Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 119 PM EDT Mon Apr 02 2018 Valid Apr 02/1200 UTC thru Apr 06/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS evaluation...including preliminary model preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper level trough over the Northwest today continuing to dig to the Upper Midwest on Tuesday... ...Surface cyclogenesis over the Plains today with a deepening low moving into the Great Lakes Tuesday... ...Low lifting into Quebec with trailing cold front clearing the East Coast through Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS; 00Z ECMWF blend Confidence: Average The 12Z NAM has a surface/925 mb low early Tuesday morning and is subsequently a little farther north with a warm front into the Ohio valley. The NAM's lower level temperatures are also colder than the remaining deterministic models in the vicinity of the surface low. Outside of these possible issues in the 12Z NAM, the upper level timing of the mid-level wave appears reasonable. The 12Z GFS and 06Z GEFS are faster and lie toward the faster end of the latest ensemble spread with the previously slower ECMWF members trending faster over the past few cycles. The latest guidance continues to show the 12Z GFS faster along with the 00Z CMC, while the 00Z ECMWF/12Z NAM and 00Z UKMET slower. Given the trends to converge toward the middle, a blend of the 12Z GFS and 00Z ECMWF appears the best route at this time. ...Low-amplitude shortwaves approaching Northwest U.S. Tuesday morning into Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GEFS Mean; 12Z ECMWF Ensemble Mean Confidence: Below Average After a period of brief shortwave mid-level ridging over the northwestern U.S. this afternoon, low amplitude shortwaves are expected to enter the Northwest tonight, downstream of a large scale trough over the coast of British Columbia. There are no significant differences with these smaller scale features, but large differences tied to the next system to impact the Northeast are described in the below section. ...Upper trough and surface cyclone approaching the Pacific Northwest late Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 00Z ECMWF and 00Z UKMET blend Confidence: Average A mid-upper level trough approaching the West Coast will allow a surface front to near the coast late Thursday. There are timing differences in the model guidance, with the 00Z CMC toward the faster side of the latest deterministic and ensemble models. There is decent support in the ensemble means to be near the 12Z NAM/00Z ECMWF/00Z UKMET regarding a negatively tilted mid-level trough offshore of the Northwest near 00Z/06, but the 12Z GFS is lacking this feature. Therefore a 12Z NAM, 00Z ECMWF and 00Z UKMET blend is recommended. ...Mid-level closed low/shortwave trough near the central U.S./Canadian border late Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 00Z ECMWF and 00Z UKMET blend Confidence: Slightly below average The ensemble means show the 12Z GFS is too fast and displaced westward with a shortwave/closed low forecast to near the north-central U.S. by 00Z/06. The ensemble means also support a surface low north of Lake Superior at this time, but the low is absent in the 12Z GFS, with the 00Z CMC displaced off toward the east. A 12Z NAM, 00Z ECMWF and 00Z UKMET blend shows enough agreement to be included in the preference given alignment with the ensemble means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto