Preliminary Forecasts
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
000
FXUS02 KWNH 190642
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
242 AM EDT FRI SEP 19 2014

VALID 12Z MON SEP 22 2014 - 12Z FRI SEP 26 2014

...OVERVIEW AND PREFERENCES...

THE MEDIUM RANGE PERIOD WILL FEATURE A SIGNIFICANT CHANGE... FROM
THE ERN PAC TROUGH AND WRN CONUS RIDGE/ERN CONUS TROUGH THAT HAS
RECENTLY BEEN A COMMON MEAN PATTERN... TOWARD A WEST COAST TROUGH
AND GRTLKS/SERN CANADA RIDGE.  A STRONG JET OVER THE PAC AS WELL
AS PSBL INFLUENCE FROM CURRENT T.S. FUNG-WONG OVER THE EXTREME WRN
PAC BASIN HAVE LIKELY BEEN CONTRIBUTING TO SIGNIFICANT
MODEL/ENSEMBLE SPREAD AND RUN TO RUN CHANGES OVER AT LEAST THE
PAST COUPLE DAYS.  HOWEVER GUIDANCE FROM THE 12Z-18Z GFS/GEFS AND
12Z ECMWF/ECENS HAS AT LEAST TEMPORARILY CONVERGED TO ALLOW FOR A
GENERAL BLEND OF THEIR SOLNS TO PROVIDE A REASONABLE FCST FOR MOST
DAYS... WITH MORE WEIGHTING OF OPERATIONAL SOLNS EARLY AND THE
ENSEMBLE MEANS LATE.


...GUIDANCE EVALUATION...

THE MOST PROMINENT TREND SEEN IN THE MODELS/ENSEMBLE MEANS OVER
THE PAST 1-2 DAYS IS TOWARD SLOWER PROGRESSION OF THE AMPLIFIED
ERN PAC TROUGH FCST TO MOVE INTO THE WRN STATES DURING THE LATTER
HALF OF NEXT WEEK.  THE 12Z CMC/CMC MEAN BECOME MUCH MORE
PROGRESSIVE WHICH EARLIER RUNS OF OTHER GUIDANCE SHOWED.  THUS FAR
THE 00Z GFS/UKMET/CMC CLUSTER WELL ALOFT WITH THE PREFERRED BLEND
OF THE 12Z-18Z GFS/GEFS AND 12Z ECMWF/EC MEAN THROUGH DAY 5 WED
HELPING TO MAINTAIN CONFIDENCE IN THE SLOWER/AMPLIFIED SCENARIO.
LATE IN THE PERIOD RECENT GFS/ECMWF RUNS HAVE BEEN SUGGESTING
POTENTIAL FOR MORE FLOW SEPARATION WITHIN THE OVERALL TROUGH
RELATIVE TO THE ENSEMBLE MEANS.  THE 12Z ECMWF BECOMES AN
AMPLIFIED EXTREME FROM LATE DAY 6 THU ONWARD WHILE THE 18Z GFS
TRENDS A LITTLE FASTER THAN CONSENSUS AFTER 12Z FRI.  THEREFORE
THE 12Z GFS BECOMES THE MINORITY WEIGHTED OPERATIONAL
REPRESENTATIVE TO ACCOUNT FOR THE POSSIBILITY OF FLOW SEPARATION.
AT THE SFC THE CONSENSUS BLEND PROVIDES A GOOD INTERMEDIATE SOLN
IN LIGHT OF TRACK SPREAD FOR STRONG LOW PRESSURE EXPECTED TO
EVOLVE OFFSHORE THE NORTHWEST COAST.

AHEAD OF THIS TROUGH AND WEAK LEADING ENERGY BRUSHING THE NWRN
STATES EARLY IN THE WEEK... A COMPACT UPR SYSTEM WILL EMERGE FROM
THE NRN ROCKIES INTO THE PLAINS.  GUIDANCE TYPICALLY HAS
DIFFICULTIES IN RESOLVING THE FINER DETAILS OF ENERGY HEADING
INTO/THROUGH MEAN RIDGES SO CONFIDENCE IS AVG AT BEST FOR EXACTLY
HOW THIS FEATURE WILL ULTIMATELY EVOLVE/PROGRESS.

OVER THE EAST THERE IS REASONABLE AGREEMENT THAT THE INITIAL
TROUGH ALOFT WILL PUSH A COLD FRONT AWAY FROM THE EAST COAST AND
SWD INTO THE FL PENINSULA AND GULF OF MEXICO... WITH ONE SFC HIGH
TRACKING FROM THE MID MS VLY EWD FOLLOWED BY A STRONGER CNTRL
CANADA TO NEW ENGLAND HIGH.  RECENT TRENDS HAVE FAVORED FASTER
DEPARTURE OF THE MEAN TROUGH ALOFT.  THE PRIMARY UNCERTAINTY
ARISES LATE IN THE PERIOD WITH THE 18Z/00Z GFS AND 12Z ECMWF RUNS
SHOWING A COMBINATION OF ENERGY ALOFT/SFC WAVINESS THAT COULD
AFFECT PARTS OF THE EAST COAST.  IMPORTANT DETAILS WILL LIKELY BE
FAIRLY SMALL IN SCALE AND TYPICALLY NOT WELL RESOLVED SEVERAL DAYS
OUT IN TIME.  AT THE VERY LEAST THE 18Z/12Z GEFS/ECMWF ENSEMBLES
DO NOT EXPECT SIGNIFICANT RNFL TO MAKE IT AS FAR INLAND AS THE 00Z
GFS.  WILL FAVOR THE MORE CONSERVATIVE ENSEMBLE MEANS AS A
STARTING POINT BUT WITH THE UNDERSTANDING THAT GIVEN THE TIME OF
YEAR AND GENERAL PATTERN SFC/ALOFT THERE COULD BE ROOM FOR A
BETTER DEFINED EVOLUTION.


...SENSIBLE WEATHER HIGHLIGHTS...

PROGRESSION OF LARGE SCALE FEATURES WILL BRING A PRONOUNCED
COOLING TREND TO THE WEST... WHILE THE CORE OF WARM ANOMALIES
SHOULD TRACK FROM THE NWRN STATES EARLY IN THE WEEK TO THE NRN
PLAINS/UPR MS VLY MID-LATE WEEK.  EXPECT SOME MAX TEMPS ACROSS THE
NRN TIER TO REACH 10-20F ABOVE NORMAL WITH GREATER COVERAGE OF
SIMILAR ANOMALIES FOR MINS.  TROUGH ALOFT MOVING INTO THE WEST
LATE IN THE WEEK WILL SUPPORT A PERIOD OF ENHANCED PCPN OVER THE
PAC NW INTO EXTREME NRN CA.  MEANWHILE THE UPR SYSTEM TRACKING OUT
OF THE NRN ROCKIES ALONG WITH SRN HIGH PLAINS MSTR... SOME
INITIALLY ASSOC WITH ODILE... MAY PROMOTE LOCALLY HVY RNFL OVER
PARTS OF THE CNTRL-SRN PLAINS... TRENDING LIGHTER/MORE SCT BY
THU-FRI.  PERSISTENT LOW LVL ELY FLOW SHOULD SUPPORT PERIODS OF
RNFL ESPECIALLY OVER THE FL PENINSULA AND SRN TX.
COVERAGE/INTENSITY OF RNFL NEAR THE CNTRL-SRN EAST COAST BECOMES
RATHER UNCERTAIN BY NEXT WED-FRI.  IT MAY TAKE MULTIPLE DAYS FOR A
CONSENSUS TO EMERGE FOR THIS ASPECT OF THE FCST.

RAUSCH

$$




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