Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Tue Apr 28 2020 Valid Apr 28/1200 UTC thru May 02/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Developing long wave trough and surface low tracking from the Mid MS Valley to the northern Mid Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET blend Confidence: Slightly below average The 12z NAM/GFS are close with short wave energy tracking from eastern MT that drops into a developing long wave trough across the Mid MS Valley through 30/00z. After that time, the 00z NAM becomes slower than the consensus, with the greatest difference occurring over the northern Mid Atlantic toward the end of the period. The 12z GFS remains closer to the consensus as the closed mid level system crosses the OH Valley, then becomes faster with this system by 02/00z. The differences with the 12z NCEP guidance appear to be driven by how the closed mid level system interacts with short wave energy dropping into it across the OH Valley and northern Mid Atlantic. By contrast, the 00z ECMWF/UKMET are more consistent with the mid level system, enjoying the support of the 00z ECMWF ensemble mean. The 12z NAM/GFS also exhibit their respective issues with the surface low associated with the mid level system, with the 12z GFS looking too fast and too far south with the system by 02/00z. Though the 00z ECMWF/UKMET form a loose consensus with the mid level and surface systems, there remains a fair amount of spread in the solutions. Based on this, forecast confidence is slightly below average. ...Short wave energy affecting the Pacific Northwest to the Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/00Z ECMWF/00z UKMET blend Confidence: Slightly below average The 12z NAM/GFS are close to the consensus taking short wave energy near 42N 138W at 29/12z and weakening it as it approaches Vancouver Island near 30/12z. After this time, both models diverge from the loose consensus, with the 12z NAM taking the bulk of the short wave energy into Alberta and Manitoba. The 12z GFS remains closer to the 00z ECMWF/00z UKMET, keeping the short wave energy closer to the International border, reaching the Northern Plains before 02/00z. Some of the spread could be tied to how a second short wave approaching the Pacific Northwest late interacts with the first short wave, causing some divergence in the solutions. Based on the increasing spread with time, forecast confidence is slightly below average. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes