Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 255 PM EDT Fri May 04 2018 Valid May 04/1200 UTC thru May 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper level trough ejecting through the Great Lakes today, with an accompanying surface low and cold front sweeping through the Great Lakes and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models are generally in good agreement with this system with their mass fields and thus a general model blend will be preferred. ...Upper level low developing near the Bahamas... ...Inverted surface trough/surface low extending into Florida this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with the details of this system as it approaches south Florida and begins to gradually become absorbed by the larger scale trough moving into the Southeast U.S. by late in the weekend. ...Southern stream trough pushing east through the southern Plains today... ...Moving across the Mid-Atlantic and Southeast this weekend... ...Multiple waves of low pressure impacting the East Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 12Z UKMET and 12Z ECMWF Confidence: Average On the large scale, the models are in good agreement with the details of the shortwave trough crossing the southern Plains and moving toward the Mid-Atlantic and Southeast this weekend. However, at the surface, there are some differences regarding the evolution of multiple waves of low pressure that will develop over the Southeast and Mid-Atlantic coastal plain and lifting up along the East Coast. The 12Z GFS may be a tad too aggressive with the initial low center that develops near the Delmarva on Sunday and lifts offshore New England Sunday night. Most of the models have a wave evolving here as the main upper trough arrives from the OH/TN Valley region, but the GFS has a bit more vort energy in the 700/500 mb layer crossing the central Appalachians which invigorates a stronger surface reflection. Meanwhile, farther south over the Southeast, the main axis of the shortwave trough will be interacting with the remnants of the system in the subtropics that lifts west and then northwest across the Florida Peninsula. The interaction between the two will favor a broad low center over GA and then up across the Carolinas in vicinity of the same aforementioned front. This wave activity will then advance off to the northeast up along the East Coast as a front sweeps gradually offshore by early Monday. The 12Z CMC is a bit stronger with the wave activity over the interior of the Southeast. Overall, the best model clustering tends to support a blend of the 12Z GFS, 12Z UKMET and 12Z ECMWF, and thus a blend of these solutions will be preferred with this energy along the Eastern Seaboard. ...Upper level trough digging into the Great Lakes on Sunday... ...Energy sweeping across the Northeast through Monday... ...Associated cold front pushing through the Midwest and Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 06Z GEFS mean, 12Z UKMET and 12Z ECMWF Confidence: Below average There remains a notable split among the models regarding trough amplitude with this digging wave. The NCEP models led by the 12Z NAM and 12Z GFS maintain a much more amplified trough and including a closed low evolution near the lower Great Lakes and Northeast by Monday. The 12Z UKMET, 12Z CMC and 12Z ECMWF all take the energy progressively across the Great Lakes and Northeast with little if any amplification down to the south. A large number of the 00Z/06Z GEFS members and 00Z ECENS members favor a more progressive solution with less amplitude, although the GEFS members tend to cluster in between the operational GFS and the non-NCEP consensus. The 12Z GEFS mean is slower than the non-NCEP consensus as well and tends to suggest a solution closer to the deterministic GFS. Will prefer a solution that at least leans toward the non-NCEP solutions, with a blend of the 06Z GEFS mean, 00Z UKMET and 00Z ECMWF preferred. Confidence is limited though. ...Low amplitude shortwave approaching British Columbia Friday... ...Secondary trough approaching the West Coast by late Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z NAM, 12Z GFS and 12Z ECMWF Confidence: Slightly above average The NAM, GFS, and ECMWF are fairly similar with their mass fields with the evolution of these systems. The 12Z CMC ends up with a bit stronger troughing over the far northern High Plains by Monday which will be downplayed for now. Will favor a 12Z NAM, 12Z GFS and 12Z ECMWF blend across the West Coast and adjacent areas of the Pacific Northwest and northern Rockies this period. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison