Prognostic Meteorological Discussion
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FXUS02 KWBC 310645
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
244 AM EDT FRI OCT 31 2014

VALID 12Z MON NOV 03 2014 - 12Z FRI NOV 07 2014

...OVERVIEW...

THE COMBINED UNCERTAINTIES OF HOW FLOW WITHIN TWO SEPARATE STREAMS
OVER THE CONUS WILL EVOLVE AS WELL AS WHETHER SOME DEGREE OF
SEPARATION WILL OCCUR OVER THE ERN PACIFIC LEAD TO OVERALL FCST
CONFIDENCE THAT IS AVG AT BEST GIVEN THAT THESE TYPES OF FCST
ISSUES HAVE A TENDENCY TO RESULT IN LARGE FCST ERRORS AT SOME
LOCATIONS.  HOWEVER SOME COMMON IDEAS DO APPEAR FOR THE LARGE
SCALE MEAN FLOW THAT SHOULD TREND SOMEWHAT LESS AMPLIFIED BY THE
END OF THE PERIOD.


...GUIDANCE EVALUATION/PREFERENCES...

FROM EARLY IN THE PERIOD THERE ARE SOME DETAIL DIFFS REGARDING THE
DEGREE/LOCATION OF SEPARATION BETWEEN NRN STREAM SHRTWV ENERGY
THAT SHOULD PROGRESS EWD/NEWD FROM THE NRN PLAINS WITH TIME AND
SRN STREAM ENERGY WHICH A NUMBER OF OPERATIONAL MODEL RUNS
ULTIMATELY SHOW CLOSING OFF OVER EXTREME NRN MEXICO OR THE SRN
PLAINS.  BEYOND THIS QUESTION THERE ARE MID-LATE PERIOD QUESTIONS
OVER EVOLUTION/PROGRESSION OF THE SRN ENERGY.  THESE DIFFS LEAD TO
SPREAD/RUN TO RUN INCONSISTENCY WITH THE EWD/SEWD PROGRESSION OF
THE SFC FRONT ACROSS NRN AREAS AND MUCH MORE SIGNIFICANT SENSIBLE
WEATHER IMPACTS OVER THE SRN TIER... GIVEN THE PSBL INCLUSION OF
SOME MSTR FROM T.S. VANCE.  CONSULT LATEST NHC PRODUCTS FOR THE
LATEST INFO ON VANCE.

LOOKING AT FEATURES IN MORE DETAIL... THE 18Z PARALLEL GFS FAVORED
THE 12Z GFS/ECMWF WHICH WERE STRONGER WITH THE NRN STREAM SHRTWV
BRUSHING NEW ENGLAND BY DAY 5 WED.  ON THE OTHER HAND THE
OPERATIONAL 00Z GFS FOLLOWS ITS 18Z VERSION IN BEING SLOWER AT THE
SFC DUE TO FLATTER/SLOWER SHRTWV.  MULTIPLE ECMWF RUNS HAVE BEEN
FAIRLY CONSISTENT WITH THE 12Z GFS/ECMWF SCENARIO.  SRN STREAM
DIFFS BEGIN TO DEVELOP BY DAY 5 WED WITH SPREAD INCREASING
THEREAFTER.  THE FULL RANGE OF 12Z ENSEMBLE GUIDANCE SUGGESTS
ANYTHING FROM A SLOW CLOSED LOW TO A PROGRESSIVE TROUGH.  THROUGH
THE 18Z CYCLE THE MODEL SPREAD WAS GREATER THAN DESIRED TO LATCH
ONTO A PARTICULAR DETERMINISTIC SOLN.  THUS THE ENSEMBLE MEANS
WERE FAVORED BY DAYS 6-7 THU-FRI... BUT WITH THE UNDERSTANDING
THAT THERE IS AT LEAST A MODERATE POSSIBILITY OF A MORE DEFINED
UPR SYSTEM OVER THE SRN TIER.  THE 00Z MODELS AND GEFS MEAN ARE
ADDING SUPPORT FOR A SRN TIER FEATURE MORE DETACHED THAN THE 12Z
ECMWF MEAN.

