Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 321 PM EDT Mon May 27 2019 Valid May 27/1200 UTC thru May 31/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall CONUS Overview... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF with some 12Z UKMET/GFS Confidence: Average ...19Z Update... The 12Z CMC has been delayed due to technical issues on the Canadian side and is not available for this discussion. The general trend in all 12Z guidance is a slower and quicker decaying low center over the central Plains Tuesday night. However, the 12Z ECMWF and UKMET did diverge a bit from the excellent agreement of their 00Z runs for Day 3. The 12Z UKMET made the most aggressive change with speed and strength while increasing the strength and speed of the rounding shortwave over northern Mexico which results in a more varied precip pattern on Day 3 with a more meridional pattern over the plains and zonal over the Midwest. The 12Z ECMWF is more subtle with the decay and timing of the main low and the shortwave timing is relatively unchanged, so its Day 3 QPF is relatively unchanged with a more cohesive diagonal precip swath from the southern Plains across the Midwest. Given the consistency the 12Z ECMWF is now the most preferred model and the 12Z UKMET and GFS are included at lower weights. ...Previous Discussion... An amplified and active weather pattern will continue over the CONUS through the next 3 days. The anomalous closed low moving northeast across the Four Corners region today and tonight will slowly move northeast across the central Plains Tuesday into Wednesday before being sheared and drawn into a deep cold core low over James Bay through Thursday as a secondary shortwave trough rounding the parent trough across the West catches up to the remnant low over the Midwest on Thursday. Meanwhile the strong subtropical ridge over the southeast US is slowly shunted south. Progression of this main low, the deep trough out west (with a shortwave trough rounding it) and the subtropical ridge suppression are all well handled by 00Z/12Z guidance with only minor details to the rate of decay of the low over the central Plains and timing of the shortwave trough in question. Particularly good agreement with these features is seen in the 12Z GFS and 00Z ECMWF/UKMET with very similar Day 2/3 QPF. The 12Z NAM is the strongest with the western shortwave trough as it digs south of AZ/NM on Wednesday and therefore has a slightly flatter QPF depiction for Day 2 across the southern Plains. This places the focus of QPF from the 12Z NAM on Day 3 farther east with the shortwave than the remnant parent low which is different than the consensus. The 00Z CMC maintains the closed parent low longest over the central Plains and therefore has a northward displacement of the main precip axis, into the Great Lakes for Day 3. Therefore the 12Z GFS and 00Z ECMWF/UKMET are preferred with slightly above average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Jackson