Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 134 PM EDT Sat May 04 2019 Valid May 04/1200 UTC thru May 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...General overview of the CONUS through 00Z/08... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS...00Z ECMWF...00Z UKMET blend Confidence: Average A broad northern stream trough will stay in place through early next week over the north-central U.S. with flow entering North America to the north of a ridge offshore of British Columbia. An active southern stream will continue as well with one shortwave reaching the Mid-Atlantic region on Sunday, followed by a mid-level trough amplifying over Texas Monday night and a closed low forecast to enter the Southwest U.S. on Monday. The biggest differences are with the southern stream shortwave amplification over Texas Monday night with ensemble trends showing slower over their past few cycles. The 12Z NAM is significantly faster here followed by the 12Z GFS and then the similar 00Z ECMWF/UKMET/CMC regarding timing. The latest ensemble means support a middle ground near the 00Z ECMWF and 12Z GFS. There are differences across the South given differences with the way each model handles convection, but those differences are outside the scope of this discussion. Farther north, some latitude differences exist with a frontal boundary across the Central Plains, but the GFS is perhaps the farthest south on Monday, with the 00Z UKMET/CMC located on the north side of the model spread. A middle ground is preferred with this boundary, nearer to the 00Z ECMWF, or a blend of the 12Z GFS, 00Z ECMWF and 00Z UKMET. The other significant difference is across the interior Northwest with the 12Z NAM more progressive with a shortwave at the base of the broad/longwave/low-amplitude trough located across Canada into the north-central U.S. There is good ensemble/deterministic support for a slower solution best represented by a non-12Z NAM blend. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Otto