Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1239 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 12Z NAM/GFS and 00Z UKMET blend...southern stream Confidence: Slightly 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 00Z UKMET shows a more progressive 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 00Z ECMWF tends to hold energy back a bit more to the west and over the Desert Southwest versus the model consensus which is a little closer to the broader Four Corners region. The 00Z CMC though appears to be much too progressive and generally too weak as it drives energy much farther east by the end of the period. The better model clustering and ensemble support favors a blend of the 12Z NAM/GFS and 00Z UKMET for the time being, and so a blend of these solutions will be preferred for the southern stream energy. Strong shortwave trough over the Pacific Northwest this weekend ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 06Z GEFS/00Z ECENS mean 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 NAM and 00Z ECMWF are a bit slower compared to the 12Z GFS, 00Z ECMWF and 00Z CMC solutions. However, there is more spread with a jet-streak and secondary shortwave diving south late Saturday along the British Columbia coast. The NAM and UKMET solutions are more pronounced with this feature versus the more subtle GFS and ECMWF. The CMC actually is the weakest with this secondary piece of energy. The 06Z GEFS mean and 00Z ECENS mean support a compromise solution between the camps, and a blend of these solutions will be preferred to attempt to resolve some of the timing/depth differences. Lower MS Valley and Gulf Coast states ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS/HREF Confidence: 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 over the next couple of days. The models are in somewhat better agreement today with gradually taking this energy off to the east-northeast and shearing it out across the Gulf Coast states. However, the 00Z non-NCEP models are all a bit more progressive in doing this as all of the 12Z HREF guidance and the 12Z NAM/GFS solutions are slower and tend to keep the energy lingering over the western Gulf Coast and lower MS Valley region for longer. Will prefer a blend of the non-NCEP guidance as a result for now. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison