Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1247 AM EDT Wed Oct 16 2019 Valid Oct 16/0000 UTC thru Oct 19/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Great Lakes closed low and developing Northeast coastal surface Low ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM and higher weight toward ECMWF Confidence: Slightly above average Closed upper low currently over eastern Wisconsin will take on more of a negative tilt as it approaches the Northeast U.S. by Thursday. The increasing diffluent pattern aloft will support rapid surface cyclogenesis along or just offshore the Mid-Atlantic coast and will track inland across New England. The 00Z NAM continues to show the most vertically stacked and deepest solution, which may be related to better higher resolution of warm Gulf Stream air, but this very strong signal departs rapidly from the other guidance members and ensemble suite/trend, leaving it out of the preference (though it may not be fully unrealistic). The rest of the guidance offers fairly good clustering through 60 hours as the low lifts northeast through Maine and into Canada. As such, will continue to lean on previous preference toward the ECMWF and continued less weighting of the NAM at this time. Record for low pressure are for non-tropical cyclone pressures in October...Post-Tropical Sandy is included in this database, so records across the lower Hudson and Mid-Atlantic are at much lower risk of being broken...please see www.wpc.ncep.noaa.gov/research/roth/SLPrecords.html. Short wave energy affecting Texas through midweek shearing thru eastern Gulf States by Fri ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/CMC/UKMET blend Confidence: Slightly below average Troughing currently moving into the Texas Panhandle will gradually reach the Gulf Coast by later this week. Interaction with an area of disturbed weather in the southwestern Gulf will eventually lead to a weak surface wave lifting northeast toward the central Gulf Coast. There is a fair amount of spread in the eventual track of any surface wave with the latest ECMWF slower/westward compared to the faster/east GFS, while the CMC lies in between. The 00Z NAM offered a good compromise/consensus approach as well. There remains above normal uncertainty in how this evolves over the coming days and what sensible weather impacts there will be, but a blend of the latest NAM/CMC/UKMET represents the consensus approach the best at this time. Western U.S. longwave trough (Wed-Thurs) shifts into Rockies with Northern Plains cyclogenesis Thurs into Fri ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Positively tilted trough will cross into the western U.S. late Wednesday and push into the central U.S. by this weekend. Model spread is average to slightly above average at this point, with the largest differences seen in timing as the shortwave moves east of the Rockies. Typical model biases are noted, with the GFS being slightly faster compared to the ECMWF/CMC/UKMET, but compared to previous cycles, the differences are not as significant. As such, a general model is preferred given the better than average model agreement. Pacific Northwest reinforcing shortwave late Thurs into Fri with broad/strong westerly Pacific jet thereafter ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average In the wake of the initial longwave trough across the Pacific Northwest, a stronger/compact shortwave piece of energy pushes into the region late Thursday into Friday. In the previous forecast cycle, the 12Z UKMET was too amplified and was not considered for the preferred blend. The new 00Z is considerably less amplified and now is in much better agreement with the rest of the deterministic models and within the model spread. A general model blend can be used here. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Taylor