Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1231 PM EDT Wed Mar 18 2020 Valid Mar 18/1200 UTC thru Mar 22/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12z NAM/GFS Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low impacting the West... ...Low pressure crossing the Central Plains into the Upper Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/00Z ECMWF blend Confidence: Average The 12z NAM/GFS are close to the consensus as they lift the closed mid level system over of the Great Basin during Thu. The short wave helps deepen surface low pressure forming over eastern CO around 19/12z, which then tracks across the central Plains into the Upper Great Lakes Thu into Fri. Through that time, the 12z NAM/GFS are close to the consensus with the track of the surface low, but gradually begin to diverge from the consensus, moving across eastern Quebec by the end of the period. By contrast, the 00z ECMWF/ECMWF mean are a bit weaker and further south with the track of the surface low, taking it across the Bay of Gaspe by 21/00. Based on its consistency, a blend of the 12z GFS/00z ECMWF is preferred with this system, though the divergence in track after the system reaches eastern Canada results in only average forecast confidence. ...Series of mid level troughs crossing the northern High Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS/00Z ECMWF Confidence: Average The 12z NAM /GFS are close to the consensus with the first short wave in the series tracking from central Manitoba into the Upper Great Lakes through 20/12z. After that time, the 12z NAM becomes faster than the consensus with the lead short wave. The next short wave in the flow crosses the northern Plains Fri night into Sat morning. The 12z NAM becomes faster and deeper with this system, while the 00z CMC is the slowest with the short wave. With both systems, the 12z GFS/00z ECMWF anchor fairly consistent timing with both short waves, so this pair is preferred for both system. However, given the spread in the remainder of the guidance (especially with the second short wave), forecast confidence is average. ...Mid level trough over southern CA Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slighty above average The 12z NAM/GFS are close to the consensus taking a closed mid level low from 32N 136W at 19/00z that weakens into a mid level trough and reaches Southern CA by 21/12z. The 00z UKMET remains the slowest and deepest with this system, and represents the western edge of the guidance envelope. With a tightly clustered solution with this system in place, a non-UKMET solution is preferred with slightly above average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hayes