Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 226 AM EDT Mon Aug 26 2019 Valid Aug 26/0000 UTC thru Aug 29/1200 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: General model blend Confidence: Above average through 78hrs slightly above average after Exception: Coastal Low: 00z GFS/NAM (slightly below average) 07z update: The mass fields, with a small exception of the Atlantic Coastal surface low (see 2nd paragraph), are in remarkable agreement particularly through 72hrs across the CONUS. Again, by 84hrs, the UKMET and NAM are still a bit too fast with the second Canadian shortwave but that is minor. The surface low of the Northeast continues to befuddle the guidance with a substantial variance noted by the UKMET, CMC and ECMWF from prior runs. The interesting point though is they are very agreeable with each other, so there may be a critical piece of data added to their assimilation that missed the NAM/GFS (which are also in strong agreement with each other). A slightly vertically deep cyclone in the new non-NCEP suite, suggests the surface low does a tricordial wobble with the anticyclonic loop of the 5H low (even manifest by the 00z NAM). This does not make it any clearer on which direction to take, but the interests along coastal New England will see a much different forecast. At this point, will not deviate too much from initial preference/continuity of the 00z GFS/NAM but reduce confidence to slightly below average for this wave. ---Prior Discussion--- The 00z NAM/GFS continued another cycle of consistency and strong deterministic guidance agreement with the synoptic pattern/evolution over the CONUS. As with any run, there are some very small scale amplitude differences, as well as, differences due to convective development/feedback. The largest differences in the mass fields/QPF axes, are driven by slight timing differences with the frontal zone crossing the Northeast and the interaction with the moisture feed from the the tropical/subtropical surface wave to the Southeast Wed into Thurs. The UKMET is a bit faster and it along with the 00z NAM suggest slightly earlier deep moisture flux for some heavy rainfall across SE ME. This is interesting, given the spacing between the UKMET and NAM is probably the largest spread with the surface wave, and the UKMET is stronger than the NAM. Overall, the deep closed low in S Canada and the frontal zone spread is small enough to support a general model blend, but the surface wave off the coast has moderate spread. The ECMWF has once again become fast and strong, paired closest to the UKMET, while the GFS and NAM are weakest and draw westward due to the approaching height-falls. The CMC also bends left but is very strong by the end of Day 3, which does not seem a good fit to continuity and the ensemble suite. Overall would favor a NAM/GFS solution with some lower weighted UKMET and some ECENS/GEFS mean in the blend. Elsewhere, there is a small timing issue with a strong shortwave across NW Canada on Day 3. The 00z NAM and 12z UKMET are too fast, though with little sensible affect to even the northern tier of the CONUS, but would shade away from those in a larger scale blend. So overall a general model blend is supported, with only exceptions noted above, with an above average confidence through about 60hrs before reducing to slightly above average afterward. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina