Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 247 AM EDT Wed Mar 25 2020 Valid Mar 25/0000 UTC thru Mar 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ East Coast cyclogenesis through Wednesday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High The surface low that has been tracking eastward across the south-central U.S. is forecast to redevelop near the Mid-Atlantic coastline and then intensify as it tracks out to sea, likely taking a track farther offshore than the recent nor'easter that affected New England Monday night. There is enough agreement in the guidance to merit the use of a multi-model blend, even though the 12Z ECMWF is slightly slower with taking the low away from the coast. Longwave trough over the western U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend after 12Z Thursday Confidence: Moderate The amplified pattern over the eastern Pacific will end up producing a positively tilted longwave trough axis which will slowly progress down the West Coast, and then gradually move inland across the Desert Southwest by Friday morning and reach the Rockies by Saturday morning. This will support lee cyclogenesis across the western High Plains along the existing frontal boundary. The main difference here is with the 12Z UKMET being slower with the progression of the trough across the Intermountain West, and thus the evolving surface low is west of the model consensus by Saturday morning. Shortwave and surface cold front approaching Pacific Northwest Saturday morning ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/00Z CMC/18Z GEFS mean Confidence: Moderate A shortwave trough originating from Alaska will track southeastward across the northeast Pacific and reach the Pacific Northwest by Saturday morning. This will bring the next significant round of precipitation to this region by the end of the forecast period. Model differences become apparent by 00Z Saturday with the 12Z ECMWF becoming more amplified, and the UKMET a bit weaker and faster. Northern stream shortwaves crossing southern Canada this week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z CMC/18Z GEFS mean Confidence: Moderate There will be three separate shortwave perturbations in the northern stream near the Canadian border that will be pivoting around the main polar vortex over northern Canada, with the first crossing the northern Great Lakes on Wednesday. This will result in a cold front dropping southward across the northern Plains and the Upper Midwest. Although there is good model agreement with the lead wave, there are some timing and amplitude differences with the next set of disturbances to move through. The GFS and NAM are stronger with the third wave, and the UKMET is more progressive. The ECMWF and CMC indicate a similar evolution with support from the ensemble means, so a blend of these solutions with the GEFS mean should serve well as a starting point. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick