Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Sun Jul 22 2018 Valid Jul 22/1200 UTC thru Jul 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and forecast confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend 12z UKMET/ECMWF after 25/00z in northern tier Confidence: Slightly above average to slightly below average after 25/00z. 19z update: The 12z CMC trended much better with the Eastern Trof, not as deep and while it remains the slowest guidance to fill and may be best to keep it out for a stronger/tighter blend. The larger spread remains across the northern tier into Canada for day 3... and while the CMC is initially slow, the Arctic shortwave kicks through very fast keeping pace with the faster NAM/GFS. This is opposed to the ECMWF/UKMET both trending slower and while the timing of the front itself is not very poor the upper level support/mass fields lag sufficiently. The 12z GEFS mean seems to split the difference between the GFS/NAM/CMC and the ECMWF/UKMET/ECENS mean...would hedge toward the UKMET/ECMWF given more continuity...but uncertainty is high enough to reduce confidence to slightly below average after 25/00z for this system. ---Prior Discussion--- The closed low over the Ohio valley to southeast will continue to fill and remain elongated between the developing subtropical ridge in the Northwest Atlantic and the large concentric high in the desert southwest that extends into the Southern Plains; guidance is strongly agreeable in the mass fields and surface features even with the muddled/complexities related to such a vast/breaking down upper level trof. The 00z CMC is a bit out of phase being a bit deeper and slower to fill through the end of day 3. Elsewhere, the deep low tracking across southern Canada still shows some modest spread, as the 12z NAM/GFS both remain a bit stronger (closer to current observations) in the mass fields further south and east compared to the ECMWF/UKMET. Still, the timing and depth of the frontal zone look good for this portion of the system to be considered for a general model blend. It is the variance Tues into Wed, when an Arctic stream shortwave rotates around the western periphery of the remaining upper low bringing another frontal zone southward. Here the GFS and NAM followed by the UKMET are faster bringing the front and reflect a stronger surface wave into MN/SW Ontario by late Wed. While the 12z GFS backed off on the compact nature of this wave, it is even faster than that NAM/UKMET by 00z Thurs. The 00z CMC is also very slow with this wave out of the Arctic stream as well, almost locking to the terrain along the BC/Alberta line around 00z Tues. As such will favor backing away from the GFS after 25/00z but Non-CMC throughout the forecast period. Confidence is slightly above average (especially over the eastern third of the continent, but breaks down to average across the northern tier on Day 3. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina