Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 238 AM EDT Sat May 05 2018 Valid May 05/0000 UTC thru May 08/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper level low near the Bahamas and Cuba this weekend... ...Inverted surface trough extending into Florida... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models are in excellent agreement with their mass fields for this system over the next couple days, and thus a general model blend is preferred. ...Trough ejecting east-northeast from the Low-Mid Mississippi River Valley to the Mid Atlantic this weekend... ...Weak surface low(s) developing off the Northeast coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z GFS; 12Z ECMWF Confidence: Slightly above average The primary difference amongst the models for this system appears to be related to timing, with the 12Z UKMET deamplifying the wave and progressing it the fastest, and the 00Z NAM and 12Z CMC on the slower end. The NAM, in particular, shows more amplification to the trough. The 00Z GFS and 12Z ECMWF are reasonably similar on timing and are both very close to the ensemble means. The preference is to lean toward these models as they have ensemble support and represent a median forecast timing. ...Upper level trough digging into the Great Lakes on Sunday and sweeping across the Northeast Monday... ...Associated cold front pushing through the Midwest and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z GFS; 12Z ECMWF; 12Z CMC Confidence: Average The 00Z NAM continues to show a more amplified trough as it digs into the Great Lakes and Northeast, with the 12Z UKMET showing slightly less amplification (but still more than the remaining models). The 00Z GFS appears to have trended closer to the ECMWF, and the GFS was previously more amplified. Given this trend and the similarity of the ECMWF to the GEFS and ECMWF ensemble means, the preference is for a blend of the GFS, ECMWF, and CMC which is fairly close as well. ...Complex trough evolution along the West Coast this weekend... ...Deamplifying Sunday with several shortwaves kicking east and leading to downstream trough development in the Northern Plains and Southeast by Monday Night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Average Despite the complexity involved in the broad trough along the West Coast this weekend, composed of several PV anomalies rotating around each other, the models all generally show a similar devolution of the trough and its impact on the downstream pattern over the CONUS early next week. The 12Z CMC seems the most difference in that it has the Northern Plains shortwave further northwest (E MT) compared to other models (Dakotas) by Tuesday morning. The CMC and 12Z UKMET also don't really show a third shortwave over British Columbia by Tuesday morning, which is highlighted by all the other models. Otherwise, there are detail differences, but it is not systematic enough from any one model to exclude from the preference with the exception of the CMC. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers