Prognostic Meteorological Discussion
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000
FXUS02 KWBC 231558
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EST SUN NOV 23 2014

VALID 12Z WED NOV 26 2014 - 12Z SUN NOV 30 2014

...OVERVIEW...

THE PASSAGE OF TIME IS DOING REMARKABLY LITTLE TO RESOLVE THE AREA
OF SIGNIFICANT SPREAD THAT GUIDANCE HAS PERSISTENTLY BEEN SHOWING
OVER THE NWRN CONUS/SWRN CANADA AS OF EARLY DAY 3 WED WITH
DOWNSTREAM IMPACTS ON THE MID LVL ENERGY/SFC SYSTEM TRACKING INTO
THE GRTLKS AND SYSTEM THAT MAY TRACK NEAR THE EAST COAST EARLY IN
THE PERIOD.  SOME ASPECTS OF UPSTREAM ERN PAC FLOW ALSO CHANGE
FROM DAY TO DAY WITH CONSIDERABLE MODEL/ENSEMBLE SPREAD AS WELL.
A GENERAL EVOLUTION TOWARD LOWER AMPLITUDE MEAN FLOW ACROSS THE
LOWER 48 BY NEXT WEEKEND MAY FURTHER REDUCE PREDICTABILITY... SO
NEEDLESS TO SAY THE CONFIDENCE IN A SPECIFIC SOLN IS BELOW AVG.


...GUIDANCE EVALUATION/PREFERENCES...

EARLY IN THE PERIOD RECENT MODEL/ENSEMBLE RUNS APPEAR TO BE
CONVERGING TOWARD THE IDEA OF A REX BLOCK CONFIGURATION OVER THE
ERN/NERN PAC BUT WITH INDIVIDUAL MODEL/ENSEMBLE SOLNS STILL
UNDECIDED OVER THE RELATIVE STRENGTH OF STREAMS DOWNSTREAM FROM
THE NRN RIDGE AND SRN TROUGH/UPR LOW.  THUS OVER THE PAST DAY
THERE HAS BEEN SURPRISINGLY LITTLE IMPROVEMENT IN MODEL/ENSEMBLE
SPREAD FROM SWRN CANADA/NWRN CONUS INTO THE PLAINS WED-FRI.  THE
FULL SOLN ENVELOPE SPANS THE FULL RANGE OF RIDGE TO TROUGH... WITH
00Z GEFS MEMBERS TRENDING MORE TOWARD THE RIDGE SIDE OF THE SPREAD
THAN 24 HRS AGO AND A DECENT NUMBER OF ECMWF MEMBERS REVERSING
COURSE FROM THE MIDDLE TO RIDGE SIDE OF THE SPREAD MORE TOWARD A
MODERATE RIDGE OR TROUGH.  RESULTING SFC DIFFS ARE DRAMATIC OVER
SOME LOCATIONS... FOR EXAMPLE 35-40MB VALID 12Z FRI IN THE 06Z GFS
VS 00Z ECMWF.  FCST SENSITIVITY IS FURTHER DISPLAYED IN GFS/ECMWF
RUNS THAT HAVE SWITCHED PLACES WITH SOME DETAILS OVER THE PAST
DAY.

GIVEN THIS UNCERTAINTY IT IS DIFFICULT TO HAVE MUCH CONVICTION IN
A SPECIFIC SOLN FOR THE MIDWEST-GRTLKS SYSTEM AND LEADING EAST
COAST WAVE DURING WED-THU.  AT THE VERY LEAST THE 00Z ECMWF/ECMWF
MEAN AND A SLIGHTLY SLOWER VERSION OF THE 00Z/06Z PARALLEL GFS
PROVIDE THE BEST INTERMEDIATE SOLN RELATIVE TO THE FULL ENSEMBLE
SPREAD WITH THE MIDWEST-GRTLKS SYSTEM... WHILE THE 06Z GFS/00Z
ECMWF ENSEMBLE MEAN OFFER THE MOST REASONABLE TRACK FOR THE EAST
COAST SYSTEM.  REGARDING THE LATTER... WIDE SPREAD PERSISTS WITH
ECMWF RUNS ON THE WEST EDGE OF THE FULL GUIDANCE SPREAD AND
CURRENTLY JOINED BY THE 00Z UKMET.  GFS/PARALLEL GFS/CMC RUNS HAVE
TENDED TO WAFFLE IN THE MIDDLE TO ERN HALF OF THE SPREAD.  THE ONE
IMPROVEMENT TODAY IS MUCH BETTER TIMING AGREEMENT.  THE PREFERRED
06Z GFS/00Z ECMWF MEAN TRACK MAINTAINS DECENT CONTINUITY FROM
PRIOR PREFS AND THE TRACK PARTIALLY INTO THE WRN HALF OF THE
ENVELOPE SEEMS REASONABLE GIVEN MULTI-DAY TRENDS SUGGESTING AT
LEAST MODERATE DEVELOPMENT OF THIS SYSTEM.

RECENT TRENDS TOWARD A BETTER DEFINED REX BLOCK PATTERN IN THE ERN
PAC DURING THE FIRST HALF OF THE PERIOD LEAD TO A SLOWER TREND
WITH THE EVENTUAL PROGRESSION OF ERN PAC TROUGH ENERGY TOWARD THE
WEST COAST BY NEXT WEEKEND IN RESPONSE TO UPSTREAM PAC FLOW.  06Z
GEFS/00Z ECMWF MEANS ARE FAIRLY SIMILAR ALOFT OVER THE ERN PAC/WRN
NOAM AS WELL AS WITH RESPECT TO FLOW DOWNSTREAM.  EXACT EVOLUTION
OF THE UPSTREAM FLOW IS STILL FAIRLY UNCERTAIN SO SOLNS MAY WELL
CHANGE FURTHER FOR THE TROUGH NEARING THE WEST COAST.

DAYS 3-4 WED-THU START PLACE PRIMARY EMPHASIS ON THE 00Z ECMWF
MEAN/06Z GFS TO REFLECT PREFS FOR THE EAST COAST SYSTEM AND YIELD
AN INTERMEDIATE SOLN ELSEWHERE... WITH MINOR ADJUSTMENTS TOWARD
CONSENSUS FOR THE SYSTEM TRACKING INTO THE GRTLKS.  DAYS 5-7 START
WITH AN EVEN BLEND OF THE 06Z GEFS/00Z ECMWF MEANS TO STAY NEAR
THE MIDDLE OF THE GUIDANCE SPREAD WHILE AWAITING FOR BETTER
CLUSTERING/CONTINUITY.


...SENSIBLE WEATHER HIGHLIGHTS...

FCST REMAINS QUITE UNCERTAIN OVER THE MID ATLC/NORTHEAST WED INTO
THU BUT THE MOST LIKELY SCENARIO AT THIS TIME IS TOWARD SOME
DEGREE OF MEANINGFUL PCPN.  DEPENDING ON EXACT TRACK THERE SHOULD
BE A BAND OF RAIN AND/OR SNOW WITH ABOVE FREEZING SFC TEMPS CLOSER
TO THE COAST AND SNOW/BELOW FREEZING SFC TEMPS FARTHER INLAND.
EXPECT PERIODS OF SNOW OVER THE GRTLKS REGION IN ASSOC WITH THE
SYSTEM TRACKING INTO THE REGION EARLY IN THE PERIOD AND LAKE
EFFECT ACTIVITY DURING PERIODS OF COLD CYCLONIC FLOW.  AS WITH
SOME ASPECTS OF THE FCST OVER THE EAST... CONFIDENCE IS NOT
ESPECIALLY HIGH WITH WRN DETAILS EITHER.  HOWEVER FOR THE 5-DAY
PERIOD AS A WHOLE THERE ARE DECENT SIGNALS TOWARD ENHANCED PCPN
POTENTIAL OVER FAVORED TERRAIN FROM THE CNTRL-NRN WEST COAST INTO
THE NRN ROCKIES.  FOR TEMPS... CNTRL-SRN PARTS OF THE WEST MAY SEE
SOME PLUS 10-20F ANOMALIES FOR HIGHS WED-FRI BEFORE HGT FALLS
ALOFT BRING A MODERATING TREND.  FARTHER EWD THE NRN TIER SHOULD
BE MOST CONSISTENTLY BELOW NORMAL WITH MULTIPLE DAYS OF SIMILARLY
NEGATIVE ANOMALIES FROM THE NRN TIER INTO UPR GRTLKS.  THE ERN
STATES SHOULD ALSO BE BELOW NORMAL WITH A LITTLE MORE VARIABILITY
IN ANOMALIES.

RAUSCH

$$




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