Prognostic Meteorological Discussion
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734
FXUS02 KWBC 271610
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1210 PM EDT SAT MAY 27 2017

VALID 12Z TUE MAY 30 2017 - 12Z SAT JUN 03 2017

PATTERN OVERVIEW AND MODEL PREFERENCES
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
THE MODEL GUIDANCE REMAINS RELATIVELY AGREEABLE IN SHOWING
PERSISTENT UPPER TROUGHING ACROSS THE NORTHEAST AND DEVELOPING IN
THE NORTHWEST...WITH HIGH AMPLITUDE RIDGING DEVELOPING IN WESTERN
CANADA AND THE ADJACENT NORTHERN PLAINS.

FOR THE PRESSURES, 500 HPA HEIGHTS, AND WIND GRIDS USED AN EVEN
SPLIT OF THE 06Z GFS/06Z GEFS MEAN/00Z ECMWF AND 00Z ECMWF
ENSEMBLE MEAN DAYS 3-5 BEFORE SWITCHING TO A STRAIGHT 50/50 BLEND
OF THE 00Z ECMWF ENSEMBLE MEAN AND 06Z GEFS MEAN THEREAFTER.

BOTH THE ECMWF AND GFS SHOWED LARGE RUN TO RUN CHANGES IN THEIR
DEPICTION OF TROUGH ACROSS THE NORTHEAST PACIFIC AND NORTHWEST
US...AND DIFFERENCES FROM THEIR ENSEMBLE MEANS.
THE UPSTREAM CLOSED LOW OVER THE NORTH PACIFIC TELECONNECTS TO A
FLAT NORTHWEST US TROUGH...SO THE 00-06Z GFS RUNS LOOK LIKE LOW
PROBABILITY SOLUTIONS.  LIKEWISE...THE HIGHER AMPLITUDE ECMWF
TROUGH WAS NOT MATCHED BY ANY OF THE 50 ECMWF ENSEMBLE MEMBERS.

THE ECMWF ENSEMBLE MEAN AND 06Z GEFS ENSEMBLE MEAN MATCHED BETTER
WITH TELECONNECTIONS WITH THE UPSTREAM NORTH PACIFIC/GULF OF AK
CLOSED LOW...SO THESE SOLUTIONS WERE USED INSTEAD OF THE LOW
PROBABILITY OPERATIONAL 00Z ECMWF/06Z GFS ON DAYS 6 FRI 02 JUN AND
DAY 7 SAT 03 JUN.

WEATHER HIGHLIGHTS
~~~~~~~~~~~~~~~~~~
COOLER THAN NORMAL TEMPERATURES ARE EXPECTED TO CONTINUE INTO NEXT
WEEK ACROSS THE GREAT LAKES AND NORTHEAST DUE TO LINGERING UPPER
LEVEL TROUGHING.  MEANWHILE, WARM CONDITIONS ARE EXPECTED ACROSS
MUCH OF INTERMOUNTAIN WEST...WITH AN APPROACHING COLD FRONT
MODERATING WITH  SOME ASSOCIATED LATE-SEASON PRECIPITATION.  NEXT
FRI-SAT THE GREATEST POSITIVE TEMPERATURE ANOMALIES ARE EXPECTED
OVER THE NORTHERN HIGH PLAINS.

MOISTURE ADVECTING NORTHWARD OUT OF THE GULF OF MEXICO WILL FUEL
SHOWERS AND THUNDERSTORMS ALONG/AHEAD OF A SOUTHERN STREAM UPPER
LEVEL TROUGH ACROSS THE SOUTHERN PLAINS TO LOWER MS VALLEY MID TO
LATE NEXT WEEK.  LOCALLY HEAVY RAINS ARE POSSIBLE BUT WITH
SIGNIFICANT MODEL TO MODEL AND RUN TO RUN DIFFERENCES THE DETAILS
ARE ELUSIVE AND CONFIDENCE LOW.

PETERSEN

$$





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