Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1228 AM EDT Thu Apr 09 2020 Valid Apr 09/0000 UTC thru Apr 12/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed Low Over Northeast; Deepening Surface Low Off New England Coast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Anomalous closed low currently over northern Great Lakes will deepen and take a negative tilt as it approaches the Northeast later today while at the surface, low pressure will move toward the eastern Great Lakes. A secondary low will develop along the I-95 corridor and deepen along coastal Maine. Overall, the mass fields have come into very good agreement with the evolution of this system over the next 24-36 hours such that a general model blend should suffice. Slow moving closed low across the Southwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: ECMWF/ECENS mean blend Confidence: Average Large, slow moving cut-off southern stream closed low over southern California is expected to gradually move eastward as it interacts with approaching northern stream energy on day 3. Until then, movement will be slow and over the last several model cycles, the ECMWF has proven to be more consistent. Both the 18Z GEFS and 00Z GFS are fast outliers with the ejection of the feature into the southern Plains on day 3, though it is worth noting that the 00Z GFS did trend slower, and is now slower than the 18Z GEFS mean, so perhaps later runs of the GFS will catch on to the trend. The UKMET is also less favored as it has its upper low too far to the southwest, and digs further south into the Baja region. Otherwise, a blend of the ECMWF/ECENS mean with some inclusion of the CMC seems like a good approach for this system mass fields. Upper level trough and cold front reaching the Northwest by end of the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: CMC/ECMWF/ECENS mean Confidence: Slightly above average Shortwave energy along the southern coast of Alaska will progress eastward to the Yukon territory, and with the accelerating/exiting jet, the upstream ridge will break down and allow for greater propagation east and then southward across southwestern Canada. The height-falls will overspread the lee of the Canadian Rockies and then northern High Plains, and support a surface cold front to drop southward across Montana and the Dakotas. Some timing differences are noted in the latest guidance, where the GFS/NAM and the UKMET to some degree where a bit faster than the 12Z ECMWF/CMC. A look at the latest ensemble means, the slower trend would be favored and the GFS/NAM are likely too fast with its progression of the cold front across the northern Plains. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor