Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1157 PM EST Wed Feb 19 2020 Valid Feb 20/0000 UTC thru Feb 23/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Positively tilted mid-level trough axis approaching the East Coast Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend Confidence: Slightly above average As a shortwave trough axis tracks east during the day on Thursday into Thursday night, a surface low will organize off of the Southeast coast. The 00Z NAM is a tad stronger and farther north with the low compared to the remaining deterministic and ensemble guidance. The 12Z CMC stands out as well with a more northward and slightly quicker trough progression off of the East Coast. The better ensemble clustering agrees best with a 00Z GFS, 12Z ECMWF and 12Z UKMET blend. ...Closed mid-level low reaching the southwestern U.S. early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend (least weight on ECMWF) Confidence: Average The ensembles have been trending slower with the closed low Friday into Sunday morning across the Southwest. The latest guidance shows the 12Z CMC much faster than the latest clustering of deterministic and ensemble guidance. Meanwhile, the 00Z NAM looks a big stronger than the remaining consensus but appears reasonable with timing. Of the reasonably well clustered 00Z GFS, 12Z ECMWF and 12Z UKMET, the 12Z ECMWF is fastest, followed by the 00Z GFS and then the 12Z UKMET. Given trends over the past 24 hours, prefer to stay in the middle to slower side of the guidance, which would put less weight on the 12Z ECMWF compared to the 00Z GFS and 12Z UKMET. ...Mid-level shortwave nearing the Pacific Northwest on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z UKMET blend (least weight on GFS) Confidence: Slightly below average Large differences in the deterministic guidance exist with a shortwave forecast to near the Pacific Northwest on Sunday. The 00Z NAM is rather flat aloft and featureless at the surface while the 12Z ECMWF/UKMET/CMC are rather wrapped up with the mid-level shortwave and surface reflection. The ensemble means are in reasonable agreement and appear to match best to the 12Z ECMWF/UKMET while the 00Z GFS is a slower and slightly weaker version of the ECMWF/UKMET. A 3-way blend (00Z GFS, 12Z ECMWF, 12Z UKMET) appears best at this time but with less weight on the somewhat slower/weaker 00Z GFS. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto