Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 249 AM EDT Mon Mar 30 2020 Valid Mar 30/0000 UTC thru Apr 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low over Great Lakes and New England with surface cyclogenesis offshore New England Monday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with the mid-level low crossing the Northeast Tuesday morning and the subsequent surface low forecast to track near 40N. No significant differences were noted with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...Southwest shortwave and southern tier surface low reaching the East Coast by Tuesday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS and 12Z ECMWF blend Confidence: Average No significant differences were noted with the 00Z ECMWF/UKMET/CMC copmared to their previous 12Z cycles. The 12Z/00Z UKMET becomes flattest with the mid-level shortwave tracking across the southern U.S. through Tuesday/Wednesday while the 12Z/00Z CMC is slower and farther south with the main vorticity max associated with the shortwave trough. Though some timing differences grow on Wednesday among the 00Z NAM, 00Z GFS and 12Z/00Z ECMWF with the mid-level trough, and subsequent surface low to strengthen offshore of the Mid-Atlantic coast, these differences have more impacts into the western Atlantic than the mainland U.S. Perhaps the 00Z NAM (western side of ensemble spread) should be given less weight on Wednesday given better ensemble agreement for the 00Z GFS and 00Z ECMWF. ...Closed upper low/trough approaching Pacific Northwest through Monday then reaching western High Plains by midweek... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS and 12Z ECMWF blend Confidence: Slightly below average A fair degree of spread remains with this system and confidence is only average given complex interactions with multiple shortwave spokes around the main closed low which sets up over southwestern Canada for Tuesday and Wednesday. Ensemble spaghetti height trends at 500 mb have been converging upon a single solution but differences remain with the GEFS and CMC members bisecting the favored middle ground. Overall deterministic trends since yesterday show greater definition with 2 or 3 main shortwave spokes tracking through the Northwest. The ensemble means show relatively good agreement with these features with the 00Z NAM, 00Z GFS and 12Z ECMWF closest to the means. The 12Z UKMET is less defined with these shortwave spokes while the 12Z CMC evolves into a fairly different pattern aloft. The main trend with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles was to be weaker or tucked close to the center of the main closed low with various shortwaves circling through the Northwest. While the 00Z ECMWF mean may just follow the 00Z ECMWF trend once it becomes available, the preference is to stay toward the middle ground, away from the edges of the deterministic guidance and toward the latest available ensemble mean blend. Timing differences among the 12Z ECMWF, 00Z NAM and 00Z GFS remain with a blended approach toward the middle of these three preferred. The 00Z GFS is likely still a bit too fast/east with a shortwave tracking into southern Manitoba on Wednesday given trends in the ensembles and the remaining placement of the deterministic guidance. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto