Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 237 PM EDT Sat May 09 2020 Valid May 09/1200 UTC thru May 13/0000 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 12Z Model Evaluation Including Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Exiting deep layer cyclone impacting the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement with the details of the deep layer cyclone impacting the Northeast today, which will be lifting off to the northeast across the Canadian maritimes through tonight and Sunday. A general model blend will be preferred. ...Compact shortwaves/surface low impacting the northern Plains and Midwest this weekend... ...Energy amplifying from the OH Valley to the Northeast Mon and Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 48 hours 12Z ECMWF/00Z ECENS mean blend...after 48 hours Confidence: Average The guidance takes the vigorous compact shortwave and associated surface low over the northern Plains southeastward across the Midwest going through Sunday. On Monday this lead energy and a fast-moving secondary shortwave in its wake will consolidate and transit the OH Valley. As the energy rounds the base of the larger scale troughing that will be persisting from the Great Lakes region into much of south-central and southeast Canada, this OH Valley energy should amplify, and by Tuesday all of the models support the idea of a negatively tilting shortwave and possible closed mid-level low crossing New England along with an intensifying surface low center. The guidance is in good agreement through about 48 hours, but thereafter the 12Z NAM suggests stronger shortwave amplification and a surface low that tends to track a tad left of the model consensus as it crosses New England by 72 hours. The 12Z GFS also becomes more progressive with the energy than any other model by that time, and the 12Z CMC is seen as being a bit slow. The CMC did shift its low track a bit to the east of the model consensus as well. Meanwhile, the 12Z UKMET shifted its low track a bit farther west. The model consensus beyond 48 hours, tends to be best supported by the 12Z ECMWF which is hanging on to good continuity from its 00Z run. The ECMWF is well supported by the 00Z ECENS mean too. So at this point, a general model blend will be preferred through 48 hours, followed by a blend of the ECMWF/ECENS mean camp. ...Shortwave energy crossing southern CA this weekend... ...Energy shearing across the southern Plains by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-NAM blend...after 60 hours Confidence: Above average The models show a weak shortwave crossing southern CA by later today, and then the Desert Southwest on Sunday. the energy is then expected to gradually shear off to the east and reach the southern Plains by Tuesday. Model spread is very modest through about 60 hours, but thereafter the 12Z NAM leans a bit stronger than the well-clustered global models. So, a general model blend will be preferred through 60 hours, followed by a non-NAM blend thereafter. ...Upper trough/closed low approaching the West Coast by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Slightly above average An upper trough and associated closed low will be approaching and possibly crossing the West Coast by Tuesday as the larger scale blocking pattern across western North America begins to break down. The 12Z NAM is the fastest to bring the height falls inland across the West Coast. The 12Z GFS and 12Z ECMWF solutions are a little slower and also have their closed low features a little north of the NAM position by the end of the period. The 12Z CMC is just a tad weaker with the energy and is perhaps just slightly north of the GFS/ECMWF camp. Meanwhile, the 12Z UKMET is the most out of phase and the slowest with its closed low evolution toward the West Coast. Nevertheless, all of the models increase the onshore flow into the West Coast, especially from northern CA to the Pacific Northwest as surface low pressure lifts northeast up off the coast. Based on very good model mass field clustering and ensemble support, a blend of the GFS and ECMWF will be preferred at this point. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison