Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1232 PM EDT Thu May 07 2020 Valid May 07/1200 UTC thru May 11/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Energy digging southeast from the northern Plains to the OH Valley and Mid-Atlantic... ...Strong vortex over southeast Canada and the Northeast... ...Deepening surface low from the OH Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF Confidence: Average A compact mid-level closed low and associated trough over the northern High Plains this morning will dig southeast across the Midwest through Thursday. By Friday, the energy will be crossing the OH Valley and will be attempting 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 over the Northeast U.S. (500 mb heights 3 to 4 standard deviations below normal), with likelihood of a rapidly deepening surface low lifting up across or just offshore of coastal New England. The model spread with the low track across the OH Valley and Mid-Atlantic is rather small, with the differences here mainly related to the 12Z GFS being a bit stronger than the model consensus. However, the differences increase markedly with respect to New England as the low tracks northeastward and deepens with time. The 12Z NAM ends up farther east, flatter and weaker than the global model suite, with exception to the 00Z UKMET which is also weaker and flatter. The 12Z GFS, 00Z CMC and 00Z ECMWF are all deeper and farther west with the low track, and suggestive of stronger/quicker phasing relative to the NAM/UKMET camp which allows the low center to tuck in closer to the New England coast and even slightly inland before exiting up across southeast Canada. The 06Z GEFS/00Z ECENS and 00Z CMCE all support a GFS/ECMWF weighted solution, with the idea that the NAM and UKMET are a bit too weak/flat and too far east, and with a likelihood that the deterministic CMC (at least from 00Z) is overall too far west. So, will prefer a blend of the 12Z GFS and 00Z ECMWF for the time being. ...Shortwaves/surface low impacting the northern Plains and Midwest this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 00Z CMC and 00Z ECMWF Confidence: Average Downstream of a sharp and elongated mid-level ridge in place over western North America on Friday and Saturday, and embedded within deep layer north-northwest flow over central Canada, a pair of shortwaves will drop down out of Canada and down across portions of the northern Plains and Midwest this weekend. The lead shortwave will have a low center and cold front associated with it which will cross the Dakotas on Saturday and then gradually weaken as it crosses the Midwest on Sunday. Model spread is relatively minimal, but the 12Z NAM is generally a tad stronger with the shortwave energy and also the surface low reflection compared to the global models. The NAM is also a tad faster with the surface low evolution. Of the global models, the 00Z UKMET is the most questionable at this time as it has a slower shortwave evolution and surface reflection relative to the model consensus and the ensemble means. The best overall model clustering and ensemble support tends to favor a 12Z GFS, 00Z CMC and 00Z ECMWF blend, and so this consensus will be preferred. ...Shortwave energy crossing southern CA by Sun morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models show a weak shortwave crossing areas of coastal southern CA and then the Desert Southwest on Sunday. Given the modest spread in timing and depth relating to this energy, a general model blend will still be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison