Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 253 AM EDT Thu Mar 26 2020 Valid Mar 26/0000 UTC thru Mar 29/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low crossing the Mid Atlantic states Thu night/Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average ...07Z update... Compared to their 12Z models, the 00Z UKMET/CMC sped up toward the remaining guidance while the 00Z ECMWF only made minor adjustments. A general model blend is now recommended with the 00Z NAM/GFS a little north compared to the 00Z ECMWF/UKMET/CMC. ...previous discussion follows... A weak surface to 850 mb low is forecast to cross the Mississippi River Valley later today and near the northern Mid-Atlantic coast Friday morning. The ensemble means do not support the slower 12Z UKMET/CMC and latitude differences remain among the remaining 00Z NAM, 00Z GFS and 12Z ECMWF. For now, a middle ground between the NAM/GFS/ECMWF is preferred, or more similar to the 00Z NAM. ...Mid-level trough tracking from the West Coast to the Central Plains through Sun morning... ...Surface low moving from eastern CO into the Mid/Upper MS Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 00Z ECMWF and 12Z UKMET blend Confidence: Slightly above average ...07Z update... The 00Z UKMET and 00Z CMC slowed the 500 mb trough axis compared to their previous 12Z models, but now fall toward the slower side of the latest ensemble spread. The 00Z ECMWF only made minor adjustments with the mid-upper trough, slightly faster than its 12Z cycle. Currently, the 00Z GFS, 00Z ECMWF and 12Z UKMET are considered best. ...previous discussion follows... Trends in the ECMWF ensembles have been slower with the mid-level trough as it crosses the Rockies into the Great Plains, but the GEFS has sped up since previous runs. The latest guidance shows the 00Z NAM with an open wave into the central U.S. which is an outlier considering the remaining deterministic and ensemble guidance. The 12Z CMC is reasonable with timing but weaker than the remaining available guidance. The middle ground is currently best supported by the 00Z GFS (slower than 18Z GEFS mean), and the similar 12Z ECMWF/UKMET. The 00Z GFS is strongest with the low to mid-level low early Saturday, but the 12Z ECMWF/UKMET become strongest by Sunday morning compared to the GFS. The 00Z GFS is also slightly faster than the agreeable 12Z ECMWF/UKMET but the trio (GFS/ECMWF/UKMET) are well within the middle of the latest ensemble spread. ...Shortwave and surface cold front approaching Pacific Northwest Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/ECMWF/UKMET blend Confidence: Average ...07Z update... At least through 12Z/29, the 00Z GFS/ECMWF/UKMET continue to appear best with the trough axis as it reaches the West Coast. The 00Z CMC remains flat like its 12Z cycle. Differences grow beyond 12Z/29 with the UKMET slowing down, but the 00Z GFS/ECMWF/UKMET are okay until that point in time. ...previous discussion follows... Timing and strength differences exist with a shortwave and related cold cold front nearing the Pacific Northwest this weekend. The 00Z NAM is faster than the ensemble means and the 12Z CMC is weakest. The 00Z GFS, 12Z ECMWF and 12Z UKMET are reasonable in the middle of the differences seen in timing and amplitude and in decent agreement with the ensemble means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto