436
FXUS02 KWBC 141756
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
156 PM EDT MON JUL 14 2008
VALID 12Z THU JUL 17 2008 - 12Z MON JUL 21 2008
THE MODELS AND ENSEMBLES LIKE YESTERDAY OFFER REASONABLY SIMILAR
LARGER SCALE MID-UPPER LEVEL FLOW PATTERN FOR MUCH OF THE UPCOMING
WEEK FROM THE OCEANS THROUGH NORTH AMERICA...BUT DIFFER
SIGNIFICANTLY WITH MANY SMALL TO MID-SIZE DETAILS. THE MEAN
MEDIUM RANGE PATTERN ALOFT REMAINS BLOCKY AT HIGHER
LATITUDES...STILL COMPRISED OF TWO DEEP CLOSED LOWS CENTERED NEAR
AK AND THE ARCTIC AND A LESS ORGANIZED E-CENTRAL CANADA LOW/TROF
POSITION...ALL SANDWICHED AROUND AN AMPLIFIED NW CANADA RIDGE. A
DIET OF MORE TRANSIENT SMALLER SCALE SYSTEMS RIDE UNDERENATH AND
INLAND FROM THE PAC INTO A MEAN NW US/SW CAN MID-UPPER LEVEL
TROF...EJECT EWD ACROSS SRN CANADA AND THE N-CENTRAL US...THEN DIP
INCREASINGLY SEWD OVER TIME INTO A MID-UPPER LEVEL TROF SLOWLY
CARVING OUT FROM E-CENTRAL CAN INTO THE NERN US.
THE MAIN DIFFERENCES SURROUND SYSTEMS EXPECTED TO TRACK FROM SW
CANADA/NW US EASTWARD WHICH ARE EXPECTED TO LEAD TO A SLIGHT
AMPLIFICATION OF A DOWNSTREAM ERN NORTH AMERICAN TROUGH. RECENT
GFS RUNS HAVE HAD ISSUES WITH THIS SYSTEM EARLY ON...WITH THE 00
UTC RUN BRINGING IT TOO FAR SOUTH BASED ON TELECONNECTIONS WITH
THE RIDGE POSITION IN NORTHWEST CANADA...WHICH LED TO A SOLUTION
THAT WAS TOO SLOW. THE 12 UTC GFS HAS BACKED OFF ON THIS. WHILE
THE 00Z CANADIAN LOOKED REASONABLE ALOFT...ITS PRESSURES LEFT MUCH
TO BE DESIRED. THE ECMWF DIFFERED SOME FROM ITS ENSEMBLE MEANS
WITH THE MOVEMENT OF THIS SYSTEM...SO PREFER TO INSTEAD
INCORPORATE FRI-NEXT MON/DAYS 4-7 MORE OF A 50/50 BLEND OF THE 00Z
ECMWF/GFS ENSEMBLE MEANS TO INCREASINGLY SMOOTH OUT LESS
PREDICTABLE DIFFERENCES OVER TIME. THIS HAS LED TO GOOD HPC
CONTINUITY...WITH RESULTANT PRELIM AND NOW VERY SIMILAR FINAL HPC
GUIDANCE SOLUTIONS THAT ARE STILL CENTERED NEAR THE MIDDLE OF THE
VARIED FULL RANGE OF ALL MODEL AND ENSEMBLE MEMBER SOLUTIONS.
IN THIS PATTERN...SLOW MOVING BOUNDARIES NEAR THE SRN EDGE OF
THESE WESTERLIES WILL REMAIN A PRIME LOCATION FOR SIGNIFICANT
AFTERNOON/OVERNIGHT CONVECTION AND AN ACCOMPANING HEAVY RAINFALL
THREAT AS PER IMPULSE PASSAGE AND LOWER LEVEL INFLUX. THIS SEEMS
ESPECIALLY EVIDENT FROM THE N-CENTRAL PLAINS AND UPPER MIDWEST
INTO THE GREAT LAKES/NERN US. SUMMERTIME VORTS ARE EMBEDDED
FARTHER SOUTH WITHIN/AROUND MUCH WEAKER FLOW WITHIN HOTTER/MORE
CAPPED MID-LATITUDE RIDGING. LOCALLY HEAVY RAINFALL ENHANCING
FEATURES AND POOLED DEEP MOISTURE SEEM BEST CONCENTRATED EARLY ON
UNDERNEATH THIS RIDGE OVER THE SERN US/FL BUT WOULD BE VERY LEERY
WITH ANY INDIVIDUAL MODEL VORT CENTER. THERE IS ALSO A LINGERING
MONSOONAL FETCH UP THROUGH MEXICO INTO THE SW US UP THRU THE
S-CNTRL ROCKIES AROUND THE WRN PERIPHERY OF THE RIDGE TO COMPLETE
THE US RING OF FIRE PATTERN.
ROTH/SCHICHTEL
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