Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 310 PM EDT Sun Jul 01 2018 Valid Jul 01/1200 UTC thru Jul 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...including final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough advancing from the upper Mississippi Valley today into Ontario tonight with accompanying cold front... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Despite some minor timing differences, the models show similarly with this system. ...Westward moving upper circulation along the Gulf Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/12Z ECMWF Confidence: Slightly above average Only a few ensemble members (ECMWF/GEFS/CMC) show a surface low near the Gulf Coast after Tuesday morning which indicates any surface reflection should be weak beyond that point in time. The 12Z NAM is stronger than the model consensus in the low-mid levels but the 00Z UKMET is strongest of the deterministic guidance and least likely to verify. In addition, a blend of the GEFS/EC mean positions at 500 mb and the surface indicates the 00Z UKMET is too slow to track the wave to the west, along with the 00Z CMC, through Tuesday night at which point the timing differences shrink. While the 12Z GFS may be too weak with the low-mid level wave tracking westward along the Gulf Coast, when blended with the similarly placed 00Z ECMWF, a favorable compromise is reached. 19Z update: The 12Z UKMET/CMC trended slightly faster but the UKMET remains stronger than the consensus and the CMC remains slowest. Adjustments in the ECMWF were minimal and so the preference remains a GFS/ECMWF blend. ...Pronounced upper low/trough taking shape over the Pacific Northwest by Monday/Tuesday... ...Secondary upper low inhabiting the east Pacific for Tuesday and Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/12Z ECMWF/12Z UKMET Confidence: Slightly above average Ensemble spaghetti heights and trends continue to show the NAM too fast with the mid-level trough advancing eastward from the Northwest U.S., with the 12Z NAM on the fastest edge of the latest ensemble members on Tuesday. On the other side of the spread, the 00Z CMC is significantly slower, only supported by 00Z CMC ensemble members. The 12Z GFS, 00Z ECMWF and 00Z UKMET have been and are currently in the best agreement with this system, and are in alignment with the latest ensemble clustering. Similarly with a secondary upper low offshore of the Northwest early to mid week, the 12Z GFS, 00Z ECMWF and 00Z UKMET show similarly with placement and therefore a GFS/ECMWF/UKMET blend works well for the entire northwestern section of the U.S. through Wednesday. 19Z update: The 12Z UKMET/CMC/ECMWF trended faster but not to the extent of the 12Z NAM. The CMC remains slowest and while the preference has been nudged faster to reflect trends and now includes the faster ECMWF/UKMET...supported by a dozen or so ECMWF members, incorporating the 12Z GFS as part of a blend appears to be the best fit right at this time. ...Upper low approaching the southeastern U.S. coast by mid-week... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z NAM blend Confidence: Average While the models show close to one another with this system, the 12Z NAM ends up fastest by Wednesday evening along the eastern Gulf Coast which is unsupported in the remaining guidance. Therefore, a non 12Z NAM blend is recommended for this system. 19Z update: The 12Z UKMET/CMC remain similar to their previous 00Z cycle, while the 12Z ECMWF sped up a bit. However, the 12Z NAM remains the faster outlier with this system. Run to run consistency in the GFS and ECMWF has been meandering about a similar position since 24 hours ago as the upper low nears the Southeast coast. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto