 500-HPA HEIGHT  
ANOMALIES OVER THE SOUTHWEST, AND WITH IT AN INCREASED LIKELIHOOD OF ABOVE  
NORMAL TEMPERATURES, COMPARED TO THE ECMWF ENSEMBLE. ABOVE NORMAL TEMPERATURES  
ARE LESS LIKELY OVER PARTS OF THE SOUTHEAST IN WEEK 2, RELATIVE TO THE 6-10 DAY  
PERIOD FORECAST, WITH THE EASTWARD PROGRESSION OF THE TROUGH OVER THE CENTRAL  
CONUS.  
 
WITH SOME WESTWARD RETROGRESSION OF THE RIDGE OVER ALASKA, ABOVE NORMAL  
PRECIPITATION IS LIKELY ONLY OVER NORTHERN AREAS OF THE STATE IN WEEK 2. THE  
PRECIPITATION FORECAST OVER THE CONUS FOR WEEK 2 IS SIMILAR TO THE 6-10 DAY  
PERIOD FORECAST WITH A COUPLE EXCEPTIONS. AN INCREASED CHANCE OF ABOVE NORMAL  
PRECIPITATION IS INDICATED OVER CENTRAL MONTANA BY CALIBRATED ENSEMBLE  
PROBABILITY FORECASTS FROM THE ECMWF AND GEFS ENSEMBLES. NEAR AND BELOW NORMAL  
PRECIPITATION ARE MORE LIKELY AND ABOVE NORMAL IS LESS LIKELY OVER PARTS OF THE  
SOUTHEAST AND ATLANTIC COAST, AS THE PREDICTED TROUGH OVER THE CONUS IS LESS  
AMPLIFIED.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 15% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 20% OF TODAY'S 6Z GFS ENSEMBLE MEAN CENTERED  
ON DAY 11, 45% 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: ABOUT AVERAGE, 3 OUT OF 5, DUE TO  
A LESS AMPLIFIED PREDICTED CIRCULATION PATTERN IN WEEK 2, RELATIVE TO THE 6-10  
DAY PERIOD.  
 
FORECASTER: D COLLINS  
 
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 21.  
 
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:  
19881217 - 19891228 - 19601229 - 19991228 - 19531226  
 
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:  
19891230 - 19991228 - 19531227 - 19601228 - 20071212  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 24 - 28 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF B B  
SRN CALIF B N IDAHO B B NEVADA B B  
W MONTANA B B E MONTANA B B WYOMING B B  
UTAH B B ARIZONA B N COLORADO B A  
NEW MEXICO B A N DAKOTA B B S DAKOTA B N  
NEBRASKA B N KANSAS B N OKLAHOMA B N  
N TEXAS B A S TEXAS B A W TEXAS B A  
MINNESOTA B B IOWA B B MISSOURI B B  
ARKANSAS B B LOUISIANA B A WISCONSIN B B  
ILLINOIS B B MISSISSIPPI B A MICHIGAN B N  
INDIANA B B OHIO B B KENTUCKY B N  
TENNESSEE B A ALABAMA B A NEW YORK B N  
VERMONT B N NEW HAMP B A MAINE B N  
MASS B A CONN B A RHODE IS N A  
PENN B N NEW JERSEY N A W VIRGINIA B A  
MARYLAND N A DELAWARE N A VIRGINIA B A  
N CAROLINA N A S CAROLINA A A GEORGIA A A  
FL PNHDL A B FL PENIN A B 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 N AK PNHDL N B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 26, 2017 - JAN 01, 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON B B NRN CALIF B B  
SRN CALIF A N IDAHO B B NEVADA N B  
W MONTANA B N E MONTANA B A WYOMING B N  
UTAH N N ARIZONA A A COLORADO B N  
NEW MEXICO N A N DAKOTA B B S DAKOTA B B  
NEBRASKA B B KANSAS B N OKLAHOMA B N  
N TEXAS B A S TEXAS B A W TEXAS B A  
MINNESOTA B B IOWA B B MISSOURI B B  
ARKANSAS B N LOUISIANA B A WISCONSIN B B  
ILLINOIS B B MISSISSIPPI B A MICHIGAN B N  
INDIANA B B OHIO B B KENTUCKY B B  
TENNESSEE B N ALABAMA B N NEW YORK B B  
VERMONT B B NEW HAMP B B MAINE B B  
MASS B N CONN B N RHODE IS B N  
PENN B B NEW JERSEY B N W VIRGINIA B B  
MARYLAND B N DELAWARE B N VIRGINIA B N  
N CAROLINA B N S CAROLINA B N GEORGIA B N  
FL PNHDL B B FL PENIN A B AK N SLOPE A A  
AK ALEUTIAN A B AK WESTERN A B AK INT BSN A N  
AK S INT A B AK SO COAST A B AK PNHDL B B  
 
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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