Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 AM EDT Sat Jun 27 2020 Valid Jun 27/0000 UTC thru Jun 30/1200 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. 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 models support the closed low actually then dropping south into the interior of the Northeast going through Monday and Tuesday. The 00Z NAM is still a little more robust with this shortwave and results in a somewhat stronger closed low that is on the southwest side of the model consensus across the Northeast by the end of the period. The global models are reasonably well clustered at this point, so a non-NAM blend will be preferred. Deep upper trough/closed low digging into the West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/UKMET/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 00Z CMC takes the upper low farther south than the other guidance. The 00Z NAM gradually ends up with a stronger upper low impacting the northern Rockies from Sunday night through early Tuesday. Will prefer a blend of the better clustered 00Z GFS, 00Z UKMET and 00Z ECMWF solutions which also again have good ensemble support. Shortwaves lifting northeast over the Plains/Midwest ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GEFS mean and 12Z ECENS mean Confidence: Average Ahead of the deep western U.S. trough/closed low will be a pair of shortwave troughs that eject northeast out of the Southwest and across the Plains and Midwest. The 00Z NAM is a strong outlier with the first shortwave as it rides northeast from the central Plains to the upper Midwest going through Sunday with the global models largely flatter. The 00Z CMC also again is stronger than the model consensus. The 00Z GFS for its part is seen as also taking this first shortwave a bit farther east across areas of the Midwest versus the model consensus. The second shortwave has some model spread noted as the 00Z ECMWF and 12Z ECENS mean support a somewhat stronger solution versus the remaining guidance which is flatter. For now, a blend of the ensemble means will be preferred with both shortwave impulses. Remnant energy across the lower MS Valley Weakness lingering over Texas ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: 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 again be preferred with the weak trough over Texas. Upper trough/low over Manitoba/Saskatchewan ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Slightly above 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 CMC is still perhaps a tad too strong with this energy, but the remainder of the guidance has come into better agreement with their mass field solutions. So, a non-CMC blend 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