273  
FXUS06 KWBC 221922  
PMDMRD  
PROGNOSTIC DISCUSSION FOR 6 TO 10 AND 8 TO 14 DAY OUTLOOKS  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK, MD  
300 PM EDT THU APRIL 22 2021  
 
6-10 DAY OUTLOOK FOR APR 28 - MAY 02, 2021  
 
TODAYS MODEL SOLUTIONS ARE IN FAIR AGREEMENT ON THE OVERALL 500-HPA FLOW  
PATTERN ACROSS THE FORECAST DOMAIN. CYCLONIC FLOW IS FORECAST ACROSS MOST OF  
THE CONUS PUNCTUATED BY A MEAN TROUGH THAT IS EXPECTED ACROSS SOUTHERN PLAINS  
AND LOWER MISSISSIPPI VALLEY. RIDGING AND ABOVE NORMAL EIGHTS ARE PREDICTED ON  
EITHER SIDE OF THIS TROUGH ACROSS THE WEST COAST AND EASTERN SEABOARD,  
RESPECTIVELY. WEAK 500-HPA FLOW IS FORECAST ACROSS MOST OF ALASKA AS A TROUGH  
FORECAST TO THE SOUTH OF THE ALEUTIANS IS EXPECTED TO KEEP ENHANCED WESTERLIES  
MOSTLY TO THE SOUTH OF THE STATE. A STRONG WESTERN PACIFIC MJO EVENT (PHASE 7  
IN THE WHEELER-HENDON CLASSIFICATION) IS CURRENTLY ONGOING, WHICH IS LIKELY TO  
INFLUENCE THE OVERALL PATTERN DURING THE OUTLOOK PERIOD. A COMPOSITE FROM PAST  
STRONG (DEFINED IN THIS CASE AS A MJO INDEX AMPLITUDE GREATER THAN 1.0) PHASE 7  
MJO EVENTS THIS TIME OF YEAR GENERALLY CORRESPOND WITH TROUGHING ACROSS THE  
GREAT LAKES AND RIDGING OVER MUCH OF THE WESTERN CONUS, WHICH WOULD REPRESENT  
AN EASTWARD DISPLACEMENT OF THE OVERALL FEATURES RELATIVE TO THE MANUAL 500-HPA  
HEIGHT BLEND. THE MANUAL HEIGHT BLEND CONSISTS PRIMARILY OF ENSEMBLE MEAN  
SOLUTIONS FROM THE NCEP, ECMWF, AND CANADIAN CENTERS AND WAS BASED ON  
CONSIDERATIONS OF RECENT SKILL.  
 
RIDGING FORECAST ACROSS THE WEST COAST AND EASTERN SEABOARD FAVORS ABOVE NORMAL  
TEMPERATURES ACROSS THESE REGIONS. ABOVE NORMAL TEMPERATURE PROBABILITIES ARE  
REDUCED ACROSS THE CENTRAL CONUS UNDERNEATH PREDICTED MEAN TOUGHING. NEAR  
NORMAL TEMPERATURES ARE FAVORED ACROSS THIS REGION DUE TO CONFLICTING SIGNALS  
AMONG DYNAMICAL AND STATISTICAL TOOLS. BELOW NORMAL TEMPERATURES ARE FAVORED  
FOR SOUTHEASTERN ALASKA DUE TO DYNAMICAL GUIDANCE FROM THE ECMWF ENSEMBLES,  
ANALOGS BASED ON THE MANUAL BLEND, AND BELOW NORMAL SSTS ACROSS PARTS OF THE  
SOUTH COAST. NEAR TO ABOVE NORMAL TEMPERATURES ARE FAVORED ACROSS MUCH OF  
WESTERN ALASKA CONSISTENT WITH CALIBRATED DYNAMICAL MODEL GUIDANCE.  
 
ABOVE NORMAL PRECIPITATION IS LIKELY ACROSS MUCH OF THE EAST-CENTRAL CONUS  
AHEAD OF A MEAN TROUGH FORECAST OVER THE PLAINS. NEAR TO BELOW NORMAL  
PRECIPITATION IS FAVORED ACROSS MOST OF THE REMAINDER OF THE CONUS UNDERNEATH  
PREDICTED RIDGING AND ASSOCIATED NEAR TO ABOVE NORMAL HEIGHTS. DRIER THAN  
NORMAL CONDITIONS ARE LIKELY ACROSS MOST OF ALASKA, AS A TROUGH PREDICTED TO  
THE SOUTH OF THE ALEUTIANS IS EXPECTED TO STEER THE MEAN STORM TRACK MOSTLY TO  
THE SOUTH OF THE STATE. HOWEVER, ENHANCED PACIFIC FLOW IS POSSIBLE FOR PARTS OF  
THE SOUTHERN PANHANDLE SOUTHWARD TO THE PACIFIC NORTHWEST, WHERE ABOVE NORMAL  
PRECIPITATION IS SLIGHTLY FAVORED.  
 
THE OFFICIAL 6-10 DAY 500-HPA HEIGHT BLEND CONSISTS OF 30% OF TODAY'S 6Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 8, 5% OF TODAY'S OPERATIONAL 0Z GFS CENTERED ON  
DAY 8, 35% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN CENTERED ON DAY 8, 5% OF  
TODAY'S OPERATIONAL 0Z ECMWF CENTERED ON DAY 8, AND 25% OF TODAY'S 0Z CANADIAN  
ENSEMBLE MEAN CENTERED ON DAY 8  
 
 
FORECAST CONFIDENCE FOR THE 6-10 DAY PERIOD: BELOW AVERAGE, 2 OUT OF 5, DUE TO  
FAIR MODEL AGREEMENT WITH SOME DISAGREEMENT AMONG THE TEMPERATURE AND  
PRECIPITATION TOOLS.  
 
8-14 DAY OUTLOOK FOR APR 30 - MAY 06, 2021  
 
DURING THE WEEK-2 PERIOD, MEAN CYCLONIC 500-HPA FLOW IS EXPECTED TO PERSIST  
ACROSS MOST OF THE CONUS. THE LOCATION OF THE ASSOCIATED TROUGH AXIS IS  
FORECAST TO SHIFT WESTWARD RELATIVE TO THE 6-10 DAY PERIOD, TO A MEAN POSITION  
ACROSS THE WEST-CENTRAL CONUS, AND DEAMPLIFY. RIDGING AND ASSOCIATED ABOVE  
NORMAL HEIGHTS ARE FORECAST TO PERSIST ACROSS THE NORTHEASTERN CONUS. RIDGING  
PREDICTED OVER THE WEST COAST DURING THE 6-10 DAY PERIOD IS GENERALLY FORECAST  
TO WEAKEN AND RETROGRADE OFF THE COAST DURING WEEK-2. ENHANCED WESTERLIES ARE  
EXPECTED TO REMAIN MOSTLY TO THE SOUTH OF ALASKA. AS A RESULT, WEAK 500-HPA  
FLOW IS EXPECTED TO CONTINUE OVER MOST OF THE STATE.  
 
ABOVE NORMAL TEMPERATURES ARE LIKELY ACROSS THE EASTERN SEABOARD, AS ABOVE  
NORMAL HEIGHTS ARE GENERALLY FORECAST TO PERSIST ACROSS THE REGION. ABOVE  
NORMAL TEMPERATURE PROBABILITIES ARE FORECAST TO WEAKEN ACROSS MOST OF THE  
WESTERN CONUS RELATIVE TO THE 6-10 DAY PERIOD AS RIDGING IS EXPECTED TO SUBSIDE  
AND RETROGRADE OFF THE COAST. THE RETROGRESSION OF THIS RIDGE MAY RESULT IN A  
MORE NORTHERLY COMPONENT OF THE MID-LEVEL FLOW OVER THE PACIFIC NORTHWEST,  
SLIGHTLY FAVORING BELOW NORMAL TEMPERATURES THERE. ENHANCED BELOW NORMAL  
TEMPERATURE PROBABILITIES ALSO EXTEND NORTHWARD TO SOUTHEASTERN ALASKA, DUE TO  
STRONG SUPPORT FROM ECMWF DYNAMICAL MODEL GUIDANCE. NEAR TO ABOVE NORMAL  
TEMPERATURES ARE FAVORED FOR THE REMAINDER OF THE STATE, DUE TO SUPPORT FROM  
THE GEFS AND FROM MJO COMPOSITES.  
 
NEAR TO ABOVE NORMAL PRECIPITATION IS FAVORED ACROSS MOST OF THE CONUS,  
UNDERNEATH PREDICTED MEAN CYCLONIC 500-HPA FLOW. HOWEVER, BELOW NORMAL  
PRECIPITATION IS SLIGHTLY FAVORED FOR PARTS OF NORTHERN NEW ENGLAND, CLOSE TO A  
PREDICTED MEAN RIDGE AXIS. NEAR TO BELOW NORMAL PRECIPITATION IS FAVORED FOR  
THE SOUTHWESTERN CONUS AS THE MEAN STORM TRACK IS EXPECTED TO REMAIN TO THE  
NORTH OF THESE AREAS AND MUCH OF THIS REGION IS CLIMATOLOGICALLY DRY THIS TIME  
OF YEAR. DRY CONDITIONS ARE LIKELY TO PERSIST ACROSS MUCH OF MAINLAND ALASKA,  
AS ENHANCED WESTERLIES ARE EXPECTED TO REMAIN TO THE SOUTH OF THE REGION.  
HOWEVER, ENHANCED PACIFIC FLOW MAY CLIP THE SOUTHERN PANHANDLE, RESULTING IN A  
SLIGHT TILT TOWARD ABOVE NORMAL PRECIPITATION THERE. THE PREDICTED ENHANCED  
PACIFIC FLOW ALSO EXTENDS FARTHER TO THE SOUTH, TILTING THE ODDS TOWARD ABOVE  
NORMAL PRECIPITATION FOR PARTS OF THE PACIFIC NORTHWEST  
 
THE OFFICIAL 8-14 DAY 500-HPA HEIGHT BLEND CONSISTS OF: 30% OF TODAY'S 6Z GFS  
ENSEMBLE MEAN CENTERED ON DAY 11, 45% OF TODAY'S 0Z EUROPEAN ENSEMBLE MEAN  
CENTERED ON DAY 11, AND 25% OF TODAY'S 0Z CANADIAN ENSEMBLE MEAN CENTERED ON  
DAY 11  
 
FORECAST CONFIDENCE FOR THE 8-14 DAY PERIOD: MUCH BELOW AVERAGE, 1 OUT OF 5,  
DUE TO CONFLICTING DYNAMICAL MODEL GUIDANCE ACROSS LARGE PORTIONS OF THE  
FORECAST DOMAIN.  
 
FORECASTER: SCOTT H  
 
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 MAY  
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:  
19900410 - 19970411 - 20050501 - 19560421 - 20020404  
 
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:  
19900409 - 20020403 - 20050502 - 19560421 - 19670504  
 
6-10 DAY OUTLOOK TABLE  
OUTLOOK FOR APR 28 - MAY 02, 2021  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON N N OREGON N N NRN CALIF A B  
SRN CALIF A N IDAHO A N NEVADA A B  
W MONTANA A N E MONTANA A N WYOMING A N  
UTAH A B ARIZONA N B COLORADO N N  
NEW MEXICO N B N DAKOTA N N S DAKOTA N N  
NEBRASKA N N KANSAS N N OKLAHOMA N N  
N TEXAS N N S TEXAS N N W TEXAS N B  
MINNESOTA N N IOWA N N MISSOURI N N  
ARKANSAS N A LOUISIANA N A WISCONSIN N A  
ILLINOIS N A MISSISSIPPI N A MICHIGAN A A  
INDIANA A A OHIO A A KENTUCKY A A  
TENNESSEE A A ALABAMA N A NEW YORK A N  
VERMONT A N NEW HAMP A B MAINE A N  
MASS A B CONN A B RHODE IS A B  
PENN A A NEW JERSEY A N W VIRGINIA A A  
MARYLAND A N DELAWARE A N VIRGINIA A A  
N CAROLINA A A S CAROLINA A A GEORGIA A A  
FL PNHDL A A FL PENIN A N AK N SLOPE A B  
AK ALEUTIAN A B AK WESTERN N B AK INT BSN B B  
AK S INT B B AK SO COAST B B AK PNHDL B A  
 
 
 
8-14 DAY OUTLOOK TABLE  
OUTLOOK FOR APR 30 - MAY 06, 2021  
 
STATE TEMP PCPN STATE TEMP PCPN STATE TEMP PCPN  
WASHINGTON B N OREGON N N NRN CALIF A B  
SRN CALIF A B IDAHO N N NEVADA A B  
W MONTANA N N E MONTANA N N WYOMING N N  
UTAH N B ARIZONA A B COLORADO N N  
NEW MEXICO A B N DAKOTA N A S DAKOTA N N  
NEBRASKA N N KANSAS N N OKLAHOMA N A  
N TEXAS N N S TEXAS N B W TEXAS A B  
MINNESOTA N A IOWA N N MISSOURI N N  
ARKANSAS N A LOUISIANA N A WISCONSIN N A  
ILLINOIS N N MISSISSIPPI N A MICHIGAN N A  
INDIANA N N OHIO A N KENTUCKY A N  
TENNESSEE A N ALABAMA A A NEW YORK A N  
VERMONT A N NEW HAMP A N MAINE A B  
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 A S CAROLINA A A GEORGIA A A  
FL PNHDL A A FL PENIN A A AK N SLOPE N B  
AK ALEUTIAN A N AK WESTERN N B AK INT BSN N B  
AK S INT B N AK SO COAST B N AK PNHDL B 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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