Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1209 PM EDT Sun May 26 2019 Valid May 26/1200 UTC thru May 30/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Preliminary Model Evaluation Including Preferences and Forecast Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall CONUS Overview... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Day 1 - Non-GFS with minimal NAM Days 2/3 - ECMWF/GFS/NAM and ensemble means Confidence: Average Amplified pattern persists through the next 3 days as a trough across the western CONUS remains entrenched between a ridge axis over Western Canada, and the Subtropical Ridge anchored over the Southeast CONUS. Through the first two days, /through Tuesday/ most of the spread involves mesoscale impulses shedding from the western trough through the middle of the country. The first of these will lift northeast tonight into Monday morning before becoming embedded in increasingly sheared flow across the Great Lakes late Monday. There exists considerable differences in both timing and intensity of this feature, with the 12Z GFS fast and weak, and the 00z/26 UKMET/CMC/ECMWF slow and strong. The NAM is somewhere in the middle and may be a reasonable compromise so can be included in the blend, but most weight will be applied on day 1 to the non-NCEP suite. During day 2 /Tuesday/ the closed low at the base of the longwave western trough will begin to eject eastward and fill. Timing and intensify differences become more significant as this feature moves into the anchored ridge across the Southeast. While initially the movement of the closed low will lead to downstream amplification of the ridge into Wednesday, eventually it will start to break down the height anomalies in the East, especially across the north as it begins to get absorbed into a vortex over Southern Canada. At that time, the handling of the binary interaction of mid-level lows across Canada becomes important as it begins to affect both the progression of the western trough moving east, as well as the intensity of the upper jet circulations. Note the operational runs tend to be on the fast side of their own ensemble envelopes, which suggests a slower solution. The preferred blend will focus predominantly on the ECMWF/GFS/NAM into day 3 as both the UKMET/CMC have a stronger and more northern displaced upper jet streak driving more progressive and higher latitudinal convection. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Weiss