Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 311 AM EDT Mon May 20 2019 Valid May 20/0000 UTC thru May 23/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough exiting the Great Lakes Monday... ...Strong height falls digging into the Northeast by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models gradually take the upper trough over the Great Lakes region off to the east on Monday and allow a cold front to sweep down across the OH Valley, Mid-Atlantic and Northeast by Monday night. On Tuesday, the guidance is in good agreement in strengthening the height falls over the Northeast as additional northern stream energy digs southeast across Ontario, and this will result in a closed low evolution for northern New England and a deepening of surface low pressure. The guidance is really in good agreement with the details of the mass field evolution of this system, and so a general model blend will be preferred. ...Deep closed low crossing the Southwest through Monday.... ...Going negative tilt across the High Plains by Tuesday... ...Leeside cyclogenesis over the High Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z HREF mean/UKMET/ECMWF blend...through 36 hours 00Z GFS/ECMWF blend...after 36 hours Confidence: Slightly above average An anomalous closed low moving across California will work through the Four Corners region on Monday and then eject out into the southern/central Plains Monday night through Tuesday, and taking on a strong negative tilt as it does so. It is then expected to slow as it lifts north toward the Dakotas by early Wednesday. At the surface, leeside cyclogenesis will take place Monday, helping to advance an anomalous plume of moisture and instability northward. In the broad, large-scale sense, the latest models are in rather good agreement with the set-up and evolution. However, the differences lie in the details, with exact boundary placement, and surface low position, especially Monday evening through Tuesday. The trend had been for a more westward position of the surface low and supporting energy aloft with a focus closer into southeast CO (like the 00Z GFS), but a couple of the 00Z non-NCEP models (notably the UKMET and ECMWF) do tend to shift the focus of the dominant low center a little farther east involving more of southwest and central KS by 36 hours. Beyond that time, the 00Z NAM at least briefly ejects the low center more off to the northeast versus the global models before then coming into better agreement as the low lifts north toward the Dakotas on Wednesday. Meanwhile, the 00Z CMC gradually becomes an outright outlier with the low track off to the northeast and right of the model consensus after about 60 hours. The hires CAM (HREF) guidance led by the 00Z ARW/ARW2/NMMB solutions tend to favor the 00Z UKMET/ECMWF solutions a bit more with low placement in the short-range (through 36 hours), but the 00Z NAM-conest is a bit farther east. Based on the latest clustering and trends, a blend of the 00Z HREF mean and 00Z UKMET/ECMWF solutions will be preferred through 36 hours for the mass fields, followed by a blend of the 00Z GFS and 00Z ECMWF thereafter given better clustering and ensemble support. Please consult the latest QPFERD for significant concerns for excessive rainfall with this event over the next 36 to 48 hours out across the central and southern Plains. ...Vigorous Pacific closed low digging into the West Tuesday... ...Teleconnecting subtropical ridge over the Southeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 72 hours 00Z GFS/CMC/ECMWF blend...after 72 hours Confidence: Above average Another strong northern stream closed low will move into the Pacific Northwest and California coast Monday and Tuesday. The main PV anomaly will drop south through California, as it becomes absorbed within the large scale troughing that will develop over the Western U.S. The 00Z cycle of guidance has come into better agreement with their timing of the height falls through the period, and the evolution of a very large closed low over the Western U.S. by the end of the period. There are some differences that appear by Wednesday night and Thursday morning as the 00Z NAM tends to eject some lead shortwave energy out into the central/southern High Plains a bit quicker than the global models. This results in a quicker onset of leeside cyclogenesis. The 00Z NAM and the 00Z UKMET actually both focus low pressure a bit north of the 00Z GFS/CMC/ECMWF solutions by the end of the period over the High Plains, but for now, there is better ensemble support for the GFS/CMC/ECMWF camp, and this will be the preference after about 72 hours. A general model blend is otherwise preferred prior to this. Aside from the deep closed low over the West by the end of the period, there will be the development of a corresponding and strong downstream subtropical ridge over the southeastern third of the country by the middle to latter part of the week which all of the guidance also supports. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Orrison