Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1232 PM EDT Wed May 02 2018 Valid May 02/1200 UTC thru May 06/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Ejecting low-amplitude shortwave crossing the Great Lakes and northern New England through tonight... ...Weak attendant surface low ejecting along a front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with this system as it cross the Great Lakes region and clips portions of northern New England. Will prefer a general model blend with this system. ...Shortwave crossing south-central Canada and the northern Plains today... ...Energy shearing downstream across Ontario/Quebec through Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement with this system, and so a general model blend will be preferred. ...Ejecting Southwest U.S. upper trough crossing the central Plains and upper Midwest through Thursday... ...Phasing with northern stream energy from south-central Canada on Friday... ...Surface low lifting from the central Plains Thursday to the lower Great Lakes on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average The models take a large portion of the Southwest U.S. upper trough/closed low and lift it northeast across the central Plains and upper Midwest through Thursday which will then gradually phase with the arrival of northern stream shortwave energy from south-central Canada on Friday. This will allow low pressure riding northeast by along a front to cross the central Plains and then attempt to deepen over the lower Great Lakes on Friday depending on how much phasing actually occurs. Collectively the models are coming into better agreement on there being more phasing, and the NAM and GFS solutions in particular have trended stronger with low pressure that crosses through the Great Lakes region. The NAM overall is still generally the most progressive, followed by the GFS and then the clustering of modestly stronger and slower CMC, UKMET and ECMWF solutions. At this point, the GFS is in close enough timing and depth agreement with the non-NCEP models that a non-NAM blend can be preferred, and that will be the choice for now. ...Lingering trough over the Southwest on Friday... ...Energy ejecting east across the southern Plains/lower MS Valley on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models maintain a portion of the Southwest U.S. trough/closed low going through Friday. Thereafter, they eject the energy east across the southern Plains and lower MS Valley. Despite some very modest timing and depth spread, the guidance is in good large scale agreement with this system. A general model blend will be preferred. ...Mid-level shortwave approaching British Columbia Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM, 12Z GFS and 00Z ECMWF Confidence: Slightly above average The models bring a shortwave in off the Pacific on Friday and in across British Columbia. The 00Z UKMET appears to be too progressive and perhaps a bit too strong overall with the energy. The 00Z CMC on the other hand is perhaps a tad too weak. The better clustered models with this system are the 12Z NAM, 12Z GFS and the 00Z ECMWF which agree well with timing and depth and are very close to the model consensus and also have good ensemble support. A blend of the NAM, GFS and ECMWF will be preferred. ...Inverted low/mid level trough impacting southern FL... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average The models take a low to mid level trough axis and perhaps an associated weak closed low west across the Bahamas and toward south Florida, the Florida Keys and adjacent areas of Cuba late Friday through Saturday. The models are in generally good agreement with this system, with exception to the CMC which has a stronger and better-defined surface low going west through the Florida Straits. A non-CMC blend will be preferred at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison