Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 124 AM EDT Sun Jun 28 2020 Valid Jun 28/0000 UTC thru Jul 01/1200 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 and accompanying shortwaves Trough impacting the Northeast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average An upper-level low initially over Quebec will sustain a broad upper-level trough centered over the East Coast through Sunday. The models are in good agreement on then gradually bringing this upper low southward early next week, with the guidance focusing it over the interior of New England Monday and Tuesday. The 00Z NAM brings the upper low farthest south, with the non-NCEP models generally clustered a little farther north, and the 00Z GFS in between these camps. Overall, the NAM is the bigger outlier so a non-NAM blend will be preferred. MCV currently over southern IL ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average The models take the MCV currently over southern IL off to the east on Sunday with the energy gradually shearing out as it arrives across the central Appalachians. The 00Z NAM is the strongest solution with this system, as the 00Z HREF guidance and the global models all agree and cluster on a somewhat flatter MCV that shears out by Sunday evening. A non-NAM blend will be preferred. Deep upper trough/closed low across the Intermountain West ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z 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 over the next couple of days as an upper-level ridge builds across the Gulf of Alaska and also across the Midwest and Great Lakes region. This will yield a quasi omega-block pattern across the central and western U.S. The 00Z NAM again tends to be on the strong side with the height fall evolution across the West as it has a stronger upper low impacting the northern Rockies Monday and Tuesday. The 12Z CMC once again tends to be slower with the trough evolution and lags the remaining model suite as the energy pivots through the Intermountain Region. The 00Z GFS, 12Z UKMET and 12Z ECMWF have some modest timing/depth differences but overall represent a reasonable cluster that is well supported by the latest ensemble guidance. Will prefer a blend of the latest GFS, UKMET and ECMWF as a result. Shortwave energy lifting from eastern CO to MN by early Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z ARW/ARW2/GFS Confidence: Average Ahead of the deep western U.S. trough/closed low will be multiple shortwave troughs that eject northeast out across the Plains and Midwest. One shortwave impulse that is already ejecting out across eastern CO is forecast to advance up over the upper Midwest and amplify into possibly a weak closed low over MN by early Monday as some modest energy lifting northeast in behind it merges and consolidates with it. The guidance has trended overall a bit stronger with this feature and the global models and HREF suite of guidance support at least a vigorous convectively enhanced shortwave regionally impacting the upper Midwest by Monday. There are some timing differences as the 00Z NAM is a bit slower than the model consensus, with the 12Z UKMET and 12Z CMC solutions overall the fastest. The 00Z GFS and 12Z ECMWF are clustered in between camps, but the ECMWF appears to be a weak outlier with this energy. The latest HREF suite of guidance led by the ARW and ARW2 support the GFS solution. Overall, the NMMB appears a bit too weak, and the NAM-conest too slow. Shortwave lifting across the central Plains Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Slightly above average A shortwave trough that is currently over the Southwest will lift northeast and reach the central Plains by Monday and is then forecast to dampen out. The 12Z UKMET is overall the weakest solution with this impulse, and so a non-UKMET blend will be preferred. Shortwave crossing the Rio Grande Valley on Sunday Amplifying toward mid MS Valley by Monday night ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z NAM and 12Z CMC/UKMET solutions Confidence: Average The guidance supports a convectively enhanced shortwave or MCV lifting northeast across the lower/middle Rio Grande Valley on Sunday which is forecast to lift northeast toward the mid MS Valley by Monday night while attempting to amplify. The 00Z NAM/GFS solutions and 12Z CMC/UKMET solutions all appear to be trending stronger with this feature and support at least a weak mid-level low center impacting areas of MO and IA going through Tuesday. The 00Z GFS ultimately ends up being more progressive as it suggests a faster interaction between this impulse and the upstream deep trough over the West. The 12Z ECMWF for its part is a decidedly weak outlier with this energy. All of the 00Z HREF models with exception of the NMMB favor a reasonably well organized mid-level shortwave trough or weak closed low center approaching the mid MS Valley as well. For now, a blend of the 00Z NAM, 12Z UKMET and 12Z CMC 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