Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1205 AM EDT Tue Apr 09 2019 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 with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Great Lakes/New England (northern stream shortwaves)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average GOES-WV suite depicts amplifying shortwave crossing the Northern Great Lakes. There is good agreement with the progression and amplification of this wave through New England with an exception of the 12z CMC which is a tad slower and less amplified. So will support a non-CMC blend at above average confidence. ...Southeast (southern stream closed low)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Closed/stacked low across MS sliding east is starting to open/stretch toward the northeast. The CMC is a bit weaker and the UKMET/00z NAM is a bit stronger to offset. So, all in all, a general model blend can be supported at above average confidence. ...Approaching Western trof Mon/Tues, amplifying through Intermountain West by Wed spurring deep Plains cyclone, Wed into Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average to above average. Models continue to show remarkable consistency with the shape/timing/orientation of the trof through the Intermountain West. The spread that does evolve appears to occur as the main axis starts vortical stretching in the lee of the Rockies into the Central Plains and small scale timing differences start to emerge but still very strong through 60hrs. At this point the 00z NAM which had been trending north away from consensus, further shifted this direction. This appears to be related to some binary interaction with lingering shortwave energy from the sheared/exiting trof across the Great Lakes being drawn West then Southwest across the Northern Red River, which in turn, drew the deepening cyclone north. This shifted the QPF axis SW to NE across northern and central MN. The UKMET is also a bit further north compared to the ECMWF/CMC/GFS but is much flatter with the orientation compared to the NAM but is still supportive in the overall envelope of solutions. The 00z GFS favorably trended a bit slower than the 18z run bringing in a very strong agreement in timing with the remaining guidance (particularly with the cold front). As such a non-NAM solution is preferred at slightly above to above average confidence, given continuity and strong agreement even with such a dynamic system. ...Wed/Thurs shortwave entering Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/GFS and 12z UKMET blend Confidence: Average Closed low over the Northern Gulf of AK has been consistently progressive though with ensemble trends toward a stronger downstream ridge. Additionally, the approach of the next very strong jet further suggests a flattening/shearing of the shortwave energy through coastal BC into the Pacific Northwest by late Wed into early Thursday. Here the 12z ECMWF continues to have a strong upstream jet to progress a stronger, less sheared wave. The 12z CMC trended this direction as well and building continuity from the last few cycles adds a bit more uncertainty. Still, given the upstream setup and the expected building of the closed ridge in SW Canada, this should provide more confidence toward the 00z NAM/GFS and 12Z UKMET and set this as the preferred blend. Confidence is average. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina