Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 225 AM EDT Tue Aug 27 2019 Valid Aug 27/0000 UTC thru Aug 30/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend TD 06L NHC Proxy: 00z UKMET/12z ECENS blend Confidence: Above average through 48hrs, slightly above average thereafter 07z update: The 00z ECMWF shifted toward solid agreement with the GFS with respect to TD 06L, but away from the current official forecast...which leaves the ECENS mean and UKMET left to represent it. Yet nearly all guidance suggests a secondary development on the frontal zone and the QPF axes continue to shift coast-ward, closer to a ECMWF/GFS blend. Elsewhere, the CMC trended back toward the average in the northern stream after 29/18z to suggest the general model blend. The UKMET trended a bit slower but still remains paired with the faster GFS (having swapped timing placement), increasing confidence slightly above average ---Prior Discussion--- Deterministic guidance, including the 00z NAM and GFS, continue to show very good model agreement with the ensemble suite with respect to the Southwest US Ridge and deep/stacked cyclone over Ontario, and the frontal system pressing across the Great Lakes, Ohio and Tennessee Valleys by early Wed, and into the East Coast by Thursday; enough to support a general model blend for these systems through 48-54hrs. The main uncertainty is the strength/interaction of deep moisture with TD 06L, which shows a fairly sizable model spread, particularly in QPF. The mass fields relative to the 03z NHC forecast is a blend of the UKMET and ECMWF. However, both the 00z NAM/GFS suggest a shift/redevelopment of this highly vertically sheared system toward the frontal zone, tightening the gradient/moisture flux across Southeast New England. The NAM is more aggressive with the moisture return, relative to the GFS, which is a little bit slower to return. Still, given NHC forecast, a blend of the UKMET/ECMWF is preferred. The secondary shortwave in the northern stream starting to undercut the closed low in SW Hudson Bay, continues to show some timing issues, especially as it enters the Upper Great Lakes and the cold front moves into the Upper Midwest. The UKMET continues its fast progress, but the NAM has slowed to match the CMC/ECMWF, and the 00z GFS has taken up the typical fast bias mantle with the UKMET. This is a more traditional timing spread in the deterministic guidance and so a general blend is preferred...speeding up the NAM/ECMWF/CMC and slowing the GFS/UKMET, confidence is average for this wave. Though the 12z CMC is removed from the preference after 29/18z, when Arctic stream shortwave energy is drawn south across the Canadian Prairies into the Red River Valley by early Friday. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina