Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1220 PM EDT Wed Apr 11 2018 Valid Apr 11/1200 UTC thru Apr 15/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Large-scale trough moving from the West Coast today, to the Plains by Friday-Saturday... ...Associated strong surface low in the Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 06Z GEFS Mean; 00Z UKMET Confidence: Average Subtle differences with this system as it emerges into the Plains continue to lead to more notable differences as the cyclone begins to occlude over the Central US. Ensemble distributions show that there has been a narrowing of ensemble spread over the past several model cycles, with a trend toward the slower solutions. This is not uncommon for deep, occluding cyclones, and recent WPC model preferences for this system have trended in that direction. With that in mind, the 12Z GFS and 12Z NAM are not preferred as they remain on the faster end of model spread, the GFS in particular. Notably, the GEFS Mean has trended slower and is now very close to the ECMWF Ensemble Mean with its height fields aloft. The GEFS is also close to the 00Z UKMET, which was preferred on the overnight shift for this system, and appears to offer a reasonable forecast for a strong, occluding spring low in the Plains. The 00Z ECMWF and ECMWF Ensemble Mean are not far off with their height fields aloft, but show the surface low and associated fronts making more of a jump to the E/SE on Friday Night. This is possible, but seems less likely given the strong closed low aloft at the same time -- such a pattern doesn't typically favor accelerating cold fronts. The UKMET and GEFS seem to offer a reasonable alternative that is still near a consensus (or just slower) in terms of timing. ...Low amplitude northern stream wave moving from Northern Plains today to the Northeast Thursday Night... ...Associated weak surface low following a similar path... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend Confidence: Above average There is a high degree of similarity between the models for this system, with the most noteworthy difference being the 00Z UKMET which has a much more amplified trough and a stronger surface low. All the other models are tightly clustered on the timing and intensity of the low, so a blend of these remaining models is preferred. ...Shortwave departing the Southeast today... ...Shortwave moving through the Northeast today and tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Models show very good agreement with these systems, and a general model blend is preferred with high confidence. ...Deep trough and upper level low slowly dropping toward the Pacific Northwest by this weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average A relatively stationary closed upper low over the Gulf of Alaska is expected to begin to devolve and dig southeast as an amplified trough toward the Pacific Northwest this weekend. Models do show some subtle differences but overall are in quite good agreement on the overall pattern, so a general model blend is preferred at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers