279  
FXUS06 KWBC 282002  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EST TUE NOVEMBER 28 2017  
 
6-10 DAY OUTLOOK FOR DEC 04 - 08 2017  
 
ENSEMBLE MEAN SOLUTIONS ARE IN GOOD AGREEMENT ON THE EXPECTED BROAD SCALE  
CIRCULATION PATTERN WITH A HIGH AMPLITUDE RIDGE DEVELOPING ALONG THE WEST COAST  
AND THE FIRST SIGNS OF AN AMPLIFYING TROUGH OVER EAST-CENTRAL NORTH AMERICA.  
DETERMINISTIC MODEL SOLUTIONS DIVERGE ON HOW MUCH TROUGHING LINGERS ACROSS THE  
FOUR CORNERS REGION. THE DETERMINISTIC 0Z ECMWF MODEL INDICATES THAT A  
SHORTWAVE TROUGH RAPIDLY EJECTS FROM THE WESTERN U.S. AND INTERACTS WITH THE  
AMPLIFYING NORTHERN STREAM, RESULTING IN A HIGHLY AMPLIFIED RIDGE (TROUGH)  
BECOMING ESTABLISHED OVER WESTERN (EASTERN) NORTH AMERICA BY DAY 8. THE  
DETERMINISTIC GFS MODEL SOLUTIONS DELAY THIS PATTERN CHANGE BY A COUPLE OF  
DAYS. SLIGHT WEIGHTING, IN CREATING THE MANUAL 500-HPA HEIGHT BLEND, WAS GIVEN  
TO THE DETERMINISTIC 0Z ECMWF MODEL SINCE ITS SOLUTION AGREES BETTER WITH  
TELECONNECTIONS UPON A PAIR OF POSITIVE 500-HPA HEIGHT ANOMALY CENTERS AT  
VANCOUVER ISLAND AND THE SOUTHERN TIP OF GREENLAND. REGARDLESS OF THE DIVERGING  
MODEL SOLUTIONS, A TREND TOWARDS MUCH COLDER TEMPERATURES IS LIKELY FOR THE  
CENTRAL AND EASTERN U.S. LATER IN THE 6-10 DAY PERIOD.  
 
LARGE POSITIVE TEMPERATURE ANOMALIES OF 10 TO 20 DEGREES F, PRECEDING THE  
LIKELY PATTERN CHANGE, FAVOR ABOVE NORMAL TEMPERATURES ACROSS AT LEAST THE  
EASTERN THIRD OF THE CONUS. GIVEN THE STRONG SIGNAL AMONG STATISTICAL TOOLS FOR  
BELOW NORMAL TEMPERATURES ACROSS THE SOUTH-CENTRAL CONUS, A LARGER COVERAGE  
WITH A FAVORED AREA FOR BELOW NORMAL TEMPERATURES IS FORECAST FOR THIS REGION  
COMPARED TO THE DYNAMICAL TEMPERATURE TOOLS. OFFSHORE FLOW LEADS TO INCREASED  
CHANCES OF ABOVE NORMAL TEMPERATURES ACROSS SOUTHERN CALIFORNIA, WHILE SURFACE  
HIGH PRESSURE AND ASSOCIATED LOW-LEVEL INVERSIONS MAY SLOW ANY WARMING TREND  
ACROSS THE INTERIOR WEST.  
 
EARLY IN THE PERIOD, AN UPPER-LEVEL TROUGH ALONG WITH EXPECTED UPSLOPE FLOW  
ENHANCES ODDS FOR ABOVE NORMAL PRECIPITATION ACROSS THE CENTRAL AND SOUTHERN  
ROCKIES AND ADJACENT GREAT PLAINS. ABOVE NORMAL PRECIPITATION IS FAVORED FROM  
THE MISSISSIPPI VALLEY TO THE EAST COAST ALONG AN EASTWARD ADVANCING COLD  
FRONT. SINCE THE PREDICTED STORM TRACK HAS SHIFTED SOUTHEAST IN THE LATEST  
MODEL GUIDANCE, THE HIGHEST PROBABILITIES FOR ABOVE NORMAL PRECIPITATION ARE  
FORECAST ACROSS THE LOWER MISSISSIPPI VALLEY. VERY HIGH PROBABILITIES FOR BELOW  
NORMAL PRECIPITATION ACROSS NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST ARE  
SUPPORTED BY THE AMPLIFYING RIDGE ALONG THE WEST COAST AND VARIOUS  
PRECIPITATION TOOLS.  
 
AN UPPER-LEVEL TROUGH OVER THE ALEUTIANS AND SOUTHWESTERLY FLOW AT THE SURFACE  
INCREASE CHANCES FOR ABOVE NORMAL TEMPERATURES AND PRECIPITATION THROUGHOUT  
MUCH OF ALASKA.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 30% OF TODAY'S 6Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 60% 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: AVERAGE, 3 OUT OF 5, DUE TO GOOD  
AGREEMENT AMONG THE PRECIPITATION TOOLS OFFSET DUE TO AN EXPECTED PATTERN  
CHANGE DURING THE PERIOD WHICH RESULTS IN HIGHLY VARIABLE TEMPERATURES DURING  
THE 5-DAY PERIOD ACROSS THE CENTRAL AND EASTERN U.S.  
 
8-14 DAY OUTLOOK FOR DEC 06 - 12 2017  
 
THE LONGWAVE PATTERN CHANGE OVER NORTH AMERICA IS EXPECTED TO OCCUR BY THE  
BEGINNING OF THE WEEK-2 PERIOD. DUE TO LOW SPREAD AMONG THE GFS AND ECMWF  
ENSEMBLE MEMBERS AND GOOD MODEL CONTINUITY, FORECAST CONFIDENCE REMAINS HIGH  
THAT THIS PATTERN BECOMES ESTABLISHED AND RESULTS IN MUCH COLDER TEMPERATURES  
TO THE CENTRAL AND EASTERN U.S. DURING WEEK-2. THE GFS ENSEMBLE MEMBERS  
CONTINUE TO INDICATE THAT THE ARCTIC OSCILLATION (AO) INDEX BECOMES MORE  
NEGATIVE WITH TIME AS POSITIVE 500-HPA HEIGHT ANOMALIES ARE PROMINENT OVER THE  
HIGHER LATITUDES OF THE NORTHERN HEMISPHERE DURING EARLY DECEMBER.  
 
THE ENSEMBLE MEANS ARE IN EXCELLENT AGREEMENT WITH A HIGHLY AMPLIFIED RIDGE  
ALONG THE WEST COAST WITH A LARGE POSITIVE 500-HPA HEIGHT ANOMALY CENTER OF  
MORE THAN 200 METERS AT VANCOUVER ISLAND (50N/130W). THE TEMPERATURE OUTLOOK  
DURING WEEK-2 IS BASED ON TELECONNECTIONS UPON THIS LARGE 500-HPA HEIGHT  
ANOMALY CENTER ALONG WITH GUIDANCE FROM THE DYNAMICAL AND STATISTICAL TOOLS. A  
LARGE INCREASE IN THE SPATIAL COVERAGE OF BELOW NORMAL TEMPERATURES IS LIKELY  
TO OCCUR EARLY IN WEEK-2. THEREFORE, BELOW NORMAL TEMPERATURES ARE FAVORED FOR  
MUCH OF THE CENTRAL AND EASTERN CONUS. THE HIGHEST PROBABILITIES FOR BELOW  
NORMAL TEMPERATURES ARE FORECAST ACROSS THE LOWER MISSISSIPPI VALLEY WHERE  
STATISTICAL TOOLS HAVE A STRONG SIGNAL. TEMPERATURE TOOLS VARY ACROSS THE  
WESTERN U.S. BUT IN GENERAL A GRADUAL WARMING TREND IS EXPECTED AS THE  
UPPER-LEVEL TROUGH EXITS THIS REGION. OFFSHORE FLOW CONTINUES TO FAVOR ABOVE  
NORMAL TEMPERATURES ACROSS SOUTHERN CALIFORNIA.  
 
MAJOR MODIFICATIONS TO YESTERDAY'S PRECIPITATION OUTLOOK WERE NECESSARY OVER  
THE NORTH-CENTRAL U.S. SINCE A LOW PRESSURE SYSTEM IS EXPECTED TO LIFT OUT WITH  
NORTHERLY FLOW BECOMING ESTABLISHED. ELEVATED ODDS FOR ABOVE NORMAL  
PRECIPITATION ARE EXPECTED TO BE LIMITED TO PARTS OF THE SOUTHEAST, GULF COAST,  
AND RIO GRANDE VALLEY DUE TO THE PRESENCE OF A FRONT AND WAVE OF LOW PRESSURE  
EARLY IN WEEK-2. STRONG COLD AIR ADVECTION IS EXPECTED TO PROMOTE LAKE-EFFECT  
SNOW WITH NEAR NORMAL PRECIPITATION FAVORED DOWNWIND OF THE GREAT LAKES. THE  
HIGHEST PROBABILITIES FOR BELOW NORMAL PRECIPITATION ARE FORECAST ACROSS  
NORTHERN CALIFORNIA AND THE PACIFIC NORTHWEST, BASED ON THE HIGH AMPLITUDE  
RIDGE ALOFT AND STRONG SUPPORT FROM STATISTICAL AND DYNAMICAL PRECIPITATION  
TOOLS.  
 
THE LONGWAVE PATTERN ALOFT AND THE FLOW AT THE SURFACE FLOW ARE EXPECTED TO  
CHANGE LITTLE DURING WEEK-2. THEREFORE, ENHANCED ODDS FOR ABOVE NORMAL  
TEMPERATURES AND PRECIPITATION ARE LIKELY TO CONTINUE THROUGH WEEK-2 ACROSS  
ALASKA.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 40% OF TODAY'S 6Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, AND 60% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN  
CENTERED ON DAY 11  
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD IS: ABOVE AVERAGE, 4 OUT OF 5, DUE  
TO GOOD AGREEMENT AMONG THE ENSEMBLE MEANS AND THE EXPECTATION THAT A PATTERN  
CHANGE OCCURS AT THE BEGINNING OF WEEK-2.  
 
FORECASTER: BRAD PUGH  
 
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:  
20031201 - 19511127 - 19971126 - 19651205 - 19901113  
 
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:  
20031202 - 19971126 - 19981124 - 19511128 - 19981119  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR DEC 04 - 08 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B B OREGON N B NRN CALIF A B  
SRN CALIF A B IDAHO B B NEVADA N B  
W MONTANA N B E MONTANA N B WYOMING N B  
UTAH B B ARIZONA A N COLORADO B A  
NEW MEXICO B A N DAKOTA N B S DAKOTA N N  
NEBRASKA N N KANSAS N A OKLAHOMA N A  
N TEXAS B A S TEXAS B A W TEXAS B A  
MINNESOTA A N IOWA A N MISSOURI A A  
ARKANSAS A A LOUISIANA N 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 A 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 A N  
AK ALEUTIAN A A AK WESTERN A A 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 06 - 12 2017  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON N B OREGON N B NRN CALIF N B  
SRN CALIF N B IDAHO N B NEVADA N B  
W MONTANA N B E MONTANA N B WYOMING N B  
UTAH N B ARIZONA N B COLORADO N B  
NEW MEXICO N B N DAKOTA N B S DAKOTA N B  
NEBRASKA N B KANSAS N B OKLAHOMA N B  
N TEXAS N B S TEXAS N A W TEXAS N A  
MINNESOTA N B IOWA N B MISSOURI N B  
ARKANSAS N B LOUISIANA N N WISCONSIN N B  
ILLINOIS N B MISSISSIPPI N N MICHIGAN N N  
INDIANA N B OHIO N N KENTUCKY N B  
TENNESSEE N B ALABAMA N N NEW YORK N N  
VERMONT N N NEW HAMP N N MAINE N N  
MASS N N CONN N N RHODE IS N N  
PENN N N NEW JERSEY N N W VIRGINIA N N  
MARYLAND N N DELAWARE N N VIRGINIA N N  
N CAROLINA N A S CAROLINA N A GEORGIA N A  
FL PNHDL N A FL PENIN N A AK N SLOPE N A  
AK ALEUTIAN N A AK WESTERN N A AK INT BSN N A  
AK S INT N A AK SO COAST N A AK PNHDL N 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.  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page