Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1211 AM EST Wed Dec 18 2019 Valid Dec 18/0000 UTC thru Dec 21/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with Preliminary Preference and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed mid-level low crossing New England on Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Trough off West Coast splits through to north-central and southern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/CMC blend Confidence: Average Timing differences show up as an upper trough crosses into the Great Basin with the 00Z NAM slowest and 00Z GFS fastest. The timing differences continue into Friday but the 12Z UKMET ends up with less of a closed mid-level low over the Southern Plains and more of an elongated positively tilted trough axis. Ensembles support their deterministic counterparts with the ECENS members slower than the GEFS members. Canadian members are in the middle but closer to the ECMWF members. There has been gradual trending toward a middle ground over the past 3 12/00Z ensemble cycles. The preference is to go toward the middle ground, near the 12Z ECMWF/CMC but with only average confidence given the remaining ensemble spread and potential for future timing adjustments. The 12Z ECMWF/CMC preference also holds true with the northern portion of the upper trough that tracks toward the Great Lakes. By Saturday morning, ensembles favor a middle ground, between that of the slower 12Z ECMWF and faster 12Z CMC which happens to be near the 00Z NAM/GFS. ...Persistent onshore flow into the Pacific Northwest...... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS and 12Z ECMWF blend, less GFS weighting by 12Z/21 Confidence: Slightly above average Onshore flow into the Pacific Northwest on Thursday begins to alter as a large mid-upper level trough axis approaches the region and steady/moist southwest flow aims into Washington and Oregon. The models have come into fairly good agreement regarding a frontal wave forecast to be about 250-300 miles west of the Olympic Peninsula 00Z/20. Afterward, timing differences appear with the base of the longwave trough axis as it begins to approach, with the 00Z GFS fastest compared to the remaining deterministic and ensemble consensus. Given the relatively consistent run to run guidance from the ensembles, and the 00Z GFS placement ahead of the ensemble clustering, less weight on the 00Z GFS is recommended toward 12Z/21, with a 00Z NAM/12Z ECMWF blend more greatly 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