Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1154 AM EST Tue Feb 13 2018 Valid Feb 13/1200 UTC thru Feb 17/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... ...Closed Mid- and Upper-Low Initially Off the CA Coast Moving Inland... Preference: 13/00Z ECMWF and 13/NCEP blend...most heavily weighted to the ECWMF. Confidence: Average The 12Z NCEP models tended to handle the closed low initially off the CA coast in a similar fashion in that a secondary vort max rotating around the low helps pull the center southward to about 32N. As the second vorticity maximum closes off and forms a second low south of 20N...the primary low loses its southward momentum and begins to fill as it eases towards the southern CA coast. The 13/00Z ECMWF also pulled the low off the CA coast southward in response to the secondary vorticity maximum...but the EC never closes a secondary low off. As a result, the 13/00Z ECMWF has a stronger vorticity maximum reaching the southern CA around 15/00Z than does the GFS/NAM...and keeps the vorticity center as a more coherent entity into Colorado than does the NCEP runs. A spaghetti plot of 5700 meter heights showed reasonably good operational and ensemble agreement through 15/00Z...at which point the differences open. The GFS had the support of the GEFS mean while the operational ECMWF had support from the ECMWF Ensembles and the 13/00Z Canadian. The 13/00Z UKMET stood out as a weak/fast outlier. At this point...think that the ECMWF may be more correct given the magnitude of upstream ridging along 145W. But the magnitude of shortwave energy dropping southward along the west coast becomes a player on day 3. Given that the ECMWF was stronger with this energy than other models, think that blending in some of the GFS/GEFS and the NAEFS may temper some of the uncertainty at this point especially on day 3. ...Shortwave energy initially over the Northeast Pacific Ocean... Preference: 00Z GEFS/NAEFS... Confidence: Average The models have a similar idea that shortwave energy initially over the Northeast Pacific and the Gulf of Alaska will drop southeast on the periphery of a broad upper ridge. The 13/00Z ECMWF was particularly strong with this wave...especially by the time it reaches the base of the mean trough over California. First reaction was that the ECMWF was too strong, but forecasters in the WPC Medium Range section pointed out a similar evolution recently which verified on the stronger side of the guidance. As a result, will recommend the 13/00Z ECMWF tempered a bit by the 13/00Z GEFS mean/NAEFs. Thinking is that doing so will keep the timing of the ECMWF while reducing the amplitude of the wave somewhat. ...Shortwaves from the Great Basin towards the Great Lakes and Northeast U.S.... Preference: 13/12Z GFS and 13/00Z UKMET/ECMWF blend Confidence: Below Average The models show a pair of 700-500 mb shortwaves 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. The waves then becomes harder to track as they weaken while they 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. Due to better agreement amongst themselves, prefer the 13/12Z GFS and 13/00Z UKMET/ECMWF. The problem is that these features are weak and prone to fairly large run to run differences. This limits our confidence in the model selection. Bann Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml