MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1127 PM EST MON DEC 28 2015 VALID DEC 29/0000 UTC THRU JAN 01/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...CLOSED LOW EXITING OUT OF THE MIDWEST AND THROUGH THE GREAT LAKES... ...SURFACE CYCLONE CROSSING THE GREAT LAKES... ...SURFACE LOW REDEVELOPMENT NEAR SOUTHERN NEW ENGLAND... PREFERENCE: GENERAL MODEL COMPROMISE...WITH LOW OVER THE GREAT LAKES 00Z GFS...WITH LOW NEAR SOUTHERN NEW ENGLAND CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN GOOD AGREEMENT IN TAKING THE CURRENT DEEP CLOSED LOW OVER THE MIDWEST OFF TO THE NORTHEAST OVER THE GREAT LAKES REGION ON TUES AND THEN WEAKENING IT RATHER RAPIDLY BY LATE IN THE DAY AS THE SYSTEM ENTERS A LARGER SCALE CONFLUENCE ZONE OVER SOUTHEAST CANADA AND NORTHERN NEW ENGLAND. THIS WILL ALLOW THE SURFACE LOW TO WEAKEN...BUT THE REMNANT ENERGY ALOFT SHOULD FOCUS SURFACE LOW REDEVELOPMENT JUST OFF SOUTHERN NEW ENGLAND BY MIDDAY TUES. THE MODELS ARE IN EXCELLENT AGREEMENT WITH THE DETAILS OF THE SURFACE LOW MOVING THROUGH THE GREAT LAKES...BUT WITH THE DEVELOPMENT NEAR SOUTHERN NEW ENGLAND...THE 00Z NAM IS A BIT OF A FASTER OUTLIER...WITH THE 12Z ECMWF THE SLOWEST SOLUTION. THE 00Z GFS OFFERS A NICE COMPROMISE WITH THIS SYSTEM NEAR NEW ENGLAND...OTHERWISE A GENERAL MODEL COMPROMISE WILL BE PREFERRED OVER THE GREAT LAKES REGION. ...SHORTWAVE TROUGH/FRONT MOVING INTO THE WEST SUN THROUGH TUES... ...CLOSED LOW DEVELOPMENT OVER THE GREAT BASIN BY TUES... ...SYSTEM EJECTING OUT INTO THE PLAINS/UPPER MIDWEST BY WED... ...WEAK MID-ATLANTIC COASTAL DEVELOPMENT THURS MORNING... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE A SHORTWAVE CURRENTLY OVER THE SOUTHERN GREAT BASIN CONTINUES TO DIG SOUTHEAST AND WILL BOTTOM OUT ACROSS THE AZ/NM/MEXICAN BOARDER TUES AFTERNOON BEFORE EJECTING PROGRESSIVELY INTO THE CENTRAL/SOUTHERN PLAINS TUES NIGHT. THEREAFTER THE ENERGY WILL SHEAR NORTHEAST INTO THE MIDWEST AND GREAT LAKES REGION THROUGH WED. THERE WILL BE A WEAK AREA OF LOW PRESSURE DEVELOPING NEAR THE GREAT LAKES ON WED AND SOME WEAK SECONDARY CYCLOGENESIS ALONG A FRONTAL ZONE OVER THE MID-ATLANTIC STATES. THE MODELS ARE IN GOOD AGREEMENT WITH THIS EVOLUTION AND SO A GENERAL MODEL COMPROMISE WILL BE PREFERRED. ...COMPACT SHORTWAVE MOVING INTO THE PACIFIC NORTHWEST... ...LARGER SCALE TROUGH OVER THE ROCKIES/NORTHERN PLAINS/MIDWEST... PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS SHOW A FAIRLY COMPACT SHORTWAVE AND SMALL CLOSED SFC LOW CENTER MOVING INTO THE PACIFIC NORTHWEST TUES NIGHT JUST IN ADVANCE OF SOME LINGERING NORTHERN STREAM ENERGY OVER SOUTHWEST CANADA. THE COMBINATION OF THIS ENERGY WILL REINFORCE A LARGER SCALE TROUGH OVER THE ROCKIES AND ACROSS THE NORTHERN PLAINS THROUGH WED AND THURS. THE 12Z UKMET TENDS TO BE SOMEWHAT WEAKER/FLATTER WITH THE ENERGY CROSSING THE NORTHERN PLAINS AND MIDWEST BY THURS...WITH THE 00Z NAM OVERALL A BIT DEEPER AND INCLUDING THE SOUTHWEST EXTENSION OF ENERGY DROPPING DOWN TOWARD THE CENTRAL ROCKIES BY EARLY THURS. STRONGER MODEL CLUSTERING WOULD SUGGEST BLENDING THE 00Z GFS AND 12Z ECMWF...AND THIS WILL BE THE PREFERENCE. ...POSSIBLE REX BLOCK DEVELOPMENT OVER THE WEST THURS AND FRI... PREFERENCE: 00Z GFS CONFIDENCE: AVERAGE THE MODELS TAKE SOME OF THE ENERGY THAT DIGS THROUGH THE NORTHWEST ON WED DOWN THROUGH THE ROCKIES AND ATTEMPTS TO PINCH OFF SOME OF IT OVER THE INTERMOUNTAIN REGION AS A STRONG RIDGE DEVELOPS OFF THE WEST COAST AND THEN MOVES INTO THE PACIFIC NORTHWEST AND SOUTHWEST CANADA BY LATE THURS. THE 12Z UKMET SUGGESTS ENOUGH ENERGY PINCHING OFF OVER THE ROCKIES FOR A CLOSED MID LEVEL LOW CENTER TO DEVELOP UNDERNEATH THE STRONG RIDGING TO THE NORTH. THE 00Z GFS/12Z CMC AND 12Z ECMWF ALSO SUGGEST THIS AS WELL BUT WITH A SOMEWHAT WEAKER VERSION OF IT. THE 00Z NAM IS LESS DEFINED BUT STILL HAS A SUBSTANTIAL AMOUNT OF TROUGHING THAT EXTENDS BACK TO THE SOUTHWEST OVER THE GREAT BASIN. THERE ARE DIFFERENCES BY FRI WITH WHERE THE FOCUS OF THE ENERGY WILL BE...AS THE UKMET IS FARTHEST SOUTH...AND THE ECMWF/NAM AND CMC ARE FARTHER NORTH. THE GFS SPLITS THE DIFFERENCE AND WILL BE THE PREFERENCE AT THIS TIME. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON