Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 251 AM EDT Tue May 14 2019 Valid May 14/0000 UTC thru May 17/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern across the CONUS... ...Northeast closed Low and small/fast shortwave crossing New England Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The closed low over the eastern Great Lakes will continue to wobble eastward through Wed before lifting north into SE Canada. Guidance is in very good agreement with this wave but also in the setup/orientation with respect to the next digging shortwave from the northwest (Ontario) by Thursday. Here there are some small amplification differences with the 00z GFS/NAM manifesting the strongest response, along with the 12z UKMET. The UKMET is generally a bit faster and therefore swings through with greater negative tilt by midday Thursday. The 12z CMC/ECMWF are a bit flatter but still strong and better timed with the GFS/NAM. All in all, this is good agreement to support a general model blend with confidence. However, unlike the closed low to this sharp shortwave, minor differences in setup toward the next shortwave toward Fri are spread enough to have some growing uncertainty (see below). ...Shortwave and surface low trekking along US/Canada into Great Lakes by Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS/12z ECMWF Confidence: Average 07z update: The 00z UKMET trended faster, while the CMC remains weak and south. The 00z ECMWF, however, displayed the largest shift, mainly in handling the northern vortex. The run still splits the vortex into two, but at least the upstream portion of the remaining trough, drops south looking like a more natural evolution (if still a bit strong/concentric with this upstream energy). As such, the ECMWF trended toward the favored 00z GFS and as such will be included to replace the 12z UKMET in the preferred blend. The 00z GEFS was also supportive of this blend strengthening confidence a bit to solidly average. ---Prior Discussion--- Broad, but slightly negative tilt shortwave trof enters the Pacific Northwest late today (Tues) and quickly slides northeast spurring lee surface wave development in S Alberta by early Wed. Here only the 12z CMC remains generally weaker with this wave and therefore is a bit south with the surface wave and slightly faster shifting the inverted trof/surface wave through MN/Great Lakes by Thurs. While the directing ridge in the CONUS looks agreeable, the evolution of the Arctic vortex in northern Canada is a different story with distinctly divergent evolution. The ECMWF and is ensemble suite have been very consistent with its slower evolution, leading to split of the vortex by late Wed into Thursday influenced by the preceding shortwave entering the Great Lakes. This enhances a stronger anticyclonically enhanced jet streak which allows the typically slower ECMWF to accelerate the discussed wave across S Canada reducing the spacing with the lead wave resulting in nearly zero downstream ridging through the Great Lakes and into the northern Mid-Atlantic by the end of the forecast period. When the ECWMF/ECENS are this stubborn in the ensemble suite, this is typically something to build confidence, however, the evolution of the wave looks quite unnatural especially for the ECMWF compared to a more consolidated vortex that helps kick the wave eastward as presented by the remainder of the deterministic and ensemble suite (including the CMC, while not favored for other reasons). The 00z NAM, opposite to the CMC, looks too strong/compact and remains well north of the remaining guidance/track (including the ECMWF). As such, WPC will favor a 00z GFS/12z UKMET blend though confidence is not particularly high especially Thursday into Fri over the Great Lakes/Northeast. ...West Coast Cyclone Wed through Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Slightly above average. 07z update: The 00z UKMET/CMC further solidified the evolution of the closed low off the coast toward the initial preference. However, the 00z ECWMF continued a slightly weaker trend noted before and therefore shifted north, splitting the difference between the GFS and NAM, and performing a greater wobble of the surface low south east of the 40N130W benchmark. The NAM is still sufficiently displaced to suggest a non-NAM preference at slightly above average confidence. ---Prior Discussion--- Ensemble suite continues to consolidate with the digging trough off the West coast, the hyper-active jet in the ECMWF over the last few days has settled and other guidance has come into stronger alignment with the eventual development of a closed low and associated surface wave late Wed into Thurs off central CA. The 00z NAM continues to amplify early and therefore well north of the growing consensus. The UKMET is an odd solution, given the northern stream is slow relative to other guidance, but the southern stream wave is on-time, slightly faster resulting in a initially broader trof and eventual southern solution that does not close off aloft. As such the NAM/UKMET are not preferred. The remaining guidance 00z GFS and 12z ECMWF/CMC blend is preferred; yet, while the mass fields are good, the QPF evolution is slightly different, enough to warrant closer assessment. This is likely attributed to the typical GFS bias of being faster. But only faster with the central Pacific shortwave/moisture stream ahead of the digging northern stream. This allows for greater duration and steadier axis of QPF into northern CA. The ECMWF is very slow with this and directs more of a broad, slightly diffluent low level stream to the plume of moisture reducing the onshore stream/flow. A compromise should be met between the guidance members given overall mass agreement, but broader probabilities/greater uncertainty could be asserted/messaged across N CA initially then into the Great Basin/Northwest toward Fri. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina