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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0627Z Jul 22, 2014)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
227 AM EDT TUE JUL 22 2014

VALID 12Z FRI JUL 25 2014 - 12Z TUE JUL 29 2014

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

LATEST GUIDANCE IS CONTINUING TO SUGGEST WELL ABOVE AVERAGE
CONFIDENCE IN THE FCST OF AN AMPLIFYING ERN CONUS TROUGH
DOWNSTREAM FROM A NWD-EXPANDING WRN RIDGE... BUT SOME OF THE
DETAILS OF HOW THE ERN TROUGH IS ULTIMATELY ACHIEVED REMAIN IN
QUESTION.

A DECENT PORTION OF THE FCST SPREAD DEVELOPS DURING THE FIRST HALF
OF THE PERIOD AS THERE APPEARS TO BE FAIRLY HIGH SENSITIVITY TO
MINOR DIFFS IN EXACTLY HOW AN UPR HIGH TO THE W/NW OF HUDSON BAY
EVOLVES... INFLUENCING THE EVOLUTION OF THE UPR LOW TO THE N OF
THE PLAINS AND FLOW AROUND THE ERN SIDE OF THE UPR HIGH.  RECENT
GFS RUNS HAVE TENDED TO KEEP THE SRN CANADA UPR LOW BETTER DEFINED
AS IT DESCENDS INTO THE GRTLKS.  THE PAST COUPLE ECMWF RUNS ARE ON
THE OTHER SIDE OF THE SPECTRUM... BEING SLOW/SHEARED WITH THE UPR
LOW ENERGY AND EVENTUALLY FEEDING MORE ERN CANADA FLOW INTO THE
DEVELOPING ERN CONUS TROUGH.  THIS RESULTS IN THE ECMWF DELAYING
THE TROUGH AMPLIFICATION SOMEWHAT.  CMC RUNS HAVE VARIED BETWEEN
THE TWO IDEAS WITH THE 12Z VERSION CLOSER TO THE GFS.

GEFS/ECMWF ENSEMBLE MEANS SHOW SOME TENDENCIES TOWARD THEIR PARENT
MODELS BUT OVERALL REPRESENT A GOOD INTERMEDIATE SOLN RELATIVE TO
THE TWO EXTREMES.  THUS PREFER TO BASE THE MANUAL FCST PRIMARILY
ON THE 18Z GEFS/12Z ECMWF MEANS.  A VERY SMALL WEIGHTING OF THE
12Z GFS/CMC WAS INCLUDED TO ACKNOWLEDGE THE POTENTIAL FOR A
SLIGHTLY STRONGER EVOLUTION THAN SEEN IN THE MEANS.  SPREAD
PERSISTS IN THE NEW 00Z CYCLE WITH THE GFS IS STILL ON THE
FASTER/STRONGER SIDE THOUGH THE GFS/CMC/UKMET AS A WHOLE STILL
OFFER LITTLE SUPPORT FOR 12Z ECMWF DETAILS.

THE MAJORITY OF GUIDANCE INDICATES ONLY VERY SLOW MOVEMENT OF A
NERN PAC UPR TROUGH/EMBEDDED LOW.  WHILE OTHER OPERATIONAL MODELS
HAVE NOT BEEN IMMUNE FROM AN ISOLD STRAY RUN... GFS RUNS HAVE
TENDED TO BE MOST EAGER TO BRING SOME OF THIS ENERGY INTO WRN
CANADA LATER IN THE PERIOD.  EVENTUALLY FLOW AROUND THE ALEUTIANS
RIDGE WILL LIKELY CAUSE SOME EJECTION OF ENERGY BUT SO FAR THE
BEST PROBABILITY IS FOR A SLOWER SOLN THAN THE GFS.


...SENSIBLE WEATHER HIGHLIGHTS...

ERN CONUS TROUGH AMPLIFICATION WILL BE REFLECTED AT THE SFC AS A
SRN CANADA SFC LOW/NRN TIER COLD FRONT PROGRESSING SEWD INTO THE
ERN STATES... IN A MANNER PERHAPS MORE REMINISCENT OF THE COOL
SEASON.  THE COMBINATION OF THIS SYSTEM AS WELL AS TRAILING ENERGY
ALOFT AND A LEADING WARM FRONT WILL SUPPORT MULTIPLE AREAS OF
SHWRS/TSTMS FROM THE NRN PLAINS/MS VLY THROUGH MUCH OF THE EAST...
AND THEN BACK TOWARD THE SRN HALF OF THE ROCKIES/HIGH PLAINS. 
RNFL OVER PARTS OF CO/NM MAY BE ENHANCED BY LOW LVL UPSLOPE FLOW
BY THE LATTER HALF OF THE PERIOD.  EXCEPT FOR A PERIOD OF TIME IN
THE CNTRL-SRN PLAINS... EXPECT CNTRL-ERN CONUS DAYTIME HIGHS TO BE
NEAR TO BELOW NORMAL WITH FAIRLY BROAD COVERAGE OF MINUS 5-10F
ANOMALIES BY NEXT MON-TUE.  ALSO EARLY IN THE PERIOD FRI-SAT ERN
CONUS HIGH PRESSURE MAY PROVIDE A COUPLE COOL MORNINGS WITH LOWS
5-10F BELOW NORMAL.  MEANWHILE THE NORTHWEST WILL TREND WARMER AS
THE WRN RIDGE ALOFT EXPANDS... WITH SOME LOCATIONS LIKELY REACHING
AT LEAST 10F ABOVE NORMAL EARLY NEXT WEEK.  MOST OTHER AREAS OF
THE WEST SHOULD SEE ABOVE NORMAL READINGS AS WELL.

RAUSCH