658
FXUS02 KWBC 231808
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
207 PM EDT WED JUL 23 2008
VALID 12Z SAT JUL 26 2008 - 12Z WED JUL 30 2008
MODEL AND ENSEMBLE DETAIL DIFFERENCES APPEAR GREATER THAN
YESTERDAY BUT IN GENERAL GUIDANCE CONTINUES TO SHOW REASONABLE
AGREEMENT WITH A PERSISTENT MEAN LONGER WAVE PATTERN INVOLVING A
NE PACIFIC/NWRN NORTH AMERICAN TROF...A CENTRAL NOAM RIDGE...AND
AN ERN NOAM TROF ALOFT.
OVERALL...THE DAYS 3-7 FCST CONTINUES TO USE A BLEND APPROACH TO
DEPICT A CONSENSUS SOLUTION THAT DOWNPLAYS UNCERTAIN DETAILS
WITHIN A WELL AGREED UPON MEAN PATTERN ALOFT WHOSE FULL ARRAY OF
SOLUTIONS HAVE BELOW NORMAL SPREAD FOR THIS TYPE OF PATTERN.
TODAY OUR PROGS HAVE BEEN PRIMARILY DERIVED FROM A NEAR 50-50
BLEND OF THE 00Z ECMWF AND 00 UTC GEFS MEAN FOR DAYS 3-4 SAT-SUN.
THEREAFTER FOR DAYS 5-7 MON-NEXT WED...THE 00 UTC ECMWF WAS
INSTEAD REPLACED WITH THE 00 UTC ECMWF ENSEMBLE MEAN THAT WAS
BLENDED 50-50 WITH THE 00 UTC GEFS MEAN TO MAINTAIN CONTINUITY
WITH A SLOWER SRN CANADA/NRN CONUS SURFACE FRONT.
..NWRN THRU N-CENTRAL US
ONE UNCERTAIN ASPECT OF THE FORECAST WITH THE POTENTIAL FOR A
LARGER SCALE EFFECT ON SENSIBLE WEATHER CONDITIONS IS IF A BUNDLE
OF SHRTWV ENERGY EJECTING FROM THE NERN PAC TROF WILL CROSS THE
NRN TIER CONUS/SRN CANADA AND APPROACH THE GRTLKS IN THE DAYS 5-7
MON-WED TIME FRAME...IN A MANNER SIMILAR TO WHAT IS EXPECTED TO
OCCUR IN THE SHORT RANGE PERIOD. THE 00Z ECMWF IS THE FASTEST
SOLUTION AND APPEARS TOO FAST TO BRING ITS ENERGY THRU THE MEAN
RIDGE. THE 00 UTC GFS/CANADIAN ARE SIMILAR AND SLOWER...BUT THE
06/12 UTC GFS RUNS ARE TRENDING SOMEWHAT FASTER. THUS FAR THE
GEFS/ECMWF ENSEMBLE MEANS WANT TO MAINTAIN THE CENTRAL NOAM RIDGE
TO A GREATER EXTENT THAN THE INDIVIDUAL RUNS OF THE
GFS/EC/CMC...WHICH LEADS TO THE ASSOCIATED NRN TIER CONUS SURFACE
FRONT BEING NOTICEABLY SLOWER IN THE ENSEMBLE MEANS. MODELS
HISTORICALLY HAVE SHOWN A BIAS TO BREAK ENERGY TOO ROBUSTLY
THROUGH RIDGES...ESPECIALLY AT MEDIUM RANGE TIME SCALES. GIVEN
CONTINUITY THAT HAS MAINTAINED A STRONG RIDGE ALOFT AND SLOWER
SURFACE FRONT SO FAR...WOULD STILL PREFER TO PRETTY MUCH HOLD ONTO
THAT IDEA EVEN WITH LATEST GFS TRENDS. HOWEVER...DID OPT TO NUDGE
THE FRONT A TAD FASTER IN THE FINAL PROGS KEEPING IN MIND GFS
TRENDS AND ALLOWING FOR A LINGERING POSSIBILITY THAT WEAK ENERGY
MAY BE ABLE TO PROGRESS ACROSS THE US NRN TIER UNDERNEATH MORE
BLOCKY CANADIAN FLOW.
..SW US INTO THE S-CENTRAL ROCKIES
GUIDANCE MEANWHILE SHOWS MORE DIFFERENCES REGARDING THE EXTENT TO
WHICH SOME MID-LEVEL ENERGY FROM HURCN DOLLY MAY SLOWLY LIFT INTO
THE SOUTHWEST/FOUR CORNERS REGION. THE ECMWF/CMC SUPPORT THIS
IDEA WHILE THE 00 UTC GFS DIVERTS MOST ENERGY WWD ACROSS NW
MEXICO. THE 00 UTC GFS DOES GENERATE A SEPARATE BUNDLE OF ENERGY
OVER THE CENTRAL ROCKIES AND VICINITY AND THE 06 UTC GFS AND
ESPECIALLY NOW THE 12 UTC GFS HAS CERTAINLY TRENDED TO BRING MORE
ENERGY UP INTO/ACROSS THE SW...LIKELY TOO QUICKLY. AT LEAST THE
TREND IF NOT THE TIMING TO BRING MORE ENERGY INTO THE SW US SEEMS
REASONABLE CONSIDERING THE LARGER SCALE FLOW AND RIDGE
POSITION/SHAPE ALOFT. THIS ACCORDINGLY SUPPORTS AN INCREASING
POTENTIAL FOR LOCALLY HEAVY DOWNPOURS WITH DEEPER REMNANT TROPICAL
MOISTURE.
..ERN US
MOST GUIDANCE DEVELOPS AND REINFORCES AN AMPLIFIED MID-UPPER LEVEL
TROF OVER THE ERN US THAT ALLOWS A WAVY AND LOCALLY SIGNIFICANT
CONVECTION FOCUSING FRONT SLIP DEEP AND HOLD SOUTH ACROSS THE
E-CENTRAL US FOR THIS TIME OF YEAR. I HAVE BEEN RELUCTANT TO GO
TOO FAR SOUTH WITH THE FRONT...BUT THERE SEEMS TO BE AMPLE
REINFORCING SUPPORT ALOFT FOR MUCH OF THIS FORECAST PERIOD. IN
THIS PATTERN...THE 00Z GFS FORECAST WAS DISCOUNTED OVER THE ERN
HALF OF THE CONUS BY THE LATTER HALF OF THE PERIOD DUE TO A
SEEMINGLY OVERDONE FEEDBACK ENHANCED WAVE THAT TRACKS THRU THE
SOUTHEAST AND THEN BECOMES QUITE VIGOROUS OVER THE MID-ATLANTIC
COAST DUE TO PHASING WITH NRN STREAM ENERGY. THE 06 AND 12 UTC
GFS RUNS NO LONGER DEVELOP THAT LOW AND THE FINAL PROGS DO NOT
PLACE LOCAL EMPHASIS ON ANY POTENTIAL FRONTAL WAVE WHOSE
PREDICTABILITY REMAINS VERY LOW.
RAUSCH/SCHICHTEL
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