Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 221 AM EDT Mon Oct 01 2018 Valid Oct 01/0000 UTC thru Oct 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern US into Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Subtropical ridging anchored over the southeast US will keep a relatively benign weather pattern in place from the TX Gulf Coast through the Mid-Atlantic regions. The absence of major weather systems with fairly persistent above normal temperatures are well represented by the model guidance. Overall, there is little spread with the major mass fields and a general model blend is acceptable. ...Closed Low approaching Southern CA Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECMWF/UKMET Confidence: Slightly below average 07z Update: The 00z CMC is a bit faster with the closed low approaching southern CA by Wednesday, though within reasonable spread compared to the consensus. The 00z UKMET lies well within reasonable spread for Day 3 as the system opens up moving onshore into southern CA. The 00z ECMWF was a bit faster compared to the 12z run and also a bit stronger with the closed low approaching southern CA. ---Previous Discussion--- Through Wednesday, there is good agreement with the mid-upper level shortwave closing off just off the coast of California. It is then by Thursday that more considerable spread in the models take place with how that energy gets absorbed within the large scale trough over the western US. The 12z UKMET and CMC are faster outliers compared to the 12z ECMWF and the 00z GFS, while the 00z NAM lies in the middle but is probably a bit too strong. ...Northern US from Pacific NW to Great Lakes region... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/ECMWF/CMC blend (non-UKMET) Confidence: Slightly below average 07z Update: The 00z UKMET is a fast outlier with the shortwave energy moving across the northern tier Wednesday as well with the system moving into the Pacific NW on Thursday. The 00z CMC agrees well with the consensus overall though might be a tad slower compared to the 00z GFS and a bit weaker overall with the strength of the shortwaves through the period. Meanwhile, the 00z ECMWF trended a bit slower compared to the fast 12z run and now is more in line with the consensus blend, which is preferred outside of the UKMET. ---Previous Discussion--- Fast zonal flow across the northern US is expected through the end of Day 3 (12z Thursday) with a stronger shortwave dropping into B.C. Canada and Pacific NW Tuesday and Wednesday. There is considerable differences in the timing and strength of these features. The 00z GFS is slower and weaker compared to the 12z ECMWF with the shortwave coming into the Pacific NW on Tuesday, while the 00z NAM was considerably stronger the shortwave energy. A secondary shortwave then drops into the Pacific NW on Thursday, where again the NAM is too strong compared to the consensus with the 00z GFS mirroring the 12z ECMWF mostly in placement/strength (and the 12z UKMET/CMC within reasonable spread as well). At the surface, a couple waves of low pressure will trek across the northern US through the period with the most noted differences occurring over the northern Great Lakes region Wednesday-Thursday. The 00z NAM was further west, more in line with the 12z UKMET while the 00z GFS trended toward the 12z ECMWF/CMC. All of the deterministic models show the low rapidly deepening over the Hudson Bay beyond Day 3. As a result, a blend of the 00z GFS with the 12z ECMWF/CMC is preferred for this portions of the CONUS. ...Tropical Cyclone Rosa (Southwest US)... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ See NHC forecast Best Proxy: General model blend Fairly tight clustering with the main deterministic guidance for Rosa. Its steering will be driven mainly by a large mid-level trough off the West Coast, pushing the system north/northeastward into the Baja California coast before dissolving over the Southwest US. While there is some speed differences (faster GFS, slower CMC), the track has fairly good agreement and so a general model blend is a good proxy for the official NHC track. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor