Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1258 PM EDT Tue Apr 14 2020 Valid Apr 14/1200 UTC thru Apr 18/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Preliminary Model Evaluation with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave shearing into the Midwest/Ohio Valley Day 3... --------------------- Model Blend Preference: 00Z ECMWF/ECmean/UKMET Confidence: Slightly above average A shortwave dropping through the inter-mountain west will shear off to the east Friday as it becomes absorbed by the westerlies in the base of a longwave eastern trough. At the same time, an upper jet streak will strengthen south of the mid-level trough, with the combination of these forcings causes weak surface low development moving through the Ohio Valley Friday. The CMC is weak with the depth of this feature, affected by poor overall synoptics upstream across the Intermountain West. The GFS becomes too progressive as the shortwave moves east, becoming a fast outlier when compared to the remaining guidance envelope. The NAM also becomes quick during D3, but also develops an upper jet streak which is too intense, placing more intense ascent a bit further south, which displaces the surface low and produces precipitation which is more robust than the remaining guidance. This leaves the consistent ECMWF/ECmean/UKMET as the preferred blend for this system. Western/Central CONUS -------------------- Model Blend Preference: Non-CMC D1-2, ECMWF/ECmean/UKMET D3 Confidence: Slightly above average Significant Pacific ridge will dominate over the next several days, while mid-level impulses rotate around it and down into the western CONUS. Two distinct features will embed within the flow racing from the NW. The first of these is a closed low well off the CA coast, and it will drop southward before pushing onshore into Baja/SoCal D3. Outside of the 00Z/CMC, the guidance is in good agreement with this feature through the first 2 days, but little to no precipitation will occur on the coast with this. By D3, precipitation spreads onshore and the UKMET becomes a bit strong compared to the consensus, and the GFS starts to push too fast, but still a general non-CMC blend is reasonable. For the second shortwave dropping from the Canadian Rockies and into the Intermountain Western CONUS, significant snow is likely with this feature and through the first 2 days a general model blend is acceptable, excluding the vastly different CMC. However, by D3 /Friday/ the GFS begins to shear the shortwave too strongly to the east, stringing out the vorticity lobe faster than the remaining guidance. The NAM lags a piece of energy well W/SW of the primary shortwave causing some interaction and retrogression of the strongest forcing, which is out of tolerance with the remaining suite. For these reasons a ECMWF/ECmean/UKMET is preferred for most of the West D3 as they are consistent and match well to each other. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Weiss