EXTENDED FORECAST DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1202 PM EDT THU MAY 05 2016 VALID 12Z SUN MAY 08 2016 - 12Z THU MAY 12 2016 ...PATTERN OVERVIEW... LARGE-SCALE UPPER-LEVEL VORTICES ON BOTH THE WESTERN AND EASTERN U.S. ARE EXPECTED TO DEAMPLIFY AND LIFTS NORTHEASTWARD THROUGH EARLY NEXT WEEK. THIS WILL THEN EVOLVE INTO A REX BLOCK/SPLIT FLOW PATTERN AS A DEEP-LEVEL RIDGE OR CUTOFF HIGH FORMS INTO CENTRAL CANADA WHILE AN UPPER-LEVEL SHORTWAVE DIGS DOWN INTO THE NORTHERN ROCKIES THROUGH EARLY TO MIDDLE OF NEXT WEEK. A LOW PRESSURE WAVE MAY DEVELOP AS IT SWINGS ACROSS IN THE GREAT LAKES REGION BY NEXT THURSDAY BUT THE UNCERTAINTY REMAINS RELATIVELY HIGH IN THIS AREA. ...GUIDANCE EVALUATION/MODEL PREFERENCES... MODELS ARE IN BEST AGREEMENT HANDLING THE INITIAL UPPER LOW SLOWLY OPENING UP AND MOVING TOWARD THE PLAINS AND MID-MS VALLEY THROUGH THE MIDDLE OF NEXT WEEK. AS FOR THE EAST COAST LOW...THE ECMWF SOLUTION APPEARS A BIT TOO WEAK WHEREAS THE GFS SOLUTION APPEARS A BIT TOO STRONG AND TOO FAR SOUTH. THEREAFTER...OPERATIONAL MODELS ARE STILL TRYING TO RESOLVE THE DEGREE OF DEVELOPMENT REGARDING THE SHORTWAVE DIGGING DOWN FROM WESTERN CANADA AND EVENTUALLY SWINGING EASTWARD INTO THE NORTHERN PLAINS. EVEN THE ENSEMBLE MEANS HAVE NOT QUITE SETTLED INTO A STEADY SOLUTION REGARDING THIS FEATURE. NEVERTHELESS...IN A BROADER SCALE...A LOW PRESSURE WAVE/SYSTEM SHOULD CONTINUE TO MOVE ACROSS THE MIDWEST INTO THE GREAT LAKES THROUGH THE MIDDLE OF NEXT WEEK. THE DETERMINISTIC 00Z ECMWF IS TAKEN OUT OF CONSIDERATION FROM DAY 5/TUE AND BEYOND AS IT SHOWS AN ANOMALOUS UPPER LOW ROTATING SOUTH FROM CANADA...RESULTING IN ANOMALOUS DEVELOPMENT OF THE LOW PRESSURE WAVE. THE 06Z GFS IS TAKEN OUT OF CONSIDERATION BY DAY 5 AS WELL...AS THE POSITION OF THE LOW IN THE PLAINS APPEARS TO FAR NORTH. THUS THE WPC BLEND BEGINS WITH THE 00Z ECMWF...AND 06Z GFS MIXING IN WITH THE RESPECTIVE ENSEMBLE MEANS FOR DAYS 3 AND 4 FOLLOWED BY TRENDING HEAVILY TOWARD THE EC MEANS THROUGH DAY 7. ...WEATHER HIGHLIGHTS/THREATS... AHEAD OF THE UPPER LOW BARRELING THROUGH THE SOUTHERN HIGH PLAINS...EXPECT A ROBUST AREA OF CONVECTION EXTENDING ACROSS THE SOUTHERN/CENTRAL PLAINS WITH SEVERE WEATHER POSSIBLE GIVEN THE LATEST SPC OUTLOOKS. UNDERNEATH THE CLOSED LOW ITSELF...STEEP MID-LEVEL LAPSE RATES WILL FAVOR ABUNDANT SHOWERS ACCOMPANIED BY BELOW NORMAL TEMPERATURES ON THE ORDER OF THE 5 TO 10 DEGREE DEPARTURES FROM CLIMATOLOGY. ADDITIONALLY...A WEST-EAST AXIS OF PRECIPITATION IS LIKELY FROM THE CENTRAL PLAINS BACK TOWARD THE OH VALLEY AS A FRONTAL ZONE MEANDERS ACROSS THE REGION. WITHIN THE AMPLIFIED NORTHERN STREAM...COOL AND UNSETTLED CONDITIONS ARE LIKELY UNDERNEATH THE INFLUENCE OF LOWER HEIGHTS ALOFT ACROSS NEW ENGLAND. FARTHER UPSTREAM...THE AFOREMENTIONED UNCERTAINTIES ACROSS THE NORTH-CENTRAL U.S. MAKES THE FORECAST CHALLENGING BUT MODELS DO SUPPORT A MARKED INCREASE IN PRECIPITATION THREATS FOR MUCH OF EARLY/MID NEXT WEEK. MEANWHILE...ACROSS THE WEST COAST...TRANQUIL CONDITIONS WILL BE FAVORED GIVEN THE BUILDING MID-LEVEL HEIGHTS. KONG/RUBIN-OSTER