Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1247 AM EDT Sun May 03 2020 Valid May 03/0000 UTC thru May 06/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z NAM/GFS Evaluation Including Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave and surface low tracking from Great Lakes to the Northeast through Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Only minor timing differences exist with this system and while the 00Z GFS remains slightly faster than the remaining model consensus, the differences are small enough such that a general model blend can be used for this system from the Great Lakes, Northeast and central/southern Appalachians. ...Mid-level shortwave over the Northwest this morning, eventually reaching the Upper Midwest on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, 12Z NAM blend Confidence: Slightly below average A complex evolution as a shortwave trough over interior portions of the Northwest tracks eastward as a closed low across southern Alberta/Saskatchewan on Monday. Meanwhile, a weaker mid-level shortwave is expected to track eastward from near the OR/CA border Sunday evening, reaching near IA Tuesday morning. At the surface, low pressure will organize over the Ozarks Monday night along a frontal boundary and reach the East Coast late Tuesday. The ensemble means paint a similar picture with strength and timing but no single model matches the means. A rough blend of the 00Z NAM (slower) with the 00Z GFS (weaker) and 12Z ECMWF (faster) is the closest of the deterministic guidance. The 12Z UKMET is significantly slower with this system while the 12Z CMC is much faster. ...Mid-level shortwave clipping the Pacific Northwest Monday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show similarly with this system. ...Next mid-level shortwave/associated cold front reaching the Pacific Northwest Tuesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/UKMET/CMC blend Confidence: Below average Yet another shortwave will near the Pacific Northwest on Tuesday with an accompanying cold front at the surface. The 00Z NAM is strongest with a compact vorticity maximum within the trough axis which reach Washington Wednesday morning. The 00Z GFS is slower with a more elongated vorticity maximum offshore of Oregon at the same time. While the semi-agreeable ensemble means show a more focused vorticity max within the approaching trough, there is not enough agreement to go with a stronger NAM solution or slower GFS solution at this time. Ensemble trends have showed convergence since yesterday with the timing of the trough Wednesday morning, but have not wavered significantly on timing. For now, a blend of the 12Z ECMWF/UKMET/CMC is closest to the middle of the ensemble guidance and closest to their means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto