Prognostic Meteorological Discussion
Issued by NWS

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3
000
FXUS02 KWBC 301554
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1153 AM EDT SUN AUG 30 2015

VALID 12Z WED SEP 02 2015 - 12Z SUN SEP 06 2015

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

THERE IS LITTLE CHANGE IN THE LARGE SCALE PATTERN FCST BUT WITH
CONTINUED UNCERTAINTY GIVEN MODEL/ENSEMBLE SPREAD OVER VARIOUS
AREAS.

AN UNSEASONABLY DEEP TROUGH NEAR OR JUST INLAND FROM THE WEST
COAST SHOULD BECOME WEAKER BY THE LATTER HALF OF THE PERIOD AS NRN
PAC FLOW APPROACHES.  GRADUAL EWD PROGRESSION OF LEADING HGT FALLS
WILL PUSH A SFC FRONT FROM THE NRN ROCKIES INTO THE NRN PLAINS.
ENSEMBLE MEANS HAVE BEEN PARTICULARLY CONSISTENT WITH THE UPR
TROUGH ASIDE FROM TYPICAL RUN TO RUN VARIABILITY IN
TIMING/AMPLITUDE... WITH OPERATIONAL RUNS NOT SURPRISINGLY
DIFFERING A LITTLE MORE WITH THE DETAILS.  RELATIVE STABILITY IN
THE MEANS THUS FAR MASKS A WIDENING SPREAD AMONG THE FULL ARRAY OF
GEFS/ECMWF/CMC MEMBERS FROM THE PAC INTO THE WRN/NRN STATES DAYS
5-7 FRI-SUN.  TELECONNECTIONS RELATIVE TO THE CORE OF POSITIVE HGT
ANOMALIES OVER ERN CANADA IN LATEST D+8 MEAN CHARTS FAVOR MODERATE
TROUGHING OVER THE WRN HALF OF THE U.S. AND A MEAN RIDGE OFF THE
WEST COAST.  THIS RELATIONSHIP WOULD AT LEAST SUGGEST LEANING AWAY
FROM 00Z/06Z GFS RUNS THAT DEVELOP TROUGHING OFF THE WEST COAST BY
THE END OF THE PERIOD.

FARTHER EWD A MEAN RIDGE WILL PREVAIL WITH A COMBINATION OF
EMBEDDED/PERIPHERAL UNCERTAINTIES.  AS SOON AS DAY 4 THU ENSEMBLE
SPREAD BECOMES MEANINGFUL WITH ERN CANADA/NEW ENGLAND FLOW WHICH
WILL INFLUENCE THE TIMING AND SWD EXTENT OF ONE OR MORE SFC
FRONTS.  MEANWHILE MODELS ARE UNCERTAIN AS TO THE ULTIMATE PATH OF
A WEAKNESS ALOFT/PSBL UPR LOW NEAR THE WRN GULF COAST AS WELL AS
ENERGY TO THE NE EXPECTED TO REACH THE EAST COAST OR BEYOND.  THIS
LATTER ENERGY MAY HAVE SOME INFLUENCE ON A SFC WAVE WHICH SOME
SOLNS SHOW EVOLVING OFF THE EAST COAST ORIGINALLY ASSOC WITH A
FRONT DROPPING INTO THE WRN ATLC.  THE 00Z ECMWF IS THE MOST
EXTREME NRN/NWRN EXAMPLE AMONG MODEL SOLNS BY THE LATTER HALF OF
THE PERIOD THOUGH IT IS WITHIN THE FULL ENSEMBLE SPREAD.  FOR NOW
A COMPROMISE BTWN THE 00Z ECMWF/LESS EXTREME 00Z ECMWF MEAN AND
MORE SUPPRESSED GFS/GEFS SOLNS APPEARS BEST.

BASED ON PREFS FROM THE ERN PAC INTO THE WRN/NRN THE PREFERRED
BLEND LEANS A LITTLE MORE TOWARD THE 00Z ECMWF/ECMWF MEAN RELATIVE
TO THE 06Z GFS/GEFS MEAN.  ALTHOUGH A MORE EVEN WEIGHTING MIGHT
ULTIMATELY BE FAVORED OVER/E OF THE EAST COAST THE INITIAL BLEND
STILL YIELDS THE DESIRED COMPROMISE.


...SENSIBLE WEATHER HIGHLIGHTS...

UPR TROUGH AND LEADING SFC FRONT WILL PROMOTE ONE AREA OF ACTIVE
WEATHER FROM THE PAC NW ACROSS THE NRN ROCKIES AND THROUGH THE NRN
PLAINS.  CURRENTLY THE BEST POTENTIAL FOR HEAVIER RNFL SHOULD BE
FROM THE NRN HALF OF THE PLAINS NEWD FRI-SUN GIVEN RELATIVELY SLOW
MOVEMENT OF THE WAVY SFC FRONT... WITH MORE LOCALIZED ENHANCED
PCPN PSBL OVER/NEAR THE NRN ROCKIES.  THE SOUTHEAST/FLORIDA WILL
BE ANOTHER FOCUS FOR HVY RNFL POTENTIAL WITH LINGERING MSTR FROM
THE REMNANTS OF ERIKA AND ONE OR MORE PIECES OF ENERGY ALOFT
AFFECTING THE AREA.  CONVECTION FARTHER NWD OVER THE EAST WILL
DEPEND ON DIFFICULT TO RESOLVE SHRTWV DETAILS WHILE MONSOONAL
ACTIVITY OVER THE SRN HALF OF THE ROCKIES SHOULD BE RELATIVELY LGT
IN MOST CASES.

COOLEST TEMPS VERSUS NORMAL UNDER THE WRN TROUGH WILL BE OVER THE
NORTHWEST THROUGH LATE WEEK WITH SOME ANOMALIES AT LEAST MINUS
10-15F... MODERATING NEXT WEEKEND AS THE TROUGH RELAXES SOMEWHAT.
ABOVE TO WELL ABOVE NORMAL TEMPS WILL PREVAIL OVER MOST OF THE
CNTRL-ERN U.S. EXCEPT FOR PARTS OF THE SOUTHEAST EXPERIENCING
CLOUDS/RNFL.  BEST POTENTIAL FOR ONE OR MORE DAYS WITH PLUS 10-20F
ANOMALIES SHOULD EXTEND FROM THE NRN-CNTRL PLAINS INTO THE
NORTHEAST.

RAUSCH

$$





USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.