Prognostic Meteorological Discussion
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000 FXUS02 KWBC 050538 PMDEPD EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 138 AM EDT SAT SEP 05 2015 VALID 12Z TUE SEP 08 2015 - 12Z SAT SEP 12 2015 AN ACTIVE HIGH-LATITUDE NORTHERN JET STREAM IS EVIDENT DURING THE MEDIUM RANGE FORECAST PERIOD---CARTING REMNANTS OF `IGNACIO` EASTWARD FROM THE ALASKA PANHANDLE AND NORTH CENTRAL BC AROUND DAY 3---BRUSHING THE UPPER GREAT LAKES AND WESTERN ONTARIO AROUND DAY 5. THIS MIGRATION COVERS A VAST AMOUNT OF DISTANCE IN A RATHER SHORT PERIOD OF TIME. AND AT 700 MBS---LIKED THE WAY THE DETERMINISTIC 4/12Z ECMWF HANDLED THE NATURE OF THE MOISTURE/TEMPERATURE ADVECTION PATTERN IN RESPONSE TO THE INCORPORATION OF THIS SUBTROPICAL DISTURBANCE (NORTH OF 50 NORTH LATITUDE) AND INTO THE NORTHERN STREAM BETWEEN 145W-130W...AND THEN OVER CANADA---EASTWARD TO 100W. THE 4/12Z DETERMINISTIC GFS IS NOT `UN-USABLE` WHATSOEVER HEADING INTO THE DAY 5 TIME FRAME. IT WAS THE WEAKER SOLUTION OVER THE SOUTHERN PLAINS AND SOUTHEAST WITH THE COLD FRONT YESTERDAY---AND LIKE YESTERDAY...WOULD BELIEVE THE MOMENTUM OF A TROPICALLY-INFUSED SYSTEM CAUGHT IN A NEARLY WEST-TO-EAST NORTHERN STREAM JET OVER CANADA WOULD BE `WEAKER` WITH THE INTRODUCTION OF APPRECIABLE COLD ADVECTION INTO THE LOWER 48...EAST OF THE DIVIDE---AND MORE IMPORTANTLY---SOUTH OF 35N LATITUDE. THE SUBTROPICAL FLOW AND ITS MID-LEVEL WARM ADVECTION DOES SPREAD QUICKLY ACROSS CANADA AND THOUGHT THE 4/12Z ECENS/GEFS MEANS WOULD BE A VERY GOOD SOLUTION---IN LIEU OF---A PURE DETERMINISTIC SOLUTION AND REMOTE CHANCE OF A `PERFECT PROG` BEYOND 120 HOURS---USING ONE OR THE OTHER (4/12Z DETERMINISTIC ECMWF/GFS). IN THIS CASE---TO COMPILE A REALISTIC DEPICTION OF THE DAY4-5 AND DAY6-7 48-HOUR QPFS---I AM NOT EMOTIONALLY `TIED` OR FAVORING ONE MODEL OVER ANOTHER. BOTH DETERMINISTIC PIECES OF GUIDANCE (ECMWF/GFS) HAVE THE LOWER THIRD OF THE MISSOURI VALLEY...AND LOWER ARKANSAS RIVER BASIN WET EARLY IN THE PERIOD---THEN GRADUALLY TRANSLATE THE PRECIPITATION DOWNSTREAM ALONG THE FRONT. A MORE PROGRESSIVE FRONTAL PUSH IS THE `STYLE` OF THE ECMWF---CREATING AN EXTREMELY WET WESTERN GULF COAST AND NEW ENGLAND FOR DAY 6-7. WHILE THE GFS---A WEAKER `STYLE` FRONTAL PROGRESSION ALONG THE NORTHERN FLANKS OF THE SOUTHEAST RIDGE---CREATES A `WETTER` OHIO VALLEY. IN EITHER CASE---THE RATHER PROGRESSIVE SERIES OF WAVES GENERATED BY THE INFLUX OF SUBTROPICAL PACIFIC MOISTURE WILL KEEP MUCH OF THE COLDER NORTHERN STREAM HIGH-LATITUDE AIRMASS LOCKED UP OVER NORTHERN CANADA AND ALLOW AN AUTUMN-LIKE EAST PAC SURFACE RIDGE TO MIGRATE INTO THE WEST COAST (AND OFFSHORE FLOW EVENT) THIS MEDIUM RANGE PERIOD. VOJTESAK $$

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