951
FXUS02 KWBC 291834
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
233 PM EDT TUE JUL 29 2008
VALID 12Z FRI AUG 01 2008 - 12Z TUE AUG 05 2008
...RECORD HIGHS POSSIBLE ACROSS THE OHIO VALLEY AND MID-ATLANTIC
STATES FROM LATE THIS WEEKEND INTO EARLY NEXT WEEK...
THE GENERAL FLOW PATTERN NEAR NORTH AMERICA REMAINS IN AGREEMENT
AMONGST THE GUIDANCE. A DEEP POLAR VORTEX IS EXPECTED TO LIFT
NORTHWARD TO THE NORTH OF ALASKA AND THE YUKON. TO THE EAST OF
THIS SYSTEM...RIDGING AS HIGH LATITUDES OF NORTH CENTRAL CANADA
LEADS TO A SUBSTANTIAL POSITIVE ANOMALY AT 500 HPA...WHICH IMPLIES
TO A PROGRESSIVE DEEP CYCLONE UNDER ITS BASE. THE MODELS DONT
DISAPPOINT...AND DETAIL ISSUES ARE BECOMING RESOLVED. FOR THE
MOST PART...A BLEND OF THE 00Z ECMWF/00Z NCEP ENSEMBLE MEAN WAS
USED FOR THE PRESSURES. SEE THE DISCUSSION BELOW FOR REGIONAL
DETAILS.
SYSTEM MOVING THROUGH SOUTHERN CANADA...
THE 00Z ECMWF IS A BIT QUICKER WITH THIS SYSTEM THAN THIS TIME
YESTERDAY...VERY CLOSE TO THE ECMWF AND GEFS ENSEMBLE MEAN
SOLUTIONS. THE 06Z GFS SLOWED WAS SLOWER DUE TO A DETAIL ISSUE IN
NORTHWEST CANADA...BUT HAS SINCE SPED UP TO THE ECMWF-LED CAMP.
IN FACT...THE 12Z GUIDANCE LOOKS SIMILAR TO THE ECMWF SOLUTION. A
BLEND OF THE 00Z ECMWF/00Z NCEP ENSEMBLE MEAN WAS USED FOR
PRESSURES WITH THIS SYSTEM...WHICH LED TO A VERY SLIGHT SLOWDOWN
WITH COLD FRONT PROGRESSION OVER THE NORTHERN TIER OF THE COUNTRY
COMPARED TO THE MANUAL PROGS FROM THIS TIME YESTERDAY.
OHIO VALLEY TO MID-ATLANTIC STATES AND CAROLINAS...
RIDGING SHIFTS FROM THE CENTRAL PLAINS INTO THE CENTRAL
APPALACHIANS BY THE END OF THE PERIOD. DOWNSLOPE FLOW SHOULD
ALLOW FOR TEMPERATURES TO CRACK THE CENTURY MARK...IN SOME PLACES
FOR THE FIRST TIME THIS SUMMER...FROM THE OHIO VALLEY INTO THE
MID-ATLANTIC STATES AND CAROLINAS. THIS IS TENTATIVE...AS THE
SPECTER OF AN MCS EMBEDDED WITHIN THE WEST TO WEST-NORTHWEST FLOW
IS POSSIBLE LATE IN THE PERIOD AS GULF MOISTURE FEEDS INTO THE
BOUNDARY ACROSS THE MIDWEST. TEMPERATURE-WISE IN THE MID-ATLANTIC
STATES LATE IN THE PERIOD...PER COORDINATION WITH THE MOUNT
HOLLY/PHILADELPHIA FORECAST OFFICE...THE NCEP ENSEMBLE MEAN/MEN
MOS WAS TOO MILD...AND A BLEND OF THE 06Z GFS AND 00Z ECMWF WAS
USED AS A STARTING POINT BEFORE MANUAL MODIFICATIONS WERE MADE.
SOUTHEAST...
THE 00Z ECMWF WAS AN OUTLIER CONCERNING ENERGY DROPPING OUT OF THE
WESTERLIES WHICH IS EXPECTED TO UNDERCUT THE WARM CORE RIDGE IN
THE CENTRAL PLAINS AND RETROGRADE THROUGH/NEAR THE NORTHERN GULF
COAST. USED A NON-ECMWF BLEND HERE...AND ADDED A WEAK LOW WHICH
RETROGRADES INLAND OF THE GULF COAST. DEPENDING UPON ITS LOCATION
OF FORMATION...IT COULD EITHER RETROGRADE ALONG THE GULF COAST OR
LIFT NORTHEAST ALONG THE LOWER EASTERN SEABOARD /A LOW PROBABILITY
ALTERNATIVE SCENARIO/ LATE THIS WEEKEND INTO EARLY NEXT WEEK.
EITHER WAY...THE EASTERN GULF COAST WILL SEE ENHANCED RAIN CHANCES
EARLY NEXT WEEK IN THE DIFLUENT/EASTERN SIDE OF THIS UPPER LEVEL
ENERGY. STAY TUNED.
ROTH
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