Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8
000
FXUS02 KWBC 271616
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1215 PM EDT MON APR 27 2015

VALID 12Z THU APR 30 2015 - 12Z MON MAY 04 2015

...UPDATE FROM PREVIOUS FORECAST...

THERE IS STILL QUITE A BIT OF UNCERTAINTY WITH THE EVOLUTION OF
FLOW OVER THE EASTERN U.S. LATE THIS WEEK.  THE 06Z GFS LOOKS
SIMILAR TO ITS 00Z RUN...WHICH KEEPS THE GFS ON THE DEEPER/WESTERN
SIDE OF MODEL SPREAD WITH A SURFACE LOW SPINNING UP OFF THE
SOUTHEAST/MID-ATLANTIC COAST THURSDAY AND FRIDAY.  ON THE FLIP
SIDE...THE LATEST/00Z ECMWF AND ECMWF ENSEMBLE MEAN SHIFTED A TAD
FARTHER EAST/MORE PROGRESSIVE WITH THE LOW.  UPSTREAM...THE MODELS
REMAINED IN GOOD AGREEMENT WITH FAST/FLAT PACIFIC FLOW SETTING UP
ACROSS THE NORTHERN TIER.

WITHOUT A DISTINCT TREND IN SOLUTIONS OVER THE EASTERN U.S. EARLY
IN THE PERIOD...THE UPDATED WPC FORECAST WAS BASED ON A BLEND OF
THE 00Z ENSEMBLE MEAN GUIDANCE AND STRAYS LITTLE FROM CONTINUITY.

GERHARDT

...OVERVIEW...

AFTER AN ERN CONUS-WRN ATLC EVOLUTION SFC/ALOFT MORE TYPICAL OF
WINTER... THE PATTERN UPSTREAM QUICKLY TAKES ON MORE OF A
SUMMERTIME LOOK WITH PROGRESSIVE LOW AMPLITUDE MEAN FLOW ACROSS
THE NRN CONUS/SRN CANADA.  MODEST MEAN TROUGHING IS EXPECTED TO
PERSIST ALONG THE SRN HALF OF THE WEST COAST.  GUIDANCE CONTINUES
TO HAVE DIFFICULTIES IN RESOLVING IMPORTANT MID LVL DETAILS OVER
THE EAST KEEPING CONFIDENCE LOWER THAN DESIRED FOR ASSOC WRN ATLC
LOW PRES.  AT THE SAME TIME AGREEMENT/CONTINUITY ARE NOT
PARTICULARLY GREAT EITHER FOR SPECIFICS OF SHRTWVS/FRONTAL SYSTEMS
CARRIED ALONG BY THE MEAN FLOW ALONG THE WRN 2/3 OF THE
US-CANADIAN BORDER.


...GUIDANCE EVALUATION AND PREFERENCES...

FOR THE ERN CONUS/WRN ATLC SYSTEM... THROUGH THE 18Z CYCLE AN AVG
OF THE 18Z GEFS/12Z ECMWF MEANS SEEMED TO OFFER THE BEST
INTERMEDIATE TRACK FOR THE SFC LOW WHILE OPERATIONAL GUIDANCE AS A
WHOLE SUPPORTED A DEEPER ADJUSTMENT TO SOME DEGREE.  THUS
INCORPORATED A BLEND OF THE ENSEMBLE MEANS AND 18Z GFS/12Z ECMWF
BUT WITH LOW ENOUGH WEIGHTING TO DOWNPLAY THE ECMWF WHICH STRAYED
TOWARD THE ERN PORTION OF THE ENSEMBLE SPREAD BY DAY 4 FRI.  SOLNS
ARE STILL VARYING WITH HOW AMPLIFYING NRN STREAM ENERGY REACHING
THE GRTLKS AND PSBLY INTO THE OH VLY BY THE START OF THE PERIOD
THU WILL EVOLVE... AND THE INTERACTION WITH EJECTING SHORT RANGE
PLAINS ENERGY.  ALBEIT WITH GROWING SPREAD WITH TIME... THERE HAD
BEEN A RELATIVE CLUSTER AMONG THE SOLNS MENTIONED ABOVE EARLY ON
TO RECOMMEND THE COMPROMISE OF THEIR IDEAS.  OVERALL THE 00Z
GUIDANCE GENERALLY SHOWS A STRONGER OH VLY/MID ATLC UPR LOW THUS
LEADING TO A FARTHER WWD SFC TRACK AT SOME FCST HRS.  THE 00Z GFS
IS LOOKING LIKE A DEEP EXTREME WITH ITS UPR LOW THOUGH... WITH THE
GEFS MEAN AND NEW ECMWF SUPPORTING MORE MODERATE DEPTH.  AT LEAST
COMPARED TO EARLIER CYCLES THIS CYCLE REPRESENTS IMPROVEMENT FOR
THE TRACK OF MID LVL ENERGY EVEN IF OTHER ATTRIBUTES REMAIN IN
QUESTION.

WITHIN THE FAST FLOW ACROSS THE NRN TIER... THERE IS SOME DEGREE
OF CONSISTENCY WITH THE LEADING SHRTWV/SFC FRONT THU-FRI BUT
OTHERWISE GUIDANCE REFLECTS A NOTICEABLE TREND TOWARD FLATTER AND
MORE PROGRESSIVE FLOW COMPARED TO EARLIER DAYS.  THIS RESULTS IN A
FASTER SERIES OF FRONTS THAT WILL HAVE A TENDENCY TO WEAKEN AS
THEY REACH BEYOND THE NRN PLAINS.  AT THE MOMENT THERE IS GENERAL
AGREEMENT TOWARD A BETTER DEFINED SHRTWV ALOFT REACHING CNTRL
CANADA AND THE NRN PLAINS BY NEXT MON... SUPPORTING A LEADING COLD
FRONT THAT MAY REACH FARTHER EWD THAN PRIOR FRONTS IN THE SERIES.
FARTHER WWD MDLS/ENSMEANS AGREE FAIRLY WELL WITH THE IDEA OF NERN
PAC ENERGY BRINGING ANOTHER TROUGH TO THE PAC NW BY DAY 7 MON.
GIVEN THE PROGRESSIVE NATURE OF THIS STREAM AND CHANGES THAT
GUIDANCE HAS MADE OVER RECENT DAYS IT WOULD NOT BE SURPRISING TO
SEE SOME ASPECTS OF THIS FCST CHANGE IN THE NEAR FUTURE.

BASED ON PREFS FOR THE WRN ATLC SYSTEM AND TO REFLECT AVBL
CLUSTERING UPSTREAM... DAYS 3-5 THU-SAT START WITH A BLEND OF THE
18Z GFS/ECMWF AND THEIR RESPECTIVE MEANS.  CONFIDENCE IN GFS
DETAILS OVER E-CNTRL CANADA DECREASES AFTER SAT SO DAYS 6-7
SUN-MON EXCLUDE THAT SOLN FROM THE BLEND.


...SENSIBLE WEATHER HIGHLIGHTS...

DURING THE FIRST HALF OF THE PERIOD DIFFS IN TRACK FOR WRN ATLC
LOW PRES STILL LEAD TO GREATER THAN AVG UNCERTAINTY IN
COVERAGE/INTENSITY OF RNFL NEAR THE EAST COAST AND LOCATIONS THAT
MAY BE AFFECTED BY ENHANCED WINDS.  IMPROVED CLUSTERING IN
GUIDANCE FOR PATH OF BEST DEFINED UPR ENERGY EARLY IN THE PERIOD
AT LEAST RAISES CONFIDENCE IN THE POTENTIAL FOR SOME RNFL OVER THE
APLCHNS/MID ATLC THOUGH LIKELY NOT TO THE EXTENT OF THE 00Z GFS
GIVEN ITS EXTREME DEPTH ALOFT.  CONFIDENCE REMAINS LOWER IN HOW
MUCH MSTR REACHES THE NORTHEAST DUE TO SENSITIVITY IN THE SFC LOW
TRACK.  AS NRN PAC FLOW CONTINUES ALONG THE US-CANADIAN BORDER...
ASSOC FRONTS SHOULD HELP TO EXPAND AREAL COVERAGE OF RNFL WITH
TIME FROM THE NRN-CNTRL ROCKIES INTO THE GRTLKS.  IN RELATIVE
TERMS HEAVIEST ACTIVITY SHOULD OCCUR LATE IN THE PERIOD.  COOL
TEMPS EARLY IN THE PERIOD OVER THE EAST SHOULD STEADILY TREND
WARMER TO NEAR/ABOVE NORMAL.  ASIDE FROM NEAR NORMAL READINGS OVER
THE SOUTH... THE REMAINDER OF THE CONUS SHOULD SEE ABOVE NORMAL
READINGS FOR MOST OF THE PERIOD.

RAUSCH

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.