Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 234 AM EDT Sun May 06 2018 Valid May 06/0000 UTC thru May 09/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough deamplifying as it pushes through the Mid Atlantic today, with weak surface lows developing just offshore... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The models generally show similarity with this system. The 12Z CMC shows more differences, with a more rapid deamplification of the trough and a more pronounced downstream ridge just offshore of the East Coast. This has less support among the deterministic models and ensemble members, so the preference is to lean toward the broader consensus. ...Upper level trough digging into the Great Lakes today and sweeping across the Northeast Monday... ...Associated cold front pushing through the Midwest and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Models are also in very good agreement with this system, other than some minor differences in the mass fields. Overall, there is not enough of a systematic bias in any one model to exclude it from consideration, so a general model blend is preferred. The 12Z CMC does show slightly less amplification to the trough, but not to the degree that it does with the trough further south over the Mid Atlantic. ...Shortwave ejecting from the West Coast today to the Northern Plains by Tuesday with lee cyclogenesis over the Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z GFS; 12Z ECMWF; 12Z UKMET Confidence: Average There is better agreement now on the progression of the southern stream PV anomaly / shortwave in the West Coast trough, currently located near northern California. Models eject this wave through the northern Rockies and into the northern Plains. The 00Z NAM appears to have the strongest mid-upper level vorticity maximum associated with this wave, and has it concentrated further southeast than the other models. This does affect its QPF, and it is not preferred for this system. The 12Z CMC shows a much weaker wave overall, and has the strongest mid-level vorticity concentrated much further north, near the Canadian border. This is also not preferred for this system. Otherwise, the GFS, ECMWF and UKMET offer similar forecasts, and a consensus of those three models is the preference. ...Upper level trough approaching the West Coast by Tuesday... ...Accompanying offshore surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z GFS; 12Z ECMWF Confidence: Average The timing of this trough on the models is actually in reasonably good agreement, with all models showing a trough axis from near 50N/133W to central Oregon by 09.12Z (Wednesday morning). The main difference is with strength and amplitude. The 00Z NAM and 12Z CMC show a more amplified trough with the base of the higher mid-upper level vorticity reaching well into Oregon. The 12Z UKMET has a stronger wave with a closed low through the entire forecast period, but is not quite as amplified as the NAM or CMC. The 00Z GFS and 12Z ECMWF, meanwhile, have a less amplified trough as they show a continued devolution of the closed low from offshore over the Pacific Ocean. There is more support from the ensemble clusters for the GFS and ECMWF scenario, so the preference is to lean in that direction for now. ...Lingering upper level trough over the Southeast from Monday through Tuesday Night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Slightly above average Models show similarity with this system, with the exception of the 12Z CMC which does not lift the trough out of the Southeast from Tuesday into Wednesday as the other models do. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers