MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1228 PM EDT FRI APR 25 2014 VALID APR 25/1200 UTC THRU APR 29/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE NAM ANS GFS ...SHORTWAVE TROUGH/SURFACE LOW IMPACTING THE OH/TN VALLEYS/MID-ATLANTIC/NORTHEAST... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: ABOVE AVERAGE A SHORTWAVE TROUGH AND SFC LOW NOW MOVING ACROSS THE OH/TN VLYS WILL ADVANCE PROGRESSIVELY EASTWARD TODAY AND MOVE THROUGH THE NRN MID-ATLANTIC AND THE NORTHEAST TONIGHT THROUGH EARLY SAT. THE MODELS AGAIN ADVERTISE THIS SYS WEAKENING AND DAMPENING OUT BY LATE SAT IN FAVOR OF STRONGER UPSTREAM HEIGHT FALLS APPROACHING. OVERALL THERE IS VERY GOOD MODEL AGREEMENT ON THE LARGER SCALE WITH THE SHORTWAVE EVOLUTION AN ATTENDANT SFC LOW. HOWEVER...THE 12Z NAM DOES FOCUS SFC LOW PRESSURE NEAR THE DELMARVA AND OFFSHORE SRN NEW ENGLAND OVERNIGHT A BIT TO THE NORTH OF THE GLOBAL MODEL CONSENSUS. WILL PREFER A NON-NAM CONSENSUS AS A RESULT. ...SHORTWAVE TROUGH/CLOSED LOW ADVANCING FROM THE UPPER MIDWEST TO THE NORTHEAST... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: ABOVE AVERAGE THE MODELS SHOW A SHORTWAVE TROUGH AND ASSOCD CLOSED LOW CURRENTLY OVER THE UPR MIDWEST ADVANCING EASTWARD OVER THE NEXT COUPLE OF DAYS THROUGH THE GRT LAKES AND NORTHEAST. THE 12Z NAM IS A LITTLE SHARPER AND FASTER WITH HEIGHT FALLS OVERSPREADING ESP THE NORTHEAST ON SAT. GIVEN STRONG MODEL CLUSTERING ASIDE FROM THE NAM...WILL PREFER A NON-NAM CONSENSUS. ...DEEP UPPER TROUGH/CLOSED LOW CROSSING THE SOUTHWEST/FOUR CORNERS REGION THIS WEEKEND... ...POWERFUL SURFACE LOW DEVELOPING ACROSS THE MIDDLE OF THE U.S... PREFERENCE: 00Z ECMWF/00Z GEM COMPROMISE CONFIDENCE: AVERAGE THE DEEP LAYER FLOW IS AGAIN EXPECTED TO AMPLIFY SHARPLY ACROSS THE SOUTHWESTERN U.S. BY EARLY THIS WEEKEND AS STRONG SHORTWAVE/JET ENERGY DIGS IN OFF THE ERN PAC OCEAN AND ACROSS CA. THERE IS VERY STRONG MODEL AGREEMENT IN EJECTING THIS AMPLIFYING TROUGH INTO THE FOUR CORNERS REGION ON SAT AND THEN THE HIGH PLAINS ON SUN BY WHICH TIME THE UPPER TROUGH WILL HAVE GONE NEG-TILT AND CLOSED OFF. ON MON...MOST OF THE MODELS INDICATE A DEEP CUT-OFF LOW THAT WILL BE FOCUSED OVER THE CNTRL U.S. AND SOUTH OF A VERY STRONG RIDGE CLOSING OFF OVER SRN CANADA NEAR HUDSON BAY. THIS WILL MAKE UP A STRONG REX BLOCK AND THE MODELS HAVE BEEN INSISTING IN THIS FOR SOME TIME NOW. MODEL DISAGREEMENT BEGINS BY EARLY SUN OVER THE CNTRL ROCKIES/HIGH PLAINS WHEN THE 12Z NAM BEGINS TO SUGGEST A STRONGER SOLN OVERALL VS THE GLOBAL MODEL CONSENSUS. THE 00Z UKMET ALSO BEGINS TO DEVIATE IN SUGGESTING A MUCH MORE POLEWARD ADVANCE OF THE CLOSED LOW/TROUGH. THE 12Z GFS ALSO TENDS TO LIFT ITS CLOSED LOW A BIT FARTHER NORTH...BUT NOT TO THE EXTENT OF THE UKMET. AT THE SFC...ALL OF THE MODELS SUGGEST A STRONG SFC LOW DEVELOPING IN THE LEE OF THE CNTRL ROCKIES...WITH LOW PRESSURE GRADUALLY ADVANCING EAST AND APPROACHING THE MIDWEST BY LATE MON. THE NAM AND UKMET TAKE THEIR SFC LOW CENTERS FARTHEST EAST BY LATE MON. THE 00Z ECMWF AND 00Z GEM CLUSTER MORE STRONGLY AT THE SFC AND ALOFT WITH LOW PRESSURE FOCUSED MORE OVER THE CNTRL PLAINS INVOF OF NEB. THE LATEST GEFS MEAN AND ECENS MEAN TEND TO FAVOR THE ECMWF/GEM CLUSTER AND SO THIS WILL BE FAVORED. ...SHORTWAVE TROUGH EDGING INTO THE NORTHWEST SAT AND SUN... PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: ABOVE AVERAGE ALL OF THE MODELS INDICATE A NEW PACIFIC TROUGH AND AN ASSOCD COLD FRONT GRADUALLY ADVANCING EAST INTO THE NORTHWEST THIS WEEKEND. ON THE LARGER SCALE THERE IS VERY GOOD AGREEMENT...BUT THE 12Z NAM DOES GRADUALLY TEND TO BE A BIT STRONGER THAN THE GLOBAL MODEL CONSENSUS WITH THE HEIGHT FALLS. WILL PREFER A NON-NAM CONSENSUS WITH THIS SYS. www.wpc.ncep.noaa.gov/html/model2.shtml... ORRISON