Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 130 PM EST Thu Feb 20 2020 Valid Feb 20/1200 UTC thru Feb 24/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Positively tilted mid level trough axis approaching the East Coast tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The 12z NAM/GFS are close to the consensus with the positively tilted trough moving from the Mid MS Valley to the Mid Atlantic states tonight into early Friday, as the trough elongates. After that time, the 12z GFS becomes faster than the consensus, but by that time, the trough is well offshore. Both the 12z NAM/GFS are close to the consensus as the surface wave forms off the NC/SC coasts this evening. The 12z GFS becomes faster with the surface low at that time (and a bit weaker), but this is not surprising considering the mid level support is also faster. Later in the period, the 12z ECMWF/00z ECMWF Ensemble mean becomes slower than the consensus, but by that time, the sensible weather should be exiting the Mid Atlantic coast. Therefore, a general model blend is preferred with respect to the mass fields. ...Closed mid level low reaching the Central/Southern Rockies Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12z UKMET blend Confidence: Slightly below average The 12z NAM/GFS are close to the consensus with the closed mid level low approaching the southwest CA by 22/12z. After that time, both models become faster than the consensus as the mid level low tracks across the central and Southern Rockies into the Central Plains by late Sunday. In contrast, the 12z non-NCEP guidance is slower with the closed low, keeping it west of the NCEP camp by 24/00z (though the 12z CMC sped up, creeping closer to the NCEP models) Most of the guidance (with the exception of the NAM) has been slowing with this feature (and its attendant surface low), including the 12z GFS. Based on the slowing, the non-NCEP guidance is preferred, but given the dichotomy in the guidance, forecast confidence is slightly below normal. ...Mid level shortwave crossing the Pacific Northwest Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12z NAM blend Confidence: Average While the 12z NAM is close to the consensus with the short wave near 50N 150W at 22/12z, it becomes much slower as that solution builds mid level ridging ahead of it across central and northern British Columbia into Sunday. The 12z CMC is also slower for the same reason, but not nearly as slow as the 12z NAM. The 12z GFS is closer to the consensus with the short wave energy as it crosses the Pacific Northwest during Sunday. The 12z UKMET is close to the 12z GFS with respect to timing, but is flatter with the wave at the end of the period. The 12z ECMWF/00z ECWMF ensemble mean is a bit deeper with the short wave by 24/00z though the timing is close to the 12z GFS/12z GEFS mean. Outside of the 12z NAM, there is reasonable agreement with the short wave, so a non-12z NAM blend is preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes