817
FXUS02 KWBC 101820
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
219 PM EDT SUN AUG 10 2008
VALID 12Z WED AUG 13 2008 - 12Z SUN AUG 17 2008
MODELS AND ENSEMBLES STILL PAINT A QUITE SIMILAR AND AMPLIFIED
LONGWAVE PATTERN ALOFT OVER NOAM FOR THE UPCOMING WEEK...BUT STILL
OFFER SOME CONTINUITY DIFFERENCES WITH EMBEDDED SMALLER SCALE
WEATHER FEATURES. IN THIS PATTERN...A SUMMERTIME WRN NOAM RIDGE
BUILDS IN ADVANCE OF AN AMPLIFYING NE PAC TROUGH. A DEEP CYCLONE
DIGS SHARPLY FROM SW-CENTRAL CANADA INTO THE US TO THE LEE OF THE
RIDGE...LEADING TO A RETROGRESSION OF AN EARLY WEEK ERN NOAM
TROUGH BACK TO THE E-CENTRAL US. THE COOLING SYSTEM SHOULD ALSO
ACT TO FOCUS A LINGERING PERIOD OF POTENTIALLY LOCALLY HEAVY
RAINFALL AS DEEP GULF MOISTURE FEEDS/POOLS DOWNSTREAM. THE EXTENT
OF MID-UPPER LEVEL TROUGH/CLOSED LOW DIGGING DIFFERS BETWEEN
MODELS AND ENSEMBLES BUT THERE IS A CLEAR RECENT TREND TO FAVOR AN
INCREASINGLY AMPLIFIED SOLUTION. EVEN ACTING CONSERVATIVELY FOR
AUGUST...AN AMPLITUDE THAT DEVELOPS NEAR THE MIDDLE OF THE FULL
RANGE OF MODEL AND ENSEMBLE MEMBER SOLUTIONS WOULD STILL PRODUCE
QUITE A POTENT TROUGH WITH 500 MB HEIGHTS UPWARDS OF 3 STANDARD
DEVIATIONS BELOW NORMAL. THIS WOULD BE SIMILAR TO THE EARLY TO
MID AUGUST 2004 PATTERN. THIS SEEMS CONSISTENT AS PER EXPECTED
STRENGTH OF THE UPSTREAM RIDGE IN ALMOST ALL MODEL AND ENSEMBLE
RUNS. THIS TROUGH COULD EVEN PUMP UP DOWNSTREAM WESTERN ATLANTIC
RIDGING ENOUGH TO ALLOW FOR THE POSSIBILITY OF TROPICAL
DISTURBANCES NEAR THE GREATER ANTILLES/CARIBBEAN SEA.
THE MODELS ARE IN GOOD AGREEMENT ON THIS FLOW PATTERN SO HPC PROGS
REMAIN PRIMARILY DERIVED FROM A NEAR 50-50 BLEND OF THE 00 UTC GFS
AND 00 UTC ECMWF THAT HAD GOOD SUPPORT FROM THE 00 AND EVEN MORE
AMPLIFIED 06 UTC GFS ENSEMBLE MEAN AND THE 00 UTC ECMWF ENSEMBLE
MEAN. HOWEVER...THE FINAL HPC PROGS DID HEDGE THAT BLEND ABOUT
20% TOWARD THE 12 UTC GFS THAT IS TRENDING INCREASING TOWARD A
SOLUTION WITH DETAILS CLOSER TO THE 00 UTC ECMWF.
ROTH/SCHICHTEL
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