Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Sun May 26 2019 Valid May 26/0000 UTC thru May 29/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall CONUS Overview... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-NAM blend through 28.12z, ECMWF/GFS blend day 3 Confidence: Slightly above average 07z update: With the rest of the 00z guidance now in, there continues to average to slightly above average confidence in the mass fields through the next 3 days across the CONUS. The biggest model differences occur across the Upper Midwest toward the end of the forecast period as the closed low from the western US opens up. The UKMET trended toward the NAM being a faster, more open and progressive solution. The ECMWF and GFS are nearly identical and is similar to the CMC. For now, the slower solution seems more likely given the strength of the ridge downstream over the eastern US, so will prefer mainly a GFS/ECMWF blend for day 3. ---previous discussion--- Over the next 3 days the flow pattern will start off fairly locked/persistent with the strong subtropical ridge over the southeast US and western trough, but toward day 3 /Tuesday into Wednesday/, the trough axis will move across the central US while the southeast US ridge is shunted down somewhat. For Sunday, shortwave troughing over the central US / mid-MS River Valley will move through the Ohio Valley and Mid-Atlantic. There is fairly good clustering in the deterministic models with that feature moving through. In the western US, impressive closed low will settle over southern California by late Sunday while a leading piece of energy ejects out in the southwest US. Again, positioning and strength of the closed upper level is very similar with the guidance through at least 48 hours (Monday evening). There are differences that creep up at the surface level, where the NAM takes a surface low expected to form Monday morning over the central US further north compared to the GFS/CMC/ECMWF/UKMET. Another wave of low pressure developing late Monday into Tuesday also exhibits the same bias (NAM north, GFS/CMC middle, ECMWF/UKMET south) with the spread from Nebraska to southern Kansas. By day 3 /Tuesday night into Wednesday/ the model differences creep up with respect to the closed low that ejects out into the central US and begins to open up over the Upper Midwest. The NAM is considerably faster with its position by 12z Wednesday while the GFS is also on the faster end of the model spread. The ECMWF and CMC are on the slower side, holding onto the stronger southeast ridge a bit longer. In this scenario this is favored, so a non-NAM, less weight to the GFS blend is preferred for day 3. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor