Preliminary Forecasts
Issued by NWS

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FXUS02 KWNH 010637
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
234 AM EDT WED JUL 01 2015

VALID 12Z SAT JUL 04 2015 - 12Z WED JUL 08 2015

THROUGH DAY 5 --- THE 30/12Z ENSEMBLE MEANS HAD DECENT AGREEMENT
ACROSS NORTH AMERICA --- ALLOWING THE PREVAILING AMPLIFIED FLOW
PATTERN TO CONTINUE THROUGH THIS MEDIUM RANGE FORECAST PERIOD. THE
MEANS HAVE A MUCH BETTER RUN-TO-RUN CONSISTENCY ACROSS CENTRAL
CANADA...CONCERNING THE ESTABLISHMENT OF A STABLE LONGWAVE TROUGH
INVOF 95W LONGITUDE ---WHILE THE DETERMINISTIC GUIDANCE TENDS TO
VARY WITH THE STRENGTH OF MID-LEVEL WAVE ENERGY ENTERING WESTERN
CANADA---MOVING ATOP THE UPPER-LEVEL RIDGE AND INTO THE BASE OF
THE THE DOWNSTREAM TROUGH.

IN PRINCIPLE--- THE DETERMINISTIC ECMWF...GFS AND CANADIAN ARE
SIMILAR TO THEIR RESPECTIVE MEANS WITH THE AMPLITUDE OF THE WAVE
PATTERN -- AND THOUGHT USING A BIT OF THE 30/12Z DETERMINISTIC
ECMWF INTO DAY 5 (6/12Z) WOULD PRODUCE THE LEAST AMOUNT OF CHANGE
IN THE SENSIBLE WEATHER PARAMETERS --- FROM THE DAKOTAS EASTWARD
INTO THE CENTRAL APPALACHIANS.

OUT WEST...HAD TO USE THE 30/12Z ECENS/NAEFS/GEFS MEANS OUTRIGHT
BEYOND DAY 5 --- GIVEN THE CANADIAN/GFS DETERMINISTIC SOLUTIONS
ARE SIMILAR --- ALLOWING SOME MID-LEVEL ENERGY TO PERIODICALLY
MIGRATE ALONG THE NORTHWEST FLANKS OF THE UPPER-LEVEL RIDGE AND
MOVE INLAND ACROSS NORTHERN CALIFORNIA AND SOUTHERN OREGON. ON THE
OTHER HAND... THE DETERMINISTIC ECMWF ALLOWS MOST OF THE ENERGY TO
REMAIN OFFSHORE AND AWAY FROM THE WEST COAST. THE DIFFERENCES ARE
SIGNIFICANT ENOUGH (ESPECIALLY THE ECMWF`S DEPARTURE) TO BLEND THE
ENSEMBLE MEANS AT A 50/30/20 RATIO (FOR POPS AND TEMPS) ---UNTIL
THOSE DETAILS CAN SORT THEMSELVES OUT.

VOJTESAK








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