Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 241 AM EDT Sat Mar 14 2020 Valid Mar 14/0000 UTC thru Mar 17/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Final Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed Low dropping along the West Coast through Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Slightly above average 07Z Update: Guidance remains well clustered and no changes to the preferences are suggested. The guidance is in very good agreement with the evolution of a close low moving southward from just off the Washington State coast to west of the central California coast Tuesday morning. There is little discrepancy in the position or intensity of this mid-level feature in any of the available guidance. Although the primary synoptic evolution is well agreed upon, there does exist discrepancy in timing and intensity of smaller-scale shortwave rotating around the parent low and ejecting onshore the west coast. These are too small to be modeled well beyond near term time ranges, and since the general evolution is well modeled, a general blend is acceptable. ...Weakening mid-level shortwave moving from the Southwest to the Mid-Atlantic into Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z NAM/GFS blend Confidence: Slightly above average 07Z Update: The 00Z non-NCEP suite has overall sped up its ejection and shearing of this shortwave as it moves across the Ohio Valley and into the Mid-Atlantic. This leads to a more clustered general consensus, but with the GFS remaining on the fast side of the guidance envelope, and the NAM still the strongest solution, suggest still a blend which excludes the NAM/GFS. The 00Z GFS is by far a fast outlier with the ejection of this weakening wave, becoming well ahead of the consensus and other models as early as 12 hours into the forecast period. Recently the GFS has been verifying too fast, so expect this evolution is also too quick and the GFS is removed from the blend for this reason. The NAM is deeper overall, as it is slower to shear into the westerlies, so despite its similar placement compared to the preferred consensus its strength makes it an outlier. Otherwise, the 12Z non-NCEP blend combined with the 18Z GEFS leaves a solution that is reasonable and preferred. ...Base of longwave trough over the north-central U.S. by Monday evening... ...Related cold front across the Upper Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/UKMET/GEFS and 12Z ECENS Confidence: Average 07Z Update: No significant changes to the preferences as the previous similarities and differences in the guidance remain with the 00Z non-NCEP suite. The 00Z GFS is too fast with the trough axis digging through the Northern Plains, while the NAM is on the other end of the guidance making it a slow outlier. The 12Z CMC is generally in good agreement with the timing of the trough as it pivots eastward, but it the strongest of the guidance and drives the cold front further south than the preferred consensus. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss