Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1221 AM EDT Sat May 16 2020 Valid May 16/0000 UTC thru May 19/1200 UTC ...See NOUS42 KWNO (ADMSDM) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Shortwave and surface low tracking across the northern tier states ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF, and 12Z ECENS blend Confidence: Average Shortwave energy skirting through the northern Rockies is expected to amplify and deepen as it moves toward the Upper Mississippi River Valley by Sunday, with the shortwave energy taking on a more negative tilt. In the increasing amplified pattern over the CONUS (thanks to a digging longwave trough over the western US and building heights over the central Plains), the shortwave is forecast to expand and close off over the lower Great Lakes and Ohio Valley early next week. This setup offers average at best forecast confidence but the obvious outliers at this point appear to be the 12Z CMC and 12Z UKMET which are open/faster compared to the more closed off NAM/GFS and ECMWF solutions. The trend over the last few days has been for the cut-off low to remain stationary or slowly wobble in the area. The 00Z NAM however appears to be overdone and too deep with the low by 72-84 hours. As such, the preferred blend is for a compromise of the 00Z GFS and 12Z ECMWF with some incorporation of the 12Z ECENS mean. Deep upper level trough developing along the West Coast by Monday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A large closed mid/upper level low is forecast to move from the eastern Pacific toward the Pacific Northwest coast through the period. Given the highly amplified pattern, the model guidance shows above average agreement, with only some minor differences at 500 mb on day 3 noted. As the system approaches the coast late on day 2 and into day 3, it will stall and the surface low weakens. Model agreement is above average in this setup and a general model blend should suffice. Southern stream trough tracking from Texas and along the Gulf Coast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average A subtle/weak southern stream shortwave will move across southern Plains through this weekend with the mid-level wave dampening out over the northern Gulf by early next week. Model guidance shows average to slightly above average agreement with just minor timing differences noted in the 500 mb pattern. The CMC was a slow outlier while the GFS was on the faster side of the model spread. But these differences appear to be fairly minor and a general model blend is favored at this point. A relatively weak southern stream trough will move across the southern Plains through early Saturday, and gradually the mid level low crosses the Gulf Coast states by late in the weekend. The 12Z NAM is a little farther north with the 700mb low across Texas, and this results in less QPF compared to the other models through Saturday evening. The UKMET is noted as a slower solution by Monday, and therefore heavier QPF across the central Gulf Coast region. A blend of the ECMWF/GFS would serve as a good starting point since there is decent ensemble support for this initial blend. Low pressure developing near the Bahamas...moving up the southeast coast through early next week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 60 hours /18.12Z/ then non-GFS Confidence: Average An area of low pressure off the southeast Florida coast is expected to gradually further develop this weekend and then turn northward this weekend before tracking off the NC coast by early next week. Model agreement has come into better focus through 60 hours, with a reasonable spread between the various deterministic guidance. The latest /00Z/ GFS offers a solution west of its 18Z ensemble mean and is also on the western side of the model spread envelope. The 12Z ECMWF is on the eastern side of the spread with the NAM/UKMET/CMC in the middle. Given the outlier western solution the GFS is advertising at this point and without the ensemble support, a non-GFS blend after 18.12Z is preferred. For more information on this system and potential development, see the latest from the National Hurricane Center. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor