Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 157 AM EST Fri Dec 21 2018 Valid Dec 21/0000 UTC thru Dec 24/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend east of Rockies 00z ECMWF/CMC and 12z ECENS mean for the West esp after 23/00z Confidence: Slightly above average east of Rockies Below average in Intermountain West 07z update: The 00z solutions from the UKMET/CMC have seemed to resolve the more significant differences across the Eastern half of the US through 00z Monday, though the center of the upper low along the US/Canadian boarder is a bit stronger/slower on the 00z NAM/CMC and the UKMET remains a bit more amplified through the Ohio Valley but this appears generally minor overall suggesting a lower weighting may suit best. However, the progressive flow out of the Pacific remains quite variable. Though the strength/track of the deep surface low toward Vancouver Island is consolidating, at least with minor exception to the 00z NAM in mass fields though the GFS looks out of place in QPF timing. The 00z ECMWF supported by the new 00z CMC and UKMET have trended to a secondary strong/compact wave entering the picture by 12z Monday. Still believe hedging to a middle ground solution near the ensemble suite means, will be best by the end of day 3. As such a general model blend is supported east of the Rockies through the forecast period... but shift toward an ECENS mean/00z ECMWF/CMC solution for the Pacific Northwest and Intermountain West at below average confidence. ---Prior Discussion--- Large full latitude trof is starting to lift out of the Southeast later today exiting fully by midday Sunday across the Northeast with much tighter model agreement including internal smaller scale waves/interactions, to suggest a general model blend would be a high confidence solution for this system. With its exiting, the pattern will shift across the CONUS as strong Pacific energy will be quite progressive across the West into the Central US with a more zonal pattern look to the overall flow. The static larger scale trof across the Northern Gulf of AK will shed shortwave/jet streak energy into the Pacific Northwest 12-24 hours or so. This pattern is very chaotic and has low fidelity in predictability mainly in timing of these wave features but also some times in amplification. We have seen this in the last 4-5 cycles of the ensemble suite especially along the 546 through 552 dm spaghetti analysis, where each model and ensemble suite members cannot latch onto specific timing/depth of the waves particularly after crossing the Cascades into the Intermountain West/Rockies and eventually into the Central Plains. The current system/tropical moisture plume is the best handled system now fully into the best sampling network crossing the Canadian Rockies into the Southern Prairies by early Sat. Here the 12z CMC is quick, south and generally weak an the 12z UKMET appears a bit north. The next wave shed out of the Gulf of AK into the Pacific Northwest later today shows over amplification in the UKMET, likely due to some spacing/enhanced outflow from the prior system being too far north, as it treks through the Rockies. As such a Non-CMC/UKMET solution is preferred for this next pair even through the Great Lakes/Ohio Valley in the late weekend/early workweek. The next progressive wave (Sun/Mon into the NW) has trended favorably in ensembles toward a common solution with a strong surface cyclone reaching Vancouver island late Sat into Sunday and directing broad moist/onshore flow into WA/OR/N CA terrain, however begin to devolve after crossing the Cascades into the Intermountain West. Here traditional negative model bias begin to manifest a bit more with the 00z NAM/GFS fast, 12z ECMWF slow. The 12z UKMET is strong and quick continuing with less preference here. The 00z GFS has backed off a stronger/more amplified trailing surface wave/moisture slug entering S OR/N CA toward 00z Monday than the 12z/18z runs but this solution continues to be on the fringes of the ensemble suite and away from the mean overall. Here, while possibly too slow the ECMWF and CMC and a mix of the 00z NAM seem a good compromise with inclusion of the ECENS/GEFS mean. Given strong but progressive and unstable run to run continuity...confidence is below average for this wave. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina