Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 135 PM EST Tue Feb 25 2020 Valid Feb 25/1200 UTC thru Feb 29/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Eastern Half of North America... Preference: Blend of 12Z NAM/ECMWF/UKMET Confidence: Average Gradual phasing of northern and southern streams will lead to mature cyclone development over the northeastern U.S. and southeast Canada by Thursday. The then-mature, full latitude trough will occupy the eastern U.S. for another day or two. The models are all generally agreeable aloft. The main deviant model, as noted overnight, was the 00Z Canadian with its more fully developed coastal low. This corrected on the 12Z run, although the Canadian now lifts the primary low center farther northwest into Quebec compared to other guidance. Most solutions do have a semblance of a double-barrel low, with the primary tracking into Quebec, and another low attempting to form along the coast from Maine to the Canadian Maritimes. In the 12Z cycle what stands out is a sudden and stark deepening trend in the GFS, which takes the primary surface low down to 983 mb at 28/00z. The 12Z GEFS mean supported this to a degree, and even the ECMWF did offer a deeper surface low than before, but the GFS is more greatly developed at all levels, producing 500-mb heights that are 60 meters colder than the other models on Thursday. The GFS gets there by means of a sharper, more energetic wave emerging from the southern Rockies this evening. Although 500-250 mb observed winds were impressive at Albuquerque and Amarillo this morning, there does not appear to be anything especially impressive about this wave, and the fact that the NAM - whose bias is strong and deep - does not support this trend, perhaps speaks volumes. We therefore prefer the NAM along with the consistent ECMWF and UKMET. ...Western U.S... Preference: 12Z ECMWF Confidence: Slightly Below Average A minor shortwave trough will scoot through the northwest U.S. today and tomorrow. Then expect a building shortwave ridge in advance of what looks like a Day 4 system to arrive Friday night / Saturday. The NCEP solutions have been noticeably much faster than the other global guidance in bringing the next wave toward the coast on Friday. On the other hand, the 00Z UKMET and now the 12Z Canadian set the slow and strong side of the envelope (note that the 12Z UKMET was radically different than the 00Z). Wave spacing across the Pacific suggest a trough about in the position of the ECMWF solution at 29/00Z, and that model has been the most consistent over the last couple of runs. This is our preference, noting that the GFS did trend a bit toward this preference while still looking a tad fast. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Burke