Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Thu May 03 2018 Valid May 03/1200 UTC thru May 07/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Ejecting Southwest U.S. upper trough crossing the central Plains and upper Midwest through Thursday... ...Phasing with northern stream energy from south-central Canada on Friday... ...Surface low lifting from the central Plains Thursday to the lower Great Lakes on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average There is generally very good agreement among the models with how this trough lifts into the Upper Midwest and Great Lakes. The 12Z CMC trended just a little stronger with this run and it is now very close to the model consensus. Will prefer a general model blend as a result at this point. ...Lingering trough over the Southwest on Friday... ...Ejecting east into the Lower MS Valley by Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Average The models maintain a portion of the Southwest U.S. trough/closed low going through Friday. Thereafter, they eject the energy east across the southern Plains, lower MS Valley and then the TN Valley going into Saturday. Model spread is rather limited until Saturday when the guidance begins to diverge with the level of shortwave amplification over the TN Valley. The 12Z NAM ends up stronger and a bit farther south on Saturday with its shortwave. The 12Z ECMWF also leans toward the stronger side of the guidance. The 12Z GFS, 12Z UKMET and 12Z CMC are collectively a little weaker than the ECMWF. Based on the latest ensemble clustering, the NAM is the easy model at this point to discontinue, and so will continue with a non-NAM blend. ...Upper trough dropping down across the Great Lakes by Saturday... ...Associated cold front dropping down across the Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring a northern stream trough along with an attendant cold front down across the Great Lakes and adjacent portions of the Midwest by Saturday. This energy will be attempting to interact with the aforementioned energy arriving across the TN Valley on Saturday. Model spread is remains modest with the northern stream mass field details, so a general model blend will be preferred with this feature. ...Low amplitude shortwave approaching British Columbia Friday... ...Upper level low/trough approaching the West Coast by late Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average The models have come into reasonably good agreement with the weak shortwave entering British Columbia by late Friday and Saturday and the model spread with this feature is rather minimal. Meanwhile, the models bring an upper trough and associated closed low in toward the West Coast on Saturday which will foster at least a little bit of binary interaction with the energy near British Columbia. The 12Z NAM is a bit stronger than the model consensus with the energy crossing the West Coast. The remaining global models are reasonably well clustered with just some modest differences. Given concerns over the depth of the NAM solution with the energy arriving inland across the West Coast and eventually the depth of energy over British Columbia, a non-NAM blend will be preferred. ...Upper level low developing near the Bahamas by Friday... ...Inverted surface trough developing by Friday, and extending into Florida this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Upper level low will develop at the cusp of a lobe of higher PV to the south of an anticyclonic wave breaking event over the western Atlantic. Models again are in fairly good agreement with this taking place near the Bahamas by tonight and Friday morning, and show very little difference in their mass fields. The 12Z CMC is a bit weaker than its previous run, and the latest models show very good agreement on the details of surface low pressure impacting south Florida by late Saturday. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison