154
FXUS02 KWBC 171855
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
255 PM EDT MON AUG 17 2009
VALID 12Z THU AUG 20 2009 - 12Z MON AUG 24 2009
PRELIMINARY UPDATE...
USED THE 00Z/17 ECMWF TO UPDATE THE PRELIMINARY FRONTS AND
PRESSURES FOR DAYS 3 AND 4...WITH A PROGRESSIVE BLEND TOWARD THE
00Z/17 EC ENSEMBLE MEAN THEREAFTER. THIS COMBINATION HAS PROVED
TO BE A SKILLFUL ONE THIS WARM SEASON FOR SURFACE PRESSURES ACROSS
THE CONTIGUOUS UNITED STATES...SOUTHERN CANADA...AND NORTHERN
MEXICO. THE GFS AND GEFS MEAN HAVE NOT SCORED AS WELL...WITH POOR
RUN TO RUN CONTINUITY IN THE DETERMINISTIC GFS FURTHER DIMINISHING
ITS USEFULNESS. A RECENT EXAMPLE OF THE GFS INSTABILITY IS ITS
HANDLING OF THE TROPICAL CYCLONES CURRENTLY OVER THE ATLANTIC.
JUST A FEW DAYS AGO...THE GFS WAS DIRECTING AT LEAST ONE OF THESE
SYSTEMS INTO THE GULF OF MEXICO AND EASTERN STATES...WITH LITTLE
EVIDENCE OF THE SIGNIFICANT NORTHERN STREAM TROUGH THE GUIDANCE
HAS FINALLY CONVERGED UPON CROSSING THE EASTERN GREAT LAKES.
FOR THIS PARTICULAR FORECAST...THE STRENGTH AND TRACK OF THE
SHORTWAVE THE 00Z/17 ECMWF SENDS ALONG THE CANADIAN BORDER OVER
THE NORTHERN PLAINS LATE IN THE PERIOD IS PERHAPS THE MOST
CONTENTIOUS FEATURE. THIS IMPULSE IS NOT CARRIED BY THE OTHER
DETERMINISTIC MODELS...AND WAS NOT PRESENT IN THE 12Z/16 ECMWF
RUN. IT WAS...HOWEVER...IN THE 00Z/16 ECMWF SOLUTION. THE 00Z/17
EC ENSEMBLE MEAN DOWNPLAYS ITS AMPLITUDE...WHICH HOPEFULLY WILL
AFFORD A ROBUST CORRECTIVE IN THE MANUAL BLEND CHOSEN FOR THIS
UPDATE PACKAGE.
FINAL...
THE 12Z/17 ECMWF TRENDED TOWARD THE 00Z/17 EC ENSEMBLE MEAN DAYS 5
THROUGH 7...WITH A MORE POSITIVELY TILTED TROUGH OVER THE MIDWEST
DAY 5...AND LESS AMPLITUDE WITH THE SHORTWAVE PASSING ALONG THE
CANADIAN/NORTH DAKOTA BORDER DAY 7. THE INCORPORATION OF A
SUBSTANTIAL CHUNK OF THE OLD MEAN IN THE UPDATE PACKAGE COVERED
THESE DIFFERENCES ADEQUATELY...SO MADE NO CHANGES FOR THE FINAL
ISSUANCE. THE GFS IS STILL NOT ON THE SAME PAGE WITH THE TIMING
AND WAVELENGTH OF THE BIG TROUGH CROSSING THE EAST.
CISCO
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page