Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EST Mon Feb 12 2018 Valid Feb 12/1200 UTC thru Feb 16/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... Please refer to the WPC QPFPFD precipitation forecast discussion for details on model preferences and system timing until the next PMDHMD is issued at 1645 UTC. ...Mid-upper level low and 700 mb trough drifting across CA into the adjacent southwest US... Preference: Blend of 12Z UKMET, 12z NAM, 00z/12z ECMWF Confidence: Average The models are in good agreement is showing a closed low near the CA/NV border tonight that drifts southwest across CA into the eastern Pacific near the CA coast, and then turn southeast along the CA coast. Differences in the model mass fields mostly emerge on Wednesday, with the gfs forecasting the original center to move further offshore and a new center to form within the 700 mb trough as it moves across southern CA. The GFS winds up with a slightly more amplified wave than the other models. One aspect of the gfs that improved from the 00z run was it slowed down the 700 mb trough timing to be in better agreement with the NAM, 00-12z ECMWF, and UKMET. The preference is to use the majority cluster of the NAM/UKMET/00-12z ECMWF due to excellent agreement. ...Shortwaves Ejecting Across the Northern Tier of States... Preference: Blend of 00Z/12z ECMWF, 12z GFS Confidence: Average The models show a pair of 700-500 mb wave in the northern stream, with the first wave starting in the northern Plains tonight and moving into the upper MS Valley Tue as it deamplifies and becomes harder to track as it weakens approaching the upper Great Lakes. On Wed, a new wave ejects from the northern Plains and moves east northeast across the upper MS Valley and Lakes,then into the lower lakes and northeast Thu. The primary differences appear to be related to timing. The 12Z NAM appears to be the fastest, while there in better agreement among the GFS, UKMET, and 00z ECMWF. This group of 3 models also deamplifies the wave on Thu. Due to better agreement, the majority cluster of the GFS/UKMET/00z ECMWF is preferred. The 12z ECWMF has trended slower, and is on the slow edge of the guidance distribution. ...Wave crossing the Pacific northwest/northern Rockies Wed and into the northern Plains to central Great Basin and southern CA Thu... Preference: Blend of 00Z/12z ECMWF, 12z UKMET Confidence: Slightly above average The models are in better than average agreement in showing a 500 mb wave crossing Vancouver Island Tue night and then the Pacific northwest and northern Rockies Wed, followed by the northern and central Great Basin and then south across CA. The GFS and NAM area few hours fast with a slightly less amplified trough crossing WY and CO. The 00-12z ECMWF, UKMET and 09z SREF Mean all show slower timing. Usually in a pattern with an amplified upstream ridge (models forecasting a closed eastern Pacific high by 00z Fri)the slower solution pan out better, so the slower ECMWF/UKMET/SREF Mean are preferred. Petersen Previous model trends at www.wpc.ncep.noaa.gov/html/model2.shtml Previous 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml