Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1259 AM EDT Wed Mar 14 2018 Valid Mar 14/0000 UTC thru Mar 17/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation...including model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Nor'easter weakening over New England... ...Secondary occluded low impacting eastern Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models all gradually weaken the current nor'easter impacting the Northeast over the next 24 hours, however, there will be a new low offshore that develops and deepens on its way up across the Canadians maritimes going through Thursday. The guidance on the larger scale handles the evolution of these features reasonably well at this point through Thursday, and thus a general model blend will be preferred. ...Shortwaves digging over the Great Lakes/Northeast Thursday... ...New closed low formation over northern New England Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM, 00Z GFS, and 12Z CMC Confidence: Average, becoming below average by Saturday The models all take multiple northern stream shortwaves down across the Great Lakes region and the Northeast through Thursday and Friday, which ultimately helps to lead to a new closed low/vortex over northern New England by Saturday. The guidance is in good agreement generally through Thursday with some of the lead shortwave energy dropping down over the Great Lakes, but then there are more substantive differences by Friday as the 12Z UKMET wants to amplify this energy over the Gulf of Maine versus the remaining guidance. The 12Z CMC also appears a little flat across this region with the height falls. Additionally, mass field differences also begin showing up over western Quebec Friday as energy currently west of Greenland and north of the Arctic Circle drops south-southeastward through the period. This digging energy will renew a deep closed low near northern New England by Saturday, but there are some significant latitudinal differences with the placement of this feature by then. The 00Z GFS and 12Z CMC are farthest north with the closed low, with the 12Z ECMWF farthest south and also not quite as deep. The 12Z UKMET splits the difference between these camps regarding position but is stronger like the GFS and CMC solutions. The 00Z NAM on the other hand is a little weaker like the ECMWF, but is also a little farther north. The 18Z GEFS mean and 12Z ECENS mean suggest the ECMWF and to a lesser extent the UKMET has too much energy too far south. There is more ensemble support for the NAM, CMC and GFS by comparison. WPC will favor a blend of this latter camp of solutions for now, with confidence quite limited by the end of the period. ...Large closed low/trough moving into the West... ...Surface low impacting western OR by Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Blend of the 00Z GFS and 12Z ECMWF...after 60 hours Confidence: Above average A large deep layer closed low offshore the West Coast will be moving east over the next few days and gradually into the Western U.S. as multiple shortwaves round the base of the trough. One shortwave will focus a surface low pressure in across coastal areas of western OR by Thursday, with low pressure then reorganizing over the Great Basin on Friday as the energy shifts inland. The models are in reasonably good agreement through 60 hours with their respective mass field details, but then after that the 00Z NAM begins to become a bit of a progressive outlier. Will prefer a general model blend through 60 hours, and then a non-NAM consensus thereafter led by a blend of the 00Z GFS and 12Z ECMWF given their more favorable mass field clustering. ...Shortwave ejecting out across the central Plains by Friday... ...Surface low evolution off to the east across Kansas... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF Confidence: Below average A lead shortwave progressing downstream from the large upper trough/closed low moving into the West by Thursday will eject out across the central Rockies and over the central Plains though early Friday. Thereafter, this energy will be encountering highly confluent flow aloft across the Eastern U.S. because of the closed low/vortex near northern New England. Surface low pressure initially over the central High Plains will advance east and approach the middle MS Valley by Saturday. The 00Z NAM is again weaker and faster with this system and will be discounted. The 12Z CMC for its part is the slowest solution overall but has a depth that is supported by the 12Z UKMET and 12Z ECMWF. The difference is that the UKMET gradually takes this system north of every model by the end of the period. the ECMWF is just a little faster than the CMC. The 00Z GFS for a period of time going through Friday is also north of every model but then loses latitude by Saturday as the system encounters the downstream confluence aloft and begins to weaken. The 18Z GEFS mean and 12Z ECENS mean both suggest the GFS and UKMET take their surface lows too far north. More support is toward the ECMWF by comparison, and as a result the ECMWF will be the preference with this system albeit with limited confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison