Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1239 AM EDT Sat Mar 30 2019 Valid Mar 30/0000 UTC thru Apr 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation With Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central Plains to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...weighted toward the 00Z GFS/12Z ECMWF Confidence: Above average A southern stream shortwave currently ejecting east out across the central High Plains will gradually become absorbed on Saturday by a much stronger northern stream trough digging down across the Midwest and Great Lakes region. The larger scale northern stream height falls will then pivot across the OH Valley, Mid-Atlantic and Northeast through Sunday and Monday while gradually taking on a negative tilt. This will allow a strong cold front to move through the eastern U.S. as a wave of low pressure rides northeast along it from the mid-MS Valley to the lower Great Lakes region and then up across the St. Lawrence River Valley. The models are in very good agreement generally with the mass field details of this entire system, but it has been noted that the 00Z NAM, like with previous cycles, is probably a bit too cold with its boundary layer temperatures immediately behind the frontal passage. A general model blend will otherwise be preferred, but with a tad more weighting toward the 00Z GFS and 12Z ECMWF. ...Four Corners to Southern Plains trough/closed low... ...Reaching the Gulf Coast/Southeast by Mon/Tues... ...Cyclogenesis near the Southeast Coast by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/18Z GEFS mean/12Z UKMET Confidence: Average...through 60 hours Below average...after 60 hours A secondary shortwave moving east from the West Coast behind the initial wave will drift down over the Four Corners area into Sunday underneath a closed high center that drops southeast from southwest Canada. This trough then ejects southeast across the southern Plains through Monday. On Tuesday, the energy will be traversing the Gulf Coast states and moving toward the Southeast. By the end of the period, an area of low pressure is expected to form along a frontal zone draped from the eastern Gulf of Mexico northeast across the FL Peninsula and up offshore the Carolinas. The 00Z NAM is the strongest solution with the closed low/trough that ultimately swings through the southern Plains and it hangs onto stronger height falls as it crosses the Gulf Coast states which helps to drive cyclogenesis by early Tuesday over the eastern Gulf of Mexico. The NAM is also a little slower than the global model consensus by the end of the period. The 00Z GFS and the non-NCEP models (especially the 12Z CMC) are all a bit weaker with the energy by comparison and tend to favor the main focus of cyclogenesis off the east coast of the FL Peninsula. However, the 12Z ECMWF does suggest some wave activity initially over the eastern Gulf of Mexico before tucking low pressure in rather close to the coastal areas of southeast GA by the end of the period. There are a fairly large number of 12Z ECENS members that are farther north with the evolution of this low center by the end of the period versus the 12Z GEFS members and the 18Z GEFS mean. A large number of ECENS members also tend to favor cyclogenesis over the Gulf of Mexico versus offshore the Southeast coast. Generally the 12Z CMC ensemble suite is a bit more supportive of the GFS and the GEFS camp. Although the deterministic 12Z CMC/UKMET solutions actually tend to be a bit more suppressed than the GFS. Based on the latest model trends, clustering and ensemble spread, confidence becomes a bit limited toward the end of the period, but a blend of the 00Z GFS/18Z GEFS mean and 12Z UKMET will be preferred for now. ...Trough/Low approaching the West Coast on Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z CMC/ECMWF Confidence: Average The guidance depicts a fairly compact closed low approaching northern CA by late Monday which will be gradually opening up into a trough axis Monday night through early Tuesday while advancing inland. There will also be a wave of low pressure focused a bit farther north that will be approaching coastal areas of the Pacific Northwest and also under the influence of a northern stream trough/closed low west of Vancouver Island. The 12Z UKMET is generally the biggest outlier as it takes the energy approaching northern CA farther off to the north, whereas the 00Z NAM/GFS solutions and the 12Z CMC/ECMWF solutions all support at least a fairly vigorous shortwave trough crossing central to northern CA by early Tuesday. The NAM though is perhaps a tad more progressive than the global models with this energy. Regarding the surface low, the 00Z NAM/GFS and 12Z UKMET advance the low pressure center a bit farther north up the coast versus the 12Z CMC/ECMWF solutions. A fair number of 12Z GEFS/ECENS members tend to be a bit south of the 00Z NAM/GFS and 12Z UKMET, although the 18Z GEFS mean is actually a bit farther north like the latest GFS. Based on the latest clustering of solutions and ensemble spread, a blend of the 00Z GFS, 12Z ECMWF and 12Z CMC will be preferred. ...Upper trough over the Northern Plains/Midwest Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The guidance support the intrusion of a new northern stream trough digging down over the northern Plains and Midwest by Tuesday along with a cold front. The 12Z CMC is more out of tolerance with the remaining guidance as it has a slower cold front evolution and also is weaker with low pressure over south-central Canada and the details of the upper trough. Will prefer a non-CMC blend with this system. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison