MODEL DIAGNOSTIC DISCUSSION NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 129 AM EDT WED JUN 03 2015 VALID JUN 03/0000 UTC THRU JUN 06/1200 UTC ...SEE NOUS42 KWNO (ADMNFD) FOR THE STATUS OF THE UPPER AIR INGEST... 00Z NAM/GFS EVALUATION...INCLUDING PRELIMINARY PREFERENCES ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ WELL DEVELOPED NORTHERN STREAM UPPER LOW ROLLING ACROSS NEW ENGLAND SURFACE LOW PASSING JUST OFF NOVA SCOTIA ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: BLEND OF OPERATIONAL MODELS CONFIDENCE: ABOVE AVERAGE NO SIGNIFICANT MODEL DIFFERENCES WERE NOTED...ABOVE AVERAGE CONFIDENCE EXISTS GIVEN THE SHORT TERM NATURE OF THE FORECAST AND VERY GOOD AGREEMENT AMONG THE LATEST GUIDANCE. CLOSED LOW FORECAST TO WEAKEN EWD ACROSS THE SOUTHERN APPALACHIANS- SOUTHERN MID-ATLANTIC ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: GFS/UKMET/12Z ECMWF CONFIDENCE: SLIGHTLY ABOVE AVERAGE THE GFS HAS SLOWED SOME FROM ITS 12Z SOLUTION...PLACING ITS TIMING INTO BETTER AGREEMENT WITH THE UKMET/12Z ECMWF AS THE SYSTEM DRIFTS EAST. HOWEVER...THE NAM HAS REMAINED CONSISTENT WITH ITS 12Z RUN...LEAVING IT ALONG THE LEADING EDGE OF THE GUIDANCE. GIVEN THE SLOW PROGRESSION OF THIS TROUGH UP UNTIL NOW...AND THE PRESENCE OF RIDGING ACROSS THE WESTERN ATLANTIC...PREFER TO KEEP WITH THE SLOWER SOLUTIONS. SHORTWAVE SHEARING OUT ALONG U.S./CANADIAN BOARDER NORTHERN HIGH PLAINS CYCLOGENESIS SOUTHERN STREAM SHORTWAVE EJECTING INTO CENTRAL PLAINS THURSDAY ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NAM CONFIDENCE: BELOW AVERAGE THE 00Z NAM HAS BACKED AWAY FROM ITS 12Z SOLUTION WITH A FLATTER SHORTWAVE TROUGH AND LESS AMPLIFIED SURFACE LOW OVER THE UPPER MIDWEST EARLY THU. THIS PUTS IT INTO BETTER AGREEMENT WITH THE REMAINING OPERATIONAL GUIDANCE. HOWEVER...NUMEROUS OTHER DETAIL DIFFERENCES ARE NOTED IN WHAT REMAINS A COMPLEX SITUATION ACROSS THE PLAINS...WHERE SEVERAL WEAK IMPULSES EMBEDDED WITHIN SOUTHWEST FLOW ARE EXPECTED TO EJECT OUT FROM THE WESTERN CONUS AND MOVE ACROSS THE TOP OF A STRONG RIDGE. CONVECTIVE DETAILS MUDDLE THE FORECAST AND FEATURES ARE DIFFICULT TO TRACK GIVEN THE RELIANCE ON YET TO BE SEEN CONVECTIVELY DRIVEN VORTICITY MAXIMA. FOR EXAMPLE...DIFFERENCES EVOLVE WITH THE SHORTWAVE TROUGH FORECAST TO AMPLIFY AS IT SPILLS OFF OF THE TOP OF THE RIDGE INTO THE MID-UPPER MS VALLEY THU NIGHT-FRI MORNING. THE GFS/UKMET ARE SIMILARLY TIMED...BUT ARE FURTHER TO THE NORTH AND MORE WRAPPED UP THAN THE NAM/00Z ECMWF ACROSS THE UPPER MS VALLEY EARLY FRI. IN CONTRAST...THE 12Z ECMWF IS THE LEAST AMPLIFIED ALOFT AND MORE PROGRESSIVE ACROSS THE MID MO/MS VALLEYS INTO THE OH VALLEY LATE THU-FRI. BY LATE FRI INTO SAT THE 12Z ECMWF BECOMES MUCH MORE PROGRESSIVE DIGGING ENERGY FURTHER TO THE SOUTH INTO THE SOUTHERN APPALACHIANS EARLY SAT. AT THIS POINT...WHILE CONFIDENCE IN ITS DETAILS ARE VERY LIMITED...THE NAM OFFERS THE BEST COMPROMISE OF THE LATEST OPERATIONAL RUNS. UPPER TROUGH RELOADING OVER THE WEST BY WED/THU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ PREFERENCE: NON-UKMET BLEND CONFIDENCE: ABOVE AVERAGE ONLY MINOR PLACEMENT/TIMING DIFFERENCES EXIST WITH A CLOSED LOW FORECAST TO FORM OVER CALIFORNIA BY MID-DAY THURSDAY...HOWEVER...WHILE TRENDING TOWARD THE REMAINING OPERATIONAL MODELS...THE 00Z UKMET STILL STANDS OUT A BIT FROM THE OTHER OPERATIONAL MODELS REMAINING SOMEWHAT MORE OPEN IN THE 700-500 MB LAYER. GIVEN THE OVERALL GOOD AGREEMENT AND THE TREND IN THE UKMET...THE PREFERENCE REMAINS FOR A NON-UKMET BLEND OF MODELS. SHORTWAVE TROUGH IMPACTING THE NORTHERN ROCKIES HIGH PLAINS SAT MORNING ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ PREFERENCE: GFS/NAM/UKMET CONFIDENCE: AVERAGE THE GFS/NAM/UKMET ARE IN FAIRLY GOOD AGREEMENT WITH A SHORTWAVE TROUGH FORECAST TO CENTER NEAR THE MT/ND BORDER SAT MORNING. THE 12Z ECMWF IS A RELATIVE OUTLIER HERE WITH A MORE AMPLIFIED SOLUTION. www.wpc.ncep.noaa.gov/html/model2.shtml... www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml... PEREIRA