Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 144 AM EST Mon Feb 24 2020 Valid Feb 24/0000 UTC thru Feb 27/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Mid-level shortwave and attendant front clipping the Great Lakes/northern ME through Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. No significant changes were noted with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...OK/KS closed low and its interaction with an upstream amplifying northern stream wave across Plains/Great Lakes Mon/Tuesday... ...Associated surface low crossing the Mississippi River and into the Great Lakes Tue/Wed... ...Developing East Coast low Wed night.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z ECMWF, blended with the non 00Z GFS deterministic guidance Confidence: Average to slightly below average after ...07Z update... No significant changes were noted with the closed low as it weakens east into the Ohio River Valley through Tuesday morning. Regarding the upstream, large scale trough, the 00Z UKMET trended a little slower, while the 00Z CMC trended a little faster compared to their 12Z cycles. The 00Z ECMWF also trended slower and slightly weaker with the trough progression beginning Tuesday afternoon. From Tuesday through Thursday morning, the 00Z deterministic guidance shows reasonable agreement outside of the faster 00Z GFS, though minor non-GFS differences remain. Given some of the changes from cycle to cycle, the final preference will not be to jump completely on board with the non 00Z GFS suite of models (despite their relative agreement), but to nudge in that direction from the 12Z ECMWF position. Therefore, the final preference is to take the 12Z ECMWF and blend it with a 00Z ECMWF/UKMET/CMC/NAM blend. ...previous discussion follows... ...12Z/24 until 12Z/25... Regarding the closed low currently near the KS/OK border, the models show reasonable agreement on this feature quickly weakening toward the ENE into the Ohio Valley through Monday night. The related surface low will reach southwestern IN around 12Z/25, and the scatter low ensemble low plots have been fairly consistent with this position so confidence in a general model blend is good up until this point into the Ohio Valley. Farther west, an amplifying trough will begin to reach the Central Plains by Tuesday morning, with the 12Z UKMET/CMC straying early from the ensemble mean and remaining deterministic consensus. While the 00Z GFS begins to pull ahead by 12Z/25 over the Central Plains at 500 mb, a 00Z NAM, 00Z GFS and 12Z ECMWF blend will be reasonable. ...12Z/25 until 12Z/26... As the system evolves, the model consensus is for a small closed low and positively tilted trough axis extending southwest from the low to sweep toward the south and east. The 00Z GFS is a bit faster than the remaining model consensus, while the 00Z NAM becomes slower and the 12Z ECMWF placed somewhere in the middle but closer to the GFS than NAM. Meanwhile, the 12Z UKMET is a bit weaker and south with the mid-level core of the trough, and the 12Z CMC is slower. A 3-way blend of the 00Z NAM, 12Z ECMWF and 00Z GFS is preferred here, but with less weight on the 00Z NAM by 12Z/26. ...12Z/26 until 12Z/27... As the center of the mid-level low lifts through the Great Lakes, interaction occurs with an upper trough to the north. The lead shortwave will quickly swing east while coastal low development occurs along the Mid-Atlantic coast. The ensemble means are in good agreement, although trends in the ensembles have been faster over the past few cycles. The current ensemble mean placement is a little slower than a 00Z GFS/12Z ECMWF blend. The 00Z GFS is fastest, followed by the 12Z ECMWF and then the slower 00Z NAM. The GFS and NAM have trended a little slower with their 00Z cycles so this is in contrast to ensemble trends. Placement near the 12Z ECMWF is considered best but with some incorporation of the 00Z NAM and 00Z GFS. ...Mid-level shortwave trough/surface cold front clipping the Pacific Northwest on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average ...07Z update.. No significant changes were noted with the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...previous discussion follows... The models are in reasonable agreement with the shortwave and cold front that enter British Columbia and northern Washington, moving into a strong mid-level ridge. There are some minor longitude differences with the shortwave as it reaches the Great Plains on the lee side of the ridge axis, but at least through the end of the short range period (12Z/27), a general model blend will work for this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto