Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1208 PM EDT Sun Mar 17 2019 Valid Mar 17/1200 UTC thru Mar 21/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave crossing the OH Valley/Mid-Atlantic thru Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The guidance shows very good mass field agreement with this system as it advances east through the OH Valley today and tonight, and then across the Mid-Atlantic region on Monday. A general model blend will be preferred. ...Shortwaves dropping southeast across the Plains/Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS/06Z GEFS mean/00Z UKMET Confidence: Average The models show multiple shortwave troughs dropping southeast from southern Canada and down across the northern/central Plains and adjacent areas of the Midwest. The 12Z GFS, 00Z UKMET and 00Z CMC support a rather strong lead shortwave arrives across the northern Plains by late Monday and digs southeast through the middle MS Valley by early Wednesday and the TN Valley by Wednesday evening. The 12Z NAM and 00Z ECMWF take the same shortwave down across the northern/central Plains and then appear to struggle with how much energy gets trapped underneath a blocking high over southwest Canada and the northern High Plains. The ECMWF consolidates a closed low near the central High Plains/Front Range by Wednesday whereas the NAM elongates and stretches out the vorticity from the central High Plains east across the middle MS/lower OH Valleys. There is considerably stronger ensemble support for the more progressive camp led by the GFS and UKMET. The CMC for its part is progressive but also supports a stronger closed low evolution over the mid MS Valley that is not well supported at this time. Meanwhile, a second shortwave by Wednesday will be dropping down across the Great Lakes region, and in this case, the GFS and UKMET are a bit sharper with the trough versus the NAM, CMC and ECMWF. There is a bit better ensemble support for the sharper trough, at least from the GEFS mean. And based on the trends/clustering of solutions with both shortwaves, the model mass field preference will be toward a blend of the 12Z GFS, 06Z GEFS mean and 00Z UKMET. ...Upper trough /closed low moving into CA by Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...led by the 12Z GFS/00Z ECMWF Confidence: Slightly above average An upper trough will be digging into CA by Wednesday along with likely development of a closed low. The 12Z NAM is the most aggressive with its height falls, with the global models all a bit weaker. There are some modest timing differences with the height falls within the global model suite, but for now the preference will be a non-NAM blend led by the 12Z GFS and 00Z ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison