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
000
FXUS02 KWBC 211556
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1056 AM EST FRI NOV 21 2014

VALID 12Z MON NOV 24 2014 - 12Z FRI NOV 28 2014

...OVERVIEW...

GUIDANCE IS CONTINUING TO INDICATE THAT A SIGNIFICANT AMOUNT OF
FCST UNCERTAINTY WILL ORIGINATE FROM THE ERN PACIFIC.  THERE ARE
STILL MEANINGFUL DIFFS IN HOW FLOW WITHIN THE TROUGH NEAR 150W
WILL SEPARATE AROUND DAY 4 TUE... WHICH IMPACTS DOWNSTREAM DETAILS
THEREAFTER... ALONG WITH HOW UPSTREAM NRN PAC ENERGY WILL INTERACT
WITH THE UPR LOW/TROUGH THAT IS LEFT BEHIND AFTER THE SEPARATION
OCCURS.  THUS FCST CONFIDENCE DECREASES FAIRLY RAPIDLY AFTER
REASONABLE AGREEMENT AMONG SOLNS INTO TUE.  TRENDS THAT ARE
EVIDENT OVER THE PAST DAY ARE SUGGESTING SOMEWHAT LONGER
PERSISTENCE OF THE WEST COAST RIDGE/ERN CONUS TROUGH MEAN PATTERN.


...GUIDANCE EVALUATION/PREFERENCES...

MODEL/ENSEMBLE SPREAD ORIGINATING FROM ERN PAC TROUGH SEPARATION
ARRIVES INTO WRN NOAM BY EARLY DAY 5 WED WITH SPAGHETTI PLOTS
ALREADY SHOWING A FULL RANGE OF SOLNS FROM A STRONG RIDGE TO FLAT
SHRTWV TROUGH OVER THE NWRN CONUS.  RECENT TRENDS OF MOST
OPERATIONAL MODELS ASIDE FROM THE UKMET NOW LEAN TOWARD
MAINTAINING A STRONGER WEST COAST RIDGE INTO WED WITH LESS SHRTWV
ENERGY PASSING THROUGH THE INTERIOR WEST... WHICH IS A SCENARIO
THAT HAD BEEN MORE CONSISTENTLY INDICATED IN PRIOR GFS/GEFS
GUIDANCE.  SUCH A SOLN IS NOT UNREASONABLE GIVEN RECENT
TELECONNECTIONS RELATIVE TO THE ERN NOAM TROUGH/ATLC RIDGE PATTERN
THOUGH OTHER PATHS TO THE FAVORED MEAN PATTERN WERE QUITE POSSIBLE
AS WELL.  BESIDES THE WIDE ENSEMBLE SPREAD FROM THE ERN PAC INTO
THE CONUS DAYS 5-7... THE LACK OF STABILITY IN THE FCST IS MORE
SIMPLY ILLUSTRATED BY GFS/ECMWF FCSTS VALID WED-THU WITH THE 00Z
GFS SHOWING SOME SIMILARITIES TO YDAYS 12Z ECMWF WHILE THE 00Z
ECMWF IS MORE SIMILAR TO YDAYS 12Z GFS.  THE NWD MOVEMENT OF THE
ERN PAC UPR LOW INTO WED-THU IN THE 00Z ECMWF IS NOT WELL
SUPPORTED FROM MOST OTHER GUIDANCE THOUGH.  ONCE UPSTREAM NRN PAC
FLOW COMES INTO THE PICTURE... THE MOST AGREEABLE GUIDANCE SHOWS
SUFFICIENT PROGRESSION TO PUSH A POSITIVELY TILTED TROUGH TOWARD
THE WEST COAST BY LATE NEXT WEEK BUT WITH TIMING PERHAPS MORE
TOWARD THE SLOWER 00Z ECMWF MEAN VERSUS LATEST GEFS MEANS.

YET TO BE RESOLVED ISSUES UPSTREAM LEAD TO UNCERTAINTIES IN SOME
IMPORTANT SHRTWV DETAILS WITHIN THE AMPLIFIED ERN TROUGH AFTER THE
DEPARTURE OF THE STRONG UPR GRTLKS/SERN CANADA STORM.  ONE FCST
ISSUE INVOLVES WAVINESS ALONG THE SFC FRONT REACHING THE WRN ATLC
AFTER TUE... WITH THE 00Z ECMWF IN THE WRN HALF OF THE ENSEMBLE
SPREAD BUT RECENT GFS/PARALLEL GFS RUNS MORE TOWARD THE ERN HALF.
BEHIND THIS FRONT SOLNS VARY CONSIDERABLY WITH A SFC WAVE/FRONT
THAT MAY AFFECT THE CNTRL-ERN CONUS WITH DEPENDENCE ON PAC ENERGY
ROUNDING THE WEST COAST RIDGE AND FLOW FROM CANADA.  PREFER A
CONSERVATIVE ENSEMBLE MEAN APPROACH UNTIL OPERATIONAL RUNS AND
INDIVIDUAL ENSEMBLE MEMBERS BEGIN TO EXHIBIT SOME DEGREE OF
CONVERGENCE.

AN EVEN BLEND OF THE 06Z GFS/00Z ECMWF IS PREFERRED TO REFLECT
OPERATIONAL CONSENSUS FOR SIGNIFICANT FEATURES DAYS 3-4 MON-TUE.
A SLIGHT MAJORITY WEIGHTING OF THE 00Z ECMWF MEAN WITH LESSER
INPUT FROM THE 00Z GEFS MEAN AND WPC CONTINUITY/12Z ECMWF MEAN
SERVES AS THE STARTING POINT FOR DAYS 5-7 WED-FRI.  THIS SOLN
YIELDS THE DESIRED TIMING OFF THE WEST COAST AND A COMPROMISE FOR
THE WAVY FRONT OFF THE EAST COAST MID-LATE PERIOD.


...SENSIBLE WEATHER HIGHLIGHTS...

SOME LOCALLY HVY RAIN/HIGHER ELEV SNOW IS PSBL OVER FAVORED
TERRAIN IN PARTS OF THE PAC NW/NRN ROCKIES.  TRENDS TOWARD A
STRONGER RIDGE ALOFT INTO MIDWEEK HAVE PUSHED THE AXIS OF HIGHEST
TOTALS SOMEWHAT NWD FROM PREVIOUS DAYS BUT GUIDANCE SPREAD IS
STILL SUFFICIENT TO HOLD FCST CONFIDENCE TO MODERATE LVLS AT BEST.
 A FURTHER UNCERTAINTY LATE IN THE PERIOD IS HOW MUCH ERN PAC
TROUGHING APPROACHES THE WEST COAST WITH SOME INCREASE IN MSTR
ALONG THE CNTRL-NRN WEST COAST PSBL LATE NEXT WEEK.  FARTHER EWD
ONE FAVORED AREA OF PCPN WILL BE FROM THE GRTLKS INTO THE
APLCHNS/NEW ENGLAND WITH LAKE EFFECT SNOW BEHIND THE DEEP STORM
TRACKING AWAY FROM THE UPR GRTLKS AND PERHAPS ANOTHER EPISODE WITH
A TRAILING WAVE/FRONT LATER IN THE PERIOD.  MSTR ALONG THE EARLY
PERIOD EAST COAST FRONT MAY SUPPORT SOME ENHANCED RNFL OVER/NEAR
THE FL PENINSULA.  ONCE THE FRONT REACHES THE WRN ATLC THE
POTENTIAL FOR ONE OR MORE EMBEDDED WAVES WILL HAVE TO BE WATCHED
AS THE WRN PERIPHERY OF THE MSTR SHIELD MAY CONTAIN SOME SNOW.
CONFIDENCE IN DETERMINING THE TRACK OF A PARTICULAR WAVE IS BELOW
AVG AT THIS TIME THOUGH.  FOR TEMPS... WHAT CLUSTERING ALOFT
EXISTS TODAY SUPPORTS GREATER PERSISTENCE OF BELOW NORMAL READINGS
OVER THE ERN HALF OF THE CONUS/NRN PLAINS BEHIND THE GRTLKS
STORM/COLD FRONT WITH MOST DAYS FEATURING SOME AREAS OF MINUS
10-20F ANOMALIES.  ON THE OTHER HAND THE WEST WILL BE ON THE MILD
SIDE WITH WARMEST HIGHS OF 10-15F ABOVE CLIMO MOST LIKELY OVER THE
GRTBASIN/SW/CA AROUND WED-THU.

RAUSCH

$$




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