MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 1227 AM EDT FRI APR 28 2017 VALID APR 28/0000 UTC THRU MAY 01/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z MODEL EVALUATION...PRELIMINARY MODEL PREFERENCES/CONFIDENCE ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...LARGE UPPER TROUGH/FRONTAL SYSTEM EXITING THE GREAT LAKES/UPPER MS VALLEY... ...COLD FRONT REACHING THE MID-ATLANTIC/NORTHEAST BY EARLY FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE ONLY VERY MODEST MASS FIELD SPREAD IS NOTED WITH THIS SYSTEM. A GENERAL MODEL BLEND SHOULD SUFFICE. ...UPPER LOW OVER SOUTHERN ALBERTA MOVING SLOWLY EAST ACROSS SASKATCHEWAN BY SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GENERAL MODEL BLEND CONFIDENCE: ABOVE AVERAGE THERE ARE SOME MINOR TIMING/DEPTH DIFFERENCES WITHIN THE MODELS WITH THIS SYSTEM AS IT SLOWLY MOVES EAST INTO SASKATCHEWAN BY SAT...BUT THE MODELS AGREE IN DAMPENING THE ENERGY OUT BY SUN. A GENERAL MODEL BLEND WILL BE PREFERRED. ...INITIAL TROUGH/HEIGHT FALLS OVER THE HIGH PLAINS ON FRI... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 12Z UKMET AND 12Z ECMWF CONFIDENCE: AVERAGE THERE WILL BE THE EMERGENCE OF SOME LEAD SHORTWAVE ENERGY AND RESULTING HEIGHT FALLS OUT ACROSS THE CENTRAL HIGH PLAINS THROUGH FRI WITH THE MODELS INDICATING A SMALL SCALE MID LEVEL LOW CENTER NEAR THE CO/KS BORDER THAT WILL LIFT NORTH INTO WESTERN NEB. BY FRI NIGHT...THIS ENERGY WILL WEAKEN IN LIEU OF STRONGER TROUGH AMPLIFICATION BACK OVER THE FOUR CORNERS REGION. THE 00Z GFS APPEARS TO BE A BIT TOO STRONG WITH THE LEAD ENERGY OVER WESTERN NEB...WITH THE 00Z NAM AND THE 12Z NON-NCEP GUIDANCE ALL A TAD WEAKER. THIS IS SUPPORTED BY THE 18Z GEFS MEAN AND 12Z ECENS MEAN TOO. THE 00Z NAM THOUGH BEGINS HAVE ITS OWN APPARENT BREAK AWAY FROM THE MODEL CONSENSUS BY FRI NIGHT/EARLY SAT OVER SOUTHWEST KS WHERE IT SUGGESTS A STRONGER SMALL SCALE CLOSED 700 MB CENTER EJECTING NORTHEAST FROM NEAR THE BORDER OF FAR SOUTHEAST CO AND THE OK PANHANDLE. THIS DRIVES A SIGNIFICANT QPF DIFFERENCE BETWEEN THE NAM AND THE GLOBAL MODEL CONSENSUS. THE 12Z UKMET AND 12Z ECMWF TEND TO HAVE STRONG MODEL CLUSTERING AND ARE VERY CLOSE TO THE MODEL CONSENSUS ACROSS THIS REGION...SO WILL PREFER A UKMET/ECMWF BLEND FOR NOW FOR THE MASS FIELDS. ...AMPLIFYING TROUGH OVER THE INTERMOUNTAIN WEST... ...CLOSED LOW DEVELOPMENT OVER THE FOUR CORNERS REGION FRI/SAT... ...SYSTEM EJECTING ACROSS THE PLAINS/MIDWEST THROUGH SUN/MON... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF THE 00Z GFS AND 12Z ECMWF CONFIDENCE: AVERAGE THERE CONTINUES TO BE GOOD LARGE SCALE AGREEMENT WITH THE EVOLUTION OF A LARGE CLOSED LOW/TROUGH EVOLVING ACROSS THE CENTRAL/SOUTHERN ROCKIES AND INTO THE CENTRAL AND SOUTHERN PLAINS THIS WEEKEND. BY EARLY NEXT WEEK...THE MODELS TAKE A STRONG CLOSED LOW CENTER NORTHEAST ACROSS THE MIDWEST. LOW PRESSURE ASSOCIATED WITH THIS SYSTEM WILL FOCUS OVER THE SOUTHERN PLAINS BEFORE THEN LIFTING NORTHEAST ACROSS THE RED RIVER VALLEY AND THEN UP ACROSS THE MID MS VALLEY AND UPPER MIDWEST. THE 12Z UKMET BECOMES AN OUTLIER IN TAKING ITS LOW AND MID LEVEL MID LEVEL LOW CENTERS FASTER OFF TO THE NORTHEAST AND ESPECIALLY BY SUN AND MON AS THE SYSTEM LIFTS OUT OF THE PLAINS AND ACROSS THE MIDWEST. THE UKMET IS ALSO PROBABLY A LITTLE TOO DEEP AS WELL. THE REMAINING MODELS ARE MUCH BETTER CLUSTERED WITH THEIR TIMING BY COMPARISON. HAVING SAID THAT...THE 00Z GFS IS A LITTLE FASTER THAN THE 12Z ECMWF...AND THE 00Z NAM DOES TRACK A BIT MORE ENERGY TO THE LEFT OR NORTH OF THE GFS/ECMWF CLUSTER. THE 12Z CMC IS OCCASIONALLY APPEARING A LITTLE TOO WEAK WITH ITS MID LEVEL CENTER. BASED ON THIS AND THE ENSEMBLE MEAN SOLUTIONS...A BLEND OF THE GFS AND ECMWF WILL BE MAINTAINED. ALSO OF NOTE...THIS LARGE SCALE CLOSED LOW EVOLUTION WILL BE DRIVING SIGNIFICANT AND HIGH-IMPACT RAINFALL...INCLUDING WIDESPREAD FLASH FLOODING...ACROSS PARTS OF THE PLAINS/MS VALLEY AND THE OH VALLEY. PLEASE CONSULT THE LATEST QPFPFD AND QPFERD FOR MORE DETAILS ON THESE IMPACTS. ...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC NORTHWEST SAT... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-12Z UKMET BLEND CONFIDENCE: AVERAGE THE 12Z UKMET STANDS AS A NEAR OUTLIER TO THE SOUTH WITH A 500 MB TROUGH AMPLIFYING ACROSS THE NORTHWEST COAST OF THE CONUS COMPARED TO THE LATEST ENSEMBLE AND DETERMINISTIC SOLUTIONS. A NON 12Z UKMET BLEND IS PREFERRED GIVEN THE RELATIVELY SIMILAR NON-12Z UKMET SOLUTIONS. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ ORRISON