MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 242 PM EDT TUE APR 12 2016 VALID APR 12/1200 UTC THRU APR 16/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION...INCLUDING THE UKMET/CMC/ECMWF ...UPPER TROUGH TRACKING ACROSS THE GREAT LAKES/NORTHEAST... ...ASSOCIATED SURFACE LOW/COLD FRONT... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 12Z ECMWF LARGELY KEPT PACE WITH ITS SLIGHTLY SPED UP RUN FROM 12/00Z AND IT WAS CLOSE TO THE MODEL CONSENSUS. THIS IS ALSO TRUE OF THE ASSOCIATED COLD FRONT EJECTING ACROSS THE NORTHEAST DURING THE DAY TODAY. WILL CONTINUE TO PREFER A GENERAL MODEL COMPROMISE AS A RESULT. ...UPPER LOW CURRENTLY OVER THE SOUTHWEST... ...ENERGY SHEARING EAST/NORTHEAST OVER THE NEXT COUPLE OF DAYS... PREFERENCE: 12/12Z ECMWF CONFIDENCE: ABOVE AVERAGE...THROUGH 36 HOURS BELOW AVERAGE...AFTER 36 HOURS THERE IS GOOD MODEL AGREEMENT ON THE SYNOPTIC SCALE WITH THIS NEXT UPPER LOW TRAVERSING THE SOUTHWEST AND SOUTHERN ROCKIES BEFORE THE GUIDANCE SLOWS THE ENERGY DOWN LATER TONIGHT AS IT MOVES THROUGH THE SOUTHERN PLAINS AND INTO THE LOWER/MID MS...EVENTUALLY REACHING THE TN VALLEYS ON THURS. THERE IS VERY GOOD AGREEMENT WITH THE TIMING OF THE HEIGHT FALLS THROUGH THE PERIOD...BUT THERE ARE SOME NOTABLE DIFFERENCES WITH DEPTH...AND ESPECIALLY WITH A WEAK SURFACE REFLECTION OVER THE GULF COAST STATES BY WED AND THURS. NOT MUCH CHANGED IN THE 12/12Z MODEL RUNS IN TERMS OF THE NAM HAVING A SYSTEM MAKING ITS WAY ALONG THE GULF COAST WHICH IS REFLECTED BY A STRONGER SURFACE LOW AND PCPN BEING PULLED NORTH OF OTHER MODELS. AT THE SAME TIME...SFC PRESSURES FROM THE GFS RUN SOME 3 TO 5 MB HIGHER THAN THE ECMWF/SREF/NAM ACROSS THE SOUTHEAST. THE 12/12Z RUN OF THE ECMWF WORKS AS COMPROMISE IN TERMS OF POSITION AND STRENGTH. ...UPPER LOW IN THE GULF OF AK... ...SHORTWAVES AIMING FOR THE PACIFIC NORTHWEST... ...DEEPENING TROUGH OVER THE WEST BY THURS/FRI... PREFERENCE: BLEND OF THE 12/12Z CMC AND 12/12Z UKMET CONFIDENCE: AVERAGE...THROUGH 30 HOURS BELOW AVERAGE...AFTER 36 HOURS THERE IS PRETTY GOOD MODEL AGREEMENT THAT A SHORTWAVE TROUGH AND ASSOCIATED SURFACE COLD FRONT MOVING INTO THE PACIFIC NORTHWEST TODAY. THERE IS BROAD AGREEMENT THAT A STRONGER SHORTWAVE WILL ROUND THE BASE OF THE UPPER LOW OVER THE GULF OF AK BY THIS EVENING AND ALL OF THE MODELS SHOW THIS SHORTWAVE AMPLIFYING INTO A ROBUST UPPER LOW THAT WILL IMPACT THE PACIFIC NORTHWEST BY THURS AND DIG INTO THE INTERMOUNTAIN WEST BY FRI. THE TIMING AND DEPTH DIFFERENCES WIDEN LATER THIS EVENING OR EARLY WEDNESDAY. WHILE THE GFS SPED UP A BIT COMPARED WITH ITS 12/00Z RUN IT REMAINED ON THE SLOW SIDE OF THE GUIDANCE WHILE THE 12/12Z ECMWF REMAINED ON THE EASTERN/FASTER SIDE OF THE GUIDANCE. CONSIDERING THAT A SLOW GFS/FAST ECMWF IS AT ODDS WITH THEIR TYPICAL BIASES...WE TENDED TO RESORT TO THE UKMET AND THE ENSEMBLE MEANS. THE NEW NAM WAS SIMILAR TO THE PREVIOUS CANADIAN..BUT IT STILL APPEARS TO FOCUS TOO MUCH ENERGY OUTSIDE THE OF THE GREAT BASIN. SPLITTING THE DIFFERENCE IN SPACE TENDED TO BE A REASONABLE COMPROMISE POSITION BETWEEN THE EC ENSEMBLES/GEFS MEAN/UKMET. ...SURFACE LOW ACROSS THE HIGH PLAINS BY THURS/FRI... PREFERENCE: BLEND OF THE 12Z GFS/CMC/UKMET CONFIDENCE: BELOW AVERAGE THE GFS STILL DEVELOPS AN ELONGATED AXIS OF LOW PRESSURE IN THE LEE OF THE CENTRAL/NORTHERN ROCKIES BY THURS...WITH LOW PRESSURE ATTEMPTING TO PUSH FARTHER EAST ON FRI INTO THE CENTRAL AND NORTHERN PLAINS. THIS LOW PRESSURE AXIS IS TIED INTO THE STRONG HEIGHT FALLS OVER THE WESTERN U.S. BY THIS PERIOD. THE 00Z NAM AND 00Z ECMWF ARE LIKELY DISPLACING THEIR LOW DEVELOPMENT TOO FAR NORTH BY EARLY FRI. THE 12Z GFS/CMC/UKMET SOLUTIONS CONTINUE TO HAVE BETTER ENSEMBLE SUPPORT...AND THIS CONSENSUS WILL BE PREFERRED BUT WITH LIMITED CONFIDENCE. ...ENERGY AMPLIFYING INTO THE NORTHEAST/MID-ATLANTIC BY THURS... PREFERENCE: NON-UKMET CONSENSUS CONFIDENCE: ABOVE AVERAGE THE MODELS TAKE A WEAK SHORTWAVE CURRENTLY CROSSING THROUGH SOUTHWEST CANADA AND GRADUALLY AMPLIFY THE ENERGY ACROSS THE EASTERN GREAT LAKES/MID-ATLANTIC AND NORTHEAST THROUGH THURS. OVERALL...THE 12Z UKMET REMAINS A SLOWER AND DEEPER OUTLIER SOLUTION WITH THE TROUGH EVOLUTION OF THE FEATURE AT THE SURFACE AND ALOFT. THE REMAINING MODELS ARE IN GOOD AGREEMENT WITH TIMING AND DEPTH...AND SO WILL CONTINUE TO PREFER A NON-UKMET CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... BANN