Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 321 PM EDT Thu Sep 19 2019 Valid Sep 19/1200 UTC thru Sep 23/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Overall Pattern across the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z ECMWF/CMC blend Exception: Include the 12z NAM in Northwest/West Day 3. Confidence: Average 19z update: The 12z ECMWF/CMC both trended a bit faster with the the trof lifting out of the Rockies into day 3, yet still much slower than the GFS/NAM. This appears more likely, though the UKMET has significantly slowed, particularly with the upstream shortwave/jet streak digging out the increasingly positively tilting base to said trof across the Central Rockies/High Plains by Day 3. This slowing and westward trend in the shortwave ridging between the next approaching system, appears to negatively affect the upstream wave depth as well, delaying it. As such, would prefer to remove the 12z UKMET from the initial preference. Otherwise, the new ECMWF/CMC for the west are similar enough to continue a CMC/ECMWF/NAM blend for the second trof in the West on Day 3. Confidence in the blend remains average but slightly reduced compared to earlier given the increase in uncertainty/spread by the end of Day 3 with both waves. ---Prior Discussion--- Large scale synoptic setup remains consistent for the past few weeks, with a strong southeastern ridge with western troughs developing and lifting northeastward over the northwest periphery. The current concentric shortwave entering the Great Basin is expected to follow a similar pattern, closing off crossing S ID into the northern Rockies spurring a surface cyclone across the northern High Plains by Friday morning. The 12z GFS and NAM slowed a bit lifting out compared to prior runs but both continue to be much faster than the 00z ECWMF/UKMET/CMC and even the GEFS mean slows compared to the operational GFS runs. This slower solution is more expected given the pattern setup, especially with a subtle shortwave jet speed max rotating southwest to delay the base of the trof lifting out as well; denoted well in the ECMWF. Additionally, the next shortwave trof approaching will support a greater elongation toward the south with sharper/earlier impact to the shortwave ridging between it and the exiting system. This also favors the ECMWF/UKMET and CMC approaching the west coast late Sat into Sunday. Here the 12z NAM may be a bit more useful, showing greater timing/depth placement to the non-GFS guidance. As such a 00z ECMWF/UKMET/CMC blend is supported through the bulk of the CONUS (particularly the northern stream). There is mild spread with the wave lifting through the northern Plains into southern Canada, to have only average confidence in this blend. ...Imelda.... Low level circulation of Imelda as become a SE to NW inverted trof with weak closed low along the convective band where latent heat pressure falls support it. The mid-level circulation, however continues to lift away toward the north feeling some of the height-falls approaching from the west and western periphery of the subtropical ridge over the Southeast. The global scale deterministic guidance is fairly agreeable in the mass fields, depicting a highly sheared toward the NE with depth remaining system. The surface wave is expected to be overwhelmed by onshore flow, and instability driven convection may keep the mid-level circulation a tad further west then some of the eastern solutions, like the NAM/GFS. Still, hi-res CAMs support something close to the ARW/ARW2 and 12z HRRR solutions particularly in QPF. However, for larger scale mass fields, UKMET/ECMWF/CMC blend will work especially given timing of the upstream height-falls. Model trends at www.wpc.noaa.gov/html/model2.html 500 mb forecasts at www.wpc.noaa.gov/h5pref/h5pref.shtml Gallina