Prognostic Meteorological Discussion
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000
FXUS02 KWBC 281559
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1158 AM EDT THU APR 28 2016

VALID 12Z SUN MAY 01 2016 - 12Z THU MAY 05 2016

...OVERVIEW...

THE 00Z/06Z CYCLE OF GUIDANCE MAINTAINS THE SAME THEME FROM RECENT
RUNS... NAMELY A FAIRLY RAPID DISSIPATION OF A BRIEF WRN NOAM REX
BLOCK CONFIGURATION FOLLOWED BY INCREASINGLY AMPLIFIED ERN NOAM
TROUGHING IN RESPONSE TO A STRONG ERN PAC/WEST COAST TROUGH AND
W-CNTRL NOAM RIDGE.  THERE IS STILL GOOD AGREEMENT FOR THE LARGE
SCALE EVOLUTION IN PRINCIPLE BUT PERSISTENT UNCERTAINTY IN SOME
EMBEDDED DETAILS THAT WILL HAVE A MEANINGFUL IMPACT ON SENSIBLE
WEATHER OVER SOME AREAS.


...GUIDANCE EVALUATION/PREFERENCES...

DIFFS OVER THE ERN PAC/WRN U.S. ARE GENERALLY MODEST.  INITIAL
GRTBASIN/SOUTHWEST UPR LOW ENERGY SHOULD OPEN UP BY DAY 4 MON AND
THEN BE REPLACED BY A STRENGTHENING RIDGE WHOSE AXIS SHOULD REACH
THE ROCKIES HIGH PLAINS BY DAY 7 THU.  WITH THE ERN PAC TROUGH
NEARING THE WEST COAST THERE HAS BEEN A SLIGHTLY FASTER TREND OVER
THE PAST 1-2 DAYS.  THIS MIGHT FAVOR LEANING AWAY FROM THE 00Z
NAEFS MEAN THAT IS A TAD SLOWER THAN THE GUIDANCE AVG.  HOWEVER IT
REMAINS TO BE SEEN HOW MUCH LONGER THIS FASTER TREND CAN CONTINUE
GIVEN THE STRONGLY AMPLIFIED NATURE OF THE PATTERN BY LATE IN THE
PERIOD... SO WOULD ALSO TEND TO LEAN AWAY FROM THE 06Z GFS THAT IS
A BIT FASTER THAN MOST OTHER SOLNS WITH LEADING HGT FALLS.  AT THE
MOMENT THERE IS A DECENT SIGNAL THAT AN EMBEDDED UPR LOW MAY CLOSE
OFF NEAR THE CA COAST BY NEXT THU.

SOMEWHAT GREATER SPREAD/UNCERTAINTY EXIST FOR SOME DETAILS OVER
THE ERN HALF OF THE LOWER 48.  IN THE PAST COUPLE DAYS THERE HAS
BEEN A PRONOUNCED FASTER TREND WITH THE SYSTEM FCST TO TRACK FROM
THE MS VLY/OH VLY REGION INTO THE CANADIAN MARITIMES SUN-TUE.
MODEL/ENSEMBLE CLUSTERING IS BETTER THAN IN PREVIOUS DAYS BUT
LINGERING ISSUES WITH STREAM INTERACTION CONTINUE TO TEMPER
CONFIDENCE.  COMPONENTS ALOFT AFFECTING SFC EVOLUTION WILL INCLUDE
INITIAL ENERGY EJECTING FROM THE PLAINS... GRTLKS/ERN CANADA
FLOW... AND MORE INDIRECTLY THE UPSTREAM SHRTWV ENERGY TRACKING
SEWD FROM CNTRL CANADA.  PREFER TO ADHERE TO THE MAJORITY CLUSTER
THAT INCLUDES THE 00Z GFS/ECMWF-EC MEAN/UKMET AND 00Z/06Z GEFS
MEANS.  IN SPITE OF RECENT TRENDS THE COMPLEXITY OF THE FCST
FAVORS WAITING FOR MORE CONFIRMATION BEFORE TRENDING AS FAST AS
THE 06Z GFS.

BEHIND THIS SYSTEM GUIDANCE IS MIXED AS TO WHAT DEGREE THE
COMBINATION OF EJECTING WRN UPR LOW ENERGY AND ERN U.S. TROUGH
ENERGY WILL SUPPORT FRONTAL WAVINESS OVER THE SERN STATES BY DAY 5
TUE.  BASED ON THE FULL ARRAY OF CURRENT AND RECENT GUIDANCE THE
BEST SOLN APPEARS TO LIE BTWN THE SUPPRESSED GFS RUNS AND WELL
NWD/NWWD ECMWF RUNS.  TOWARD WED-THU THE AMPLIFYING UPR TROUGH
SUPPORTS AN AXIS OF LOW PRESSURE ALONG THE EAST COAST... WITH
DETAILS EVENTUALLY COMING INTO CLEARER FOCUS AS SHRTWV EVOLUTION
ALOFT BECOMES BETTER RESOLVED.  UPSTREAM THE GUIDANCE HAS BEEN
CONSISTENT WITH THE IDEA OF A COLD FRONT DROPPING SEWD THROUGH THE
UPR MS VLY/GRTLKS AND BEYOND BUT WITH SOME RUN TO RUN TIMING
DIFFS.  TOWARD THE END OF THE PERIOD THE 06Z GFS IS THE ONE
PARTICULARLY QUESTIONABLE PIECE OF GUIDANCE AS IT BECOMES WEAKER
THAN CONSENSUS WITH THE CORE OF THE ERN TROUGH ALOFT AND TRACKS S
OF CONSENSUS WITH A DEEP COMPACT UPR LOW OVER CANADA.

BASED ON DECENT CLUSTERING THROUGH MID-PERIOD THE LATEST WPC FCST
REFLECTS A CONSENSUS BLEND THAT EMPHASIZES THE 00Z GFS/ECMWF/UKMET
MORE THAN THE GEFS/ECMWF MEANS THROUGH DAY 5 TUE.  DECREASING
CONFIDENCE IN SPECIFICS WITH TIME LEADS TO INCREASING WEIGHT OF
THE ENSEMBLE MEANS RELATIVE TO THE 00Z GFS/ECMWF BY DAYS 6-7
WED-THU.

...WEATHER HIGHLIGHTS/THREATS...

RNFL OF VARYING INTENSITY WILL ACCOMPANY THE SYSTEM TRACKING
THROUGH THE EAST SUN ONWARD.  THOUGH NOT TO THE EXTENT SEEN IN
PREVIOUS DAYS THERE IS STILL A FAIR AMOUNT OF SPREAD REGARDING
FOCUS OF HEAVIEST ACTIVITY.  MEANWHILE THE UPR LOW INITIALLY OVER
THE WEST WILL GENERATE AREAS OF ENHANCED PCPN OVER PORTIONS OF THE
SOUTHWEST/FOUR CORNERS/SRN ROCKIES FROM SUN INTO EARLY NEXT WEEK.
SOME SNOW IS PSBL AT HIGHER ELEVS.  OPENING UP/EJECTION OF THIS
ENERGY SHOULD SUPPORT SOME POCKETS OF LOCALLY HVY RNFL ACROSS THE
SRN PLAINS AND WRN-CNTRL GULF COAST.  CONFIDENCE IS BELOW AVG FOR
COVERAGE/AMTS OF RNFL THAT MAY SPREAD EWD/NEWD FROM THE SRN PLAINS
AFTER SUN.  TOWARD THE LATTER HALF OF THE PERIOD THE WEST COAST
STATES SHOULD SEE A GRADUAL INCREASE IN MSTR AHEAD OF THE
APPROACHING UPR TROUGH.

EXPECT THE WRN-CNTRL STATES TO SEE THE MOST EXTREME ANOMALIES FOR
TEMPS DURING THE PERIOD.  ON THE COLD SIDE A CHILLY SFC RIDGE OVER
THE HIGH PLAINS WILL LIKELY SUPPORT HIGHS AS MUCH AS 20-30F BELOW
NORMAL AT SOME LOCATIONS ON SUN WITH MINUS 10-25F ANOMALIES
PERSISTING INTO MON.  ON THE OTHER HAND THE NWRN STATES SHOULD SEE
MULTIPLE DAYS WITH HIGHS 10-20F ABOVE NORMAL... WITH SOME OF THIS
WARMTH EVENTUALLY EXTENDING INTO THE NRN HIGH PLAINS.

RAUSCH

$$





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