Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 238 AM EDT Tue Apr 21 2020 Valid Apr 21/0000 UTC thru Apr 24/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Developing long wave trough over New England with an associated surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 00z NAM/GFS are close to the consensus with short wave energy tracking from Manitoba across the the Upper MS Valley, which then drops into the bottom of a developing long wave trough headed for New England after 21/12z. The short wave takes the long wave trough negative across New England and nearby Quebec, as a closed low forms over south central Quebec. These solutions are also close to the consensus with the developing surface low over Quebec. In general, there is good model agreement with the mid level and surface features, so a general model blend is preferred with this system, with above average forecast confidence. ...Mid level trough tracking from across the Southwest and southern Plains to the Mid Atlantic... ...Surface low associated with the mid level trough... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/00z ECMWF blend Confidence: Average The 00z NAM/GFS are close to the consensus taking the short wave energy over Southern CA early in the period across the Southern Plains before 22/12z. After that time, the 00z NAM becomes slower than the consensus, closing off a mid level low over AR (though not quite as slow as the 00z UKMET, which has been consistently slow with the feature for the past three model cycles). The 00z NAM is also slower with the surface low across the southern Plains into the Lower MS Valley during this time. By contrast, the 00z GFS is close to the 00z ECMWF with the timing of the short wave, as well as the track of the surface low through 23/12z, and have their respective ensemble means supporting their solutions. The 00z CMC continued to slow its mid level trough and surface wave, so much so that is probably no longer a viable solution for this system across the Mid MS Valley. There is some model spread as the surface low tracks off the Mid Atlantic coast late in the period, as the 00z ECMWF/12z ECMWF ensemble mean remain faster than the 00z GFS/00z GEFS mean. This seems to be to the speed of the mid level support exiting the Mid Atlantic coast, as the 00z GFS tends to build a stronger short wave ridge across the Mid Atlantic, slowing the progress of the surface system. For much of the period, the 00z GFS/00z ECMWF are solid as a preferred solution, with spread toward the end of the period reducing forecast confidence with time. Because of this, forecast confidence is only average. ...Short wave and surface low tracking from western Canada to the Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/00z ECMWF/00z UKMET blend Confidence: Average The 00z NAM/GFS are close to the consensus tracking short wave energy from western Canada in the very fast mid level flow across the Northern Plains before 23/00z. The 00z NAM becomes slower than the 00z GFS after this time, eventually placing the trough over western ND (as does the 00z CMC, though not as far west as the 00z NAM). The 00z GFS is close to the 00z ECMWF/UKMET with the trough position extending from ND south through NE by 24/12z. There is more spread with the placement of the resulting surface low from ND into NE. Since there has been some consistency with the 00z GFS/00z ECMWF/00z UKMET with this feature, these models comprise the preferred blend. However, due to the slower solutions of the 00z NAM/00z CMC and the spread in the placement of the surface low at the end of the period, forecast confidence is only average. ...Short wave energy tracking from the Pacific Northwest to the Southern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The 00z NAM/GFS are close tracking short wave energy from WA/OR after 23/00z in the fast mid level flow to a position over the western High Plains by the end of the period. They form a loose cluster with much of the 00z guidance with the short wave, and its associated surface low developing over northern and central TX. Since there generally good model agreement with the mid level and surface systems, a general model blend is preferred. Given the speed of the mid level flow, it is not yet clear if smaller scale interactions might yet result in more instability in the timing of the mid level and surface systems. Because of this, forecast confidence is simply 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