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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0643Z Jul 21, 2014)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 AM EDT MON JUL 21 2014

VALID 12Z THU JUL 24 2014 - 12Z MON JUL 28 2014

...OVERVIEW AND PREFERENCES...

GUIDANCE REMAINS AGREEABLE AND CONSISTENT IN FORECASTING A STABLE
MEAN PATTERN CONSISTING OF A STRONG FOUR CORNERS RIDGE AND
AMPLIFIED ERN CONUS TROUGH.  TELECONNECTIONS RELATIVE TO POSITIVE
HGT ANOMALY CENTERS OVER/NEAR THE ALEUTIANS AND N OF HUDSON BAY
CORRESPOND TO THE FCST PATTERN IN PRINCIPLE.  WITHIN THIS
CONFIGURATION THE PRIMARY INTEREST THIS PERIOD WILL BE HOW A
VIGOROUS UPR LOW EJECTING FROM THE PAC NW AND PSBLY SURROUNDING
CANADIAN FLOW SETTLE INTO THE MEAN TROUGH POSN.  CURRENTLY THE 18Z
GFS/12Z ECMWF AND THE 12Z GEFS/ECMWF MEANS REFLECT THE MOST
SIMILAR CLUSTER OF GUIDANCE AND YIELD FAIRLY GOOD CONTINUITY ASIDE
FROM TYPICAL CYCLE TO CYCLE DETAIL DIFFS.

SUCH A PRONOUNCED WRN RIDGE/ERN TROUGH PATTERN HAS MADE FEW
APPEARANCES DURING THE JULY/AUG TIME FRAME IN RECENT YEARS BEFORE
2014.  HOWEVER COMPOSITE ANALOGS BASED ON SOME OF THE D+8
MULTI-DAY MEANS VALID AT THE START OF NEXT WEEK REVEAL MULTIPLE
INSTANCES OF A SIMILAR PATTERN IN JULY AND/OR AUG OF EARLIER
YEARS.  IN REVERSE CHRONOLOGICAL ORDER THESE INCLUDE
2003..2000..1996..1994..1993..1990 AND 1989.  AFTER A LENGTHY GAP
THE YEARS 1969..1967..1962 AND 1956 ALSO FEATURED THIS TYPE OF
PATTERN AT SOME POINT IN JULY AND/OR AUG.    


...GUIDANCE EVALUATION... 

CONFIDENCE IS HIGH IN THE GENERAL EVOLUTION OF AN INITIAL ERN
TROUGH BEING EJECTED IN FAVOR OF LOWERING HGTS THAT SHOULD YIELD A
CORE OF NEGATIVE HGT ANOMALIES OVER/NEAR THE GRTLKS BY THE END OF
THE PERIOD NEXT MON.  EXACTLY HOW THIS HAPPENS REMAINS IN
QUESTION.  THE MOST COMMON SCENARIO IS FOR THE UPR LOW TRACKING
AWAY FROM THE NWRN STATES TO CROSS SRN CANADA AND THEN DROP INTO
THE UPR MIDWEST/GRTLKS REGION... BRINGING SOME HGT ANOMALIES OF AT
LEAST 2 STDEVS BELOW NORMAL.  HOWEVER AN UPR HIGH FCST TO CLOSE
OFF FOR A TIME W/NW OF HUDSON BAY REMAINS A COMPLICATING FACTOR IN
LEADING TO TRACK/TIMING/STRENGTH DIFFS WITH THE INITIAL UPR LOW AS
WELL AS E-CNTRL CANADA FLOW THAT MAY BECOME INCORPORATED INTO THE
OVERALL TROUGH.  THE NEW 00Z GFS/UKMET/CMC EACH ILLUSTRATE
POTENTIAL DEVIATIONS FROM THE INITIALLY FAVORED CONSENSUS.

