Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 241 PM EDT Wed Jun 24 2020 Valid Jun 24/1200 UTC thru Jun 28/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over Ontario/Quebec Trough crossing the eastern U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The upper-level low in place over the northern Great Lakes is expected to lift north/northeastward over the next few days while there will be some southward expansion on the longwave trough over the eastern U.S., which pushes a cold front through much of the Mid-Atlantic and New England before washing out over the Southeast. From a synoptic point of view, mass fields are in good shape in the region and a general model blend is preferred. Shortwave crossing the Pacific Northwest and Plains/Midwest Energy digging into the Southwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend...northern stream Non-CMC blend...southern stream Confidence: Above average The latest guidance continues to advertise a shortwave trough crossing the Pacific Northwest through tonight and then advancing progressively downstream across the central/northern Rockies going through Thursday. As this is occurring, some of the energy will be separating out and digging farther south into the Southwest. Going through Friday and Saturday, the northern portion of the original trough will eject out across the northern Plains and upper Midwest, with the guidance favoring a southern stream trough lingering near the Four Corners region. With the initial surge of the northern stream portion of the trough, the models are in good agreement although the 12Z UKMET shows a slightly more progressive and weaker trough compared to the other models by the end of the period as the energy crosses the Great Lakes region. Will prefer a non-UKMET blend as a result with this northern stream trough evolution. With the southern stream energy, the 12Z CMC is a bit weaker and more progressive with the energy compared to a reasonably well-clustered set of models otherwise which keep more energy a tad farther back to the west. This includes the 12Z ECMWF which trended a tad farther east and in line with the 12Z NAM, 12Z GFS and 12Z UKMET. So, a non-CMC blend will be preferred at this point with the southern stream energy. Strong shortwave trough over the Pacific Northwest this weekend ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Average A strong shortwave trough from the Gulf of Alaska is forecast to drop south along the British Columbia coast and arrive across the Pacific Northwest by Saturday morning. With the initial surge of height falls, the 12Z GFS is now overall the most progressive as the modestly slower 12Z NAM is getting better clustering/support from the 12Z CMC, 12Z UKMET and 12Z ECMWF. The GFS is more out of tolerance also with additional jet energy digging south late Saturday along the British Columbia coast. There is some support for the GFS though from the latest 12Z GEFS mean. However, the 00Z ECENS mean favors the full non-NCEP suite of guidance and the NAM. So, for now a non-GFS blend will be preferred. Lower MS Valley and Gulf Coast states ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Weak flow aloft with pieces of shortwave energy becoming removed from the westerlies will drift over the Texas Gulf coast and lower MS Valley. The models are in better agreement today with gradually taking some of this off to the east-northeast and shearing it out across the Gulf Coast states over the next 2 to 3 days. However, the models all agree in maintaining a broad mid-level weakness over Texas through the period. The 12Z non-NCEP suite of guidance trended toward the slower NAM/GFS and HREF clustering of solutions with the individual vorts, and based on the better agreement, a general model blend will now be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison