Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 228 PM EDT Thu May 23 2019 Valid May 23/1200 UTC thru May 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preferences and Forecast Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall CONUS Overview... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Exception: 12z GFS/ECMWF blend in West Day 2/3 Confidence: Above average except in West Day 2/3 (Average) 19z update: The 12z GEFS, ECMWF, CMC and UKMET all get much better overall with the systems east of the Rockies in the short-term to support a general model blend at above average confidence. The same cannot be said for the West, where the CMC continues to over amplify the lead shortwave leading to a slower and further west secondary wave along N CA by 27.00z. The UKMET got better but remains unfavorable compared to a blend between the 12z ECMWF and GFS. The 12z GEFS helps solidify this pairing as well. Confidence in this blend is average. ---Prior Discussion--- Large scale pattern remains locked through short range period with persistent trof in the West spitting out shortwaves into the Central Plains and Upper Midwest where they eventually roll eastward over the 2-3 StDev Subtropical Ridge in the South/Southeast. ---Northeast day 1/2--- Today's ridge-rider is currently through the Great Lakes entering New England and clipping the northern Mid-Atlantic and continues to be well handled with solid model agreement in synoptic depth/placement and timing for high confidence in a general model blend through the Canadian Maritimes. ---Central US Day 1/2, northeast Day 2/3 --- The very compact shortwave/closed low in AZ, will lift north through the Central Rockies into the Northern High Plains today and Friday, spurring a classic late spring surface wave in the central High Plains connected to the deeper surface wave as it emerges across WY early Friday morning. It will traverse the Dakotas into N MN and SW Ontario through Day 2, with fairly good model agreement. Only the 00z UKMET is a shade slow with the surface wave. Downstream ridging will help deflect the mean shortwave north, but the convective induced MCV/shortwave further south near the surface triple point will track across the Great Lakes stretching the frontal zone through New England late Sat into Sun, once again clipping the northeastern portions of the Mid-Atlantic as well. While the spread increases by day 3, due likely to the upscale influence of the convection from prior days, there is still strong agreement to support a general model blend for the synoptic timing/placement of the energy, though with standard to slightly above average confidence for a Day 3 period at this time of year. ---West Day 2/3--- The remainder of the now positive tilt trof in the West by Sat is fairly well agreed upon as well, even ejecting the weak/subtle remaining shortwave energy out of the Southwest Sat. It is the upstream energy over the Gulf of AK that leads to the largest spread as it starts to recarve out the base of the trof late Sat into Sunday. Guidance has finally started to agree on how to handle the pair of shortwave foci, favoring the upstream, second wave and away from the lead wave. The lead wave does however, does drop into W WA/OR early Sat with fairly good model agreement, but spread emerges on how it is to shear or delay (shorten the wavelength) due to the binary interaction with stronger upstream jet/shortwave. The ensemble suite suggests a tighter/shorter wavelength is more likely and therefore weakens/slows the lead height-falls through N CA late Sat into Sun. The UKMET followed by the CMC, therefore are on the outside of the ensemble suite and trends. The 12z NAM may have trended a bit too far with this cycle, shortening the length to the point of accelerating the shortwave down the coast too fast outpacing the ensemble suite. The 12z GFS has been fairly consistent and while a shade faster than the ECMWF, the ECMWF is a bit slower than the ensemble suite too, so a great compromise favoring a GFS/ECMWF blend at average confidence. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina