323  
FXUS06 KWBC 151902  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EDT WED AUGUST 15 2018  
 
6-10 DAY OUTLOOK FOR AUG 21 - 25 2018  
 
THE MANUAL BLEND FROM TODAY SHOWS A DEEP TROUGH CENTERED OVER THE BERING SEA  
CORRESPONDING WITH NEGATIVE 500-HPA HEIGHT ANOMALIES. DOWNSTREAM OF THE TROUGH,  
THERE IS A STRONG RIDGE ALONG THE WEST COAST OF THE CONUS WITH POSITIVE HEIGHT  
ANOMALIES EXTENDING INTO EASTERN ALASKA. THIS RIDGE IS STRONGEST EARLY IN THE  
PERIOD BEFORE FLATTENING OUT. A SECOND RIDGE AMPLIFIES IN THE NORTHEAST PACIFIC  
TOWARD DAY 10. THIS EVOLUTION IS SUPPORTED BY TODAY'S 06Z OPERATIONAL GFS, 00Z  
OPERATIONAL ECMWF, 00Z OPERATIONAL CANADIAN, AND THEIR RESPECTIVE ENSEMBLE  
MEANS. DYNAMICAL GUIDANCE AND TELECONNECTIONS SUPPORT THE AMPLIFICATION OF A  
LONGWAVE TROUGH INTO THE CENTRAL CONUS, MOST ROBUST IN THE 00Z ECMWF  
OPERATIONAL AND ENSEMBLE MEANS. TO THE EAST POSITIVE HEIGHT ANOMALIES ARE  
EXPECTED AHEAD OF THE AFOREMENTIONED TROUGH.  
 
THE RIDGE ALONG THE WEST COAST OF THE CONUS IS PROJECTED TO FAVOR ABOVE NORMAL  
TEMPERATURE ANOMALIES FOR MUCH OF THE WESTERN CONUS EXTENDING NORTHWARD THROUGH  
ALASKA. TEMPERATURES ARE MORE UNCERTAIN FOR SOUTHERN ALASKA AND THE ALEUTIANS  
WHICH ARE CLOSER TO THE TROUGH AXIS OVER THE BERING SEA. MOST OF THE ANOMALOUS  
WARMTH IS PROJECTED IN THE EARLY PART OF THE FORECAST PERIOD WITH SOME SIGNAL  
FOR MORE NORMAL CONDITIONS LATE. TODAY'S 06Z GEFS SHOW TEMPERATURES MODERATING  
TO NEAR AVERAGE OVER THE PACIFIC NORTHWEST AROUND DAY 10, WITH MORE WARMTH  
LINGERING IN THE 00Z ECMWF AND CANADIAN SUITES. IN THE MIDWEST CONUS, NEGATIVE  
TEMPERATURE ANOMALIES ARE STILL EXPECTED IN ASSOCIATION WITH THE BROAD TROUGH  
EXPECTED TO BE AMPLIFYING IN THAT REGION EARLY IN THE PERIOD. POSITIVE  
TEMPERATURE ANOMALIES ARE FAVORED FOR THE EASTERN SEABOARD AND SOUTH TEXAS.  
 
AMPLIFICATION OF THE CENTRAL CONUS TROUGH LEADS TO INCREASED ABOVE NORMAL  
PRECIPITATION PROBABILITIES DOWNSTREAM. HOWEVER, INCONSISTENCIES AMONG THE  
MODELS MAKE IT DIFFICULT TO HIGHLIGHT WHERE THE BEST CHANCES FOR ABOVE NORMAL  
PRECIPITATION WILL BE. TODAY'S 06Z GEFS CONTINUE TO SHOW THE BEST CHANCES FOR  
ABOVE NORMAL PRECIPITATION IN THE TENNESSEE VALLEY, BUT UNCERTAINTY IS HIGHER  
DUE TO THE ECMWF AND CANADIAN ENSEMBLES PRODUCING LOWER PROBABILITIES IN THIS  
REGION. THE TROUGH OVER THE BERING SEA FAVORS HIGH PROBABILITIES OF ABOVE  
NORMAL PRECIPITATION FOR SOUTHERN ALASKA. BELOW NORMAL PRECIPITATION IS  
FAVORED FOR THE PACIFIC NORTHWEST, INFLUENCED BY RIDGING OVERHEAD, WITH BELOW  
NORMAL PRECIPITATION PROBABILITIES EXTENDING THROUGH THE NORTHERN GREAT PLAINS  
ON THE BACKSIDE OF THE TROUGH AXIS.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 30% 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, 10% OF  
TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND 10% OF TODAY'S 0Z CANADIAN  
ENSEMBLE MEAN CENTERED ON DAY 8  
 
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: AVERAGE, 3 OUT OF 5, DUE TO FAIR  
MODEL AGREEMENT.  
 
8-14 DAY OUTLOOK FOR AUG 23 - 29 2018  
 
THE OVERALL DAY 8-14 PATTERN IN THE MANUAL BLEND SHOWS A DEAMPLIFICATION OF  
500-HPA HEIGHTS RELATIVE TO THE DAY 6-10 PERIOD. A RIDGE IS EXPECTED TO BUILD  
IN THE NORTHEAST PACIFIC WITH A SHORTWAVE TROUGH POSSIBLY IMPACTING THE  
NORTHWEST CONUS. THE TROUGH OVER THE CENTRAL CONUS WILL BEGIN TO FLATTEN WITH  
INCREASED RIDGING OVER THE EASTERN CONUS FAVORED LATER IN THE PERIOD. TROUGHING  
IS EXPECTED TO REMAIN IN PLACE OVER THE BERING SEA.  
 
