| PRELIMINARY EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 329 AM EDT TUE JUN 02 2009 VALID 12Z SAT JUN 06 2009 - 12Z TUE JUN 09 2009 THE LATEST MODEL CYCLE SHOWS GOOD LARGE-SCALE AGREEMENT THROUGH THE MEDIUM RANGE PERIOD...WITH THE OMEGA-BLOCK OVER THE NORTHEAST PACIFIC GIVING WAY TO A STRONG PACIFIC UPPER JET THAT ERODES THE RIDGE COMPONENT OF THE BLOCK AND ALLOWS FOR AN INCREASINGLY PROGRESSIVE SHORTWAVE PATTERN TO EVENTUALLY FORM OVER THE CONUS TOWARD THE LATTER HALF OF THE PERIOD. MULTI-MODEL ENSEMBLE MEANS ARE REMARKABLY SIMILAR...SHOWING A POSITIVELY-TILTED TROUGH EXTENDING FROM GREENLAND TO CALIFORNIA BY DAYS 6/7. HOWEVER...THE DETERMINISTIC RUNS VARY CONSIDERABLY WITH SOME OF THE DETAILS...MOST NOTABLY THE GFS...WHICH APPEARS UNUSUALLY STRONG OVER ALBERTA DAYS 3/4 WHILE DISAGREEING WITH ITS OWN ENSEMBLE MEAN...AND THE ECMWF...WHICH BECOMES A STRONG OUTLIER OVER PARTS OF THE NORTHEAST DAY 7. THUS....THE PREFERENCE IS FOR 100 PERCENT OPERATIONAL ECMWF DAY 3 WHEN CONFIDENCE IS HIGHEST...THEN TRANSITIONING TO 100 PERCENT GEFS MEAN BY DAY 7 WHEN CONFIDENCE IS LOWEST. JAMES EXTENDED FORECAST DISCUSSION NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD 236 PM EDT MON JUN 01 2009 VALID 12Z THU JUN 04 2009 - 12Z MON JUN 08 2009 THE CURRENT GUIDANCE ADVERTISES THE BREAKDOWN OF LARGE-SCALE BLOCK OVER THE EASTERN PACIFIC TOWARD THE MIDDLE OF THE MEDIUM RANGE PERIOD AND ALLOWING FOR MORE PROGRESSIVE FLOW TO PENETRATE INTO THE NORTHERN MID-LATITUDES. A FAIRLY PERSISTENT BROAD NEGATIVE ANOMALY STRETCHES EAST-WEST ACROSS SOUTHERN QUEBEC WHICH FAVORS TROUGHING NEAR CALIFORNIA AND A SUBTROPICAL RIDGE ACROSS THE SOUTHEAST...WHICH IS ALSO SUPPORTED BY THE SUBTROPICAL RIDGE CENTER NEAR 30N 140W. THIS SOLUTION IS MOST IN LINE WITH BOTH THE 00Z ECMWF AND 06Z GEFS MEAN...WHICH HAVE THE SUPPORT OF ONE-QUARTER OF THE 00Z GEFS MEMBERS AND ONE-QUARTER OF THE 00Z ECMWF ENSEMBLE MEMBERS. THE MORE PROGRESSIVE FLOW AT HIGHER LATITUDES IS EXPECTED TO PICK UP A PORTION OF THE UPPER LOW HOVERING OFF THE CALIFORNIA COAST...BUT THE PROGRESSION AND STRENGTH OF THE SOUTHERN STREAM ENERGY ESCAPING THE WESTERN TROUGH AND ITS PHASING WITH THE CANADIAN SYSTEM REMAIN UNCLEAR. THE 00z ECMWF/ITS ENSEMBLE MEAN ARE QUICKER IN EJECTING A MORE SUBSTANTIAL PIECE OF THE WESTERN TROUGH THAN THE 12Z ECMWF/06Z GFS/ITS ENSEMBLE MEAN. A 50/50 BLEND OF THE 00Z ECMWF/06Z GEFS MEAN CONTINUED TO BE USED TO CREATE THE PRESSURES/FRONTS THIS CYCLE WITH ABOVE AVERAGE CONFIDENCE INTO FRIDAY MORNING AND AVERAGE CONFIDENCE THEREAFTER TO ACCOUNT FOR THE FORECAST UNCERTAINTY. THIS SOLUTION KEPT GOOD CONTINUITY WITH THE EARLIER PRESSURES. CALIFORNIA/NORTHERN CONTINENTAL DIVIDE... TO THE NORTHEAST OF THE MAIN UPPER CYCLONE/TROUGH EXPECTED TO REMAIN NEAR CALIFORNIA THROUGH THE PERIOD MOST SIMILAR TO THE 12Z ECMWF/06Z AND 12Z RUNS OF THE GEFS MEAN...SOME ENERGY IS EXPECTED TO SHEAR OUT TO THE NORTHEAST ACROSS NORTHERN CALIFORNIA/OREGON/IDAHO/SOUTHWEST MONTANA THROUGH EARLY SATURDAY...WHICH SHOULD ALLOW FOR 1-2 INCH AREAL AVERAGE RAINFALL FOR THE REGION AS SHOWN BY THE 00Z ECMWF AND 06Z GEFS MEAN. LOCAL AMOUNTS IN THE SISKIYOU AND NORTHERN CONTINENTAL DIVIDE SHOULD BE HIGHER IN THE UPSLOPE REGIONS OF THE HIGHER TERRAIN. UPPER MIDWEST/UPPER MISSISSIPPI VALLEY/GREAT LAKES... MODERATE TO HEAVY RAINS ARE EXPECTED AS A SURFACE LOW TRACKS NORTHEAST FROM KANSAS TOWARDS THE GREAT LAKES THIS WEEKEND INTO EARLY NEXT WEEK. THE CURRENT PROGS SHOW AN ACCELERATED VERSION OF THE 00Z ECMWF SOLUTION...WHICH WAS ON THE SOUTHWEST FRINGE OF THE 00Z CANADIAN/ECMWF ENSEMBLE SPREAD WITH THIS CYCLONES POSITION AND TRACK. SOUTHEAST... THE FRONTAL WAVE POSITIONS USED FOR THE SYSTEM MOVING THROUGH THE REGION OFFSHORE NORTH CAROLINA SATURDAY MORNING ON OUR PROGS ARE SPLITTING THE DIFFERENCE OF MODERATE SPREAD SEEN IN THE 00Z MULTI-MODEL ENSEMBLE MEMBERS...WHICH IS A DEPARTURE OF THE BLEND OTHERWISE USED OVER THE REMAINDER OF THE LOWER 48. THIS SHOULD BE A WET SYSTEM FOR THE MID-SOUTH AND THE CAROLINAS AS IT INTERACTS WITH THE HIGH PRECIPITABLE WATER VALUES ANTICIPATED ACROSS THE GULF COAST AND LOWER PORTION OF THE EASTERN SEABOARD. ROTH/JAMES |