EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
205 PM EDT FRI JUL 03 2009
 
VALID 12Z MON JUL 06 2009 - 12Z FRI JUL 10 2009
 

FINAL FRONTS AND PRESSURES FOR DAYS 3 THROUGH 5 USED A BLEND OF
THE 00Z/03 ECMWF ENSEMBLE MEAN WITH THE 00Z ECMWF AND LESS
WEIGHTING ON THE 00Z GEFS MEAN.  ON DAYS SIX/SEVEN...THE BLEND
SWITCHED TO THE ECMWF ENSEMBLE MEAN/GEFS MEAN...WITH LESS
WEIGHTING ON THE 00 ECMWF AND 06Z GFS.  THE ECMWF AND GEFS MEAN
STANDARDIZED ANOMALIES SHOW THE HIGHER HEIGHTS PERSISTING NEAR
150W THROUGH THE PERIOD.  TELECONNECTIONS WITH THIS INDICATE A
TROUGH ALONG THE WEST COAST AND EAST COAST...WITH A RIDGE ACROSS
THE CENTRAL STATES.  THE MODELS ARE IN GOOD AGREEMENT WITH THIS
PATTERN.

THE 12Z GFS STILL INSISTS ON A FASTER DEPARTURE OF THE NORTHEAST
CUTOFF LOW. THE CANADIAN GLOBAL/UKMET HOLD IT IN PLACE LONGER. 
FOLLOWING SEVERAL RUNS WHERE THE GFS RAISED HEIGHTS TOO FAST IN
THE NORTHEAST...WE ARE NOT INCLINED TO USE THE 12Z GFS.  THE GFS
COMPOUNDED ISSUES BY OFFERING UNREALISTIC CIRCULATIONS FOLLOWING
CONVECTIVE EPISODES WITH UPPER DIVERGENCE/LOWER CONVERGENCE BULLS
EYES AND AN ARTIFICIAL LOWERING OF HEIGHTS 925-700 MB ACRS
MS-AL-GA DAYS THREE-FOUR AND ACROSS EASTERN MT-ND DAY SIX. 

PRIOR DISCUSSION...

EAST...
THE 00Z AND 06Z GFS...SHOW A FASTER DEPARTURE OF THE CLOSED LOW
OVER THE NORTHEAST DAYS THREE AND FOUR.  THIS LOOKS TO BE UNLIKELY
GIVEN THE BLOCKING DOWNSTREAM FROM THE CANADIAN MARITIME PROVINCES
INTO THE NORTH ATLANTIC..AND LACK OF AN UPSTREAM KICKER.  

DAYS SIX/SEVEN...THE SUBTROPICAL RIDGE OVER BOTH THE SOUTHWEST
ATLANTIC AND SOUTHERN PLAINS EXPANDS...GRADUALLY RAISING HEIGHTS
OVER THE SOUTHEAST.  CONSISTENT WITH THE UPSTREAM PATTERN...THE
NORTHEAST TROUGH DEAMPLIFIES DAYS SIX/SEVEN.  THE OPERATIONAL
ECMWF/GFS WERE A LITTLE FASTER MOVING THE TROUGH AXIS OFF THE
COAST THAN THE ECMWF/NCEP ENSEMBLE MEANS...WITH A BLEND USED TO
MITIGATE THE DIFFERENCES.  THE 06Z GFS AGREED WITH THE ECMWF
ENSEMBLE MEAN ON THE WAVE ALONG THE FRONT OFF THE SC COAST THU 09
JUL....THEN WEAKENING AND MOVING FURTHER OFFSHORE FRI. 

WEST...
THE MODELS ARE IN GOOD AGREEMENT IN SHOWING A PERSISTENT TROUGH
ALONG THE WEST COAST...WHICH SHOULD RESULT IN BELOW NORMAL
TEMPERATURES ACROSS MUCH OF THE PACIFIC NORTHWEST...NORTHERN GREAT
BASIN...AND NORTHERN ROCKIES. DEAMPLIFICATION OF THE LONGWAVE
PATTERN OVER THE NORTH PACIFIC OCCURS DAYS 6/7 THU 09 JUL TO FRI
10 JUL...WITH THE UPSTREAM RIDGE DECREASING IN AMPLITUDE.  THIS
RESULTS IN A GRADUAL DECREASE IN THE AMPLITUDE OF THE WEST COAST
TROUGH. 

THE 00Z GFS WAS AN OUTLIER IN SHOWING THE STRONGEST 850-500 MB LOW
EJECTING OUT OF THE PACIFIC NORTHWEST/NORTHERN ROCKIES WED 08 JUL
INTO SOUTH CENTRAL CANADA DAY 6 THU 09 JUL.  
THE 06Z GFS HAS BACKED OFF THIS SOLUTION AND IS NOW IN BETTER
AGREEMENT WITH THE 00Z UKMET/00Z ECMWF/00Z GEFS MEAN/00Z ECMWF
ENSEMBLE MEAN WITH THE TROUGH AMPLITUDE AND PHASING ACROSS THE
REGION.  THE CLUSTERING OF SOLUTIONS LEADS TO A BLEND OF THE ECMWF
ENSEMBLE MEAN/GEFS MEAN/00Z ECMWF/06Z GFS FOR DAYS SIX/SEVEN.  


CENTRAL US...
THE MODELS SHOW THE HIGH AMPLITUDE RIDGE OVER THE SOUTHWEST US
BUILDING EAST INTO THE SOUTHERN TO CENTRAL PLAINS...WITH GRADUAL
STRENGTHENING DAYS SIX/SEVEN THU 09 JUL FRI 10 JUL. THE ECMWF
MOVES THE 500 MB HIGH/ASSOCIATED RIDGE A LITTLE FURTHER NORTH THAN
THE 00Z ECMWF ENSEMBLE MEAN/00Z GEFS MEAN/06Z OPERATIONAL GFS. 
THE LATTER THREE SOLUTIONS CLUSTER BETTER AND THE GRADUAL
DEAMPLIFICATION OF THE WESTERN TROUGH NEXT THU-FRI STACKS THE ODDS
IN FAVOR OF LESS NORTHWARD EXPANSION OF THE MID LEVEL HIGH.  ONLY
4 OR 5 OF THE ENSEMBLE MEMBERS EXPAND THE 588 DM HEIGHT CONTOUR AS
FAR NORTH AS THE OPERATIONAL ECMWF THU 09 JUL AND FRI 10 JUL. THIS
PATTERN WOULD LEAD TO A HOT STRETCH ACROSS KS/OK/RED RIVER VALLEY.
 

PETERSEN