Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 302 PM EDT Sat Mar 30 2019 Valid Mar 30/1200 UTC thru Apr 03/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation With Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Cold front moving through the eastern third of the nation through Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average ...19Z update... No significant changes were noted in the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. ...previous discussion follows... Only minor differences remain with this system. Trends in timing have been converging upon the steady ECWMF mean, with the latest guidance showing reasonable agreement. Therefore, a general model blend is preferred with this system. ...Four Corners to Southern Plains trough/closed low... ...Reaching the Gulf Coast/Southeast by Mon/Tues... ...Cyclogenesis near the Southeast Coast by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/ECMWF/UKMET blend Confidence: Average ...19Z update... The 12Z CMC/UKMET adjusted faster toward the consensus early on near the Southwest, but the 12Z CMC ends up slower and more amplified, like the 12Z NAM toward the Southeast Tuesday morning. The 12Z UKMET adjusted closer to the 12Z GFS with a faster shortwave aloft and a surface low offshore of the southeastern coast farther offshore. The 12Z ECMWF adjusted north with the surface low offshore bit a little bit. Ensemble scatter low plots support a middle ground best represented by a blend of the 12Z or 00Z ECMWF, 12Z GFS and 12Z UKMET. ...previous discussion follows... The 12Z GFS appears to be too fast as the mid-level shortwave reaches Texas with a strong remaining consensus slower with the wave. The 00Z CMC/UKMET are slower but the 12Z NAM ends up on the slowest side of the ensemble envelope and a bit stronger as the shortwave moves into the southeastern U.S. Recent trends with the GFS and GEFS have been to slow down with shortwaves progressing from west to east in this flow pattern and the 12Z GFS lies on the faster edge of the guidance. Therefore, given some differences aloft with the 00Z UKMET/CMC earlier with the handling of the shortwave, the 00Z ECMWF, when blended with the 12Z GFS slightly, is preferred for this system. ...Trough/Low approaching the West Coast on Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/ECMWF/UKMET blend Confidence: Average ...19Z update... Adjustments by the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles look favorable with this system, in the direction of the previous preference (12Z GFS), but the 12Z CMC continues to lag in amplitude across the West on Tuesday. ...previous discussion follows... Reasonably good agreement exists with this system until late Monday into Tuesday when the amplitude of the upper trough shows differently in the models. The 00Z UKMET/CMC are near outliers with their handling of the mid-level energy resulting in a closed low off of Vancouver Island. The 12Z NAM is deeper with the trough amplitude out West while the 00Z ECMWF is a bit flatter. The 12Z GFS appears to be a good middle ground for this system. ...Upper trough over the Northern Plains/Midwest Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/12Z ECMWF blend Confidence: Average ...19Z update... Only minor changes were noted in the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. Therefore, the final preference remains the same as the preliminary...other than replacing the 00Z ECMWF with the 12Z ECMWF. ...previous discussion follows... The 12Z GFS is faster, noted with the 850-700 mb timing of the wave, with the 00Z ECMWF and 12Z NAM showing good agreement from the latest ensemble guidance. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Otto