Prognostic Meteorological Discussion
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000
FXUS02 KWBC 301600
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1159 AM EDT THU OCT 30 2014

VALID 12Z SUN NOV 02 2014 - 12Z THU NOV 06 2014

...STRONG COASTAL LOW HEADING FOR ATLANTIC CANADA EARLY IN THE
PERIOD...

...RAIN LIKELY FOR THE WEST AND SOUTHERN PLAINS...


...OVERVIEW...

AMPLIFIED TROUGH/RIDGE/TROUGH PATTERN IS FORECAST TO DE-AMPLIFY
THROUGH THE MEDIUM RANGE PERIOD... BUT THE ACTIVE WEATHER WILL
CONTINUE OVER VARYING PARTS OF THE CONUS. IN THE WEST... INCOMING
POSITIVELY TILTED TROUGH WILL LIKELY SPLIT NE/SW AND BE THE
IMPETUS TO HELP GUIDE NEWLY FORMED TROPICAL DEPRESSION 21-E
NORTHWARD INTO MEXICO AROUND TUESDAY PER THE LATEST NHC FORECAST.
THAT COULD EXACERBATE THE HEAVY RAINFALL POTENTIAL IN THE SOUTHERN
PLAINS BY THE END OF THE PERIOD NEXT THURSDAY... BUT ENSEMBLE
SPREAD REMAINS HIGH /PW... QPF... ETC/. IN THE EAST... THE
DEPARTING MULTI-FACTED SYSTEM SHOULD PULL AWAY THROUGH SE CANADA
AND CLIP ESPECIALLY NORTHEASTERN NEW ENGLAND WITH WIND AND
RAIN/SNOW.


...GUIDANCE PREFERENCES AND UNCERTAINTY ASSESSMENT...

THE WESTERN TROUGH REMAINS CHALLENGING... WITH THE VARIOUS PIECES
OF DETERMINISTIC GUIDANCE GRAPPLING WITH THE NATURE OF THE
UPPER-JET STRUCTURE ALONG THE I-10/I-8 CORRIDOR FROM THE COLORADO
RIVER TO THE RIO GRANDE EARLY ON IN THE EVOLUTION OF THIS FORECAST
PERIOD. AND JUST AS CHALLENGING WILL BE THE TRANSITION OF THE FLOW
BEHIND THIS SYSTEM LATE IN THE PERIOD ALONG THE WEST COAST.

SPLIT-FLOW JET SHOULD PROVIDE ENOUGH MOMENTUM TO SPIN UP AND
MIGRATE A SURFACE CYCLONE ACROSS THE HIGH PLAINS INTO SOUTHERN
CANADA SUN-MON. QUESTIONS REMAIN AS TO HOW TO HANDLE THE SW ENERGY
-- I.E... ITS SPEED. THIS WILL BE SOMEWHAT COMPLICATED BY THE
EVOLUTION OF TD 21-E AS WELL. THE 06Z PARALLEL GFS OFFERS A
REASONABLE FORECAST BETWEEN THE 00Z GFS AND ECMWF... WHICH LIES
NEAR THE ECMWF ENSEMBLE MEAN.

OVERALL THE GUIDANCE ARE IN GOOD AGREEMENT THROUGH THE PERIOD...
BETTER THAN AVERAGE CONSIDERING THE CHANGING PATTERN. THE ECMWF
ENSEMBLES BECOME QUICKER THAN THE CMC/GEFS ENSEMBLES BY NEXT THU
WITH THE NORTHERN ENERGY THROUGH THE GREAT LAKES... PERHAPS
INITIALLY DUE TO UPSTREAM DIFFERENCES OVER ALASKA AND THEN
COMPOUNDING EFFECTS THEREAFTER. GIVEN THE PREFERENCE TOWARD THE EC
ENSEMBLES UPSTREAM... HAVE GIVEN THEM MORE WEIGHT IN THE FORECAST
BY MID-LATE NEXT WEEK. PARALLEL 06Z GFS LIES ON THE QUICKER SIDE
WHILE THE 00Z ECMWF IS SLOWER /OPERATIONAL GFS RUNS ARE SLOWER
STILL/... LEAVING THE EC MEAN AS A GOOD MIDDLE GROUND.


...SENSIBLE WEATHER HIGHLIGHTS...

DEPARTING SYSTEM JUST EAST OF THE 40N/70W BENCHMARK WILL USHER IN
A BRISK NORTH AND NORTHWEST WIND IN THE EAST... WITH MUCH COLDER
AIR AND SOME MOUNTAIN SNOWS POISED TO WRAP AROUND THE DEEPENING
STORM. EASTERN MAINE WILL LIE CLOSEST TO THE SYSTEM BUT SE CANADA
IN GENERAL SHOULD FEEL THE DIRECT IMPACTS MOST. THE SENSIBLE
WEATHER EFFECTS OF THIS SYSTEM WILL BE FELT AS FAR SOUTH AS THE
GULF COAST AND FLORIDA WITH A DISTINCTLY AUTUMN-LIKE OR EVEN EARLY
WINTER DRY AND COOL/COLD FEEL TO THE AIRMASS BEHIND THE COLD FRONT
UNTIL ABOUT TUESDAY. LOW TEMPERATURES COULD APPROACH RECORD LEVELS
IN SOME AREAS GIVEN A GOOD TRAJECTORY DOWN THE PENINSULA.

IN THE WEST... AN ACTIVE PACIFIC SYSTEM DIGGING ACROSS THE GREAT
BASIN ON SUN WILL SPREAD PRECIP THROUGH THE CENTRAL BUT ESPECIALLY
NORTHERN ROCKIES. WESTERN MONTANA EAST OF THE DIVIDE SHOULD SEE A
QPF/SNOW MAX AS THE SFC LOW TO THEIR SE/E MOVES INTO S CANADA.
PRECIP FOCUS SHOULD THEN TURN TO THE SOUTH. WHAT STARTS OUT AS
MILD... WINDY... AND DRY IN THE CENTRAL AND SOUTHERN
PLAINS/ROCKIES AND LOWER HALF OF THE MISSOURI VALLEY BECOMES MUCH
MORE STORMIER AND WETTER BY EARLY/MID-WEEK THANKS TO BROAD SW FLOW
AND A SLOWLY MOVING SFC FRONT.


FRACASSO / VOJTESAK

$$





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