Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 233 AM EST Thu Feb 20 2020 Valid Feb 20/0000 UTC thru Feb 23/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Positively tilted mid-level trough axis approaching the East Coast Thursday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z NAM 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. However, the 00Z CMC trended slower, toward the remaining model consensus. Therefore, the better ensemble clustering agrees best with a non 00Z NAM blend of guidance. ...Closed mid-level low reaching the southwestern U.S. early Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 00Z ECMWF, 12Z UKMET, 00Z CMC blend 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. However, the 00Z CMC slowed down near the 00Z GFS timing while the 00Z UKMET slowed down relative to its 12Z cycle. The 00Z NAM looks a big stronger than the remaining consensus but appears reasonable with timing. The reasonably well clustered 00Z GFS, 00Z CMC, 00Z ECMWF and 12Z UKMET appear best, staying away from the slower 00Z UKMET at this time given less support for its timing. Given trends over the past 24 hours, prefer to stay in the middle to slower side of the guidance, which is in line with much of the 00Z deterministic guidance. ...Mid-level shortwave nearing the Pacific Northwest on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z NAM blend 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 00Z ECMWF/UKMET/CMC trended toward the latest ensemble means keeping the 00Z NAM as an unlikely outlier. The ensemble means are in reasonable agreement and appear to match best to a non 00Z NAM blend with the 00Z GFS a bit slower and slightly weaker. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto