Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1254 PM EDT Mon Apr 09 2018 Valid Apr 09/1200 UTC thru Apr 13/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Model Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern stream shortwave moving from the Great Lakes today to near Maine and northern New England by Tuesday Night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The 00Z CMC has higher heights through the depth of this trough from eastern Canada down to Florida, and the lower amplitude affects the overall forecast. The other models are relatively similar and fairly close to ensemble means as well. Therefore, the preference is for a non-CMC blend. ...Southern stream shortwave over the southern Plains today, reaching the southeast Atlantic Coast by Tuesday Night... ...Stalled surface front in the vicinity of Florida... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS; 00Z ECMWF Confidence: Slightly above average The GEFS and ECMWF ensemble means are very close to each other for this system, and demonstrate reasonable run-to-run consistency. The 12Z GFS and 00Z ECMWF are similar to those ensemble means as well, and given the overall consistency, those models are preferred for this system. The 00Z UKMET and 12Z NAM dig the shortwave more over the Gulf of Mexico, leading to a more amplified trough overall, while the 00Z CMC is much less amplified than the ensemble means. ...Shortwave or lobe of the Hudson Bay low digging into Great Lakes Wednesday and reaching Canadian Maritimes Thursday... ...Weak surface low passing just north of the Canadian border... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET; 00Z ECMWF Ensemble Mean Confidence: Average Models show some timing differences with the shortwave, and the 12Z NAM and GFS are slightly slower, with the 00Z CMC and ECMWF a little faster. The 00Z UKMET and ECMWF Ensemble sit somewhat in the middle of these extremes. Given the overall run-to-run consistency of the ECMWF Ensemble, the preference is to lean toward that and the UKMET (which is similar but with slightly more amplitude to the trough). ...Lead shortwave and associated surface wave passing northeast through the Pacific Northwest on Tuesday... ...Secondary shortwave just behind, reaching the northern Rockies by Wednesday and Great Lakes Thursday... ...Surface low development over the Northern Plains Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF Ensemble Mean Confidence: Slightly below average The primary disagreement with this system is the latitude of the surface low track, with the 00Z ECMWF and CMC further north and the 12Z GFS and NAM further south. The 00Z UKMET sat a little north of the middle of a consensus. The GFS has actually trended south over the past several model runs, while the ECMWF has been relatively consistent. The 00Z ECMWF Ensemble Mean was also very consistent with previous runs, and was approximately a median scenario at this point. Given the consistency and support from GEFS+ECMWF ensemble clusters, the preference is to lean toward the ECMWF Ensemble. ...Trough and associated surface front arriving on the West Coast on Wednesday and reaching the Plains by Thursday... ...Strong lee cyclogenesis over the central Plains Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF Ensemble Mean Confidence: Average There is a difference in timing with the trough pushing into the Western U.S. by midweek. The 12Z NAM and GFS are slightly faster, while the 00Z ECMWF, CMC and UKMET are slower. As with other systems, the ECMWF Ensemble Mean has demonstrated reasonable consistency, despite quite a bit of run-to-run variance from operational deterministic models and ensemble members. The ECMWF Ensemble Mean also sits in the middle of the model spread, perhaps most closely matched by the operational ECMWF. This is the preference for this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers