Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1255 PM EDT Thu Apr 11 2019 Valid Apr 11/1200 UTC thru Apr 15/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Preliminary Model Evaluation Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep Plains Cyclone through Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend (least weight on 00z/9 CMC) Confidence: Above average Overall the model suite remains well clustered with the slowly departing significant low. The NAM remains, as it has been throughout, on the north edge of a thin guidance envelope through Friday, but can still be used sparingly. The 00z/11 CMC starts to outpace the rest of the guidance Friday night and should be used with caution into day 2. ...Amplifying Southwest through Friday, with eventual cyclogenesis in Texas on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Ensemble means consensus Confidence: Average The trend among the recent guidance has been for slightly stronger energy shearing into the Southwest upper low, and a stronger closed low over TX Saturday. The previous trends noted overnight persist when compared to the 12Z NAM/GFS in that the UKMET/CMC are too slow with the propagation of the upper trough, the CMC lagging the other guidance the most, but the UKMET closing the trough too rapidly. While these are not included in the current blend, the means of all ensembles can be included as they lag the operational runs just a bit. The NAM has a similar position to the consensus, but is much stronger with secondary energy rounding the closing trough over the Four Corners Saturday. This leaves the GFS/ECMWF as the best available operational guidance. That being the case, the 00z/11 ECMWF is stronger with its developing northern stream jet atop the closing circulation, pushing the dominant diffluent region further north and supporting heavier snow across OK/TX. The slightly slower progression of this (keeping the southern jet dominant longer) is supported by the 12Z GFS/NAM, but differences are minor in the mass fields. Additionally, late on Saturday into Sunday, the GFS starts to outpace the consensus with its cold front across the South and becomes an outlier. For this reason a blend of the means is supported with potentially significant weather impacts across the South. ...Low amplitude longwave trough with embedded shortwaves and surface cold front into the Pacific Northwest Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Overall model spread is minimal at this time, although the 12Z GFS/NAM have edged stronger with the leading shortwave into British Columbia Saturday. This continues the trend from the overnight suite however, and any differences are minor. The GFS into Sunday becomes a bit faster with the ejection of the trough into the West in response to subtly flatter ridging across the Pacific, but still lies within a reasonable envelope late on day 3. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Weiss