Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 224 PM EDT Mon Mar 18 2019 Valid Mar 18/1200 UTC thru Mar 22/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/CMC/GFS for central/eastern US General model blend for western US Confidence: Above Average 1830z update: For the shortwave trough moving across the Plains and eventually the southeast US, the UKMET trended faster and less amplified compared to its 00z version, but is still an outlier as it digs well south of the model spread. The 12z CMC falls in line with the 12z GFS. Temporally, the models trended a bit faster compared to the 00z runs and is closer in line with the 12z NAM. As the trough moves off the southeast US, energy phases and a surface low forms off the NC coast. All of the operational models feature this scenario, though the NAM is closest to the coast (thus higher QPF is onshore) compared to the GFS/CMC and UKMET which keep the highest amounts offshore at this time. For the 12z ECMWF, its shortwave trough falls in line with the GFS as it progresses through the Plains and southeast US. Its surface low off the NC coast is closer to the coast and similar to the NAM, though is further north (closer to the NC/VA border). Overall, the forecast confidence drops off with how this will evolve by Thursday/Thursday night. For now, will keep the preference of a blend of the ECMWF/GFS/CMC for the central/eastern US while out west, a general model blend seems reasonable. ---previous discussion--- The biggest model discrepancies in the forecast period are focused on the digging shortwave trough across the Plains Tuesday-Wednesday and then as it rounds the base of the longwave trough over the southeast US. Across southern California and the southwest US, a longwave trough will gradually move eastward and likely close off over the Four Corners region. For the Plains shortwave, the 00z UKMET is considered an outlier with its over amplified solution and also is considerably slower than the rest of the guidance. The 12z NAM has trended faster with its progression, which is plausible, but also is much faster than some of the 00z guidance, particularly the ECMWF/GFS/CMC. The consensus at this point is for a general blend of the ECMWF/GFS/CMC for this feature, which seems to be well within the ensemble spread. As the shortwave trough moves toward the east coast, the NAM spins up a surface low off the NC coast with an axis of heavier QPF right along the NC/SC coast. For now this is considered an outlier, so the NAM will be not included for the central/eastern US. For the western US as the trough moves onshore, the NAM appears to be in better shape spatially and temporally, and the UKMET is also a reasonable solution. As such, a general model blend appears sufficient. The rest of the CONUS has relatively benign weather and for the mass fields, the models are in pretty good agreement so a general model blend, leaning on the ECMWF/GFS solutions, is the overall recommendation. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor