Prognostic Meteorological Discussion
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000
FXUS02 KWBC 271601
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1201 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
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.


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 DESPITE AN EXPECTED COLD FRONT PASSAGE
WITH SOME ASSOCIATED LATE-SEASON PRECIPITATION.  THE GREATEST
POSITIVE TEMPERATURE ANOMALIES ARE EXPECTED BETWEEN THE COLUMBIA
BASIN AND IDAHO THROUGH THE PERIOD.

MOISTURE ADVECTING NORTHWARD OUT OF THE GULF OF MEXICO WILL FUEL
POTENTIALLY HEAVY RAIN AND THUNDERSTORMS ALONG/AHEAD OF A FRONTAL
BOUNDARY ACROSS PORTIONS OF TX, THE DEEP SOUTH, THE
MID-MISSISSIPPI VALLEY, AND OHIO VALLEY EARLY TO MID WEEK.  THE
TAIL END OF THE BOUNDARY IS EXPECTED TO STALL AND INTERACT WITH A
PAIR OF CLOSED LOWS APPROACHING THE SOUTHERN PLAINS, BRINGING
ADDITIONAL HEAVY RAINFALL TO PORTIONS OF TX, THE LOWER- TO
MID-MISSISSIPPI VALLEY, AND MID-SOUTH LATE NEXT WEEK.

PETERSEN

$$




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