Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1115 AM EST Fri Feb 16 2018 Valid Feb 16/1200 UTC through Feb 20/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z GFS/NAM Evaluation with preliminary model preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ NAM/GFS initialization errors do not seem to degrade their short range forecasts. Low moving from the Southeast offshore New England and its associated shortwave aloft ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend; confidence average The guidance shows good agreement with the parent shortwave through tonight. Thereafter, the 00z ECMWF becomes a bit more amplified than the other guidance with the shortwave while the 12z NAM ultimately is the weakest (far from its typical bias). This may not be a bad move on Saturday as the shortwave could gain some amplitude as it moves under the base of the strong mid-level vortex over Nunavut. However, the shortwave moves through an increasingly zonal/confluent flow thereafter which should lead to a weaker/broader shortwave with time. At the surface, the 00z UKMET is the most northwesterly and has minority 00z global ensemble support so did not consider it viable. However, the rest of the guidance is within the ensemble spread and could not be easily discounted. Considering the above, a compromise of the 00z ECMWF, 12z GFS, 12z NAM, and 00z Canadian is preferred with average confidence. Upper trough digging into the West Pressure pattern in the Plains/Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non NAM-blend; confidence above average As usual, the 12z NAM is the strongest with the upper trough -- its usual bias. As the surface, its low depiction in IA late Tuesday falls outside the 00z global ensemble spread. A compromise of the 12z GFS, 00z UKMET, 00z ECMWF, and 00z Canadian is preferred with 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