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356
FXUS02 KWBC 021515
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1115 AM EDT TUE SEP 02 2014

VALID 12Z FRI SEP 05 2014 - 12Z TUE SEP 09 2014

FOR MID-LATITUDE NORTH AMERICA...
AND DAYS 3-4, THE DETERMINISTIC 2/06Z GFS AND 2/00Z ECMWF AND
THEIR ENSEMBLE MEANS WERE DECENT PIECES OF FORECAST GUIDANCE
CONCERNING THE SURFACE CYCLONE DEPTH, FRONTAL STRUCTURE AND
PROGRESSION THROUGH THE NORTHEAST QUARTER OF THE CONTINENT. A
DEEPENING CYCLONE IN QUEBEC LENDS SUPPORT TO A SECONDARY ...DEEPER
LOW-LEVEL COLD POOL LAGGING A GOOD 150-250 MILES BEHIND THE
MID-/UPPER-LEVEL FRONT (850-500MB LAYER). THIS UPPER-LEVEL FRONT
IS WHERE THE QPF OUTPUT VARIES WITHIN THE DETERMINISTIC GUIDANCE.

FOR EARLY NEXT WEEK (DAYS 6-7), THE DETERMINISTIC GUIDANCE BEGAN
TO LOSE SOME OF THE KEY DETAILS ALONG BOTH NORTH AMERICAN
COASTS---NOTABLY, THE GFS BEING THE SLOWER...MORE AMPLIFIED
SOLUTION ALOFT IN THE WEST AND MORE DEFINITIVE WITH THE SOUTHWARD
PUSH OF A MODIFIED CANADIAN LOW-LEVEL FRONT SURGING THROUGH THE
MOUNTAINS AND ENTERING THE COASTAL PLAINS OF THE MID-ATLANTIC
STATES/DELMARVA REGION. THE DETERMINISTIC ECMWF/CANADIAN WERE NOT
MUCH BETTER WITH RESPECT TO CONSISTENCY...AND THEIR 2/00Z RUNS
HANG THE UPPER-LEVEL FRONT ALONG THE APPALACHIANS AND SHEAR THE
ENERGY NORTHEASTWARD THROUGH MAINE AND NOVA SCOTIA/NEW BRUNSWICK.
IN THE WEST...BOTH (ECMWF-CANADIAN) WERE GENERALLY FASTER THAN
THEIR MEANS ALONG THE CANADIAN BORDER-NORTHERN DIVIDE.

CONCERNING UNCERTAINTIES ASSOCIATED WITH THE SUBTROPICAL MOISTURE
ORIGINATING INVOF BAJA CALIFORNIA-WESTERN GULF OF MEXICO...

THE 2/00Z CANADIAN WAS THE ONLY DETERMINISTIC SOLUTION NOT LEAVING
SOME MID-LEVEL ENERGY BEHIND---INVOF NORTHERN CALIFORNIA NEXT
WEEKEND. THE LAST 3 RUNS OF THE DETERMINISTIC GFS EMPHASIZED
CLOSED MID-LEVEL ENERGY AND A WELL-DEFINED CIRCULATION INVOF
COASTAL CALIFORNIA. THIS CANNOT BE RULED OUT CONSIDERING THE
UPSTREAM RIDGING BUILDING RAPIDLY INTO THE SOUTHEASTERN GULF OF
ALASKA. THE 2/06Z GEFS...ECENS AND NAEFS MEANS ALL SUPPORT A
GFS-LIKE TIMING AND PROGRESSION---IE A SLOWER MIGRATION OF THE
500MB TROUGH THROUGH SOUTHERN BC-PUGET SOUND FROM 8/00Z THROUGH
9/00Z. CAN THE SLOWER PROGRESSION DEVELOP A CLOSED LOW? YES.
ENOUGH ENSEMBLE CLUSTERING FROM ALL 3 MEANS SUPPORT ROUGHLY A 40%
PROBABILITY OF OCCURRENCE. A CUTOFF LOOMS AS A CONDUIT THROUGH
WHICH CHANNELED SUBTROPICAL MOISTURE/ENERGY CAN FLOW DOWNSTREAM
INTO THE GREAT BASIN. THIS WILL REMAIN A CHALLENGE IN THE MEDIUM
RANGE FORECAST FROM THE LOWER COLORADO RIVER BASIN EASTWARD INTO
THE SOUTHERN PLAINS...WHERE A WEAKNESS IN THE SUBTROPICAL RIDGE IS
ANTICIPATED TO EXIST THROUGH A LARGE PORTION OF THIS PACKAGE.

LAST BUT NOT LEAST--IS THE OUTCOME OF `DOLLY` AND ITS TROPICAL
PLUME. OUR DAY 3 GRAPHIC ALLOWS FOR SOME REMNANT `TROUGHING` AN
ALLEY-WAY ACROSS THE MID-RIO GRANDE VALLEY. THIS APPEARS TO
DEVELOP THE INITIAL `WEAKNESS` ALONG THE WESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE.

...SENSIBLE WEATHER HIGHLIGHTS...
MUCH OF THE SENSIBLE WEATHER FOCUS THIS MEDIUM RANGE PERIOD WILL
FOCUS ON ENERGY ORIGINATING ALONG THE WESTERN FLANKS OF THE
SUBTROPICAL RIDGE AXIS. ONE AREA OF CONCERN WILL BE IN THE FOUR
CORNERS REGION...WHERE AN ORGANIZED SHORTWAVE WILL EJECT
NORTHEASTWARD AND DEVELOP INTO A MODERATE-INTENSITY SURFACE
CYCLONE THAT TRACKS NORTHEASTWARD THROUGH THE UPPER MS VALLEY AND
WESTERN ONTARIO EARLY DAY 3.

IT`S THE CANADIAN COLD FRONT AND SURFACE HIGH THAT FOLLOW--WHERE
THE FOCUS FOR SHOWERS/STORMS WILL CONCENTRATE AND MIGRATE ACROSS
THE OHIO VALLEY AND NORTHEAST. WITH SOME CERTAINTY---COOLER AND
DRIER CANADIAN AIR WILL SPREAD OVER THE UPPER MIDWEST AND NEW
ENGLAND BEHIND THE FRONT. IF THERE IS A WILD-CARD IN THE QPF
FORECAST...IT`S WITH AN AREA OF UPSLOPE (RETURN) FLOW ALONG THE
WESTERN PERIPHERY OF THE SURFACE HIGH...COUPLED WITH TROPICAL
MOISTURE ASSOCIATED WITH `DOLLY`. COULD END UP BEING LITTLE MORE
THAN A SECONDARY AREA OF THICK CLOUD COVER WITH FOCUS FOR SHOWERS
AND THUNDERSTORMS ALONG ISOLATED HIGH TERRAIN OF THE UPPER RIO
GRANDE. AT THIS POINT IN TIME...A PESSIMISTIC APPROACH WOULD BE TO
INCLUDE RAINFALL ACROSS THE LOWER VALLEY FLOORS OF THE FOUR
CORNERS REGION AND LEE OF THE SOUTHERN ROCKIES---INCLUDING THE NEW
MEXICO-SOUTHEAST COLORADO PORTION OF THE I-25 CORRIDOR.

THE THIRD AREA OF CONCERN DOES RELATE TO THE WESTERN FLANKS OF THE
SUBTROPICAL RIDGE---YET THE SOURCE REGION FOR THE MID-LEVEL ENERGY
AND MOISTURE WILL ORIGINATE IN THE SUBTROPICAL PACIFIC. THE
CONSEQUENCES BEING--A MONSOONAL-LIKE CHARACTER TO THE SENSIBLE
WEATHER PATTERN FOR THE DESERT SOUTHWEST...UPPER-HALF OF THE RIO
GRANDE VALLEY AND PORTIONS OF THE WEST ALONG/SOUTH OF 40N
LATITUDE. AS WAS MENTIONED IN THE MIDNIGHT SHIFT PMDEPD...A SURGE
OF MOISTURE AHEAD OF A MID-LEVEL TROPICAL DISTURBANCE SYSTEM
CURRENTLY BEING MONITORED BY THE NATIONAL HURRICANE
CENTER---APPROXIMATELY 200SW OF MANZANILLO MX---CONTAINS
PRECIPITABLE WATER ANOMALIES OF GREATER THAN +1 STANDARD
DEVIATIONS ABOVE NORMAL (70 PERCENT OF THE GEFS ENSEMBLES) FOR
DAYS 5-7 IN SOUTHERN/CENTRAL ARIZONA.

VOJTESAK

$$






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