7/25 NWS Medium Range US Weather Outlook

By: National Weather Service
By: National Weather Service

EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
200 PM EDT SUN JUL 25 2010

VALID 12Z WED JUL 28 2010 - 12Z SUN AUG 01 2010

FINAL SEA LEVEL PRESSURES/FRONTS USED A BLEND OF THE 00Z ECMWF/06Z
GFS PARALLEL/00Z UKMET AND ENSEMBLE MEANS FROM THE ECMWF AND
00-12Z NCEP THROUGH DAY FIVE AND AN EVEN BLEND OF THE ECMWF/NCEP
ENSEMBLE MEAN MEANS DAYS SIX/SEVEN. MAJOR CHANGES IN THE GFS OVER
CANADA AND ADJACENT NORTHERN TIER OF STATES AND CONTINUING
DISAGREEMENTS WITH THE GFS PARALLEL AND ENSEMBLE MEAN LEAD TO A
CONTINUED RELIANCE ON THE MEAN UNTIL CLEARER RESOLUTION OF THE
ISSUES DEVELOPS. THE 12Z UKMET AND CANADIAN GLOBAL FALL WITHIN
THE ONGOING ENVELOPE OF SOLUTIONS...SO NO SIGNIFICANT CHANGES WERE
MADE.

MULTI-DAY MEANS REMAIN FAIRLY STABLE IN THEIR FCSTS OF THE LARGE
SCALE PATTERN...WITH TROFS NEAR THE WEST COAST AND OVER ERN
CANADA/NERN CONUS ALONG WITH A MEAN RIDGE PREVAILING ACROSS THE
GREAT BASIN/CENTRAL TO NORTHERN ROCKIES/SOUTHERN PLAINS.
MODEL/ENSEMBLE GUIDANCE DISPLAYS FAIRLY MINOR DIFFS THRU DAY 5
FRI. THERE IS SOME INCREASE IN SOLN SPREAD LATER IN THE PERIOD AS
ENERGY IS EXPECTED TO WEAKEN/EJECT FROM THE WEST COAST MEAN TROF.

COMPARING OPERATIONAL MODELS AND ENSEMBLES...THE 00Z CANADIAN
GLOBAL MODEL BECOMES AN AMPLIFIED EXTREME WITH THE 500 MB RIDGE IN
THE NORTHERN HIGH PLAINS SAT AND THEN THE NORTHERN PLAINS SUN 01
AUG. THE CANADIAN ENSEMBLE MEAN AGREES MUCH BETTER WITH THE
COMPOSITE MODEL AND ECMWF/NCEP ENSEMBLE MEAN CLUSTER WITH A LOWER
AMPLITUDE/LONGER WAVELENGTH RIDGE IN THE NORTHERN PLAINS.

FARTHER WESTWARD... THE 00-06Z GFS IS SHOWING A 500 MB TROUGH
EJECTING FROM THE WEST COAST TROUGH ALONG THE US/CANADIAN BORDER
STARTING IN THE NRN ROCKIES SAT AND THEN THE NORTHERN PLAINS SUN
01 AUG. THE 06Z GFS WAS AN OUTLIER WITH THE STRENGTH OF THE 500
MB CLOSED LOW IN WESTERN CANADA...AND THE 06Z GFS PARALLEL WAS IN
SHARP CONTRAST WITH A CLOSED LOW FURTHER WEST OFF THE BRITISH
COLUMBIA COAST 12Z SUN 01 AUG AND ANOTHER CLOSED LOW OVER WA/OR.
CONFIDENCE IS LOW IN THE GFS AND GFS PARALLEL HERE AS EACH ARE OUT
OF PHASE WITH THE ECMWF/NCEP/CANADIAN ENSEMBLE MEANS.

IN THE DESERT SOUTHWEST...THE 00Z ECMWF/00Z CANADIAN/06Z GFS/00Z
ECMWF ENSEMBLE MEAN SHOW A WEAKNESS IN THE 500 MB FLOW OVER THE
REGION...WITH AN INVERTED TROUGH MOVING WEST ACROSS THE REGION.
HIGH POOLED PW VALUES ARE FORECAST TO PERSIST NEAR THE AZ/CA
BORDER NEXT WEEKEND. THIS SUGGEST POTENTIAL FOR ENHANCED
MONSOONAL SHOWERS/STORMS NEXT WEEKEND.

GOOD CLUSTERING AMONG LATEST GUIDANCE FAVORS AN
OPERATIONAL/ENSEMBLE BLEND OF THE 06Z GFS PARALLEL/ECMWF/UKMET/00Z
GEFS MEAN/00Z ECMWF ENSEMBLE MEAN FOR DAYS 3-5 WED-FRI.
FOR DAYS SIX/SEVEN (SAT-SUN 31 JUL-01 AUG)...AN EVEN 50/50
WEIGHTING OF THE 00Z GEFS/00Z ECMWF ENSEMBLE MEANS WERE USED. THE
ECMWF WAS FLATTER WITH THE EAST COAST TROUGH BY SUN 01 AUG AND
TELECONNECTIONS FROM THE CENTRAL GREAT BASIN-CENTRAL ROCKIES
ANTICYCLONE SUPPORTS PERSISTENCE OF THE NORTHEAST US
TROUGH...WHICH IS BETTER REFLECTED IN THE ECMWF/GEFS MEAN
SOLUTIONS.

PETERSEN/RAUSCH


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