Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 238 PM EDT Sun May 06 2018 Valid May 06/1200 UTC thru May 10/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Trough deamplifying as it pushes through the Mid Atlantic today, with weak surface lows developing just offshore... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show sufficient model mass field agreement that a general model blend can be preferred with this energy. ...Upper level trough digging into the Great Lakes today and sweeping across the Northeast Monday... ...Associated cold front pushing through the Midwest and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models are also in very good agreement with this system, other than some minor differences in the mass fields. Will prefer a general model blend. ...Shortwave crossing the Northwest and arriving across the Northern Plains by Tuesday... ...Lee cyclogenesis over the Plains... ...Secondary shortwave dropping southeast over the Northern Plains along with an attendant front on Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Average The shortwave trough moving across the West Coast today will traverse the Northwest through Monday and then begin digging southeast out across the central/northern Plains by Tuesday where it will focus an area of low pressure. As this energy approaches the Midwest by Wednesday, there will be a secondary shortwave dropping southeast from southern Canada along with an attendant front that will attempt to phase with the lead energy. With the lead energy, the models are in good agreement until about 48 hours when the 12Z NAM focuses its low pressure over the Plains a little north of all of the 12Z global models. By Wednesday though, the CMC becomes a bit of an outlier with its stronger low pressure crossing southern MN and moving into western WI. Regarding the secondary shortwave, the NAM is the weakest solution, with the UKMET the strongest. The GFS and ECMWF are clustered in between only modest timing differences and are supported by the CMC with this energy. Will suggest a blend of the GFS and ECMWF with both shortwave impulses given their good clustering and ensemble support. ...Upper level trough approaching the West Coast by Tuesday... ...Accompanying offshore surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 12Z CMC and 12Z ECMWF Confidence: Average The models are in generally good agreement through about 60 hours with the timing and overall depth of the system as it approaches the West Coast on Tuesday. However, as it crosses the West Coast and pivots northeast across the Pacific Northwest Tuesday night and Wednesday, the 12Z NAM does tend to be a little more aggressive with the height falls and especially as they push toward southern British Columbia. The 12Z UKMET also is seen as trending a little slower and deeper with its closed low solution west of British Columbia at the end of the period which translates into a surface low evolution that is out of tolerance with the model consensus. The better clustered solutions are the 12Z GFS, 12Z CMC and 12Z ECMWF which are better supported by their respective ensemble suites. Thus a blend of the GFS, CMC and ECMWF will be preferred at the surface and aloft. ...Lingering upper level trough over the Southeast from Monday through Tuesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement with this system as the 12Z CMC finally trended more progressive and is close to the otherwise well clustered guidance. The CMC also trended away from its solution of a stronger surface low off to the East Coast on Wednesday. A general model blend will be preferred as a result. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison