Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Mon Oct 14 2019 Valid Oct 14/0000 UTC thru Oct 17/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Final Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Southern Canada Low Pressure through Tuesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The deep upper vortex and surface low over Ontario is now moving towards the northeast and should reach northern Quebec by Tuesday afternoon. The primary front has stalled over the Southeast U.S. whilst the secondary front will track eastward across the central/northern Appalachians on Monday. A couple impulses riding along the front will enhance precipitation totals. The global deterministic model guidance is in excellent agreement with the synoptic features and therefore a general model blend is preferred. Shortwave trough and low across the north-central U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 00Z Wednesday, then CMC/EC mean Confidence: Slightly above average Shortwave energy originating from the Pacific Northwest will cross the Northern Rockies and then the Northern Plains by Monday Night. The northern stream trough will deepen and close off as it approaches the Upper Midwest and Great Lakes, becoming a longwave trough over the eastern U.S. with a negative tilt by Wednesday night. This will spawn a surface low over the Upper Midwest on Tuesday and also phase with the southern stream disturbance across the Southeast. The result will likely be a nor'easter near the Northeast coast by Wednesday night. The models are in good agreement through Tuesday evening, after which the 00Z NAM and UKMET becomes more amplified aloft, and the 00Z GFS becomes slightly faster. By the end of the forecast period, the 00Z ECMWF becomes much stronger with the surface low near New England Thursday morning, and likewise the NAM as well. In terms of the ensemble means, the EC mean appears closer to the model consensus than the GEFS mean. Therefore a blend of the CMC/EC mean should work well after 00Z Wednesday as a starting point. Southern tier shortwave and resulting surface low ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: NAM/GFS/ECMWF Confidence: Average Troughing moving through the western US will eventually pinch off a southern stream shortwave across southern California early Monday. The models have come into slightly better agreement with the amplitude and axis orientation as the shortwave tracks across the Four Corners region. By Tuesday morning this will spur the development of a surface low across the central Plains that will eventually reach the Southeast U.S. by Wednesday and merge with the northern stream system by early Thursday. The 00Z UKMET begins to differ by 00Z Wednesday with higher heights across the southern Plains. Therefore a blend of the NAM/GFS/ECMWF should suffice as a good starting point. Pacific Northwest by midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Deterministic model blend Confidence: Average A strong storm system originating from the Gulf of Alaska is expected to begin approaching the Pacific Northwest coast by late Tuesday night after a period of relatively quiet weather early in the week. Although the surface cold front is forecast to pass through the region mid-week, the parent surface low is expected to remain well to the north across western Canada. There are only minor model differences with the synoptic scale features at this time, so a blend of the deterministic guidance should work well. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Hamrick