Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1159 AM EST Fri Mar 01 2019 Valid Mar 01/1200 UTC thru Mar 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation Including Preliminary Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low offshore New England Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/00Z UKMET blend Confidence: Slightly Above Average ECMWF members have been consistent with the low track over their past 4 cycles, while the GEFS members have trended toward the ECMWF clustering. The 12Z GFS and 00Z UKMET are in agreement with one another's track and also agree with the latest ensemble clustering, hence the preference. The 12Z NAM is a fast outlier with the low track and the 00Z ECMWF is on the eastern side of the ECMWF ensemble members. Put simply, a non 12Z NAM blend works well for this system given the non-12Z NAM differences are relatively minor. ...West Coast shortwave Saturday morning, tracking into the eastern U.S. Sunday night with corresponding surface low from the Lower Mississippi Valley to near the New England coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF through 00Z/04 00Z ECMWF/12Z GFS blend 00Z/04-00Z/05 Confidence: Average Some minor timing differences appear with a shortwave nearing CA early Saturday morning with the 00Z UKMET fastest and 00Z CMC slowest. It turns out that these two models (UK/CMC) are also flatter with the shortwave as it reaches the Lower Mississippi Valley compared to the remaining model guidance. Ensemble scatter low plots show the 12Z NAM as a faster outlier while the 12Z GFS appears a bit fast as well through about 00Z/04 with the 00Z ECMWF near favorable timing and latitude. However, just beyond 00Z/04, a secondary surface low will develop just off of the Mid-Atlantic coast and track offshore of New England for early Sunday morning. The 12Z NAM continues its fast outlier pace while the 00Z ECMWF tracks the low closer to the coast compared to many of the remaining models. The ECMWF/CMC/GEFS ensembles have all shown a southward shift with their 00Z/01 cycle compared to their previous and consistent three 12/00Z cycles. Currently, the favored track is to be in the middle of the ECMWF/GEFS/CMC members but with more weight on the ECMWF/GEFS, falling in between the 12Z GFS and 00Z ECMWF. This middle ground has general support from the 00Z UKMET/CMC positions. Confidence would be higher if not for the inconsistencies observed from cycle to cycle in the deterministic and ensemble guidance. ...Deep mid-level vortex over Ontario... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Average Only minor timing/placement/magnitude differences show up with this feature, with no strong support to go one way or the other. Therefore given the relatively minor differences between the guidance, a general model blend is preferred. ...Closed mid-level low nearing the coast of Washington on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z ECMWF blend Confidence: Average The ensembles show the 00Z ECMWF toward the northern/slower side of the spread with the 00Z ECMWF mean closer toward the non-00Z ECMWF consensus. While non-ECMWF differences are present, they are relatively minor for day 3 across the Pacific Northwest with a general non-00z ECMWF blend preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto