Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Wed Mar 25 2020 Valid Mar 25/1200 UTC thru Mar 29/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Model Evaluation with Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...East Coast surface low tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Both the 12Z NAM/GFS are close to the model consensus with the surface low developing along the Mid Atlantic this afternoon. Eventually, the 12z NAM become a bit deeper and slower with the surface low, as it represents the western edge of the solution envelope. Given the tight clustering with this system, a general model blend is preferred, with above average confidence. ...Surface low crossing the Mid Atlantic states Thu night/Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 12Z NAM/GFS are close to the consensus with the surface wave that develops on the front over the OH Valley Thu night. As the wave reaches the northern Mid Atlantic coast, it begins to deepen, and there is some spread on how quickly this might occur. With little in the way of mid level support, the differences in development timing/placement may be due to diabatic heating effects from the Gulf Stream. Once the surface wave reaches the Gulf Stream, there is generally good model agreement with the strength and track of the low. A general model blend is preferred with this system, though the timing differences concerning when the wave starts to deepen result in only slightly above average forecast confidence. ...Long wave trough tracking from the West Coast to the Central Plains... ...Surface low moving from eastern CO into the Mid/Upper MS Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF/UKMET blend Confidence: Slightly above average While the 12Z NAM/GFS remain close to the consensus with the track and timing with the positively tilted long wave trough over CA this afternoon, the 12Z NAM seems to develop the surface low too far south (as does the 00Z CMC), at least when compared with the consensus, and ends up southeast of that consensus. The 12Z GFS remains close to the consensus (as well as 06z GEFS and the 00Z ECMWF ensemble mean) with the surface low, and clusters well with the 00Z ECMWF. The 00Z UKMET has slowed its forward movement and is close to the GFS/ECMWF solutions. Based on the above, a 12Z GFS/00Z ECMWF/UKMET blend is preferred. Since only the 12Z NAM/00Z CMC are not close with the position of the surface low late, forecast confidence is slightly above average. Shortwave and surface cold front approaching Pacific Northwest Sat ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF blemd Confidence: Average There is a fair amount of spread with the system as it tracks from south of the Gulf of AK toward the Pacific Northwest toward the end of the period. The 12Z NAM seems to be too fast, and has been accelerating with this solution. The 12Z GFS has slowed its progress, though it is not as slow as the 00Z ECMWF. Not surprisingly, the ensemble means support their parent models, suggesting that there is still some way to go before the model differences can be rectified. Based on this, a blend of the 12Z GFS/00Z ECMWF is preferred, but given the spread, forecast confidence is average at best. Hayes Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes