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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0633Z Feb 25, 2015)
 
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EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
133 AM EST WED FEB 25 2015

VALID 12Z SAT FEB 28 2015 - 12Z WED MAR 04 2015

...OVERVIEW...

IN THE LARGE SCALE... GUIDANCE HAS BEEN CONSISTENT WITH THE IDEA
THAT A POSITIVELY TILTED MEAN TROUGH EXTENDING FROM NERN CANADA
THROUGH THE WRN CONUS SHOULD LEAD TO A FAIRLY ACTIVE PERIOD OF
PRECIPITATION.  HOWEVER ESPECIALLY BY THE LATTER HALF OF THE FCST
SOME OF THE DETAILS BECOME INCREASINGLY UNCERTAIN GIVEN THE SPREAD
FOR ENERGY EXPECTED TO REACH THE NWRN STATES BY EARLY NEXT WEEK
AND DIFFS IN HOW INITIAL WRN CONUS TROUGHING WILL EJECT NEWD.


...GUIDANCE EVALUATION AND PREFERENCES...

THROUGH THE 12Z/18Z CYCLE SOME GUIDANCE DISPLAYED NOTABLE DIFFS
WITH THE WWD AMPLITUDE OF FAST MOVING ENERGY PROGRESSING FROM THE
ERN BERING SEA/ALASKA TOWARD THE NWRN CONUS SAT-MON.  THERE WERE
GENERALLY TWO CLUSTERS... ONE CONSISTING OF THE 12Z ECMWF/ECMWF
MEAN/UKMET/CMC WHICH BROUGHT A CONCENTRATED UPR SYSTEM TOWARD/INTO
THE NORTHWEST... VERSUS THE 12Z-18Z GFS/GEFS MEANS THAT WERE
WEAKER/MORE SHEARED.  THE 12Z CMC MEAN LEANED CLOSER TO THE ECMWF
CLUSTER WHILE THE GFS/GEFS MEAN SOLNS WERE GENERALLY ON THEIR OWN
WITH A FARTHER SEWD TRACK FOR AN UPR LOW TO THE SW OF THE ALASKA
MAINLAND.  THESE CONSIDERATIONS ALONG WITH THE ESTABLISHED PATTERN
THAT HAS FAVORED DECENT WWD/SWWD ELONGATION OF WRN CONUS/WEST
COAST ENERGY SEEMED TO RECOMMEND LEANING AT LEAST 2/3 TOWARD THE
ECMWF CLUSTER.  NEW 00Z GUIDANCE STILL OFFERS VARIED SOLNS WITH
THE 00Z CMC HEDGING A LITTLE AWAY FROM THE 12Z RUN BUT THE 00Z GFS
TRENDING MODESTLY MORE AMPLIFIED WITH ITS OPEN SHRTWV.

EXACTLY HOW THE AFOREMENTIONED FLOW EVOLVES WILL LIKELY HAVE
CONSIDERABLE INFLUENCE ON HOW THE LEADING WRN ENERGY EJECTS NEWD
DURING THE LATTER HALF OF THE PERIOD.  INTO MON THERE IS DECENT
CLUSTERING AMONG GFS/ECMWF RUNS AND THEIR ENSEMBLE MEANS WHILE 12Z
AND NEW 00Z UKMET/CMC RUNS DEVIATE IN VARYING WAYS FROM THE
MAJORITY SOLN.  THEN AS THE REMAINING SHRTWV DEPARTS FROM THE WRN
STATES... SOLNS EVENTUALLY RANGE BTWN A POS TILTED/SHEARED FEATURE
AS IN THE 12Z ECMWF TO A CONCENTRATED/NEG TILTED SHRTWV AS IN
18Z-00Z GFS RUNS.  THE OVERALL SHAPE OF THE MEAN PATTERN SHOULD
SUPPORT A GREATER PROBABILITY OF THE WEAKER SCENARIO SO PREFER TO
LEAN AWAY FROM THE DEEP/NWD SFC LOW SOLNS OF THE 18Z-00Z GFS BY
DAY 7 WED.  CONTINUITY FOR TIMING OVER THE PAST 1-2 DAYS HAS BEEN
STABLE TO SOMEWHAT SLOWER.  AT THE VERY LEAST THE SLOWER TREND
WITH THE LEADING COLD FRONT SEEMS REASONABLE GIVEN THE RIDGING
ALOFT OVER THE CARIBBEAN/GULF OF MEXICO.

ONE OTHER ITEM OF NOTE... THERE IS A RECENTLY DEVELOPED FASTER
TREND IN GUIDANCE TO BRING SHRTWV ENERGY ACROSS THE GRTLKS/NEW
ENGLAND LATE SUN-EARLY MON.  THIS RESULTS IN A FASTER PROGRESSION
OF THE LEADING FRONT.

RELATIVE CONSENSUS EARLY IN THE PERIOD AND PREFS LEANING MORE
TOWARD THE ECMWF/ECMWF MEAN CLUSTER WITH WRN FLOW MON ONWARD LEAD
TO 70 PCT TOTAL WEIGHTING OF THE 12Z ECMWF/ECMWF MEAN DAYS 3-5
SAT-MON WITH THE OTHER 30 PCT CONSISTING OF THE 18Z GFS/12Z NAEFS
MEAN.  BY DAYS 6-7 TUE-WED OPERATIONAL ECMWF WEIGHTING IS
GRADUALLY PHASED OUT IN FAVOR OF MORE 12Z ECMWF MEAN... WITH
ENOUGH OF A COMPROMISE IDEA PRESENTED IN THE 12Z CMC MEAN TO ALLOW
FOR 20 PCT INCLUSION OF THE NAEFS MEAN.


...SENSIBLE WEATHER HIGHLIGHTS...

INITIAL WRN CONUS TROUGH THAT WILL EVENTUALLY EJECT EWD/NEWD AS
WELL AS DOWNSTREAM SWLY FLOW ALOFT WILL SPREAD A BROAD SHIELD OF
MSTR FROM THE SRN 3/4 OF THE WEST ACROSS THE CNTRL-SRN PLAINS AND
MOST OF THE EAST.  INCREASING LOW LVL GULF INFLOW SHOULD ALSO
ENHANCE ACTIVITY FROM THE PLAINS EWD.  TIMING MAY BE DELAYED A BIT
COMPARED TO 24-36 HRS AGO BUT THE SIGNALS FOR HEAVIEST PCPN REMAIN
OVER SIMILAR AREAS... FROM CNTRL AZ INTO CO/NRN NM AND THEN FROM
THE ERN PLAINS/AR TOWARD THE CNTRL-SRN APLCHNS.  THIS LATTER AREA
MAY BE SENSITIVE TO HVY RNFL GIVEN HVY ACTIVITY IN THE PAST WEEK
AND PSBL SNOW MELT AT SOME LOCATIONS.  EXPECT SNOW AND LOW ELEV
RAIN OVER THE WEST WITH SNOW/WINTRY MIX FROM THE CNTRL HIGH PLAINS
EWD-NEWD.  UPSTREAM ENERGY FLOWING INTO THE WEST SHOULD BRING
ANOTHER AREA OF PCPN THROUGH THE REGION DURING NEXT MON-WED.

TEMPS SHOULD AVERAGE BELOW NORMAL OVER A MAJORITY OF THE LOWER 48
WITH THE PRIMARY EXCEPTION BEING OVER THE SRN TIER WHERE MINS IN
PARTICULAR MAY BE QUITE WARM BY MON-WED.  MUCH OF THE CNTRL-ERN
STATES SHOULD SEE MINUS 10-25F ANOMALIES ON SAT FOLLOWED BY
CONSIDERABLE MODERATION SUN-MON.  ANOTHER SURGE OF COLD AIR SHOULD
BRING SIMILAR ANOMALIES INTO THE PLAINS NEXT TUE-WED WITH EVEN NRN
PARTS OF THE WEST PSBLY SEEING TEMPS AS LOW AS 10-20F BELOW NORMAL
AT THAT TIME.

RAUSCH