EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 AM EDT SUN MAY 26 2013

VALID 12Z WED MAY 29 2013 - 12Z SUN JUN 02 2013

...PATTERN OVERVIEW AND PREFERENCES...

A COMBINATION OF NERN PAC AND INITIAL WRN CONUS ENERGY SHOULD
CONSOLIDATE OVER THE NRN PLAINS BY LATE IN THE WEEK AND THEN DRIFT
EWD/NEWD... WHILE AMPLIFICATION OF AN E-CNTRL PAC TROUGH LATE IN
THE PERIOD SHOULD ENCOURAGE RIDGING OFF THE WEST COAST AND
DEVELOPMENT OF A TROUGH NEAR 120W BY DAY 7 SUN.  MEANWHILE A
FAIRLY STRONG RIDGE SHOULD BUILD OVER PORTIONS OF THE MID ATLC
WITH ABOVE NORMAL HGTS PERSISTING THROUGH NEXT WEEKEND. 
MODELS/ENSEMBLES MAINTAIN REASONABLE AGREEMENT AND CONTINUITY WITH
MOST OF THE BROADER ASPECTS OF THE FCST BUT CONTINUE TO DIFFER
WITH SOME DETAILS THAT WOULD HAVE IMPACTS ON A MORE REGIONAL/LOCAL
SCALE... IN PARTICULAR WITH EVOLUTION OVER THE PLAINS AND FLOW
AROUND THE NRN PERIPHERY OF THE ERN RIDGE.  A BLEND OF THE 18Z
GEFS/12Z ECMWF ENSEMBLE MEANS REFLECTS THE MOST AGREEABLE ASPECTS
OF MEDIUM RANGE GUIDANCE WHILE WAITING FOR BETTER CLUSTERING IN
THE OPERATIONAL MODELS.


...GUIDANCE/UNCERTAINTY EVALUATION...

ASIDE FROM OPERATIONAL ECMWF RUNS TRENDING FASTER/MORE OPEN WITH
LEADING ENERGY OVER THE SRN HALF OF THE ROCKIES AS OF EARLY WED...
NOT A LOT HAS CHANGED WITH THE GENERAL SPREAD OF SOLNS FOR THE
CONSOLIDATION OF WRN CONUS/NERN PAC MID LVL ENERGY INTO A CLOSED
LOW OVER THE NRN HIGH PLAINS BY FRI OR THE ASSOC SFC SYSTEM. 
ECMWF RUNS AND TO SOME DEGREE CMC RUNS STILL WRAP THE SFC LOW
FARTHEST WWD... TO THE EXTENT OF BEING ON THE WRN EDGE OF THE
ENSEMBLE SFC LOW PLOTS FROM THE 12Z CYCLE.  ON THE OTHER HAND THE
OPERATIONAL GFS RUNS HAVE TENDED TO LEAN A BIT ON THE FASTER SIDE
OF THE SPREAD ONCE THE MID LVL SYSTEM OPENS UP AND PROGRESSES TO
THE E/NE.  THE 18Z GEFS/12Z ECMWF ENSEMBLE MEANS STILL OFFER A
GOOD INTERMEDIATE SOLN GIVEN THE GFS/ECMWF POSITIONS RELATIVE TO
THE FULL GUIDANCE SPREAD AND RESPECTIVE BIASES.

WITH THE TROUGH WHICH GEFS/ECMWF/CMC ENSEMBLE MEANS DEVELOP NEAR
120W BY DAY 7 SUN... RECENT GFS RUNS INCLUDING THE 00Z VERSION
DIFFER THE MOST FROM CONSENSUS AS THEY ARE MUCH FLATTER WITH ALL
BUT THE SRN PART OF THE TROUGH.  THIS LIKELY HAS SOME INFLUENCE ON
THE FASTER DOWNSTREAM TIMING IN THE GFS BY NEXT WEEKEND.

OVER THE NERN STATES THERE IS STILL AVG TO ABOVE AVG UNCERTAINTY
REGARDING FRONTAL POSN FROM LATE THIS WEEK ONWARD... DUE TO
CONSIDERABLE SPREAD IN HANDLING FEATURES WITHIN ERN CANADA FLOW AS
WELL AS SHRTWV ENERGY CROSSING SERN CANADA/NRN NEW ENGLAND. 
LATEST GFS RUNS HAVE TRENDED MORE AMPLIFIED ALOFT AND SWD WITH THE
MEAN FRONTAL BNDRY WHILE THE PAST TWO ECMWF RUNS HAVE BACKED AWAY
FROM EARLIER AMPLIFIED SOLNS.  MOST OTHER GUIDANCE KEEPS THE SFC
FRONT FARTHER NWD... LEAVING THE 12Z ECMWF MEAN AS THE BEST OPTION.

AS PER ITS BIAS WITH LOW LATITUDE FEATURES... THE CANADIAN MODEL
IS MUCH MORE ENTHUSIASTIC THAN OTHER GUIDANCE WITH A SFC
REFLECTION NEAR THE SOUTHEAST IN RESPONSE TO A WEAKNESS FCST TO
EVOLVE S OF THE MID ATLC RIDGE ALOFT.  THUS FAR THE CMC SCENARIO
IS WELL IN THE MINORITY OF ENSEMBLE GUIDANCE.


...SENSIBLE WEATHER HIGHLIGHTS...

EXPECT CONVECTION TO BE QUITE ACTIVE OVER A BROAD AREA FROM THE
NRN ROCKIES INTO THE MS VALLEY AND SWD THROUGH THE SRN PLAINS IN
RESPONSE TO ENERGETIC EVOLUTION SFC/ALOFT.  SOME TSTMS WILL LIKELY
PRODUCE HVY TO EXCESSIVE RNFL AND SEVERE WEATHER IS ALSO A
POSSIBILITY.  LOCATIONS FROM THE GRTLKS TO NORTHEAST MAY ALSO SEE
SOME ACTIVITY EARLY IN THE PERIOD WITH A WARM FRONT LIFTING
THROUGH THE REGION... AND LATER WITH A SFC FRONT WHOSE POSN OVER
NEW ENGLAND REMAINS IN QUESTION.  ELY FLOW AT THE SFC AND A
WEAKNESS ALOFT WILL LIKELY SUPPORT PERSISTENT RNFL FOCUSED OVER
THE ERN/SRN PARTS OF THE FL PENINSULA THROUGH THE PERIOD.  PCPN
OVER THE NRN HALF OR 2/3 OF THE WEST SHOULD GRADUALLY TAPER OFF
WITH TIME.  TEMPS OVER THE WEST SHOULD MODERATE NEXT WEEKEND AFTER
HIGHS GENERALLY 5-15 F BELOW NORMAL WED-FRI.  SOME OF THIS COOL
AIR WILL EXTEND INTO THE NRN PLAINS BY LATE THIS WEEK.  ANOMALIES
WITH VERY WARM DAYTIME HIGHS OVER THE EAST SHOULD BE GREATEST FROM
THE GRTLKS/UPR OH VALLEY INTO PARTS OF THE NORTHEAST.

RAUSCH