696
FXUS02 KWBC 301837
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
236 PM EDT SUN AUG 30 2009
VALID 12Z WED SEP 02 2009 - 12Z SUN SEP 06 2009
AMPLIFIED RIDGING IN WESTERN CANADA WITH AN APEX IN THE NORTHWEST
TERRITORIES CORRESPONDS TO ENERGY UNDERCUTTING THE RIDGE 20
DEGREES TO THE SOUTH...NEAR THE US/CANADIAN BORDER. THE MODELS
WHICH SHOW THIS IDEA BEST ARE THE 00Z GFS/00Z AND 12Z
CANADIAN...BUT BOTH HAVE ISSUES. THE 00Z AND 12Z CANADIAN APPEAR
SOMEWHAT FAST WITH THE MOTION OF THE FIRST SYSTEM IN THE SERIES
WHILE THE 00Z GFS LEFT A LESS THAN DESIRABLE SYNOPTIC PATTERN IN
THE NORTHEAST PACIFIC LATE IN THE PERIOD. A COMPROMISE OF THE 00Z
ECMWF/06Z GFS SOLUTIONS LED TO A MORE PREFERABLE SOLUTION AS A
WHOLE...ALTHOUGH THIS SOLUTION WAS TINKERED WITH IN THE WESTERN
ATLANTIC PER 00Z MULTI-MODEL ENSEMBLE LOW CLUSTERING.
SOUTHWEST FROM FRIDAY ONWARD...
THE LATEST NHC FORECAST FROM 15Z BRINGS HURRICANE JIMENA NORTHWARD
TO NORTHERN BAJA CALIFORNIA BY FRIDAY. PER ITS EXPECTED WEAK
NATURE THEREAFTER DUE TO COOL SEA SURFACE TEMPERATURES AND LAND
INTERACTION...EXPECT THE WEAKENING SYSTEM TO MOVE WEST TO
SOUTHWEST THEREAFTER STEERED BY THE SPRAWLING SURFACE HIGH IN THE
EASTERN PACIFIC. NEVERTHELESS...THE DAMAGE WILL ALREADY BE DONE
AS A MONSOON SURGE IS EXPECTED TO MOVE IN TANDEM WITH THE SYSTEM
UP THE GULF OF CALIFORNIA/SEA OF CORTEZ BRINGING
SHOWERS/THUNDERSTORMS DURING THE AFTERNOON AND EVENING HOURS TO
ARIZONA AND EVENTUALLY THE CENTRAL ROCKIES FROM FRIDAY THROUGH
NEXT WEEKEND.
SYSTEM MOVING IN THE PACIFIC NORTHWEST MID THIS WEEK...
THE LARGE UPPER VORTEX IN THE NORTHEAST PACIFIC EARLY THIS WEEK
WILL MOVE INTO THE REGION WEDNESDAY-THURSDAY AND THE MODELS DIFFER
CONSIDERABLY ON THE AMPLIFICATION OF THE TROUGH MOVING INTO THE
COAST. THE 00Z AND 06Z GFS/UKMET ARE SHARPLY AMPLIFIED WITH THIS
FEATURE... WHILE THE LAST TWO ECMWF RUNS OFFER A MUCH MORE COMPACT
UPPER TROUGH WITH THE SHORT WAVE DYNAMICS RACING INTO WESTERN
CANADA. THE 00Z GEFS MEAN ACTUALLY ENDS UP SUPPORTING THE ECMWF
MORE THAN THE GFS/UKMET OVER THE FIRST COUPLE OF DAYS. AS THIS
SHORT WAVE MOVES FURTHER NORTH AND EAST INTO CENTRAL CANADA AND
SURFACE COLD FRONT SLIDES INTO THE NRN ROCKIES/THROUGH THE PACIFIC
NORTHWEST... ANOTHER POTENT MARITIME SHORT WAVE TROUGH WILL BEGIN
TO APPROACH THE PACIFIC NORTHWEST LATE THIS WEEK. THIS IMPULSE
HAS THE CHANCE TO DIG A BIT MORE AND HELP PUSH THE SURFACE COLD
FRONT INTO THE NORTHERN HIGH PLAINS LATE NEXT WEEKEND. THIS SYSTEM
SHOULD SPREAD MODERATE RAINS...POTENTIALLY HEAVY IN THE
TERRAIN...ACROSS THE PACIFIC NORTHWEST/NORTHERN ROCKIES FROM
FRIDAY ONWARD.
PLAINS EASTWARD...
AN IMPRESSIVE MID-LEVEL LOW OVER THE DAKOTAS AND A RATHER LARGE
UPPER WEAKNESS OVER THE EAST ARE EXPECTED THIS PERIOD. THE
WEAKNESS OVER THE EAST WILL FEATURE A MID-LEVEL FEATURE STARTING
OFF OVER THE OH/TN VALLEYS WHICH GRADUALLY LIFTS THROUGH THE
APPALACHIANS/MID-ATLANTIC INTO THE NORTHEAST. DURING THIS TIME...
A SHEAR AXIS ALONG THE EDGE OF AN AMPLIFIED UPPER RIDGE WILL KEEP
A STATIONARY SURFACE BOUNDARY JUST OFFSHORE OF THE
SOUTHEAST/MID-ATLANTIC STATES WHICH IS EXPECTED TO BE CONVECTIVELY
ACTIVE. WHAT WILL RESULT BY THE LATTER PART OF THE FCST PERIOD
SHOULD BE RIDGING TO BECOME MORE PROMINENT ACROSS THE SOUTHEAST
WITH AN INCREASE IN UPPER HEIGHTS. THE MID-LEVEL FEATURE OVER THE
DAKOTAS WILL BEGIN TO DIG INTO THE CENTRAL PLAINS BEFORE REACHING
THE MID MS VLY AND BASICALLY BECOME STATIONARY... TRAPPED WELL
SOUTH OF THE STEERING CURRENT... BEFORE POSSIBLY LIFTING INTO THE
UPR MS VLY. THIS SYSTEM WILL BRING MODERATE TO HEAVY RAINFALL TO
THE CENTRAL PLAINS/MISSISSIPPI VALLEY/MIDWEST. THE 00Z AND 06Z
GFS/00Z ECMWF ARE GENERALLY SIMILAR WITH THESE FEATURES DURING THE
PERIOD OVER THIS REGION. ADJUSTMENTS TO THE LOW POSITION OFFSHORE
THE EAST COAST WERE MADE PER THE 00Z MULTI-MODEL ENSEMBLE LOW
CLUSTERING.
ROTH/MUSHER
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