Prognostic Meteorological Discussion
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000
FXUS02 KWBC 260643
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
243 AM EDT SUN MAR 26 2017

VALID 12Z WED MAR 29 2017 - 12Z SUN APR 02 2017

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

MULTI-DAY MEANS SHOW FAIRLY GOOD AGREEMENT ON THE MAINTENANCE OF A
LONGWAVE TROUGH OVER THE WRN STATES WITH FLAT FLOW TO MODERATE
MEAN RIDGING PREVAILING DOWNSTREAM OVER THE EAST, WHILE A SEPARATE
NRN STREAM PROGRESSES ALONG EITHER SIDE OF THE CANADIAN BORDER.
WITHIN THIS CONSENSUS MEAN PATTERN MODELS AND ENSEMBLES HAVE BEEN
SHOWING A LOT OF SPREAD FOR SOME EMBEDDED FEATURES.

SIGNIFICANT DIFFS ARISE ALREADY BY EARLY DAY 3 WED WITH A SYSTEM
OFF THE NEW ENGLAND COAST.  RECENT GFS/GEFS MEAN RUNS HAVE BEEN
EARLIER TO CLOSE OFF ENERGY ALOFT RESULTING IN A DEEPER/WWD SFC
SYSTEM THAN MOST OTHER SOLNS.  PREFS BASED ON DATA THROUGH THE
12Z/18Z CYCLES AND SHORT RANGE MODEL DIAGNOSTICS REFLECTED LOWER
PROBABILITY OF THE GFS SCENARIO.  HOWEVER UPR SUPPORT APPEARED
STRONG ENOUGH TO ALLOW FOR A SOMEWHAT STRONGER/WWD SYSTEM THAN
FCST BY THE 12Z ECMWF.  ARRIVAL OF THE 00Z GFS/UKMET/CMC DOES NOT
ADD ANY CLARITY AS THE UKMET TRENDED MORE TO THE GFS BUT THE CMC
REMAINS SIMILAR TO THE 12Z ECMWF.

THE COMBINED EVOLUTION OF THE ABOVE SYSTEM AND UPSTREAM FLOW
ALONG/N OF THE CANADIAN BORDER WILL INFLUENCE THE TRACK OF THE
STRONG UPR LOW AND ASSOC SFC SYSTEM INITIALLY OVER THE SRN
ROCKIES/PLAINS.  THE PLAINS SYSTEM CLUSTERS FAIRLY WELL INTO EARLY
DAY 4 THU BUT THEN SOLNS RAPIDLY DIVERGE DEPENDING ON FLOW OVER
THE NERN U.S./SERN CANADA.  GFS/GEFS SCENARIO OF MORE PERSISTENT
NERN U.S. TROUGHING ALOFT, NOW JOINED BY THE 00Z UKMET, RESULTS IN
A MUCH MORE SUPPRESSED TRACK OF THE PLAINS SYSTEM AS IT CROSSES
THE EAST.  THUS FAR THE MAJORITY SOLN HAS BEEN MORE IN THE REALM
OF THE ECMWF/CMC AND THEIR MEANS WITH A SFC TRACK INTO THE GRTLKS,
CLOSER TO THE PRIOR LOW TRACKS WITHIN THE ESTABLISHED MEAN
PATTERN.  EVEN WITH THE DISPARITY IN TRACKS OVER THE EAST, THERE
MAY BE SOME CONVERGENCE IN SOLNS OFF THE EAST COAST.

UPSTREAM RECENT ADJUSTMENTS BY OPERATIONAL MODELS HAVE IMPROVED
AGREEMENT FOR AMPLIFYING SHRTWV ENERGY REACHING THE WEST COAST
AROUND EARLY THU AND CLOSING OFF A LOW THAT WILL LIKELY TRACK
TOWARD AZ/SWRN NM BY FRI-SUN.  ECMWF MEAN RUNS HAVE PROVIDED THE
MOST STABLE UPR LOW TRACK AND LATEST GEFS/ECMWF MEANS ARE
FAVORABLY TRENDING DEEPER TOWARD THE OPERATIONAL GUIDANCE.  BY DAY
7 SUN THERE IS ENOUGH OPERATIONAL MODEL SUPPORT TO RECOMMEND
MAINTAINING A CLOSED LOW VS THE OPEN TROUGH AS DEPICTED IN THE
MEANS.

BEHIND THE RIDGE THAT BUILDS IN BEHIND THE WRN TROUGH/UPR LOW,
ENSEMBLES BECOME QUITE CHAOTIC FOR SPECIFICS OF ERN PAC INTO WRN
U.S. FLOW BY NEXT WEEKEND.  THUS CONFIDENCE OVER THIS AREA
DECREASES CONSIDERABLY LATE IN THE FCST PERIOD.

THE DAYS 3-5 WED-FRI FCST STARTED WITH A MULTI-MODEL BLEND
INCLUDING THE 12Z ECMWF/CMC/UKMET AND 18Z GFS, REFLECTING MODEL
DETAIL FOR THE UPR LOW CLOSING OFF OVER THE WEST ALONG WITH
INTERMEDIATE SOLNS CLOSER BUT NOT COMPLETELY TO THE ECMWF CLUSTER
FOR THE PLAINS AND NEW ENGLAND/CANADIAN MARITIMES SYSTEMS.  FOR
DAYS 6-7 SAT-SUN THE FCST QUICKLY TRANSITIONED TOWARD THE 18Z
GEFS/12Z ECMWF MEANS WITH ABOUT 2/3 WEIGHT ON THE LATTER, WITH
SUBSEQUENT EDITS TO REFLECT A BETTER DEFINED SWRN U.S. UPR LOW BY
DAY 7.


...SENSIBLE WEATHER HIGHLIGHTS/POTENTIAL HAZARDS...

COMBINATION OF THE SYSTEM TRACKING EWD/NEWD FROM THE SRN PLAINS
TUE ONWARD AND THEN THE UPR LOW THAT IS MOST LIKELY TO TRACK INTO
THE VICINITY OF AZ/NM NEXT WEEKEND SHOULD YIELD THE GREATEST
POTENTIAL FOR HEAVY TO EXCESSIVE RNFL WITHIN AN AREA FROM THE
CNTRL-SRN PLAINS INTO THE LOWER MS VLY WITH SOME LOCATIONS LIKELY
TO RECEIVE 5-DAY TOTALS OF SEVERAL INCHES.  AREAS OF ENHANCED RNFL
MAY EXTEND FARTHER EWD/NEWD BUT FAIRLY HIGH UNCERTAINTY FOR THE
TRACK OF THE PLAINS SYSTEM AS IT HEADS INTO THE EAST MAKES IT
DIFFICULT TO PINPOINT SUCH AREAS AS WELL AS THE NWD EXTENT OF THE
OVERALL MSTR SHIELD.  THERE IS ALSO A RISK FOR SEVERE CONVECTION,
MOST LIKELY OVER THE SRN PLAINS BUT PERHAPS OVER A BROADER AREA.
CONSULT SPC OUTLOOKS FOR LATEST DETAILS ON SEVERE THREATS.

ELSEWHERE THE INITIAL SRN PLAINS SYSTEM WILL LIKELY PRODUCE A
CONCENTRATED AREA OF RAIN/SNOW DEPENDING ON ELEVATION OVER PARTS
OF CO/NM AROUND THE START OF THE FCST PERIOD.  UPSTREAM AMPLIFYING
ENERGY AND EVENTUAL CLOSED LOW WILL BRING LOCALLY ENHANCED
RAIN/HIGHER ELEV SNOW FROM THE PAC NW SEWD ACROSS THE ROCKIES AND
LIKELY GREAT BASIN AS WELL.  AMOUNTS AND PERSISTENCE OF RAIN/SNOW
OVER NEW ENGLAND EARLY IN THE PERIOD ARE MORE UNCERTAIN THAN USUAL
FOR A DAY 3 FCST GIVEN THE CONSIDERABLE GUIDANCE SPREAD SFC/ALOFT.

THE SPLIT FLOW PATTERN ALOFT SHOULD PROMOTE MOSTLY ABOVE NORMAL
TEMPS, WITH POCKETS OF BELOW NORMAL DAYTIME HIGHS NEAR EACH UPR
LOW CENTER AND WHERE CLOUDS/PRECIP PERSIST, AS WELL AS LOCATIONS
EXPERIENCING COOL ONSHORE FLOW ALONG THE EAST COAST.  THE NRN
PLAINS AND SOUTHEAST SHOULD BE MOST CONSISTENTLY ABOVE NORMAL AND
SEE THE HIGHEST 5-DAY AVG ANOMALIES DURING THE PERIOD.

RAUSCH

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