Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Tue Mar 31 2020 Valid Mar 31/1200 UTC thru Apr 4/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preliminary 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. Broad upper level gyre over Northwest with northern Plains shortwave ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z ECMWF/00Z 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 00Z CMC a tad slower with the trailing cold front. Shortwave tracking across Intermountain West by end of the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET/ECMWF 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. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick