Prognostic Meteorological Discussion
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FXUS02 KWBC 271413
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1012 AM EDT WED MAY 27 2015

VALID 12Z SAT MAY 30 2015 - 12Z WED JUN 03 2015

THE MEDIUM RANGE DAYS 3-6 HEIGHTS/SEA LEVEL PRESSURES WERE
COMPOSED OF A BLEND OF THE 06Z GFS/06Z GEFS MEAN/00Z ECMWF/00Z
ECMWF ENSEMBLE MEAN AND THEN THE ECMWF ENSEMBLE MEAN DAY 7.

OVER THE WEST...THE INITIAL 500 MB CLOSED LOW OVER BRITISH
COLUMBIA WEAKENS AND SHEARS EAST...ALLOWING HEIGHTS TO RISE OVER
THE PACIFIC NORTHWEST DOWNSTREAM FROM THE APPROACHING CLOSED LOW.
THE CLOSED LOW APPROACHES THE COAST AND SHOULD ARRIVE MON 01 JUN
WITH AN INCREASE IN SHOWER ACTIVITY OVER THE PACIFIC NORTHWEST AND
THEN THE NORTHERN ROCKIES BY TUE 02 JUN.  WITH THE SLOW EASTWARD
PROGRESSION OF THE UPSTREAM CENTRAL PACIFIC CLOSED LOW...THIS
TROUGH WILL MOVE SLOWLY EAST ACROSS THE GREAT BASIN TUE-WED.
TYPICAL TIMING/AMPLITUDE DIFFERENCES EXIST WITH A CONSENSUS
SOLUTION PREFERRED TO RESOLVE DIFFERENCES DAYS 3-6.  THE GUIDANCE
SHOWS WAVY LOW PRESSURE DEVELOPING ON THE PLAINS DAY 7 WED 03
JUN...WITH NORTH-SOUTH SPREAD ON THE LOW POSITIONS.

ON DAY 7 WED THE 00Z ECMWF/00Z GFS/00Z ECMWF ENSEMBLE MEAN HAD
LOWER HEIGHTS ACROSS THE SOUTHWEST US.  THIS IS PREFERRED AS
TELECONNECTIONS FROM THE CENTRAL PACIFIC CLOSED LOW TRANSLATE INTO
A FAVORED SOUTHWEST TO WEST COAST TROUGH.  THE 00-06Z GEFS AND
NAEFS ENSEMBLE MEANS WERE FLATTER/LOWER AMPLITUDE AND THUS LESS
PREFERRED.

IN THE EAST...THE TROUGH IN THE UPPER MS VALLEY ON DAY 3 SAT 30
MAY SPLITS WITH THE SOUTHERN EXTENSION LAGGING OVER THE MID TO
LOWER VALLEY WHILE THE NORTHERN END DEAMPLIFIES AS IT CROSSES THE
EASTERN GREAT LAKES...OHIO VALLEY AND NEW ENGLAND.  SHOWERS ARE
EXPECTED IN THE BAND OF ENHANCED MOISTURE AND LIFT IN THE
PRE-FRONTAL ENVIRONMENT ACROSS THE GREAT LAKES/NORTHEAST/MID
ATLANTIC. THE COLD FRONT STALLS AS IT CROSSES SOUTH ACROSS THE MID
ATLANTIC STATES...RETURNING NORTH AS A WARM FRONT IN THE OHIO
VALLEY AND GREAT LAKES DAYS 6-7...RESPECTIVELY.

IN THE SOUTHEAST AND GULF COAST/FL... THE BROAD AND WEAK MID LEVEL
TROUGH DRIFTS SLOWLY EAST FROM THE MID-LOWER MS VALLEY FROM THE
WEEKEND THROUGH THE MIDDLE OF NEXT WEEK.  THE 00-06Z GFS AND GEFS
MEAN ESTABLISH THE TROUGH AXIS WEST OF THE ECMWF/CANADIAN AND
THEIR MEANS.  TELECONNECTIONS AND CLIMATOLOGY FAVOR THE MORE
EASTERN CLUSTER SO LESS WEIGHT WAS GIVEN TO THE 00-06Z GFS AND
GEFS MEAN SOLUTIONS...AND MORE TO THE 00Z ECMWF ENSEMBLE
MEAN/CANADIAN ENSEMBLE MEAN ON DAY 7.  THE DEVELOPING PERSISTENT
EAST SOUTHEAST CONFLUENT FLOW ACROSS THE CARIBBEAN AND BAHAMAS
ALLOWS AN INCREASE IN PRECIPITABLE WATER VALUES TO OCCUR WITH THE
ENHANCED MOISTURE MOVING INTO FLORIDA DAYS 7 AND BEYOND.  THERE
ARE TIMING DIFFERENCES WITH THE ENHANCED MOISTURE GREATER IN
MAGNITUDE IN THE GFS/CANADIAN THAN THE ECMWF/ECMWF ENSEMBLE MEAN.
THE FORECAST IS GETTING INTO JUNE...THE RAINIEST MONTH IN
PENINSULAR FLORIDA...SO CHANCES OF RAIN WILL BE GOING UP NEXT WEEK
IF THE MODELS ARE CORRECT IN THE INCREASED AVAILABLE MOISTURE.

PETERSEN


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