ESPECIALLY WITH THE NEW 00Z GUIDANCE INCLUDED... THERE SEEMS TO BE
WANING SUPPORT FOR RECENT ECMWF RUNS THAT HAD SEPARATED ERN PAC
FLOW LEADING TO FAST NRN STREAM FLOW AND A SEPARATE TRAILING
FEATURE NEARING THE WEST COAST BY DAY 7 FRI.  BEST CONSENSUS SHOWS
AT LEAST A MODERATELY VIGOROUS SYSTEM OFFSHORE THE PAC NW/BC ON
WED AND THEN REACHING THE NRN PLAINS/SRN CANADA BY EARLY FRI.
BRIEF AMPLIFICATION THAT OCCURS AHEAD OF THIS PAC SYSTEM SHOULD
SUPPORT THE DIGGING OF SHRTWV ENERGY INTO THE GRTLKS AND
VICINITY... REFLECTED AT THE SFC AS LOW PRES TRACKING FROM THE UPR
GRTLKS/ONTARIO TOWARD THE CANADIAN MARITIMES.  OPERATIONAL MODEL
RUNS SUGGEST THE ENSEMBLE MEANS MAY BE ON THE WEAK SIDE WITH BOTH
SYSTEMS.  THE 12Z ECMWF MEAN IS BETTER DEFINED AT THE SFC THAN
OTHER MEANS SO WOULD FAVOR GREATER WEIGHT OF ITS SOLN AFTER WED.
EVEN WITH A FAIR AMOUNT OF CLUSTERING IN PRINCIPLE LATE IN THE
PERIOD... THE FULL ENVELOPE OF ENSEMBLE SOLNS BECOMES QUITE BROAD
WITH VARIOUS MEMBERS OUT OF PHASE AND/OR VERY DIFFERENT IN
AMPLITUDE.  THE ENSEMBLE MEANS PROVIDE A GOOD CONSERVATIVE
STARTING POINT UNTIL SPREAD IMPROVES.

BASED ON ABOVE CONSIDERATIONS THE 12Z GFS/ECMWF ARE EMPHASIZED
EARLY IN THE PERIOD WITH 12Z GEFS/ECMWF MEAN DATA GIVEN NEARLY
EQUAL WEIGHTING WITH THE OPERATIONAL RUNS BY DAY 5 WED.  DAYS 6-7
THU-FRI ARE CLOSE TO A 70/30 BLEND OF THE 12Z ECMWF MEAN/12Z GEFS
MEAN DUE TO BETTER NRN STREAM FEATURE DEFINITION IN THE FORMER.


...SENSIBLE WEATHER HIGHLIGHTS...

RNFL ACCOMPANYING THE FRONTAL BNDRY INITIALLY OVER THE PLAINS
SHOULD BECOME HEAVIER DURING THE FIRST HALF OF THE WEEK... AIDED
BY LOW LVL GULF INFLOW AND EVENTUALLY THE PSBL INCLUSION OF MSTR
FROM T.S. VANCE.  DEPENDING ON HOW SRN TIER ENERGY EVOLVES THERE
IS POTENTIAL FOR RNFL TO LINGER OVER OR NEAR THE SRN PLAINS FOR A
PERIOD OF TIME AS WELL.  THE PAC NW/EXTREME NRN ROCKIES WILL BE
THE OTHER AREA TO SEE ONE OR MORE PERIODS OF ENHANCED PCPN DURING
THE PERIOD.  EXPECT LIGHTER PCPN ASSOC WITH FEATURES FROM THE NRN
PLAINS EWD.  AFTER A VERY CHILLY START ON MON THE EAST COAST
SHOULD TREND WARMER UNTIL PASSAGE OF ANOTHER FRONT LATE IN THE
WEEK.  MEANWHILE THE UPR TROUGH/PSBL CLOSED LOW AFFECTING THE
SOUTHWEST/ROCKIES INTO THE SRN PLAINS SHOULD BRING ONE OR MORE
DAYS OF COOLER THAN NORMAL HIGHS.  ELSEWHERE THE PROGRESSION OF
FEATURES SHOULD LEAD TO VARIABLE TEMPS.

RAUSCH

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