506
FXUS02 KWBC 031845
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
245 PM EDT MON AUG 03 2009
VALID 12Z THU AUG 06 2009 - 12Z MON AUG 10 2009
TELECONNECTIONS WITH A POSITIVE ANOMALY CENTER NEAR 40N 150W FAVOR
TROUGHING ALONG THE WEST COAST AS WELL AS ACROSS THE
NORTHEAST...SIMILAR TO THE PATTERN SEEN IN LATE SPRING INTO JUNE
ACROSS THE LOWER 48...AND RIDGING NEAR ARKANSAS/EASTERN OKLAHOMA.
THE MODELS GENERALLY FAVOR THESE IDEAS...AND WITH THE APPEARANCE
OF THE 12Z ECMWF...ARE MOSTLY RESOLVED. WHERE THE GUIDANCE WAS
SIMILAR LATE THIS WEEK...USED A COMPROMISE OF THE 00Z ECMWF/06Z
GFS. FROM FRIDAY AFTERNOON ONWARD...A BLEND/COMPROMISE OF THE 06Z
GFS AND 00Z GEFS MEAN WAS USED WHICH WAS ON THE MORE AMPLIFIED
SIDE OF THE GUIDANCE NEAR THE WEST COAST. THIS SUMMER...A MORE
AMPLIFIED PATTERN HAS VERIFIED BETTER...SO SAW NO PROBLEMS WITH
THIS PREFERENCE. THE MAIN PRECIPITATION AXIS THIS PERIOD IS
EXPECTED TO STRETCH FROM THE PACIFIC NORTHWEST AND NORTHERN
ROCKIES/NORTHERN PLAINS SOUTHEAST THROUGH THE MIDWEST INTO THE
SOUTHEAST.
SOUTHEAST CANADA/NORTHERN PLAINS/GREAT LAKES/NEW ENGLAND...
THE BIGGEST ISSUE EARLY THIS MORNING CONCERNED AN OCCLUDED CYCLONE
THAT MOST OF THE DETERMINISTIC GUIDANCE AND AT LEAST ONE-THIRD OF
THE 00Z ECMWF ENSEMBLE MEMBERS TRACK FROM ONTARIO INTO NORTHERN
QUEBEC LATE IN THE PERIOD...WHICH HAS REPERCUSSIONS FOR FRONTAL
TIMING ACROSS THE NORTHERN PLAINS AND GREAT LAKES. THESE PROBLEMS
LEAD TO 30 HPA OF SPREAD IN THE PRESSURE PATTERN ACROSS SOUTHERN
CANADA...AND RELATE TO THE 00Z ECMWF SLOWER TIMING WITH A TROUGH
MOVING THROUGH THE NORTHEAST. THIS SITUATION PARTIALLY RESOLVED
ITSELF IN THE 12Z ECMWF...THOUGH NOW ALL THE DETERMINISTIC
GUIDANCE OUTPACES THE BULK OF THE 00Z MULTI-MODEL ENSEMBLE
MEMBERS. OVERALL...THE MODEL CLOSEST TO THE 00Z MULTI-MODEL
ENSEMBLE CLUSTERING WITH SURFACE LOW POSITIONS...AS WELL AS THE
06Z GEFS/00Z ECMWF ENSEMBLE MEAN MID-LEVEL PATTERNS...WAS THE 06Z
GFS. AFTER SEEING THE NEW 12Z GUIDANCE...ONLY MINOR CHANGES WERE
MADE TO CONTINUITY.
LOWER MISSISSIPPI VALLEY/SOUTHEAST...
NONE OF THE GUIDANCE IS QUITE WHERE THE TELECONNECTION-FAVORED
PATTERN PREFERS THE POSITION OF THE RETROGRADING WARM CORE RIDGE.
THE 00Z ECMWF IS THE CLOSEST HERE...SO MOVED THE MID-LEVEL
ANTICYCLONE TO THE ECMWF POSITION FOR THE 500 HPA HEIGHT
PROGS...WHICH IS THE ONLY PLACE WHERE THE 00Z ECMWF IS
SPECIFICALLY PREFERRED.
ROTH
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