Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 255 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/ECMWF and 00Z 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 guidance has collectively trended stronger and farther north with the low track of the system, with the NAM on the stronger side of the model spread. The CMC and ECMWF have their low tracks very close to that of the NAM, with the UKMET and GFS clustered a tad farther south and east by comparison. The UKMET is overall the weakest deterministic solution with the low center. The 12Z GEFS mean did trend stronger and farther north with its low center, but still is weaker than the NAM/GFS/ECMWF cluster and the ECENS mean. So, based on the latest trends and model clustering, the preference will be the same as before, except to swap out the 00Z ECMWF for the 12Z ECMWF. Thus a blend of the 12Z NAM/GFS/ECMWF and the 00Z ECENS mean at this point is preferred. ...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 12Z UKMET and 12Z CMC are the slowest solutions, with the 12Z ECMWF now the fastest. The 12Z NAM and 12Z GFS cluster in between slower and faster camps. The 12Z GFS generally is closest to the model consensus at this point, and since it had good agreement from the 00Z ECMWF, the prior model preference will be maintained for the time being. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison