849
FXUS02 KWBC 061908
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
307 PM EDT WED AUG 06 2008
VALID 12Z SAT AUG 09 2008 - 12Z WED AUG 13 2008
MODELS AND ENSEMBLES SHOW AN INTERESTING AND COMPLEX FLOW REGIME
ACROSS NORTH AMERICA.
IN THIS FLOW...SRN LATITUDE IMPULSES INCLUDING RESIDUAL DEEP
TROPICAL MOISURE AND LOCAL RAINFALL THREAT FROM THE REMANANTS OF
EDOUARD ROTATE UP INTO THE WRN US AROUND THE WRN PERIPHERY OF AN
ESTABLISHED SW US RIDGE BEFORE CURVING EASTWARD OVER THE RIDGE
INTO THE CENTRAL US AND EXTENDING CONVECTIVE POTENTIAL. FARTHER
NORTH...PACIFIC SYSTEM ENERGY SLIDES INLAND TO CARVE OUT AN
UNSEASONABLY AMPLIFIED AND COOLING/PCPN FOCUSING MID-UPPER LEVEL
TROUGH THIS WEEKEND THAT MOST GUIDANCE SLOWLY TRACKS FROM SW
CAN/NW US TOWARD SOUTH-CENTRAL CANADA AND THE NRN PLAINS INTO
MIDWEEK. AN EVEN MORE NRN STREAM BRANCH SPLIT OVER NW CANADA
LEADS INTO A POTENTIALLY DEEP SRN HUDSON BAY VORTEX.
THE COMPLEX INTERACTION OF THESE FLOWS LEADS TO MORE PRONOUNCED
MODEL AND ENSEMBLE DIFFERENCES DOWNSTREAM FROM THE CENTRAL THROUGH
ERN US SUN-WED WITH RESPECT TO THE EXTENT OF IMPULSE DIGGING AND
THE ASSOCIATED DEPICTION OF LOWER LEVEL FRONTAL LOW AND ASSOCIATED
LEAD THEAT-E ADVECTION RETURN. WE REMAIN CONCERNED THAT THE 00
UTC ECMWF MAY BE DEVELOPING A MIDWEST TO NERN US SURFACE LOW AND
THETA-E ADVECTION/PCPN PATTERN TOO ROBUSTLY AND RECENT GFS RUNS
AND GFS ENSEMBLE GUIDANCE SUPPORT A MUCH MORE SUPRESSED SYSTEM
INTO THE LEAD AMPLIFIED ERN US MID-UPPER LEVEL TROF POSITION.
HOWEVER...00 UTC ECMWF ENSEMBLES REMAIN MUCH CLOSER TO A SMOOTHED
VERION OF THE 00 UTC ECMWF THAN ANY GFS/GEFS SOLUTION AND
YESTERDAYS 12 UTC ECMWF WAS NOT UNDULY INCONSISTENT WITH THE 00
UTC RUN. OVERALL...OPT FOR A MORE SOUTHWARD SUPPRESSED AND WEAKER
THAN 00 UTC ECMWF LOW TRACK IN THE FINAL HPC PROGS WITH THE
UNDERSTANDING THAT PREDICTABILY WITH THESE TYPES OF TRANSIENT
SMALLER SCALE SYSTEMS SIGNIFCANTLY ALTER THE LOCAL SENSIBLE
WEATHER FOCUS.
MY RESULTANT GUIDANCE BLEND OVER NOAM AND SURROUNDING OCEANS WAS
PRIMARILY DERIVED FROM ABOUT A 50-50 BLEND OF THE 00 UTC ECMWF AND
00 UTC ECMWF ENSEMBLES THAT SEEMED REASONABLE OVER THE W-CENTRAL
US...BUT WAS SIGNIFICANTLY MANUALLY ADJUSTED AFTERWARDS FROM THE
CENTRAL TO ERN US...ESPECIALLY WITH SURFACE DEPICTIONS AS
ADDRESSED ABOVE.
OVERALL...UNCERTAINTY REMAINS NEAR NORMAL OVER W-CENTRAL NOAM.
UNCERTAINTY REMAINS ABOVE NORMAL OVER THE EAST-CENTRAL US...BUT IS
BOLSTERED A BIT AS BOTH OF TODAYS NEW 12 UTC GFS/ECMWF RUNS SHOW
FAVORABLE TRENDS TOWARD OUR BLENDED SOLUTION SO MAINTAINING
CONTINUITY WITH THE HPC PROGS FINAL PACKAGE SEEMS PRUDENT.
SCHICHTEL
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