MOST FORECAST UNCERTAINTY IN THIS PERIOD IS DUE TO THE PRESENCE OF A TROUGH  
OVER THE PACIFIC NORTHWEST IN SOME OF THE DYNAMICAL GUIDANCE, WHICH WOULD ACT  
TO DECREASE PROBABILITIES FOR ABOVE NORMAL TEMPERATURES IN THAT REGION. THE  
TROUGH IS MOST ROBUST IN TODAY'S 00Z CANADIAN ENSEMBLE, BUT DOES HAVE SUPPORT  
FROM THE 06Z GEFS. THE 00Z ECMWF ENSEMBLE MEAN PRESENTS A FLATTER SOLUTION, AND  
IS THEREFORE THE WARMEST. TODAY'S FORECAST STILL FAVORS ABOVE NORMAL  
TEMPERATURES FOR THE NORTHWEST CONUS, BUT HAS LOWER PROBABILITIES RELATIVE TO  
YESTERDAY'S OUTLOOK. THE WEAKENING TROUGH IN THE MIDWEST CONUS FAVORS COOLER  
ANOMALIES, ESPECIALLY EARLY IN THE PERIOD. WARMER TEMPERATURE ANOMALIES ARE  
FAVORED TO THE EAST AS HEIGHTS BEGIN TO FLATTEN AND RIDGING BECOMES DOMINANT.  
 
PERSISTENT TROUGH PATTERN OVER THE BERING SEA WILL KEEP PROBABILITIES FOR ABOVE  
NORMAL PRECIPITATION INCREASED FOR MOST OF ALASKA. BELOW NORMAL PRECIPITATION  
IS FAVORED FOR THE NORTHWEST CONUS WITH MORE UNCERTAINTY DUE TO THE EVOLUTION  
OF THE 500-HPA HEIGHT PATTERN WITH THE 00Z CANADIAN ENSEMBLE YIELDING THE  
WETTEST SOLUTION AND THE 00Z ECMWF ENSEMBLE PRODUCING THE DRIEST. THE 06Z GEFS  
SPLITS THE DIFFERENCE AND TODAY'S FORECAST WILL MAINTAIN THE BELOW NORMAL  
PRECIPITATION PROBABILITIES FOR THE NORTHWEST CONUS BUT WILL KEEP NEAR NORMAL  
PRECIPITATION FORECAST FOR AREAS FARTHER EAST. FOR THE EASTERN CONUS, A SLIGHT  
CHANCE OF ABOVE NORMAL PRECIPITATION WILL BE FAVORED. ENHANCEMENT OF THE  
MONSOON IS EXPECTED TO INCREASE ABOVE NORMAL PRECIPITATION PROBABILITIES IN THE  
SOUTHWEST.  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 20% OF TODAY'S 0Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 30% 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: SLIGHTLY BELOW AVERAGE, 2 OUT OF 5  
DUE TO MODEL DIFFERENCES  
 
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  
AUGUST 16.  
 
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:  
19950802 - 19910824 - 19880804 - 19610805 - 19910819  
 
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:  
19950801 - 19910823 - 19880805 - 19880810 - 20090815  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR AUG 21 - 25 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON A B OREGON A B NRN CALIF A N  
SRN CALIF A N IDAHO A N NEVADA A N  
W MONTANA A B E MONTANA B B WYOMING B A  
UTAH A A ARIZONA A A COLORADO B A  
NEW MEXICO N A N DAKOTA B B S DAKOTA B N  
NEBRASKA B N KANSAS B A OKLAHOMA B A  
N TEXAS B A S TEXAS A N W TEXAS B A  
MINNESOTA B B IOWA B N MISSOURI B A  
ARKANSAS B A LOUISIANA N A WISCONSIN B N  
ILLINOIS B A MISSISSIPPI B A MICHIGAN B A  
INDIANA B A OHIO B A KENTUCKY B A  
TENNESSEE B A ALABAMA N 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 N A NEW JERSEY A A W VIRGINIA N A  
MARYLAND A A DELAWARE A A VIRGINIA N A  
N CAROLINA A A S CAROLINA A A GEORGIA A A  
FL PNHDL A A FL PENIN A N AK N SLOPE N N  
AK ALEUTIAN N A AK WESTERN A A AK INT BSN A A  
AK S INT A A AK SO COAST A A AK PNHDL A B  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR AUG 23 - 29 2018  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON A B OREGON A B NRN CALIF A N  
SRN CALIF A N IDAHO A B NEVADA A N  
W MONTANA N B E MONTANA B B WYOMING B B  
UTAH A N ARIZONA A A COLORADO N N  
NEW MEXICO A A N DAKOTA B N S DAKOTA B N  
NEBRASKA B N KANSAS B N OKLAHOMA B N  
N TEXAS B A S TEXAS N N W TEXAS N A  
MINNESOTA N N IOWA B A MISSOURI B N  
ARKANSAS B A LOUISIANA N A WISCONSIN A N  
ILLINOIS B N MISSISSIPPI B A MICHIGAN A N  
INDIANA N A OHIO A A KENTUCKY N A  
TENNESSEE B A ALABAMA N A NEW YORK A N  
VERMONT A N NEW HAMP A N MAINE A N  
MASS A N CONN A N RHODE IS A N  
PENN A N NEW JERSEY A N W VIRGINIA A N  
MARYLAND A N DELAWARE A N VIRGINIA A N  
N CAROLINA A N S CAROLINA A N GEORGIA A A  
FL PNHDL A N FL PENIN A N AK N SLOPE N A  
AK ALEUTIAN N A AK WESTERN A A AK INT BSN N A  
AK S INT N A AK SO COAST N 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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