Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Fri Jun 26 2020 Valid Jun 26/0000 UTC thru Jun 29/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over Quebec Trough impacting the Northeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend 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. However, by Sunday, the models suggest a new shortwave trough will cross the Great Lakes and help to amplify the troughing over the Northeast with some southward advance of the closed low as well. The 00Z NAM is more aggressive with this additional energy and results in a somewhat stronger closed low and large scale trough involving the Northeast by the end of the period. Will prefer a non-NAM blend for now given good global model agreement/clustering otherwise. Deep upper trough/closed low digging into the West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average A deep upper trough and associated closed low is forecast to amplify into the West this weekend with the models supporting a strong upper low over southwest ID by early Monday. The global models are actually in very good agreement overall with the placement and depth of the system. The 00Z NAM though for its part is a bit deeper and colder than the global models and is a modest outlier as a result, but its positioning is otherwise close to the global model consensus. Will prefer a non-NAM blend for the closed low for the time being. Shortwaves lifting northeast over the Plains/Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z ECMWF/GEFS mean and 12Z 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. The 00Z NAM is overall the deepest solution with this energy. The 00Z GFS tends to be more progressive with the shortwaves versus the 00Z UKMET/ECMWF solutions and especially the 00Z CMC which is the slowest. The 00Z GEFS mean and 12Z ECENS mean actually cluster together quite well and suggest a solution in between slower and faster camps, and as a cluster appear to be at least reasonably supportive of the ECMWF. So a blend of the ECMWF, GEFS mean and ECENS mean will be preferred at this time. Given the spread in the deterministic guidance though with timing and depth of this energy, confidence remains a bit limited. 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 MS Valley will essentially shear out over top of the ridge over the next couple of days. However, there will still be a fairly broad mid-level weakness/trough lingering over Texas which should tend to retrograde westward through Saturday before then lifting north through the southern and central Plains ahead of the deep Western U.S. trough/closed low. A general model blend will be preferred with the energy over Texas and the lower MS Valley. Upper trough/low over Manitoba/Saskatchewan ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 00Z CMC and 00Z ECMWF Confidence: Average A separate closed low and associated trough over southwest Canada will drive deepening surface low pressure over areas of Manitoba and Saskatchewan going through Saturday and Sunday. The 00Z NAM appears too deep with its height falls, and the 00Z UKMET appears too fast in advancing its energy off to the northeast. Meanwhile, the 00Z NAM/GFS solutions are both on the slower side of the guidance, with the latest ensemble means a bit more supportive of the 00Z CMC/ECMWF clustering. The CMC and ECMWF are close to the model consensus, so a blend of these solutions will 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