MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1228 PM EDT SAT MAY 20 2017 VALID MAY 20/1200 UTC THRU MAY 24/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z MODEL EVALUATION/PREFERENCES AND CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...CLOSED DEEP LAYER LOW MOVING ACROSS THE PLAINS TODAY... ...CROSSING THE UPPER MS VALLEY AND GREAT LAKES SUN... ...COLD FRONT MOVING ACROSS THE CENTRAL AND EASTERN U.S.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THE MODELS ARE IN GOOD AGREEMENT WITH THE EVOLUTION OF THIS LARGE SCALE SYNOPTIC SYSTEM. A GENERAL MODEL BLEND WILL BE PREFERRED TO RESOLVE ANY LINGERING SMALLER SCALE DIFFERENCES FOR NOW. ...SHORTWAVE CROSSING THE PACIFIC NORTHWEST/NORTHERN ROCKIES... ...ENERGY DIGGING ACROSS THE GREAT BASIN/CENTRAL ROCKIES SUN... ...EJECTING OUT INTO THE SOUTHERN PLAINS ON MON... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE OVERALL THERE REMAINS PRETTY GOOD MODEL AGREEMENT IN TRACKING A RATHER WEAK SHORTWAVE FROM THE PACIFIC NORTHWEST TODAY SOUTHEAST ACROSS THE GREAT BASIN AND CENTRAL ROCKIES ON SUN...AND THEN GRADUALLY EJECTING OUT INTO THE SOUTHERN PLAINS ON MON AROUND THE BASE OF THE LARGER SCALE TROUGH OVER THE MIDDLE OF THE COUNTRY. ...SHORTWAVE MOVING INTO MT EARLY MON AROUND THE BACKSIDE OF THE UPPER MS VALLEY AND SOUTHERN CANADA CLOSED LOW... ...ENERGY AMPLIFYING OVER THE MIDWEST BY TUES... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE MODELS CONTINUE TO ADVERTISE A WELL-DEFINED SHORTWAVE DIGGING SOUTHEAST ON MON ACROSS THE MT HIGH PLAINS AND THEN AROUND THE SOUTHWEST FLANK OF THE LARGER SCALE UPPER MS VALLEY/SOUTHERN CANADA CLOSED LOW BY TUES WITH THE ENERGY AMPLIFYING AS IT ARRIVES OVER THE MIDWEST. THE 12Z NAM GRADUALLY BECOMES A BIT MORE AMPLIFIED THAN THE MODEL CONSENSUS BY TUES OVER THE MIDWEST AND DIGS ITS HEIGHT FALLS A TAD FARTHER SOUTH AS WELL. THIS RESULTS IN THE NAM ALSO TENDING TO BE A BIT STRONGER WITH ITS SURFACE LOW CENTER OVER THE REGION ON TUES AS WELL. AT THIS POINT...WILL LEAN TOWARD THE RELATIVELY BETTER MODEL CLUSTERING AMONG THE NON-NAM SOLUTIONS LED BY THE 12Z GFS AND 00Z ECMWF AND THUS MAINTAINING CONTINUITY. ...SOUTHERN STREAM WAVE ARRIVING ACROSS SOUTHEAST TX ON MON... ...SURFACE LOW TRAVERSING THE GULF COAST INTO THE SOUTHEAST TUES... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z GFS AND 00Z ECMWF CONFIDENCE: BELOW AVERAGE THE MODELS REMAIN IN AGREEMENT IN BRINGING A SOUTHERN STREAM WAVE FROM NEAR BAJA CALIFORNIA EASTWARD INTO TX BY EARLY MON. AS THIS ENERGY INTERACTS WITH A STALLED FRONT NEAR THE SOUTHEAST TX COAST...ONE OR MORE WAVES OF LOW PRESSURE SHOULD DEVELOP ALONG THIS FRONT AND THEN ADVANCE EAST-NORTHEAST AND JUST INLAND ACROSS THE CENTRAL GULF COAST BEFORE THEN LIFTING NORTHEAST UP ACROSS THE INTERIOR SOUTHEAST U.S. BY LATE TUES IN AN ELONGATED FASHION. THE 00Z ECMWF HAS THE STRONGEST AND MOST CONSOLIDATED LOW CENTER...WITH THE 12Z NAM AND 12Z GFS ALSO RATHER WELL-DEFINED...BUT THE NAM AND GFS BOTH PUT MORE EMPHASIS ON A SURFACE WAVE THAT WILL BECOME MORE CONSOLIDATED OVER THE SOUTHEAST COASTAL PLAIN BY TUES WHEREAS THE ECMWF FOCUSES IT BACK FARTHER SOUTHWEST OVER SOUTHERN MS/AL...WITH A WEAK REFLECTION AT BEST OVER THE SOUTHEAST. THE 00Z CMC TENDS TO FAVOR THE NAM/GFS CAMP...BUT THE 00Z UKMET HAS A MUCH WEAKER SURFACE LOW REFLECTION OVER THE SOUTHEAST AND SUGGESTS ITS MAIN LOW CENTER NEAR SOUTHERN LA BY LATE TUES AND WELL SOUTHWEST OF EVEN THE ECMWF. CONFIDENCE IS LIMITED ON THE MASS FIELD DETAILS...BUT THERE IS MUCH BETTER CONFIDENCE WITH RESPECT TO THE IDEA THAT THIS ENERGY TRAVERSING THE FRONT WILL SET THE STAGE FOR HEAVY RAINFALL AND CONVECTION FROM SOUTHEAST TX ACROSS THE GULF COAST STATES AND INTO THE SOUTHEAST. PLEASE CONSULT THE LATEST QPFPFD FOR DETAILS ON THIS. FOR THE MASS FIELDS...WE WILL PLAY UP THE IDEA OF TWO SEPARATE WAVES EVOLVING WITH ONE OVER THE SOUTHEAST ON TUES AND ONE NEAR THE CENTRAL GULF COAST STATES. A MULTI-MODEL BLEND WILL BE PREFERRED FOR NOW WITH A COMPROMISE BETWEEN GFS AND ECMWF SOLUTIONS. ...UPPER TROUGH APPROACHING THE PACIFIC NORTHWEST ON TUES... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-NAM CONSENSUS CONFIDENCE: SLIGHTLY ABOVE AVERAGE A RATHER STRONG UPPER TROUGH IS EXPECTED TO BE DIGGING SOUTHEAST TOWARD THE PACIFIC NORTHWEST ON TUES FROM THE GULF OF AK. THE 12Z NAM IS BY FAR THE MOST PROGRESSIVE AND STRONGEST SOLUTION WITH THIS SYSTEM COMPARED TO THE ANY OF THE GLOBAL MODELS. THE 12Z GFS HAS TRENDED SLOWER AND IS NOW ONLY A TAD FASTER THAN THE 00Z NON-NCEP GUIDANCE INCLUDING THE UKMET/CMC AND ECMWF SOLUTIONS. WILL PREFER A NON-NAM CONSENSUS AT THIS POINT. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ ORRISON