Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Tue Mar 31 2020 Valid Mar 31/1200 UTC thru Apr 04/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Southeast U.S. surface low and shortwave trough ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM compromise Confidence: High The surface low currently tracking eastward across the Southeast will emerge over the western Atlantic Tuesday night and track out to sea and north of Bermuda. Differences are relatively minor with this system for the most part. However, the 12Z NAM was the farthest northwest with the surface low which tracks across the western Atlantic and more amplified aloft compared to the other models. The preferences is toward a non-NAM consensus to account for the good agreement of the other models. There is no change necessary to the model preferences based on the latest 12Z model suite. Broad upper level gyre over Northwest with northern Plains shortwave ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z UKMET blend Confidence: Moderate An upper level low over southwest Canada will remain nearly anchored in place for the next few days, with a couple of shortwaves pivoting around it. The first shortwave perturbation will pivot northeastward across Montana and North Dakota on Wednesday, sustaining a surface low across the Dakotas. The main model difference here is with the 12 NAM, indicating a much more amplified solution by 00Z Thursday, and the 12Z GFS faster with the trailing cold front. The 12Z CMC is weakest with the amplitude of the trough axis and not as strong with the surface low. Shortwave tracking across Intermountain West by end of the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z CMC/ECMWF/00Z EC mean blend Confidence: Low-Moderate The second significant shortwave pivoting around the upper level gyre will cross the Pacific Northwest on Wednesday and then reach the Rockies by Wednesday night. This will support lee surface cyclogenesis over the western High Plains by Thursday along an existing frontal boundary. Similar to the lead shortwave, the NAM appears stronger with this feature crossing the Intermountain West and the CMC a little broader with the trough axis. The 12Z GFS is a little quicker in bringing mid-level height falls to the High Plains, and the 12Z UKMET is slightly more amplified with the trough axis, and its surface front across the southern Plains is slightly slower than the model consensus. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick