Prognostic Meteorological Discussion
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FXUS02 KWBC 260630
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
230 AM EDT THU MAR 26 2015

VALID 12Z SUN MAR 29 2015 - 12Z THU APR 02 2015

...OVERVIEW...

LATEST GUIDANCE IS CONSISTENT IN SHOWING THE TRANSITION TO A LOWER
AMPLITUDE/MORE PROGRESSIVE PATTERN THAT TYPICALLY LEADS TO GREATER
FCST DIFFICULTY.  WHILE INDIVIDUAL MODEL RUNS AND ENSEMBLE MEMBERS
SHOW THE EXPECTED INCREASE IN SPREAD FOR VARIOUS FEATURES BY THE
LATTER HALF OF THE PERIOD... LATEST ENSEMBLE MEANS AGREE
SURPRISINGLY WELL AT THAT TIME.


...GUIDANCE EVALUATION AND PREFERENCES...

THERE WILL BE TWO PRIMARY SYSTEMS OF INTEREST DURING THE PERIOD.
THE LEADING ONE WILL CROSS SRN CANADA AND BRING A TRAILING FRONT
THROUGH THE ERN HALF OF THE CONUS SUN-TUE WHILE INCOMING PACIFIC
ENERGY WILL SUPPORT A TRAILING SYSTEM EXPECTED TO TRACK ALONG THE
US-CANADIAN BORDER TUE ONWARD.  FOR THE FIRST SYSTEM THERE ARE
SOME PERSISTENT DIFFS WITH SFC LOW TRACK/SWD EXTENT OF THE
TRAILING FRONT AS GFS RUNS ARE FARTHER SWD ON BOTH COUNTS.
GUIDANCE WAS SOMEWHAT CLOSER TO BEING EVENLY SPLIT 24 HRS AGO BUT
THE PAST COUPLE UKMET/CMC RUNS TRENDED TO THE NRN CLUSTER AND EVEN
THE 18Z/00Z GEFS MEANS HAVE STARTED TO TREND NWD OF THE
OPERATIONAL GFS RUNS.  THUS TODAY THERE IS HIGHER CONFIDENCE IN A
SFC LOW TRACK IN LINE WITH ESTABLISHED CONSENSUS/CONTINUITY VERSUS
THE FARTHER SWD GFS.  FOR THE UPSTREAM SYSTEM THE ECMWF MEAN HAS
BEEN THE MOST STABLE PIECE OF GUIDANCE OVER THE PAST COUPLE DAYS
WITH A SLOWER TREND IN THE GEFS MEAN BRINGING IT TO A NEARLY
IDENTICAL POSN.  THE 12Z ECMWF RUN IS CLOSER TO THE MEANS THAN THE
PRIOR 00Z RUN.  SOME GFS RUNS HAVE TENDED TO BE SOMEWHAT SLOWER
BUT THE 00Z RUN HAS ADJUSTED PARTWAY TOWARD REMAINING SOLNS.  THE
INITIALLY ESTABLISHED WRN NOAM RIDGE COULD HINDER EWD PROGRESS FOR
A BRIEF TIME BUT MULTI-DAY CONTINUITY HAS BEEN SUGGESTING THAT THE
FLAT UPSTREAM FLOW SHOULD HAVE SOMEWHAT GREATER INFLUENCE.

DETAILS OF SRN STREAM FLOW REMAIN PROBLEMATIC AND WILL BE
IMPORTANT WITH RESPECT TO THE RNFL FCST FROM THE SRN PLAINS EWD.
OVER THE PAST DAY OR SO GFS RUNS HAVE TENDED TO BE STRONGEST WITH
ITS PRIMARY SHRTWV REACHING THE REGION BY TUE.  THUS FAR WOULD
PREFER TO LEAN TOWARD A WEAKER DEPICTION OF THIS ENERGY.

ELSEWHERE... TRAILING THE SECOND SIGNIFICANT SYSTEM ANOTHER SHRTWV
SHOULD REACH THE WEST BY DAY 7 THU WITH AN ASSOC SFC REFLECTION
STARTING TO TAKE SHAPE LATER THAT DAY.  GIVEN THE TIME FRAME AND
PROGRESSIVE/FLAT MEAN PATTERN THE GUIDANCE IS QUITE SIMILAR.
BEHIND THE LEADING ERN NOAM SYSTEM... BY LATE MON-TUE THERE ARE
SOME INDICATIONS OF SHRTWV ENERGY WHICH IN TERMS OF A PSBL SFC
REFLECTION IS MOST PRONOUNCED IN THE 12Z ECMWF.  ENOUGH MEMBERS
FROM THE 12Z ENSEMBLE SYSTEMS HAVE A SFC WAVE TO WARRANT ATTENTION
BUT LATITUDE/TIMING SPREAD IS TOO GREAT TO INCLUDE IN A
DETERMINISTIC FCST AT THIS TIME.

FOR THE FULL FCST PERIOD THE ABOVE CONSIDERATIONS SUPPORT GIVING
HIGHEST WEIGHTING TO THE 12Z ECMWF MEAN WITH SOME INPUT FROM THE
12Z NAEFS MEAN.  IN ADDITION THE 12Z ECMWF WAS SUFFICIENTLY CLOSE
TO INCLUDE IN THE BLEND SUN INTO MON WHILE DEPARTURE OF THE
LEADING ERN SYSTEM ALLOWS FOR MODEST INCLUSION OF THE 18Z GEFS
MEAN BY WED-THU.


...SENSIBLE WEATHER HIGHLIGHTS...

THE PCPN FCST FROM THE GRTLKS INTO NEW ENGLAND AS WELL AS FROM THE
SRN HALF OF THE PLAINS EWD BOTH HAVE A FAIR DEGREE OF UNCERTAINTY
AT THIS TIME.  CURRENT MAJORITY PREFS FOR THE LEADING ERN NOAM
SYSTEM WOULD LEAD TO LIGHTER AMTS AND A FARTHER NWD RAIN/SNOW LINE
THAN GFS RUNS OVER THE GRTLKS/NEW ENG.  MEANWHILE THE BEST SIGNAL
FOR ENHANCED RNFL FARTHER SWD EXTENDS FROM KS/OK INTO THE TN
VLY... WITH LESSER CONFIDENCE IN TX/GULF COAST ACTIVITY BASED ON
MOST GUIDANCE BEING WEAKER ALOFT FOR SUPPORTING MID LVL ENERGY
RELATIVE TO THE GFS.  FLATTER FLOW ALOFT COMING INTO THE NORTHWEST
SHOULD FOCUS INCREASING AMTS OF RNFL AND HIGH ELEV SNOW OVER THAT
REGION NEXT WEEK.  SOME OF THIS MSTR MAY STREAM ACROSS THE EXTREME
NRN TIER.  EXPECT AREAL COVERAGE OF ABOVE TO MUCH ABOVE NORMAL
TEMPS FROM THE WEST INTO THE NRN-CNTRL PLAINS TO BE TRIMMED FROM
THE NORTHWEST BY TUE-THU.  GREATEST ANOMALIES FOR HIGHS SHOULD
REACH PLUS 20-25F OVER THE N-CNTRL PLAINS ON TUE.  ERN STATES WILL
SEE AN UNSEASONABLY CHILLY START ON SUN FOLLOWED BY A GENERAL
WARMING TREND TOWARD MODESTLY ABOVE NORMAL READINGS BY WED-THU.

RAUSCH

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