Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 342 PM EDT Fri Jun 26 2020 Valid Jun 26/1200 UTC thru Jun 30/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 19Z Update: The 12Z UKMET trended slightly to the west with the closed low over New England compared to its 00Z run, and this also holds true for the 12Z CMC. The 12Z ECMWF trended slightly to the east with the axis of the upper level trough over the Intermountain West, but not enough to appear significant. Otherwise no major changes in the model preferences. Closed low over Quebec Trough impacting the Northeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z UKMET/12Z ECMWF Confidence: Slightly above average The models are in good agreement on the details of the large closed low over Quebec and southward extension of the trough across the Northeast U.S. going through Saturday. By Sunday, the models suggest a new shortwave trough will cross the Great Lakes and help to amplify the synoptic scale trough over the Northeast, and the core of the upper low nudges a little to the south across northern New England. The 12Z NAM is still a little more robust with this shortwave and results in a somewhat stronger closed low that is slightly to the east of the model consensus across the Northeast by the end of the period. Additionally, the 00Z CMC is a little to the southwest of the model consensus by Day 3, so therefore a GFS/ECMWF/UKMET can be recommended. Deep upper trough/closed low digging into the West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM/12Z UKMET/12Z ECMWF Confidence: Slightly above average A deep upper trough and associated closed low is forecast to amplify across the northern Rockies and Intermountain West this weekend as an upper level ridge builds across the Gulf of Alaska and also across the Midwest and Great Lakes region, suggesting a potential Omega block pattern. The models are in good agreement on the evolution through Sunday evening, after which the CMC takes the upper low farther south than the other guidance, and the GFS appears too fast to lift the low out to the northeast by Monday afternoon. Therefore, a NAM/UKMET/ECMWF blend should work well for this region. Shortwaves lifting northeast over the Plains/Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z UKMET/12Z GEFS mean/00Z ECENS mean Confidence: Slightly below average Ahead of the deep western U.S. trough/closed low will be a parade of shortwave troughs that eject northeast out of the Southwest and across the Plains and Midwest. Both the NAM and to a greater degree the GFS appear more amplified with the first shortwave, whereas the non-NCEP guidance suggests a flatter solution. The second shortwave has a greater degree of model spread, and the ECMWF/ECENS are stronger than the GFS/GEFS, with the UKMET supporting a decent middle ground solution. Therefore some weighting of the ensemble means would be prudent for the second feature crossing the central Plains. Remnant energy across the lower MS Valley Weakness lingering over Texas ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The model support a gradual building of the subtropical ridge this weekend across the FL Peninsula and adjacent areas of the Gulf Coast states. Some of the weak shortwave energy lingering over the lower Mississippi Valley should shear out over top of the ridge through Saturday. However, there will still be a broad mid-level weakness/trough lingering over Texas which should tend to retrograde westward through Saturday, before then lifting north across the southern and central Plains ahead of the deep Western U.S. trough/closed low. A general model blend will be preferred with the weak trough over Texas and Gulf Coast. Upper trough/low over Manitoba/Saskatchewan ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z UKMET/12Z ECMWF blend Confidence: Average A surface low currently over central Ontario in combination with a mid-level shortwave trough over the northern Great Lakes will continue to track east and bring a cold front across the Great Lakes region and then the interior Northeast. The 12Z NAM is stronger with this system and has a secondary surface low crossing New York on Saturday, and the GFS is slightly more progressive. The UKMET and ECMWF are close to the model consensus, so a blend of these solutions will be preferred at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick