Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 246 PM EDT Thu Jul 19 2018 Valid Jul 19/1200 UTC thru Jul 23/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model preferences and confidence intervals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: UKMET/ECMWF/GFS/Canadian blend Confidence: Above average Low in Midwest/Ohio Valley...Shortwave/sfc low lifting along the East Coast front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average 19z update: The 12z CMC while still a bit east by the end of the period compared to the ECMWF is much more in line overall to be considered in the blend. Like the GFS however, it west deeper and west with the surface reflection; compare this to the eastward track of the ECMWF and the very deep compact surface low with the UKMET... a non-NAM blend would likely work very well as a compromise to the ensemble suite/trends. ---Prior Discussion--- Run to run ensemble trends show a consolidation of solutions with the closed low over the Midwest into Ohio valley, though toward midday Sunday the 00z CMC remains deeper and concentric while the remaining guidance is filling a bit. The majority of spread remains with the shortwave and associated surface wave lifting out of the Southeast on Fri along the coast and hooking back west into New England by Sunday morning, with the CMC out of place...it is also west of the clustering. However, here the 12z NAM is also very strong but most progressive. The 12z GFS shifted a bit slower and deeper, and while a still a bit west and weaker than the remaining guidance, it appears fairly solid to the overall best clustering. The 00z UKMET may be a bit deep with this system too, but if blended with the 12z GFS and ECMWF this will work out well overall in a slightly above average confidence blend. System skirting north of US/Canadian border ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/ECMWF blend Confidence: Slightly above average 19z update: The 12z CMC shifted a bit further south with the upper low and surface low, which also delays the surface front crossing the northern tier. The UKMET continues to be fast and the 12z ECMWF showed best continuity. As such will favor a 12z GFS/ECMWF blend at slightly above average confidence. ---Prior Discussion--- Closed low drops into Southern BC late Fri and elongates in a positive tilt into the Pacific NW with fairly good agreement. Spread increases as the wave lifts Northeast into central Canada with a surface wave and trailing frontal zone through the northern tier of the US into Sun. Here the 12z NAM winds up/consolidates a bit south, along with the 00z UKMET and become progressive late Sun with a further southeast surface reflection and faster front in MT/Dakotas. This is away from the trends/ensemble suite, so would favor a 12z GFS and 00z ECMWF/CMC blend for this system at slightly above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina