Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Sun May 3 2020 Valid May 3/1200 UTC thru May 7/0000 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 Shortwave trough with cold front currently crossing the Appalachians and Mid-Atlantic will continue slowly tracking east with parent surface low exiting eastern New England by Monday afternoon. Only minor timing differences exist with this system, and although the 12Z GFS is slightly faster and the 12Z CMC a little weaker once emerging offshore near New England, 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 northern Rockies this afternoon, eventually reaching the Ohio Valley by Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/ECMWF/CMC blend Confidence: Moderate A complex evolution will take place as a shortwave trough over interior portions of the Northwest tracks southeastward in conjunction with a closed low crossing southern Alberta/Saskatchewan on Monday. At the same time, a weaker mid-level shortwave is expected to track eastward across the Intermountain West, reaching the Upper Midwest by Monday night, with some phasing between these two disturbances. At the surface, cyclogenesis is expected to develop over the Mid-South by Monday night along a frontal boundary, and then reach the East Coast by Wednesday morning as Miller-B cyclogenesis takes place east of North Carolina. The GFS trended a little more amplified across the Ohio Valley and the mid-South compared to its 6Z run, and the 12Z CMC is slightly suppressed with its surface low track. The 12Z UKMET is now the most potent with the upper level shortwave and slower to erode the primary surface low over the central Appalachians by the end of the forecast period. There has also been a trend in the non-NCEP guidance today for a more amplified trough over the eastern U.S. in comparison to their 00Z runs. There is enough synoptic scale agreement among the ECMWF/GFS/CMC to merit a blend of those models. Pair of shortwave troughs affecting the Pacific Northwest through Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF/12Z GFS/00Z ECENS blend Confidence: 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, although still a little slower than most of the guidance. The 12Z NAM is on the stronger side of the model guidance, along with the 12Z UKMET by Wednesday evening across the northern Rockies. For now, a blend of the 12Z ECMWF/GFS/00Z ECENS 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