Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1111 AM EST Tue Feb 04 2020 Valid Feb 04/1200 UTC thru Feb 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~ ...Evolving full latitude trough over the Central US through Thu... ...Surface wave developing over the Lower MS Valley...moving into the interior Mid Atlantic late ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~ Preference: 06z GEFS and 00z ECMWF/UKMET/CMC and ECENS mean Confidence: Average to slightly below average GOES-East WV depicts the full latitude trough across the Center to Southwestern portion of the CONUS. The northern stream shortwave is already departing/severing connection to the main elongated upper level trof. As such the surface pattern depicts a well defined but stationary front from the eastern Great Lakes toward the Southern Plains and high Plains over New Mexico. The shortwave at the base of the elongated trof will emerge later today and along with instability off the western Gulf, will support a surface wave that lifts through the Lower MS Valley tomorrow (Wed) and through the Upper Ohio Valley by Thursday morning. This evolution is fairly well agreed upon, with exception of the 12z GFS, which continues favor stronger influence of the central US shortwave energy over the base energy rotating north, leading to greater ridging across the Ohio Valley and therefore greater instability/moisture flux across the Cumberland Plateau. This may be keyed on the approach/interaction with the leading shortwave emerging from the strong Pacific flow over-topping the Pacific/West Coast ridge. The GFS and lesser so 12z NAM, both suggest slightly faster and more elongated jet exit region and mid-level stretching into the western side of the full-latitude trof. The 06z GEFS though is more in-line with the ECENS mean, UKMET, CMC and operational ECMWF, so would continue to favor this direction, though the spread is still fairly small. It is after this shortwave enters the base of the main trof, late Thursday, that the spread significantly changes, mainly on the shape, timing of the wave and associated jet streak rounding the base. Here, the 00z UKMET is most compact and very strong with the jet and typical of its bias is faster moving through and lifting across the Southeast into the Central East Coast Fri (though still slower than the 12z GFS). The ECMWF/ECENS mean and CMC are slowest to enter the base and dig a bit further south than the other guidance, this is similar to the 12z NAM and how it broke from the GFS. Overall, there is sizable spread/uncertainty but will continue a non-GFS blend favoring the ECMWF/ECENS mean and GEFS mean. so average to slightly below average after Friday 12z. ...Pulses along atmospheric river Wed-Fri into Pacific NW... ...Approaching rapidly deepening cyclone toward Pacific NW by end of Day 3... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~ Preference: Non-GFS trend to ECMWF/CMC/ 12z NAM blend Confidence: Average Upstream, the Western Ridge remains dominant through the forecast period, with strong supergeostrophic flow over the ridge directing a weaker but still slightly above average moisture stream/AR across the Pacific NW into the Snake River Valley and Central Rockies Thurs-Fri. This is finally disrupted by the strong shortwave energy at the base of the Bering Sea closed low, that rapidly evolves/occludes late Friday. The uncertainty, here is the placement and just like further east the GFS is further east having a less amplified ridge across British Columbia. The NAM is similar but with greater ridging and typical late day 3 amplification bias, it slows and matches the 06z GEFS mean and CMC. The 00z ECMWF shows much greater amplification of the ridge allowing for a deeper vertically stacked low which is much slower. Interestingly, the ECENS solutions suggest this may be a bit faster than the bulk of ensemble solutions. The UKMET is clearly the slowest/greatest amplified and sticks out significantly from the ensembles to have much confidence in it. As such will favor an ECMWF/CMC/NAM blend for this system, though the AR/moisture transport into the Pacific NW prior to this system may be best suited with a non-GFS blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina