Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 329 PM EDT Mon Jul 02 2018 Valid Jul 02/1200 UTC thru Jul 06/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough advancing into Ontario/Quebec tonight with accompanying cold front into the Northeast and Ohio Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Westward moving upper circulation along the Gulf Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS / 12Z ECMWF blend Confidence: Average Biggest differences are regarding strength of this feature with the 00Z CMC strongest and considered least likely to verify given a lack of support. Some combination of the stronger/more suppressed tracks is preferred best represented by a 12Z GFS/00Z ECMWF blend. 19Z update: The 12Z ECMWF/UKMET/CMC either converged toward the preference or did not significantly change. A GFS/ECMWF blend still applies for this system, but all models have some utility here. ...Upper low approaching the southeastern U.S. coast by mid-week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Some minor timing differences as the mid-upper wave nears the Southeast coast but the 12Z GFS trended faster than most guidance by Wednesday night into Thursday, so will leave it out of the preference for that reason. 19Z update: With the exception of the 12Z CMC (which trended slower), the 12Z ECMWF/UKMET trended faster like the GFS with the 12Z models now showing a spread between faster/slower. Given the differences are not too large, will allow for a general model blend as the preference. ...Upper low/trough taking shape over Canadian Rockies/Pacific Northwest Mon/Tues...lifting across Northern Plains/S Canadian Prairies into Wed/Thurs. Surface wave(s) along Northern Plains frontal zone. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ Preference: General model blend Confidence: Slightly below average Biggest uncertainty with systems across the lower 48 is here with above average ensemble spread and poor run to run consistency. Convective feedback in the vicinity of a frontal boundary across the north-central U.S. adds another layer of complexity to the forecast. The timing of the upper wave in the 00Z ECMWF appears a bit too fast given the latest ensemble clustering and the fact it is faster than its own ensemble mean. The 12Z GFS is slower/deeper, but not to the degree of the 00Z CMC, with the 00Z CMC likely a poor choice. Regarding the frontal boundary into the north-central U.S. and related surface waves, a blend of the 12Z NAM/GFS is preferred overall, but with low confidence. 19Z update: The 12Z ECWMF/UKMET/CMC adjusted toward the preference to some degree, reducing spread aloft such that a general model blend can be used but with a continued below average confidence. ...Shortwave reaching Canadian West Coast and becoming closed low off U.S. West Coast by late Wed/Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show similarly with this system. 19z update: No significant changes based on the 12Z ECMWF/UKMET/CMC. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto