Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 248 PM EDT Thu Jul 23 2020 Valid Jul 23/1200 UTC thru Jul 27/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Broad Great Lakes/Northeast trough axis and corresponding cold front impacting the OH Valley, Northeast and Mid-Atlantic into Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show similarly with this system and exhibit good run to run continuity. ...Mid-upper level troughing tracking from the Northwest into the north-central U.S. through the weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/ECMWF/UKMET blend Confidence: Average A mid-level closed low/shortwave trough will track through southwestern Canada Friday and Saturday with a cold front leading at the surface and extending into the northwestern U.S. The model agreement is fairly good through Saturday but the 12Z NAM begins to show up as fastest with the speed of the mid-level trough by late in the day. The 12Z UKMET sped up from its 00Z run to match closer to the previously preferred GFS/ECMWF. The 12Z CMC timing also looks better when compared to its previous 00Z cycle, but the center of the CMC upper low is displaced north of the consensus. While the timing differences are not large and model-driven convective boundary ahead of the main front could be more significant, it seems the 12Z GFS/ECMWF/UKMET represent the best ensemble clustering which lies in the middle of the deterministic spread. ...California/Southwest U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-12Z CMC blend Confidence: Average After the departure of a small closed low from CA tonight, another disturbance (weaker than the first) will reach the CA coast late on Saturday. Aside from the 12Z CMC, which is displaced slightly south with the low-mid level low and is weaker aloft beginning on Sunday, the models show very good agreement in the synoptic mass fields such that a non 12Z CMC blend can be used for this system. ...Tropical Depression Eight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Official NHC Forecast Best Model Proxy: 12Z ECMWF/UKMET/CMC blend Confidence: refer to NHC products The 15Z NHC advisory for Tropical Depression Eight is in general agreement with the . The latest model guidance shows fairly good agreement with the latest model guidance. However, none of the deterministic models match exactly with the NHC track for all of the next 3 days. There are differences with organization of the mid-level energy aloft as well. NHC strengthens T.D. Eight into a weak tropical storm by Friday morning and maintains a weak intensity until landfall when the system weakens back below tropical storm status. Given the track and intensity forecasts by NHC, a blend of the 12Z ECMWF/UKMET/CMC are the closest proxy to the 15Z NHC advisory. The 12Z UKMET remains the strongest with the 12Z CMC second strongest, but these cycles match closest to the NHC track. The 12Z ECMWF track is a little faster and south of the 15Z NHC advisory but is also a little weaker than the 12Z UKMET/CMC. Meanwhile, the 12Z GFS is weakest with the low-mid level organization of this system as it tracks westward through the western Gulf of Mexico. The 12Z NAM might be considered as a secondary preference but its speed was noted to be faster than the NHC advisory. For the latest official guidance, see the most recent advisory from the National Hurricane Center. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml This product will terminate August 15, 2020: www.weather.gov/media/notification/pdf2/scn20-58pmdhmd_termination. pdf Otto