Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 126 PM EDT Mon Jun 15 2020 Valid Jun 15/1200 UTC thru Jun 19/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Preliminary Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low lingering across the Southeast through Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 48hrs ECMWF/ECENS/GFS/GEFS blend after Confidence: Above average Guidance is very well clustered in the evolution of the closed low as it digs towards GA/SC and then spins nearly in place into Wednesday. Thereafter, the CMC becomes a northeast outlier as its vort impulse is much stronger which tugs the center of the closed low further NE towards MD, while the GFS and the NAM fill out the left/west side of the envelope by the end of the forecast period. Interesting that the GEFS mean is actually close to the CMC on D3, suggesting that the GFS operational is likely too far west. This leaves the ECMWF/ECENS as the center of the guidance consensus, which has some support from the UKMET, but once again the UKMET erodes the ridge to the north a bit too quickly letting it eject out late as well. A heavy weight of the ECMWF/ECENS is suggested for D3, with some light weight on the GEFS/GFS which will smooth out some of those differences. ...Secondary closed low moving into the Northwest Tuesday... ...Northern Plains surface lows/N-S frontal zone... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend until 17.18z then 00z ECMWF/CMC/UKMET blend thereafter Confidence: Above average through 17.00z, average thereafter The western preferences are dependent on the interaction of a closed low moving onshore and a trough across western Canada which will form a large closed gyre through the middle of the week. Through 48 hours a general consensus is acceptable as the spread amongst the various members is minimal. However, by Wednesday differences begin to arise in response to varying intensities of a jet streak and shortwave impulses. The NAM lags a robust shortwave on the SW side of the gyre causing the trough to sharpen well SW of the other guidance, while the GFS reaches a similar evolution by D3 being more elongated and positively tilted SW to NE, but due to a faster progression of this shortwave rotating cyclonically around the main gyre. This leaves the non-NCEP guidance, which is well clustered with the evolution of this gyre and re-closing of the upper low across the Northern Rockies late in the forecast period. Weiss Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml