Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 235 PM EDT Sat Apr 27 2019 Valid Apr 27/1200 UTC thru May 01/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern Across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM Exceptions: 12z UKMET/CMC in SW, into central Plains Day 3 Confidence: Above average except on Day 3: Average 19z update: All non-NCEP guidance trended faster and weaker with the closed low entering the Southwest, but the ECMWF continues to be most stubborn shifting east. The 12z UKMET trending a bit faster trended toward the GFS but still remains slower, while the CMC is closer to the ECMWF. As such will continue to favor the timing/placement of the CMC/UKMET and reduce influence of the ECMWF/GFS unless shifted toward the timing of the UKMET/CMC. Confidence remains average for this system. Elsewhere, the guidance remains very consistent keeping higher overall confidence in the Non-NAM blend ---Prior Discussion--- Broadly zonal flow exists across the majority of the CONUS, with the exit of the deeper trof/cyclone into SE Canada. A small but potent shortwave is currently crossing the Midwest into the Northern Mid-Atlantic today into Monday. The wave is well handled, though the GFS may be a shade too fast; a general model blend can be afforded at above average confidence. A second stronger wave starts very flat across the NW today, with some favorable larger scale divergence aloft to amplify across the Northern US High Plains Sunday. The 12z NAM is a bit more amplified mostly breaking from other guidance by pumping greater downstream ridging...this negatively affects the QPF but setting up a stronger FGEN forcing further north than being driven by more convective/vertical processes further south across the Lower MO Valley into Midwest Sunday into Mon. Otherwise, the guidance supported by fairly tight ensemble suite suggests a Non-NAM solution at above average confidence. The larger model spread exists into day 3 with the timing of a concentric closed low that begins the shearing process through the Four Corners region into the Central Plains Tuesday. The trailing northern stream shortwave energy seems well handled by most guidance in deepening across the Snake River Plain/Great Basin helping to accelerate the southern stream closed low into the Central Plains. The NAM, given the displacement from the prior system is a bit aggressive with the deepening here too and also accelerates the wave into the Plains a bit fast. The 12z GFS appears to be falling in line with typical fast bias, breaking down the closed low fast and accelerating the forcing into the Plains a bit early (leading to an eastward shift of the QPF/convective intersection with the strong return moisture stream out of the Western Gulf. However, the 00z ECWMF also appears to be falling in line with typical known negative bias, being very slow breaking down the closed low, delaying its ejection, leading to a westward QPF solution. The other guidance (UKMET/CMC) also fall into traditional timing differences, ie the CMC is slower and the UKMET is faster but more central compared to the slower EC and faster NAM/GFS. As such would favor the mass fields to utilize the timing of the CMC/UKMET but the QPF/mass fields of the GFS/ECMWF are usable but have to be shifted toward a more central location near the CMC/UKMET axis. All in all, a non-NAM solution is favored but will weight higher amount to the CMC/UKMET in the central plains and shift the GFS/ECMWF fields toward a more common/central location on Day 3 in Southwest/Central Plains. Confidence slides to average for this blend from above average elsewhere. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina