Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 251 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 GFS and 00Z ECMWF Confidence: Average 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 now through Friday with some of the lead shortwave energy dropping down over the Great Lakes, but then there are more substantive differences by Saturday. The differences relate to energy currently west of Greenland and north of the Arctic Circle that 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 latitudinal differences with the placement of this feature by then. The 00Z GFS and 00Z CMC are farthest north with the closed low, with the 00Z UKMET and 00Z ECMWF farthest. The 00Z NAM is a little weaker and more progressive, but is otherwise close to the ECMWF. The 00Z GEFS mean supports the GFS/CMC cluster, but it was noted that the UKMET trended a bit farther south from its previous run, and the ECMWF a little farther north. Thus, we have two clusters of solutions and at this point we will compromise between the two camps, which would suggest leaning toward a blend of the GFS and ECMWF. ...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 00Z 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 00Z 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: Blend of the 00Z GFS, 00Z UKMET and 00Z ECMWF Confidence: Slightly 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 00Z CMC for its part is the slowest solution and also takes its surface low the farthest to the north. The 00Z UKMET and 00Z ECMWF actually show reasonably good model clustering and are both a little south of the GFS solution. The UKMET and ECMWF did both trend a little faster and are close to the GFS in this regard. The 00Z GEFS mean is a bit south of the GFS and rather close to the UKMET/ECMWF cluster with placement, but the GEFS mean suggests a weaker solution. For now, will lean toward a consensus of the GFS, UKMET and ECMWF based on the latest trends. Confidence remains a bit limited. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison