Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 135 PM EST Sat Feb 17 2018 Valid Feb 17/1200 UTC through Feb 21/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model preferences with confidence intervals ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS initialization errors do not seem to degrade their short range forecasts. Shortwave moving offshore the Northwest in three days ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Model blend; confidence slightly above average Dispersion is narrowing with low pressure placement and depth associated with a southward moving shortwave moving down the western side of the upper level trough. Over the last several days, the guidance has been slowly dampening this feature, though some of the 12z guidance became a little stronger. The 00z global ensemble guidance has no defined surface low to track in this region, normally implying that a weaker solution would be best. The noticeable strengthening seen in the UKMET/Canadian guidance lowers consideration of the 00z global ensemble guidance to some degree. Blending the 12z GFS, 12z NAM, 12z ECMWF, 12z UKMET, and 12z Canadian accounts for the uncertainty and is preferred with slightly above average confidence. Upper trough digging into the West Pressure pattern in the Plains/Midwest/Great Lakes ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Model blend; confidence slightly above average The 12z UKMET came in looking closer to the other available guidance, close enough to be considered plausible. A blend of the 12z Canadian, 12z NAM, 12z GFS, 12z UKMET, and 12z ECMWF is preferred with slightly above average confidence. Low moving from the Southeast offshore New England and its associated shortwave aloft ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Model blend; confidence slightly above average While the 12z NAM is stronger aloft and a little more northwesterly with the surface low tonight, this type of solution has randomly seen over the last several days on various pieces of guidance, lies within the ensemble clustering, and cannot be fully ruled out. Because of this, a compromise of the 12z GFS, 12z NAM, 12z UKMET, 12z Canadian, and 12z ECMWF is preferred with this system with 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 Roth