MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1235 AM EDT TUE APR 12 2016 VALID APR 12/0000 UTC THRU APR 15/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...INCLUDING THE NAM AND GFS ...UPPER TROUGH TRACKING ACROSS THE GREAT LAKES/NORTHEAST... ...ASSOCIATED SURFACE LOW/COLD FRONT... PREFERENCE: GENERAL MODEL COMPROMISE CONFIDENCE: ABOVE AVERAGE THE 12Z ECMWF IS A TAD SLOWER THAN THAN THE MODEL CONSENSUS WITH THE TROUGH EJECTING ACROSS THE NORTHEAST ON TUES...BUT THERE IS FORTUNATELY GOOD AGREEMENT WITH THE TIMING OF THE SURFACE LOW AND ASSOCIATED COLD FRONT SWEEPING THROUGH THE MID-ATLANTIC AND NEW ENGLAND. WILL PREFER A GENERAL MODEL COMPROMISE. ...REMNANT SHORTWAVE/SURFACE LOW CROSSING THE SOUTH... PREFERENCE: NON-CMC CONSENSUS CONFIDENCE: ABOVE AVERAGE A WEAK SHORTWAVE CROSSING THE SOUTHERN PLAINS WHICH IS THE REMNANT OF THE MOST RECENT CLOSED LOW OVER THE SOUTHWEST WILL CONTINUE TO SHEAR EASTWARD OVER THE NEXT DAY OR SO ACROSS THE GULF COAST STATES. THE 12Z CMC SOLUTION IS THE WEAKEST/FLATTEST SOLUTION WITH THIS ENERGY. THE 00Z NAM/00Z GFS/12Z UKMET AND 12Z ECMWF ARE ALL CLUSTERED AROUND A STRONGER EVOLUTION BY COMPARISON AND HAVE BETTER ENSEMBLE SUPPORT. WILL LEAN TOWARD A NON-CMC CONSENSUS AS A RESULT. ...UPPER LOW CURRENTLY OVER THE SOUTHWEST... ...ENERGY SHEARING EAST OVER THE NEXT COUPLE OF DAYS... PREFERENCE: BLEND OF THE 00Z ECMWF AND 12Z ECENS MEAN CONFIDENCE: ABOVE AVERAGE...THROUGH 48 HOURS BELOW AVERAGE...AFTER 48 HOURS THERE IS GOOD MODEL AGREEMENT ON THE SYNOPTIC SCALE WITH THIS NEXT UPPER LOW TRAVERSING THE SOUTHWEST AND SOUTHERN ROCKIES THROUGH TUES. THEREAFTER THE GUIDANCE SLOWS THE ENERGY DOWN IT MOVES THROUGH THE SOUTHERN PLAINS AND INTO THE LOWER/MID MS AND TN VALLEYS BY 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. THE 12Z UKMET OVERALL IS THE WEAKEST SOLUTION ALOFT...WITH THE 00Z NAM/00Z GFS/12Z UKMET AND 12Z ECMWF ALL FAVORING A SLIGHTLY DEEPER UPPER LOW OVER THE LOWER/MID MS AND TN VALLEYS BY THE END OF THE PERIOD. AT THE SURFACE...THE 00Z NAM SUGGESTS A STRONGER WAVE IMPACTING MS/AL BY WED AND THURS...WITH THE 00Z GFS THE FLATTEST. THE 12Z UKMET/12Z CMC AND 12Z ECMWF SPLIT THE DIFFERENCE. THE 12Z ECMWF IS THE STRONGEST OF THIS NON-NCEP CAMP...AND IS REASONABLY WELL SUPPORTED BY THE 12Z ECENS MEAN. THE 18Z GEFS MEAN SUGGESTS THE 00Z GFS IS A BIT TOO WEAK. BASED ON THE SPREAD...THE 00Z ECMWF AND 00Z ECENS MEAN APPEAR TO MAKE UP A NICE COMPROMISE SOLUTION SURFACE AND ALOFT AND THUS A BLEND OF THESE WILL BE PREFERRED...BUT WITH LIMITED CONFIDENCE AFTER ABOUT 48 HOURS. ...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 00Z NAM/12Z CMC AND 12Z UKMET CONFIDENCE: AVERAGE...THROUGH 36 HOURS BELOW AVERAGE...AFTER 36 HOURS THERE IS PRETTY GOOD MODEL AGREEMENT WITH THE SHORTWAVE MOVING INTO THE PACIFIC NORTHWEST ON TUES AND THE ASSOCIATED FRONT. MEANWHILE...THERE IS BROAD AGREEMENT THAT A STRONGER SHORTWAVE WILL ROUND THE BASE OF THE UPPER LOW OVER THE GULF OF AK LATER TUES...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 WITH THE MODELS ARE RATHER MINIMAL THROUGH TUES...BUT THEREAFTER THE 00Z GFS ACTUALLY BUCKS ITS TYPICAL BIAS OF BEING TOO PROGRESSIVE AND GRADUALLY SUGGESTS A SLOWER SOLUTION THAN ANY OTHER MODEL. ON THE FLIP SIDE...THE 12Z ECMWF BEGINS TO EDGE MORE PROGRESSIVE AND BY FRI IS THE MOST PROGRESSIVE SOLUTION WITH THE HEIGHT FALLS OVER THE WEST. THE 00Z NAM/12Z CMC AND 12Z ECMWF ARE ALL BETTER CLUSTERED IN BETWEEN SLOWER AND FASTER CAMPS ALOFT AND ALSO SHOW GOOD AGREEMENT WITH EACH OTHER AT THE SURFACE WITH RESPECT TO THE SURFACE LOW IMPACTING THE NORTHWEST. THE GEFS MEAN AND ECENS MEAN BOTH SUPPORT THEIR OUTLIER DETERMINISTIC SOLUTIONS BY THE END OF THE PERIOD WHICH MAKES THE LEVEL OF CONFIDENCE LIMITED...BUT FOR NOW WILL COMPROMISE IN BETWEEN THE GFS AND ECMWF CAMPS. ...SURFACE LOW ACROSS THE HIGH PLAINS BY THURS/FRI... PREFERENCE: BLEND OF THE 12Z UKMET AND 00Z ECMWF CONFIDENCE: BELOW AVERAGE THE 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 IS DISPLACING IS LOW DEVELOPMENT NORTH OF EVERY MODEL BY EARLY FRI...WITH THE 12Z CMC FOCUSING MORE LOW PRESSURE FARTHER SOUTH. THE 00Z GFS IS ALSO FARTHER SOUTH AND SLOWER. THE 12Z ECMWF AND 12Z UKMET SPLIT THE DIFFERENCE AND MORE CLOSELY FIT THE MULTI-MODEL CONSENSUS. WILL PREFER A COMPROMISE BETWEEN THESE SOLUTIONS WITH LIMITED CONFIDENCE. ...SHORTWAVE TROUGH DIGGING ACROSS THE NORTHERN PLAINS TUES... ...SURFACE LOW OVER THE NORTHERN PLAINS TUES... ...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 DOWN TO SOUTHEAST AND GRADUALLY AMPLIFY THE ENERGY ACROSS THE GREAT LAKES/MID-ATLANTIC AND NORTHEAST THROUGH WED AND THURS. THE GUIDANCE ALLOWS A RELATIVELY WEAK SURFACE LOW TO DEVELOP AND PUSH OUT INTO THE DAKOTAS BY LATE TUES IN ASSOCIATION WITH THIS BEFORE DAMPENING OUT OVER THE UPPER MS VALLEY. OVERALL...THE 12Z UKMET IS A SLOWER AND DEEPER OUTLIER SOLUTION WITH THE TROUGH EVOLUTION AND IS OUT OF TOLERANCE WITH THE OTHER GUIDANCE WITH THE SURFACE LOW OVER THE NORTHERN PLAINS. THE REMAINING MODELS ARE IN GOOD AGREEMENT WITH TIMING AND DEPTH...AND SO WILL PREFER A NON-UKMET CONSENSUS. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... ORRISON