EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 AM EDT SAT MAY 18 2013

VALID 12Z TUE MAY 21 2013 - 12Z SAT MAY 25 2013

...OVERVIEW AND MODEL PREFERENCES...

AMPLIFIED FLOW PATTERN TO HOLD FIRM FOR THE MEDIUM RANGE FORECAST
PERIOD WITH TROUGHS ALONG BOTH COASTS AND A RIDGE OVER THE CENTRAL
STATES. BETTER THAN AVERAGE AGREEMENT ALOFT CONCERNING WEST COAST
TROUGH AND THE QUASI-STATIONARY NATURE OF ITS ASSOCIATED CLOSED H5
CIRCULATION FOR THE ENTIRE MEDIUM RANGE FORECAST PERIOD... WITH
MORE UNCERTAINTY IN THE SPECIFICS OF ENERGY ROTATING AROUND ITS
BASE DAYS 6-7. THE ECMWF HAS BEEN MOST ROBUST HERE. ABOUT AVERAGE
AGREEMENT ALOFT WITH THE WEAKENING MIDWEST CLOSED LOW AND EVENTUAL
EAST COAST TROUGH DAYS 6-7 WITH MOST UNCERTAINTY WITH THE
"ON-AGAIN/OFF AGAIN" CLOSED LOW SOMEWHERE WITHIN THE TROUGH AXIS.
MOST RECENT GFS RUNS CONTINUE JUST AN OPEN TROUGH WHILE THE 00Z
ECMWF BRINGS DOWN A CLOSED LOW FROM HUDSON BAY. THE 00Z ECMWF
REPRESENTS A MOST REASONABLE DETERMINISTIC SOLUTION DAYS 3-6...
THOUGH THE 06Z-00Z GFS RUNS WERE CLOSE BUT APPEAR TO BE TOO FAR
NORTH WITH THE UPPER LOW OVER THE PAC NW LATE IN THE PERIOD AND
PERHAPS TOO SLOW WITH THE FRONT NEARING THE EAST COAST. OPTED TO
BLEND IN BOTH THE 00Z ECENS MEAN AND 06Z GEFS MEAN FOR DAY 6
BEFORE GOING FULLY TOWARD THE ENSEMBLE MEANS DAY 7 AS NO
DETERMINISTIC MODEL HAS BEEN CONSISTENT IN THEIR DAY 7 FORECAST IN
RECENT RUNS.


...SENSIBLE WEATHER HIGHLIGHTS...

SIGNIFICANT RAINFALL AND BELOW NORMAL TEMPERATURES ARE EXPECTED
INVOF THE SLOW-MOVING UPPER-LEVEL TROUGH AND CUTOFF H5 LOW OUT
WEST... ESP COASTAL WA AND FAR NW MT. SOUTHERN ROCKIES SHOULD BE
FAR ENOUGH AWAY FROM THE UPPER LOW TO ENJOY ABOVE NORMAL TEMPS AND
LITTLE IF ANY PRECIP. A CONTINUED THREAT OF MODERATE TO HEAVY
RAINFALL OVER THE UPPER HALF OF THE MISSOURI AND MISSISSIPPI RIVER
BASINS DURING THE FIRST HALF OF THE MEDIUM RANGE WILL LIKELY
TRANSLATE EASTWARD INTO THE GREAT LAKES AND UPPER HALF OF THE OHIO
RIVER BASIN BY THE LATTER HALF OF THIS FORECAST PERIOD...
CONTINGENT UPON HOW QUICKLY THE FRONT PUSHES EAST. MODEST AMOUNTS
UP TO ABOUT AN INCH AND A HALF OR SO DAYS 6-7 /AREAL AVERAGE/ MAY
BE A GOOD COMPROMISE AT THIS TIME.


FRACASSO/VOJTESAK