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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1558Z Jul 20, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EDT SUN JUL 20 2014

VALID 12Z WED JUL 23 2014 - 12Z SUN JUL 27 2014

...SYNOPSIS...

GUIDANCE CONTINUES TO SHOW A STABLE MEAN PATTERN CONSISTING OF A
SOUTHERN ROCKIES RIDGE AND EASTERN U.S. TROUGH WHILE A POSITIVELY
TILTED LONGWAVE TROUGH BECOMES ESTABLISHED UPSTREAM IN THE GULF OF
ALASKA.  TELECONNECTIONS RELATIVE TO BOTH AN ALEUTIANS RIDGE AND A
LESS PRONOUNCED CORE OF POSITIVE HEIGHT ANOMALIES FORECAST NEAR
HUDSON BAY...CORRESPOND WELL TO THE EXPECTED U.S. PATTERN. THIS
LENDS US SOME CONFIDENCE IN THE LARGE SCALE FLOW...AND THE MODEL
SPREAD EVEN FOR THE SHORTWAVE DETAILS IS LESS THAN
USUAL...CERTAINLY LESS THAN SEEN 24 HOURS AGO.


...GUIDANCE EVALUATION/PREFERENCES... 

00Z/06Z ENSEMBLE MEANS SHOW AGREEMENT THROUGH DAY 7. THE GEFS MEAN
TRENDS TOWARD ITS USUAL BIAS...BEING FLATTER AND MORE PROGRESSIVE
AT LONGER LEAD TIMES...ESPECIALLY EVIDENT IN THE NORTH PACIFIC
THIS CYCLE. THEREFORE...WE PREFERRED A NEAR EQUAL BLEND OF THE
ECMWF ENSEMBLE MEAN AND NAEFS MEAN...THE LATTER INCORPORATING MORE
SHARPLY DEFINED FEATURES AND SLOWER PROGRESSION SEEN IN THE
OPERATIONAL CANADIAN AND ASSOCIATED ENSEMBLE MEAN. ONE OF THE
DESIRABLE TRAITS OF THE GEFS/CMC ENSEMBLE WAS TO PULL BACK JUST
SLIGHTLY ON THE FORWARD SPEED OF THE ROBUST SHORTWAVE OVER THE
NORTHWEST U.S./SOUTHERN CANADA ON DAYS 4/5. THAT SYSTEM DOES
MAINTAIN SHORT TO MEDIUM WAVELENGTH AND HAS AN UPSTREAM KICKER TO
ARGUE FOR QUICK PROGRESSION...BUT CONSISTENTLY SLOWER
GFS/CMC-BASED SOLUTIONS ALONG WITH SOME JUMPINESS IN THE
OPERATIONAL ECMWF LOWERS CONFIDENCE AS TO THE SPECIFIC TIMING.
CERTAINLY THE OPERATIONAL GFS HAS CONTINUED TO PRODUCE
PARTICULARLY DEEP AND SLOW SOLUTIONS WHICH STILL CANNOT BE
DISCOUNTED BUT WHICH HAVE LITTLE SPECIFIC SUPPORT. IN SOME SENSE
WE ARE SPLITTING HAIRS...BECAUSE ALL SOLUTIONS PRODUCE A DYNAMIC
TROUGH THAT IS AT LEAST 1.5-2.0 STANDARD DEVIATIONS BELOW
CLIMATOLOGY WITHIN THE MASS FIELDS. THESE NUMBERS INCREASE TO 3
STANDARD DEVIATIONS IN THE GFS SOLUTIONS. FOR DAYS 3 AND 4 WE WERE
ABLE TO ENHANCE OUR ENSEMBLE BLEND WITH SMALL PERCENTAGES OF THE
06Z GFS/00Z ECMWF TO FIND A CONSENSUS IN THE NORTHWEST AND WITHIN
THE MEAN TROUGH OVER THE EAST. THE RESULTS COMPARED FAVORABLY TO
THE PREVIOUS WPC FORECAST.

AS THE NORTHWEST SYSTEM HEADS TOWARD THE UPPER MIDWEST WE
ABANDONED THE 06Z GFS WHICH REMAINED ON THE SOUTHERN/DEEP END OF
THE SPREAD...BUT ALSO SWAPPED THE 00Z ECMWF FOR THE 19/12Z
VERSION. THE 00Z RUN APPEARED TOO PROGRESSIVE IN THE GULF OF
ALASKA AND ILL-DEFINED WITH THE ENERGY HEADING INTO THE MIDWEST.


...SENSIBLE WEATHER HIGHLIGHTS...

THE PACIFIC NW WILL SEE A COMBINATION OF POSITIVE AND NEGATIVE
CHANGES IN THE WEATHER WITH RESPECT TO WILDFIRE ISSUES...INCREASED
RAINFALL AND COOLER TEMPS VERSUS SOME THUNDERSTORMS WITH LIGHTNING
AND GUSTY WINDS. AS THIS SYSTEM CONTINUES EASTWARD EXPECT
CONVECTION TO DEVELOP OVER AND SE OF THE NORTHERN PLAINS/UPPER MS
VALLEY...WITH A LEADING WARM FRONT PROVIDING AN ADDITIONAL FOCUS
FOR LOCALLY HEAVY RAINFALL BY LATE WEEK. IN ITS WAKE EXPECT A
COOLING TREND OVER THE NORTHERN TIER. THE COLD FRONT REACHING THE
EAST COAST BY THU WILL BE ACCOMPANIED BY RAIN FOLLOWED BY COOL
HIGH PRESSURE TRACKING INTO THE GRTLKS. EXPECT DIURNAL CONVECTION
OVER THE SOUTHEAST WITH SOME LOCALLY HEAVY AMOUNTS POSSIBLE. THE
DETERMINISTIC MODEL QPFS ARE NOT SHOWING MUCH OF A CONSISTENT
SIGNAL...BUT WITH A STALLED SURFACE BOUNDARY AND WEAK MID LEVEL
CIRCULATION OVER THE CENTRAL GULF COAST STATES EARLY IN THE
PERIOD...COVERAGE OF DIURNALLY ENHANCED THUNDERSTORMS IS LIKELY TO
BE GREATER THAN CLIMATOLOGY FOR THAT REGION. THE MOST PERSISTENT
TEMPERATURE ANOMALIES SHOULD BE OF THE POSITIVE VARIETY NEAR THE
FOUR CORNERS UPPER HIGH...WITH PASSAGE OF THE PAC NW SYSTEM
ALLOWING FOR EXPANSION OF ABOVE NORMAL READINGS OVER MUCH OF THE
INTERIOR WEST BY NEXT WEEKEND.

BURKE/FRACASSO/RAUSCH