Prognostic Meteorological Discussion
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000
FXUS02 KWBC 291559
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT FRI APR 29 2016

VALID 12Z MON MAY 02 2016 - 12Z FRI MAY 06 2016

...OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES...

THERE ARE STILL IMPORTANT DETAIL DIFFS WITHIN A CONSENSUS
AMPLIFYING LONGWAVE EVOLUTION LEADING TOWARD AN ERN PAC-WEST COAST
TROUGH WITH EMBEDDED UPR LOW... A W-CNTRL NOAM RIDGE... AND ERN
TROUGH.

FROM THE ERN PAC INTO WRN NOAM... CONTINUITY IS GOOD WITH THE IDEA
OF AN UPR LOW FORMING JUST OFF THE CA COAST BY AROUND DAYS 5-6
WED-THU.  HOWEVER MODERATE TIMING DIFFS PERSIST WITH THE 06Z
GFS/GEFS MEAN STRAYING SOMEWHAT AHEAD OF THE BETTER CLUSTERED 00Z
GUIDANCE.  INTO YDAY THERE HAD BEEN A GRADUAL FASTER TREND BUT 00Z
SOLNS NUDGED THE SYSTEM BACK A BIT WHICH SEEMS REASONABLE GIVEN
THE HIGHLY AMPLIFIED NATURE OF THE MEAN PATTERN AND RECENT SIGNALS
THAT HAVE FAVORED CLOSURE OF AN UPR LOW.  THUS WOULD PREFER TO
FOLLOW THE 00Z GUIDANCE MORE THAN THE 06Z GFS/GEFS.  00Z/06Z
PARALLEL GFS RUNS ALSO RECOMMEND THE SLOWER MAJORITY.  ONE ADDED
CONTRIBUTION TO UNCERTAINTY LATE IN THE PERIOD IS EXACTLY HOW FLOW
WILL SEPARATE WITHIN THE OVERALL TROUGH.  THE 00Z GFS APPEARS TO
HAVE AN EVOLUTION SOMEWHAT IN THE MINORITY WITH A SEPARATE CLOSED
LOW DROPPING SWD OFF THE PAC NW/CA COAST THU-FRI.

THERE ARE STILL MULTIPLE PIECES TO THE FCST PUZZLE FARTHER EWD.
GUIDANCE IS GETTING A LITTLE MORE STABLE WITH THE WAVE TRACKING
OFF THE EAST COAST EARLY IN THE WEEK.  HOWEVER SHRTWV DETAILS
WITHIN THE INITIAL LOW AMPLITUDE ERN TROUGH ALOFT ARE STILL MURKY.
 FOR EXAMPLE 00Z/06Z GFS RUNS ALREADY DIVERGE FROM EACH OTHER AND
SOME ASPECTS OF REMAINING MODEL/ENSEMBLE GUIDANCE WITH INDIVIDUAL
SHRTWVS IN DAYS 3-4 MON-TUE.  IN ADDITION THE PAST COUPLE CYCLES
OF GUIDANCE HAVE BEEN HINTING MORE AT THE POTENTIAL FOR SOME
ENERGY TO COLLECT OVER THE ROCKIES/PLAINS TO THE S-SE OF THE
CLOSED HIGH OVER SWRN CANADA AS OF EARLY MON.  RESOLVING WHAT
HAPPENS TO ENERGY ON THE SERN SIDE OF A CLOSED HIGH HAS TYPICALLY
BEEN A CONSIDERABLE CHALLENGE FOR GUIDANCE SO CONFIDENCE IS LOW
WITH THIS ASPECT OF THE FCST.  COMBINATION OF THESE ISSUES WILL
CONTINUE TO AFFECT THE FCST FOR THE STRENGTH/TRACK OF SFC WAVINESS
OVER THE SOUTHEAST TUE-WED.  ON THE POSITIVE SIDE SFC SOLNS ARE
STARTING TO CONVERGE WITH THE 00Z ECMWF TRENDING A LITTLE MORE
SUPPRESSED WITH SFC WAVINESS VS SOME EARLIER RUNS WHILE THE GFS IS
STARTING TO SHOW MORE WAVINESS VS YDAY WHEN IT HAD HIGH PRES
DOMINATING.

HOWEVER THESE SHRTWV DETAILS EVOLVE... IN PRINCIPLE GUIDANCE
AGREES IN PRINCIPLE ON DEVELOPMENT OF A VERY AMPLIFIED ERN TROUGH
BY LATE NEXT WEEK AND AN ELONGATED AREA OF EAST COAST/WRN ATLC SFC
LOW PRESSURE.  INDIVIDUAL MODEL RUNS OFFER POTENTIAL FOR AN
EMBEDDED CLOSED LOW ALOFT SOMEWHERE OVER THE ERN STATES BUT
WITHOUT ENOUGH CONSISTENCY/AGREEMENT TO DEPICT IN A DETERMINISTIC
FCST.  MEANWHILE SOME GFS/PARALLEL GFS RUNS HAVE BEEN PARTICULARLY
AGGRESSIVE WITH THE SWD EXTENT OF A COMPACT DEEP UPR LOW
ORIGINATING OVER NRN CANADA.  PREFER THE FARTHER NWD MAJORITY
GIVEN THE EXTREME STANDARDIZED HGT ANOMALIES THAT WOULD BE ASSOC
WITH THE SRN TRACK.

BASED ON THE ARRAY OF GUIDANCE OVER THE CNTRL-ERN STATES THROUGH
THE PERIOD... OVERALL PREFER MORE OF AN ENSEMBLE MEAN APPROACH
OVER THE CNTRL-ERN STATES TO PROVIDE THE BEST BALANCE OF
CONTINUITY AND UPDATED DETAIL TRENDS.  THE 00Z ECMWF IS CLOSE
ENOUGH TO THE MEANS TO ALLOW FOR A SMALL CONTRIBUTION OF ITS SOLN
BEFORE DAY 7 FRI.


...WEATHER HIGHLIGHTS/THREATS...

UPR TROUGH/EVENTUAL CLOSED LOW NEARING THE WEST COAST WILL
INCREASE MSTR OVER THE WEST WITH TIME AND SUPPORT A COOLER TREND
FOR TEMPS OVER CA AND THE SOUTHWEST.  TEMPS WILL BE MORE
CONSISTENTLY ABOVE NORMAL OVER THE NORTHWEST/NRN ROCKIES.  SOME
LOCATIONS OVER THE WEST COULD SEE RECORD WARM MIN TEMPS ON ONE OR
MORE DAYS WHILE RECORD HIGHS MAY BE A LITTLE MORE ISOLATED.
MEANWHILE EXPECT LINGERING ENERGY ALOFT OVER THE INTERIOR
WEST/ROCKIES TO SUPPORT AREAS OF PCPN OVER PORTIONS OF THE FOUR
CORNERS STATES... MOSTLY IN THE FORM OF RAIN.  VERY CHILLY HIGHS
THAT MAY EXCEED 20F BELOW NORMAL OVER THE CNTRL-SRN HIGH PLAINS ON
MON SHOULD RAPIDLY MODERATE THEREAFTER... TRENDING ABOVE NORMAL
OVER MOST OF THE PLAINS BY THU-FRI.

QUESTION MARKS WITH SUBTLE DETAILS ALOFT CONTINUE TO AFFECT THE
FCST FOR AREAL COVERAGE/INTENSITY OF RNFL FROM THE SRN PLAINS
EWD/NEWD INTO THE ERN STATES.  AMIDST THIS UNCERTAINTY THE MOST
STABLE SIGNAL FOR ENHANCED RNFL HAS BEEN ALONG THE WRN-CNTRL GULF
COAST REGION.  SOME LOCALLY HVY ACTIVITY MAY BE PSBL FARTHER
EWD/NEWD DEPENDING ON STRENGTH/TRACK OF ENERGY ALOFT AND ASSOC SFC
WAVE(S).  DEEPENING UPR TROUGH WILL GENERALLY SUPPORT COOL AND
UNSETTLED WEATHER OVER THE EAST LATE IN THE WEEK WITH
COVERAGE/INTENSITY OF ANY PCPN DEPENDENT ON UPR DETAILS THAT
TYPICALLY HAVE LOW PREDICTABILITY 6-7 DAYS OUT IN TIME.

RAUSCH

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