Prognostic Meteorological Discussion
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000
FXUS02 KWBC 051543
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1042 AM EST THU MAR 05 2015

VALID 12Z SUN MAR 08 2015 - 12Z THU MAR 12 2015

...OVERVIEW...

THE MODELS AND ENSEMBLE MEANS ARE AGREEABLE/CONSISTENT WITH THE
MAIN THEMES OF THE LARGE SCALE PATTERN.  THESE INCLUDE PROGRESSIVE
NRN CONUS/SRN CANADA FLOW THAT SHOULD SUPPORT A SERIES OF SFC
FRONTS... A SRN ROCKIES/PLAINS INTO MEXICO MEAN TROUGH AND STRONG
RIDGE E OF THE BAHAMAS BTWN WHICH SHOULD LIE A WAVY SFC FRONT FROM
JUST OFF THE SERN COAST SWWD THROUGH THE GULF OF MEXICO... AND AN
ERN PAC UPR LOW INITIALLY NEAR 150W GRADUALLY TRACKING CLOSER TO
THE WEST COAST.  HOWEVER OVER THE PAST COUPLE DAYS THERE HAVE BEEN
IMPORTANT DIFFS WITH AMPLITUDE/TIMING WITHIN THE CONSENSUS MEAN
PATTERN... IMPACTING THE SENSIBLE WEATHER FCST FOR SOME AREAS.


...GUIDANCE EVALUATION/PREFERENCES...

RECENT ISSUES WITH NRN STREAM FLOW HAVE TENDED TO ORIGINATE FROM
TROUGH ENERGY OVER THE EXTREME NERN PAC EARLY IN THE PERIOD.  GFS
RUNS AND TO SOME EXTENT GEFS MEANS FROM THE PAST COUPLE DAYS HAVE
BEEN MORE AMPLIFIED THAN MOST OTHER SOLNS WITH THIS TROUGHING AS
IT PROGRESSES INTO AND ACROSS CANADA.  THUS FAR TELECONNECTIONS
RELATIVE TO THE MOST DOMINANT HGT ANOMALY CNTRS MID-LATE PERIOD AS
WELL AS SLOW PROGRESSION OF THE ERN PAC UPR LOW/PERSISTENCE OF THE
DOWNSTREAM RIDGE HAVE FAVORED LEANING AWAY FROM THE AMPLIFIED GFS
TROUGH REACHING WRN CANADA... WITH MORE ENERGY LIKELY FEEDING INTO
A FLAT TROUGH OVER ERN CANADA AND NERN QUADRANT OF THE LOWER 48.
AMONG RECENT GEFS MEANS THE 00Z RUN COMES CLOSEST TO THE NON-GFS
CLUSTER.

THE SRN ROCKIES/PLAINS INTO MEXICO TROUGH SHOULD AMPLIFY DURING
THE FIRST HALF OF THE PERIOD AND THEN BEGIN TO WEAKEN AS UPSTREAM
FLOW BECOMES SOMEWHAT FLATTER.  SLOWER GFS TRENDS WITH EJECTING
INITIAL ENERGY HAVE BROUGHT GUIDANCE CLOSER TOGETHER RELATIVE TO
24 HRS AGO... THOUGH THE 00Z-06Z GFS/00Z CMC ARE STILL A LITTLE
FASTER THAN OTHER SOLNS.  A GUIDANCE AVG LOOKS REASONABLE FOR THE
REST OF THE PERIOD.

FOR THE SYSTEM APPROACHING THE WEST COAST THE 00Z ECMWF MEAN
REVERSED ITS QUESTIONABLY FASTER TREND FROM THE 12Z CYCLE.  THIS
BRINGS THE ECMWF MEAN MORE IN LINE WITH OTHER ENSEMBLE MEANS BUT
THE OPERATIONAL MODELS MAINTAIN A SLOWER AND BETTER DEFINED
SYSTEM... CERTAINTY A PLAUSIBLE SCENARIO SINCE THE FEATURE SHOULD
BE RELATIVELY DETACHED FROM THE WESTERLIES UNTIL LATE IN THE
PERIOD.  NOTE THAT THE 00Z ECMWF REFLECTS A SLOWER TREND FROM
PRIOR RUNS AND THE CMC HAS ADJUSTED MUCH SLOWER OVER THE PAST 24
HRS.  MOST GFS RUNS HAVE BEEN RELATIVELY SLOW OVER THE PAST DAY.

COMBINING THE ABOVE CONSIDERATIONS YIELDS A STARTING FCST
CONSISTING OF 40 PCT WEIGHTING OF THE 00Z ECMWF WITH EQUAL
REMAINING PARTS OF THE 00Z GEFS MEAN/NAEFS MEAN/ECMWF MEAN.  BY
LATE IN THE PERIOD THE 00Z ECMWF FCST OVER THE ERN PAC IS
SUFFICIENTLY WELL DEFINED TO HEDGE THE ERN PAC/WEST COAST PATTERN
A LITTLE MORE TOWARD ITS SOLN THAN THE INDICATED WEIGHTING.


...SENSIBLE WEATHER HIGHLIGHTS...

POTENTIAL CONTINUES TO EXIST FOR ONE OR MORE EPISODES OF ENHANCED
RNFL FROM THE GULF COAST THROUGH THE SOUTHEAST AND PERHAPS EXTREME
SRN MID ATLC.  BEST FOCUS WILL BE WITH ONE OR MORE INDIVIDUAL
SHRTWVS EJECTING FROM THE UPSTREAM MEAN TROUGH ALOFT AND ON THE
COOL SIDE OF A WAVY FRONT EXTENDING FROM JUST OFF THE SERN COAST
INTO THE GULF OF MEXICO.  PERSISTENT SWLY FLOW ALOFT BTWN THE MEAN
TROUGH AND RIDGE E OF THE BAHAMAS WILL PROVIDE A STEADY STREAM OF
UPR LVL MSTR.  LATE IN THE PERIOD SOME MSTR SHOULD BEGIN TO REACH
THE WEST COAST AHEAD OF THE APCHG ERN PAC SYSTEM BUT WITH
RELATIVELY LGT AMTS GIVEN PREFS FOR MODERATELY SLOW TIMING.  ALSO
BY NEXT WED-THU A FRONT DROPPING INTO THE NRN TIER/TRAILING
UPSLOPE FLOW MAY SUPPORT LGT PCPN OVER THE NRN HIGH
PLAINS/ROCKIES.  ACROSS THE GRTLKS/NEW ENGLAND EXPECT THE SERIES
OF FRONTAL PASSAGES TO BRING AT LEAST A COUPLE PERIODS OF MOSTLY
LGT SNOW.

FOR TEMPS THE MOST PROMINENT TREND WILL BE STEADILY INCREASING
COVERAGE OF ABOVE NORMAL READINGS AS THE MEAN PATTERN ALOFT
BECOMES FLATTER.  COOLEST ANOMALIES OF MINUS 10-20F FOR DAYTIME
HIGHS SHOULD BE OVER THE SRN PLAINS/LWR MS VLY SUN-MON.  LOCATIONS
FROM THE WRN STATES THROUGH THE NRN-CNTRL PLAINS INTO UPR MS VLY
SHOULD SEE THE MOST PERSISTENT WARMTH... WITH SOME PLUS 10-20F
ANOMALIES ON MULTIPLE DAYS.  THE NRN TIER SHOULD RETURN CLOSER TO
NORMAL BY NEXT THU THOUGH.

RAUSCH

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