BASED ON AVBL GUIDANCE BEFORE 00Z... PARTIAL INCORPORATION OF
OPERATIONAL SOLNS THROUGH DAY 7 MON SEEMED REASONABLE GIVEN THEIR
BETTER DEFINED AND PLAUSIBLE ALBEIT UNCERTAIN DETAIL COMBINED WITH
GEFS MEAN TRENDS TOWARD RECENT ECMWF MEAN RUNS THAT HAVE BEEN THE
MOST DEFINED AMONG THE ENSEMBLE MEANS IN THE PAST 1-2 DAYS.  THE
12Z GEFS MEAN WAS FAVORED OVER THE 18Z RUN AS THE LATTER STRAYED
NEWD OF CONSENSUS FOR THE GRTLKS SYSTEM BY EARLY NEXT WEEK. 
MEANWHILE OVER THE PAST DAY OR SO THERE HAS BEEN SOME WAVERING OF
GUIDANCE REGARDING HOW MUCH NERN PAC TROUGH ENERGY MAY MOVE INTO
WRN CANADA.  THE GUIDANCE MAJORITY HAS GENERALLY BEEN SLOWER AND
18Z/00Z GFS RUNS NOW AGREE WITH THIS IDEA AFTER TENDING TO BE ON
THE MORE PROGRESSIVE SIDE OF THE SPREAD.  THE ENSEMBLE MEANS HAVE
BEEN THE MOST CONSISTENT WITH THE NERN PAC TROUGH THUS FAR.

THE PRIMARY ISSUE WITH THE FRONT NEAR THE EAST COAST EARLY IN THE
PERIOD IS POTENTIAL WAVINESS IMPACTING PROGRESSION.  LATEST GFS
RUNS AND THE 00Z VERSION IN PARTICULAR APPEAR TO BE ON THE SLOWER
SIDE OF THE ENVELOPE.


...SENSIBLE WEATHER HIGHLIGHTS...

RISING HGTS ALOFT OVER THE NORTHWEST SHOULD LEAD TO A PRONOUNCED
WARMING/DRYING TREND OVER THAT REGION... WITH DAYTIME HIGHS UP TO
10-15F BELOW NORMAL ON THU REVERSING TO NEARLY SIMILAR ANOMALIES
ON THE PLUS SIDE AT SOME LOCATIONS BY LATE IN THE PERIOD.  THE
FOUR CORNERS UPR HIGH SHOULD SUPPORT ABOVE NORMAL READINGS THOUGH
GENERALLY WITH LESSER ANOMALIES ELSEWHERE OVER THE INTERIOR WEST.

THE COLD FRONT NEAR THE EAST COAST AS OF THU WILL BE ACCOMPANIED
BY AREAS OF SHWRS/TSTMS OF VARYING INTENSITY.  THE FRONT WILL
LIKELY STALL FROM THE SRN MID ATLC INTO THE PLAINS AND THEN LIFT
NEWD AS A WARM FRONT AHEAD OF THE SYSTEM TRACKING OUT OF THE
NORTHWEST AND EVENTUALLY REACHING INTO THE GRTLKS AND VICINITY. 
THE COMBINATION OF THIS WARM FRONT AND SYSTEM PUSHING THROUGH THE
NRN TIER WILL BRING CONVECTION WITH LOCALLY HVY RNFL FROM THE NRN
PLAINS CONTINUING EWD/SEWD THROUGH THE MS VLY INTO THE ERN STATES.
 THE TRAILING PART OF THE NRN TIER FRONT MAY ALSO HELP TO FOCUS
ACTIVITY OVER THE S-CNTRL ROCKIES/HIGH PLAINS BY SUN-MON. 
CNTRL-ERN TEMPS SHOULD BE NEAR TO BELOW NORMAL ASIDE FROM ABOVE
NORMAL READINGS AHEAD OF THE NRN TIER FRONT.  BEHIND THIS FRONT
THERE MAY BE ONE OR MORE DAYS WITH HIGHS AROUND 10F BELOW NORMAL.

RAUSCH