Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1254 PM EDT Wed May 06 2020 Valid May 06/1200 UTC thru May 10/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper trough impacting the Mid-Atlantic/New England through Thursday... ...Consolidating/deepening surface low pressure off the East Coast through Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring a relatively strong upper trough through the OH Valley and across the Mid-Atlantic and New England through early Thursday, which includes a closed mid-level low center crossing from eastern OH through north-central PA and then up across southeast New England. The model spread is quite minimal with this. At the surface, multiple low centers are expected to consolidate off the East Coast and deepen into one dominant center that lifts away from New England Thursday. Given only modest spread in the mass fields, a general model blend will be preferred. ...Amplifying shortwave crossing the Northwest U.S. today... ...Energy digging across the Plains/Midwest Thursday... ...Phasing with strong Canadian trough/vortex... ...Deepening surface low from the OH Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS and 00Z ECMWF/ECENS mean Confidence: Average A vigorous shortwave entering the Northwest today will amplify out across MT through tonight and dig southeast through the remainder of the northern Plains and Midwest through Thursday. By Friday, the energy will be crossing the OH Valley and will be begin to phase with very strong northern stream height falls/troughing associated with a vortex settling south over eastern Ontario and southwest Quebec. This will lead to strengthening low pressure up across the OH Valley along a frontal boundary, and this low center will then cross the Mid-Atlantic by Friday evening. On Saturday, the coupling/phased resultant of energy moving into the Northeast will yield a highly anomalous closed low and associated upper trough (500 mb heights 3 to 4 standard deviations below normal) with a rapidly deepening surface low lifting up across or just offshore of coastal New England. The 12Z NAM and to an extent the 12Z GFS have both trended north with their respective surface low tracks from the OH Valley to the Northeast, but are more notably stronger than their previous runs. The 00Z ECMWF and 00Z ECENS mean generally support the NAM low track, with the GFS a bit farther south. However, the GFS/ECMWF/ECENS mean cluster is a bit weaker than the NAM, and by Saturday, the NAM ends with a low track farthest to the west with respect to New England. Meanwhile, the 00Z UKMET and much more so the 00Z CMC, are flatter/weaker solutions by comparison and have a low track a bit farther offshore relative to New England. The 06Z GEFS mean also is a notably weak outlier at this point, and especially given the latest 12Z trends. So, at this point, a blend of the 12Z NAM/GFS and the 00Z ECMWF/ECENS mean will be preferred with the evolution of this system. ...Shortwave/surface low impacting the northern Rockies and northern Plains by Friday/Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF Confidence: Average Downstream of a sharp and elongated mid-level ridge in place over western North America by Friday and Saturday, a shortwave is expected to drop southeast through central and southern Canada and over portions of the northern Rockies and northern Plains. The latest guidance also suggests a wave of low pressure will be attendant to this system. The 00Z CMC and 00Z UKMET are the slowest and deepest solutions overall, with the 12Z NAM the fastest and weakest. The 12Z GFS and 00Z ECMWF are clustered in between. A blend of the GFS and ECMWF will be preferred at this time to approximate the model consensus. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison