Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 236 AM EDT Thu Apr 16 2020 Valid Apr 16/0000 UTC thru Apr 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00z Final Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern stream short wave crossing the Rockies and the Ohio Valley Thu/Fri moving into southern New England Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/UKMET blend Confidence: Average While the 00z NAM/GFS are close to the consensus as the short wave in the Rockies crossing the Central Plains, both become faster than the consensus ahead of short wave energy dropping into the flow from the Pacific Northwest. The differences become more amplified with time across the Ohio Valley and southern New England. The faster timing of the short wave results in the surface wave moving faster along a frontal boundary stretching across Ohio Valley into Fri. The 00z ECMWF/UKMET have consistently been slower with the mid level feature and the surface wave, so this pair comprise the preferred blend here. It should be noted that as the surface low deepens off the New England coast Sat, the 00z UKMET remains faster than the 00z ECMWF/12z ECMWF ensemble mean. By that time, most of the sensible weather is expected to be off the coast. Given the spread in the NCEP vs non-NCEP guidance, forecast confidence is just average. ...Short wave energy crossing West Coast Fri and Southwest Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/UKMET blend Confidence: Slightly below average As the closed mid level low off the Northern CA coast early drops into Southern CA, it opens up into a long wave trough. The 00z NAM/GFS are close to the consensus through this point. However, as the long wave trough starts to weaken, the 00z GFS becomes faster than the consensus as it reacts to additional upstream short wave energy after 18/12z. The 00z NAM becomes flatter, seemingly losing the energy in the mid levels too quickly. With this wave, the 00z ECMWF/UKMET have the most consistency, though there are timing issues here as well. Trailing short wave energy from Northern CA follows a path similar to the first mid level wave late in the period. The interaction between the two short waves is causing some issues for the guidance, as the 00z GFS is slower than the consensus, while the 00z NAM is a bit faster. The timing issues suggest that models are not handling the interaction well. Based on this, forecast confidence is slightly below average. ...Short wave crossing Alberta/Manitoba Sat... ...Surface cold front across the Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-00z NAM Blend Confidence: Slightly above average The 00z NAM/GFS are close to the consensus dropping short wave energy into the developing broad long wave trough over the Northern Plains by the end of the period. However, the 00z NAM becomes slower than the consensus with the attending cold front across the Northern Plains and Upper MS Valley, especially after 18/00z. Since there is generally good clustering with the surface and mid level features, only the 00z NAM is not included in the preference, with slightly above average confidence. ...Short wave amplifying from BC coast into the Pacific Northwest Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/00z ECWMF Blend Confidence: Slightly below average Short wave energy dropping across western Canada after 17/12z starts eroding the mid level ridging across the Pacific Northwest, eventually forming a closed mid level over WA/OR by 19/12z. The 00z NAM/GFS are close to the consensus through this process, with the 00z GFS close to the 00z ECMWF/12z ECMWF mean with the placement of the closed low. The 00z NAM becomes faster with the mid level system. never fully closing off. This could be due to how it handles the ridging that pokes up along the BC coast. There is still a fair amount of spread with the evolution of the mid level system, so 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