Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1246 PM EDT Sun May 03 2020 Valid May 03/1200 UTC thru May 07/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Shortwave and surface low tracking from Great Lakes to the Northeast through Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: High Only minor timing differences exist with this system, and although the ECMWF is more amplified and the CMC a little weaker once emerging offshore, the differences are small enough 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: 12Z GFS, 00Z ECMWF, 00Z UKMET blend Confidence: Moderate A complex evolution will take place as a shortwave trough over interior portions of the Northwest tracks eastward as a closed low crosses southern Alberta/Saskatchewan on Monday. Meanwhile, a weaker mid-level shortwave is expected to track eastward from near the Oregon/California border Sunday evening, reaching near Iowa by Tuesday morning. At the surface, low pressure is expected to develop over the Ozarks by Monday night along a frontal boundary, and then reach the East Coast late Tuesday. The GFS trended a little more amplified across the Ohio Valley and the mid-South compared to its 6Z run, and the CMC is a little weaker than the model consensus and slightly suppressed with its surface low track. Pair of shortwave troughs affecting the Pacific Northwest through Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z ECMWF/ECENS/12Z GFS blend Confidence: Low-Moderate The first of two shortwave troughs to pivot around the broad upper level gyre over the Gulf of Alaska will clip the Pacific Northwest Monday night, with the 00Z UKMET standing out with a stronger shortwave compared to the other models. The second and stronger shortwave that follows will approach the Pacific Northwest on Tuesday/Tuesday night with an accompanying cold front at the surface. In terms of the latest model guidance, the CMC is more progressive with the trough during the Day 3 period, and the 12Z GFS trended a little faster compared to its 6Z run, albeit not to the same degree as the CMC. The 12Z NAM is on the stronger side of the model guidance. 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 00Z ECMWF/ECENS/12Z GFS 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 Hamrick