Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1228 AM EDT Mon Mar 23 2020 Valid Mar 23/0000 UTC thru Mar 26/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Nor'easter developing off the East Coast early in the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Shortwave impulses in the northern and southern streams are phasing over the Great Lakes and Ohio Valley region on Monday, spurring surface cyclogenesis over the Gulf Stream and evolving into a coastal low south of Long Island by Monday evening. This storm will intensify as it lifts towards the northeast and passes offshore of Cape Cod. The models have consolidated on the track and intensity of the low over the past 24 hours, with only differences as the GFS is slightly faster by Tuesday morning and the NAM slightly closer to the coast. These differences are small enough to merit a general model blend for this region. Initial closed low over California reaching East Coast by Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z CMC/00Z NAM Confidence: Near average The closed low currently over central California is forecast to evolve into an open wave as it crosses the Intermountain West, but still remaining intact as it reaches the Plains and ultimately the eastern U.S by midweek. This will result in lee cyclogenesis over the western High Plains Monday night with the surface low reaching the central Appalachians by Wednesday morning, with secondary cyclogenesis is likely off the Mid-Atlantic coast by Wednesday afternoon. In terms of the models, the 12Z UKMET becomes weaker with the trough over the central Plains and then slower. The 18Z GEFS mean is slightly slower and farther norther with the surface low as it tracks towards the Ohio Valley, with the operational 00Z GFS more in line with the NAM and UKMET positions, and the ECMWF and EC mean on the more progressive side. Broad upper level trough over the northwestern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF/12Z CMC Confidence: Near average An upper low slowly dropping southeastward along the British Columbia Coast is forecast to evolve into a large scale positively tilted trough by Tuesday and into Wednesday. A shortwave should break eastward away from the parent trough and cross the southern tier of Canada, along with a well-defined surface low, and the main portion slowly sinking southward along the West Coast. The NAM is considerably stronger with the northern shortwave, and the GFS becomes slightly more progressive by Tuesday night. The UKMET is slower with the progression of the trailing cold front across the Upper Midwest. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick