Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1258 PM EDT Wed May 27 2020 Valid May 27/1200 UTC thru May 31/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Northern stream, upper level trough tracking from the northern Plains today to the Great Lakes on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Near the 00Z ECMWF Confidence: Slightly above average Model differences with timing begin to appear late Thursday into Friday morning as the 12Z GFS begins to track the trough axis more quickly to the east, while the 12Z NAM begins to slow its timing relative to the remaining model guidance. These differences continue through Saturday. For reasons mentioned below, the 00Z CMC given its differences with how a closed low to the south merge into the trough axis progressing through the Great Lakes region. The 00Z UKMET is on pace with the 00Z ECMWF until Friday night when it slows down compared to the 00Z ECMWF. Since the ensemble means show good agreement and match closely to the 00Z ECMWF, and run to run consistency has been fairly good with the 00Z ECMWF and its ensemble mean, a preference near the 00Z ECMWF is recommended for this system. ...Deep closed low over the southern Plains and lower MS Valley, weakening toward the OH/TN Valleys by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non-00Z CMC blend Confidence: Above average 12Z Only the 00Z CMC differs significant with this system as it is slower to bring the weakening closed low northward toward the central Appalachians. Good support exists with the remaining deterministic and ensemble guidance to support a non-00Z CMC blend. ...Tropical Storm Bertha along the southeastern U.S. coast...--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/GFS closest to 15Z NHC advisory Confidence: refer to NHC products Compact T.S. Bertha made landfall along the central coast of SC earlier this morning and is currently tracking inland. As the system weakens, it is forecast by NHC to move northward into the central Appalachians. The 00Z UKMET/CMC stand out early and are already southwest/slower with the center of Bertha compared to observations, with the deviation continuing through Thursday. A blend of the 12Z NAM/GFS are relatively close to observations at 15Z today regarding position and match reasonably well to the 15Z NHC advisory track before the system weakens/merges with an advancing mid-level trough over the Great Lakes region late Thursday. ...Subtropical closed low reaching central CA by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z/30 near the 00Z ECMWF 00Z/30 - 00Z/31 Confidence: Slightly above average The models show good agreement on the track of a closed low approaching CA this weekend but differ with timing by Saturday morning (12Z/30). The 12Z NAM, 00Z UKMET and 00Z CMC end up slower to bring the low inland across northern CA. by Saturday evening (00Z/31), the 12Z GFS pulls ahead of the remaining guidance. Ensemble support and trends support a middle ground best represented by the 00Z ECMWF on Saturday. Prior to Saturday however, a general model blend can be used for this system. ...Deep trough/closed low over the northeast Pacific... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto