Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 321 AM EST Wed Jan 01 2020 Valid Jan 01/0000 UTC thru Jan 04/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation with preferences/confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low entering Mexico and weakening Wednesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average 08Z update: No significant changes noted with the rest of the 00Z guidance and the previous model blend preference remains. Latest guidance has trended better with the closed upper level low over Mexico and its transition/weakening over the next 24-36 hours. Earlier differences between the GFS/ECMWF seem to have lessened and now there is reasonable agreement and clustering with the early 00Z guidance. Beyond 36 hours, the energy becomes absorbed into the developing longwave positively tilted trough across the central US associated with incoming shortwave energy from the Pac NW and central Rockies. Overall, given the improved consistency and model agreement, a general model blend is preferred. ...Amplifying longwave trough across the central U.S. Thursday evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 03.00z, then GEFS/ECENS mean blend Confidence: Slightly below average 08Z update: Through 60 hours /03.18Z/ there is fairly good agreement now but still differences with the northern stream closed low/shortwave. Here the NAM is still too fast/deep while the ECMWF/GFS offer a slower, more southerly solution. The operational runs of the GFS/ECMWF are notably stronger than their ensemble means, so will continue to favor a GEFS/ECENS mean blend for Day 3. A longwave trough will develop over the Great Plains Thursday into Friday with its associated surface low tracking from the southern Plains toward the Ohio Valley and Great Lakes. There remains fairly good agreement aloft with the 500 mb height evolution but sizable differences at the surface with the low track/strength from 03.00Z onward. The ECMWF and ECENS low plots are on the southern/southeastern spread, while the GEFS/CMCE are further north/northwest. These differences become amplified by the end of the forecast period, with a much below forecast confidence by Day 3. As such, will lean on the GEFS/ECENS for Day 3 given the forecast spread. ...Shortwave trough and surface low approaching Pacific Northwest Friday/Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: GFS/NAM Confidence: Slightly below average 08Z update: The ECMWF remains too slow with the initial surface low impacting portions of British Columbia, whereas the rest of the models show fairly good clustering (and have trended toward the faster GFS/NAM idea). With the secondary low swinging through toward the end of the forecast period, the UKMET is noticeable weaker compared to the rest of the guidance and is considered an outlier. The GFS/NAM still look reasonable and even some components of the CMC appear useful through Day 3. There remains a fair amount of spread and timing differences with the approach of the next shortwave trough for the Pacific Northwest in the Friday/Saturday time frame. The trend has been for a faster solution with the low track, which favors the GFS/NAM compared to the non-NCEP solutions which are slower. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor