Prognostic Meteorological Discussion
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FXUS02 KWBC 200632
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
231 AM EDT SAT SEP 20 2014

VALID 12Z TUE SEP 23 2014 - 12Z SAT SEP 27 2014

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

AFTER A COUPLE RUNS OR SO OF REASONABLE AGREEMENT IN THE
GUIDANCE... THE 12Z CYCLE AND THUS FAR THE NEW 00Z CYCLE DEVELOP
SIGNIFICANT DIFFS IN SOLNS OVER THE PAC/WRN NOAM BY THE LATTER
HALF OF THE PERIOD.  THUS CONFIDENCE IN A PARTICULAR SCENARIO
DECLINES AFTER A MODEL/ENSEMBLE MEAN CONSENSUS OFFERS A REASONABLE
FCST FROM DAY 3 TUE INTO EARLY DAY 5 THU.  DOWNSTREAM FROM INITIAL
ERN PAC TROUGHING HGTS ARE FCST TO BE RELATIVELY HIGH OVER MOST OF
THE ERN 2/3 OF THE CONUS THOUGH WITH TWO OR MORE WEAKNESSES... ONE
OVER/NEAR THE PLAINS CONTAINING ENERGY FROM A COMPACT NRN HIGH
PLAINS UPR FEATURE AND ANOTHER ONE OR MORE CLOSER TO THE EAST
COAST.

THE DIVERGENCE SEEN OVER THE ERN PAC/WRN NOAM BY THU-SAT
ORIGINATES FROM DIFFS IN HANDLING AN UPR SYSTEM OVER THE SWRN
BERING SEA/WRN ALEUTIANS EARLY IN THE PERIOD.  THE 12Z ECMWF/EC
MEAN AND 12Z-00Z CMC/12Z CMC MEAN TREND STEADILY FASTER WITH THIS
FEATURE... ULTIMATELY FEEDING INTO A NEW ERN PAC TROUGH AND
EJECTING THE INITIAL ERN PAC TROUGH THROUGH THE WEST IN
PROGRESSIVE/FLATTER FASHION.  INTERESTINGLY THE ECMWF CLUSTER
REFLECTS A SOLN DEPICTED BY AN ISOLD ECMWF MEAN RUN FROM 36 HRS
AGO.  MEANWHILE THE GFS/GEFS RUNS AS WELL AS NEW 00Z UKMET THROUGH
LATE THU HOLD ONTO A SLOWER/MORE AMPLIFIED LEADING TROUGH JUST
APPROACHING THE WEST COAST BY LATE THU.

TELECONNECTIONS AND CONTINUITY PROVIDE SOME GUIDANCE FOR DECIDING
WHICH SCENARIO TO FOLLOW.  THE MOST COMMON ASPECT OF MULTI-DAY
MEANS BY D+8 IS A STRONG CORE OF POSITIVE HGT ANOMALIES W/SW OF
JAMES BAY... WITH TELECONS RELATIVE TO THIS FEATURE SUPPORTING A
MODERATE MEAN TROUGH OVER THE INTERIOR WEST.  ALSO CONSENSUS
CONTINUITY HAD FAVORED A SOLN CLOSER TO THE CURRENT GFS/GEFS IDEA
BEFORE THE 12Z SOLNS DIVERGED.  THUS PREFS LEAN TO THE 12Z GEFS
MEAN AND 00Z/19 ECMWF MEAN BY DAYS 6-7... WITH JUST ENOUGH
BROADNESS TO THE TELECON-FAVORED WRN MEAN TROUGH TO PSBLY ALLOW
FOR A LITTLE MORE PROGRESSION THAN THE 18Z GEFS MEAN.

WHILE SFC HIGH PRESSURE SHOULD DOMINATE OVER THE EAST FOR MOST OF
THE PERIOD... UNCERTAINTY IN DETAILS OF A PSBL WEAKNESS ALOFT
CONTINUES TO TEMPER CONFIDENCE IN PRECISE SFC DETAILS NEAR THE
SERN/MID ATLC COAST.  CMC RUNS HAVE BEEN MOST EXTREME WHILE THE
00Z UKMET HAS TRENDED MUCH WEAKER RELATIVE TO ITS 12Z RUN.  AFTER
SPORADIC STRONGER RUNS... LATEST GFS/ECMWF RUNS HAVE CURRENTLY
SETTLED UPON ONLY MODEST INVERTED TROUGHING AND MOSTLY CONFINED TO
JUST OFF THE COAST.


...SENSIBLE WEATHER HIGHLIGHTS...

TROUGH ALOFT MOVING INTO THE WEST WILL BRING A PERIOD OF UNSETTLED
WEATHER TO AREAS AT LEAST FROM THE NRN HALF OF THE WEST COAST INTO
NRN ROCKIES... AND BASED ON CURRENT PREFS FARTHER SEWD OVER THE
WEST BY LATER IN THE PERIOD AS WELL.  BEST ENHANCEMENT SHOULD BE
ALONG THE NRN CA/PAC NW COAST.  MID LVL FEATURE OVER THE PLAINS
MAY PROMOTE LOCALLY HVY ACTIVITY OVER THE CNTRL PLAINS PRIMARILY
DURING THE FIRST HALF OF THE PERIOD.  AREAS NEAR THE SRN HALF OF
THE EAST COAST AND ALONG MOST OF THE GULF COAST MAY SEE RNFL OF
VARYING INTENSITY THROUGH MOST OF THE WEEK.  EXPECT THE MOST
EXTREME ANOMALIES FOR TEMPS TO BE OF THE POSITIVE VARIETY ACROSS
THE NRN TIER AS SUPPORTED BY STRONG SRLY FLOW BETWEEN ERN CONUS
HIGH PRESSURE AND THE FRONT EMERGING INTO THE NRN HIGH PLAINS LATE
IN THE PERIOD... WITH SOME PLUS 10-20F ABOVE NORMAL READINGS
LIKELY FOR MIN/MAX TEMPS MOST DAYS.

RAUSCH

$$




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