Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1122 PM EST Sat Feb 09 2019 Valid Feb 10/0000 UTC thru Feb 13/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Western U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours Blend of the 00Z GFS, 12Z ECMWF...after 48 hours Confidence: Average Three systems impacting the western US, mainly the Pacific Northwest region, will keep an active weather pattern in place. The first system, a mid/upper level closed low well defined in IR imagery off the coast of Oregon, will drift southeast then eastward into the Intermountain West as it opens up and becomes absorbed into the large scale troughing over the region. The current model guidance has a fairly good handle on this with respect to the mass fields as it crosses through the West. A second mid/upper trough will drop into Washington State Sunday night and is then also followed by a stronger Pacific system that comes through Monday. This pair eventually phase into a longwave positively tilted trough that hangs up over the region into mid-week. The GFS/NAM appear to be stronger and faster with the upper level feature by Monday evening, bringing the closed low close to shore. As the system stalls, the wave opens up and model differences are not extreme until the end of the forecast period when the ECMWF/GFS diverge quite a bit with how the energy moves onshore, but this is just beyond the valid forecast period. Given the model spread toward the end of the period, a blend of the GFS/ECMWF with their respective ensemble means is preferred beyond 48 hours. ...Central/Eastern U.S... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF blend Confidence: Slightly below average A weak lead shortwave tracking through the Rockies currently will continue to dampen as it moves into the central Plains and Upper Midwest through Sunday night. There is above average consensus in the latest model guidance with this feature and a general model blend can be preferred with this feature. The deeper closed low currently off Oregon will track through the Rockies and move into the Plains by Monday evening, taking on a slight negative tilt by Tuesday morning as it lifts through the lower Great Lakes. A surface low developing in response is expected to take a Colorado to Missouri to Michigan track. There is somewhat better agreement with the key synoptic features with this system. The GFS/NAM are a bit faster compared to the ECMWF/CMC/UKMET solutions with the trough axis, particularly by 18z Tuesday onward. This is also when the GFS continues to show a deeper solution (though not nearly as much of an outlier as 24 hours ago). By the end of the forecast period, the system becomes more absorbed into the fast zonal flow developing across the central/eastern US. While differences with the surface low are relatively minor across the central US, as the system moves into the mid-Atlantic and Northeast, bigger model differences develop. The inland low is forecast to be replaced by a developing coastal low somewhere off the NJ/NY coast then it tracks up the New England coastline. There are differences in how deep the low may be but also its forward speed. The GFS/NAM are faster, taking the low up toward Maine by 13.12z while the ECMWF/CMC/UKMET are slower. Over the past few model runs, the GFS has trended slower and the ECMWF faster, so the trend is for better model agreement. As such, will lean on a blend of the 12z ECMWF and 00z GFS for this cycle. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor