MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 108 PM EDT SAT APR 29 2017 VALID APR 29/1200 UTC THRU MAY 03/0000 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 12Z NAM/GFS INCLUDING PRELIMINARY MODEL PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...STRONG CLOSED LOW REACHING THE PLAINS ON SUNDAY AND UPPER MISSISSIPPI VALLEY ON MONDAY...SPURRING DEEP SURFACE CYCLONE... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF 12Z GFS/00Z ECMWF CONFIDENCE: AVERAGE WHILE TRENDS HAD PREVIOUSLY BEEN SLOWER WITH THE EJECTION OF THE CLOSED LOW THROUGH THE CNTRL PLAINS ON SUN...THE PREVIOUSLY CONSISTENT ECMWF MEAN HAS JOINED THE FASTER TRENDING CAMP OF THE 00Z MODELS AND 12Z NAM/GFS. CURRENTLY...THE 12Z NAM STANDS AS A SLOWER OUTLIER. GIVEN THE FASTER TRENDS FROM OVERNIGHT CONTINUES TO BE SUPPORTED IN THE LATEST AVAILABLE 12Z GUIDANCE...THE 12Z NAM APPEARS A LOW PROBABILITY SOLUTION. WHILE WOBBLING BACK TO A SLOWER SOLUTION IS POSSIBLE WITH FUTURE DETERMINISTIC MODEL CYCLES...THERE IS ENOUGH AGREEMENT IN THE LATEST ENSEMBLE CLUSTERING FOR A POSITION NEAR THE 12Z GFS AND 00Z ECMWF. CONFIDENCE IS ONLY AVERAGE GIVEN THE INCONSISTENCIES FROM RUN TO RUN SINCE YESTERDAY. ...PACIFIC FRONTAL SYSTEM REACHING BRITISH COLUMBIA/PACIFIC NORTHWEST SAT TRANSLATING ACROSS THE S CANADIAN ROCKIES SPURRING LEE SURFACE WAVE THAT SLIDES OUT OF ALB/SASK ACROSS N TIER LATE MON/TUES... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS...00Z ECMWF...00Z UKMET BLEND CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE 12Z NAM CONTINUES TO BE MUCH STRONGER THAN THE REMAINING DETERMINISTIC AND ENSEMBLE MODEL CONSENSUS ACROSS SWRN CANADA ON MON MORNING. THE RESULT OF THE STRONGER 12Z NAM SHOWS SOME MINOR INTERACTION WITH THIS WAVE AND A LARGE CLOSED LOW LOCATED OVER THE UPPER MISSISSIPPI VALLEY LATER MON INTO TUE. OUTSIDE OF THE 12Z NAM...THIS SOLUTION IS NOT REPRESENTED AND SO A NON 12Z NAM IS RECOMMENDED. THE 00Z CMC IS ON THE NRN EDGE OF THE SPREAD AND WHILE THERE IS SOME MINOR ENSEMBLE SUPPORT FOR THE 00Z CMC...BETTER AGREEMENT EXISTS FOR THE MIDDLE ROAD BEST REPRESENTED BY THE 12Z GFS...00Z ECMWF AND 00Z UKMET. ...NEXT WEAK PACIFIC WAVE ENTERING PACIFIC NORTHWEST LATE MON AND CROSSING N ROCKIES BY TUES MORNING... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS / 00Z ECMWF BLEND CONFIDENCE: AVERAGE A WEAK SHORTWAVE TOPS THE MEAN RIDGE IN THE EASTERN PACIFIC AND MOVES SOUTHEAST ACROSS THE PACIFIC NORTHWEST AND NORTHERN ROCKIES MONDAY AND THEN INTO THE NORTHERN TO CENTRAL PLAINS AND CENTRAL ROCKIES TUE. THE DEGREE OF RIDING UPSTREAM WILL INFLUENCE THE DEGREE AND TIMING OF DEEPENING OF THIS FEATURE DOWNSTREAM ACROSS THE ROCKIES. THE 00Z CMC SHOWS TOO DEEP WITH RESPECT TO THE ENSEMBLES AS THE SHORTWAVE CROSSES THE WEST COAST. SOME LATITUDE DIFFERENCES ARE BEST RESOLVED WITH A 12Z GFS AND 00Z ECMWF BLEND GIVEN THESE TWO MODELS SEEM TO REPRESENT THE ENDS OF THE LATEST ENSEMBLE CLUSTERING. ...PACIFIC CYCLONE OFFSHORE OF THE PACIFIC NORTHWEST LATE TUE... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: 12Z GFS/ECMWF BLEND CONFIDENCE: AVERAGE RELATIVELY MINOR DIFFERENCES EXIST WITH A SURFACE CYCLONE AHEAD OF A SHORTWAVE ADVANCING AT THE FRONT EDGE OF CLOSED LOW IN THE GULF OF ALASKA ON TUE. ENSEMBLE SPREAD IS AVERAGE WITH THIS SYSTEM...AND THE 12Z GFS AND 00Z ECMWF ARE SIMILAR TO THE MIDDLE OF THE SPREAD. WWW.WPC.NCEP.NOAA.GOV/HTML/MODEL2.SHTML... /ALL LOWER CASE/ WWW.WPC.NCEP.NOAA.GOV/H5PREF/H5PREF.SHTML... /ALL LOWER CASE/ OTTO