Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 130 AM EST Thu Dec 05 2019 Valid Dec 05/0000 UTC thru Dec 08/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Exception: Remove 00z NAM across N ID/MT into the Northern Plains after 72hrs. Confidence: Slightly above average 07z update: The 00z UKMET trended very close to the initial preference, particularly across the South and off the East Coast after 60hrs, and so is included more heavily in the blend. The 00z CMC has a weaker presentation across the south as well as the West coast, before the northern stream shortwave digs strongly off the NWPac Coast at the end of the forecast period; making it not favored throughout the CONUS. The 00z ECMWF trended a bit faster across the West particularly north, but still in typical EC fashion, retains a slow filling, weakening of the surface low coming into the N CA coast, as the trof sharpens on Sun. This is in line with the GFS, UKMET, and at least the inner core of the NAM along with the 00z GEFS mean. As such, a non-CMC blend is favored with the only exception of removing the faster/stronger 00z NAM across ID/MT into the Northern Plains after 72hrs. ---Prior Discussion--- Model agreement continues to be strong through the new 00z NAM/GFS with low ensemble spread through day 2. However, by day 3, model spread continues to waffle/vary as the main features start to break down a bit faster/slower or start enhancing other features elsewhere. Current potent shortwave crossing the Southwest/Southern Great Basin, will progress across the Southern states with fairly good agreement. The 12z UKMET is a bit stronger/compact and eventually lifts a bit north, off the Atlantic coast by 12z Sat, which helps to elongate the northern stream a bit more, making it a bit less favorable in any blend. So a non-UKMET blend is favored through the South and then offshore of the Northeast for Day 3. On the heels of the shortwave, a strong closed low in the Central Pacific progresses eastward expanding to maturity around 00z Fri, under strong agreement. As the closed low breaks down, model spread increases under typical bias, ie NAM is stronger by day 3, ECMWF is slower, GFS is faster. The 00z GFS while still faster, is able to draw more energy from the northern stream 00z Sunday into the Pacific Northwest, to slow the wave a bit more sensibly to the ensemble mean (including the 18z GEFS). The CMC is uncharacteristically fast due to a weakening of the inner core of the low on Sat. This leads to the wave progressing a bit too fast into the west, with greater north-south orientation of the wave axis compared to the remaining guidance and ensemble suite (so is not favored after day 2). The UKMET looks very good within the suite, however, has a very wet subtropical stream compared to the remaining guidance, tapping the tropics a bit more than other solutions, while the remaining mass fields are strong, given the QPF, it is not favored in the Southwest for late day 2 into day 3. The 00z NAM is very strong with the inner core to the closed low which is on par/favored but the northern stream that is digging becomes a bit strong as well as fast, pressing the cold front through the northern plains by Sunday but also sharpening the trof out of Alberta/Montana. So this makes it less useful for those sections late Sat into Sunday. All considered, preference is very close to the ECENS/GEFS means which is best represented by the 12z ECMWF/GFS and UKMET north of 40N and 00z NAM (except N ID/MT into the Northern Plains). Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina