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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