Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 241 PM EDT Fri Mar 13 2020 Valid Mar 13/1200 UTC thru Mar 17/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed Low developing over Pacific NW through Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z/16 12Z ECMWF/UKMET/CMC blend 00Z/16 - 00Z/17 Confidence: Slightly above average Model differences remain small until Sunday evening when the 12Z GFS ends up farther south with the 700-500 mb low off of the West Coast. The 12Z GFS is not an outlier when considering the available ensemble guidance but given greater support for a non-GFS solution by Sunday. The new 12Z ECMWF/UKMET/CMC came in and split the difference between the southward displaced 12Z GFS and slower/northern 12Z NAM. This middle ground looks preferable and so the final preference has been adjusted to reflect the updated thinking. ...Weakening mid-level shortwave tracking through the Southwest today, weakening across the Midwest late Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-12Z NAM blend Confidence: Slightly above average Only minor timing/amplitude differences remain with the mid-level shortwave as it tracks east through the OH Valley. The 12Z NAM, as with previous cycles, continues to look too fast, however not by a lot. A non-12Z NAM blend of guidance looks reasonable with this system. There are some latitude differences with the trailing front across the southern states by Saturday into Sunday with a weaker surface low noted in the 12Z GFS tracking across the Mississippi River Valley allowing for a more southern-placed warm front. The GFS is not an outlier, but there is less support for it among the remaining deterministic guidance. Ensemble means support a middle ground which can be represented by a general blend, removing the faster timing of the 12Z NAM across the eastern U.S. The 12Z ECMWF/UKMET/CMC did not make significant differences from their previous 00Z cycles, so the preference remains the same for this final discussion. ...Base of longwave trough over the north-central U.S. by Monday evening... ...Related cold front across the Upper Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-12Z GFS blend Confidence: Average The 12Z GFS stands out as the faster model with this system, a non 12Z GFS blend will be preferred given the remaining deterministic and ensemble guidance (including the 06Z GEFS) is slower than the 12Z GFS. While the 12Z GEFS matches the timing of the 12Z GFS with the front, no significant changes noted with the 12Z ECMWF/UKMET/CMC translate into keeping the preference the same for this final discussion. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto