Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 144 AM EST Sun Feb 23 2020 Valid Feb 23/0000 UTC thru Feb 26/1200 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 Sun/Mon... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average Differences with this system are relatively minor and can be resolved with a general model blend. No significant changes were noted in the 00Z ECMWF/UKMET/CMC compared to their previous 12Z cycles. ...Closed mid level low reaching the central/southern Rockies Sun, weakening over the Upper MS/OH Valley Mon into Tues... ...Surface low tracking from northeast NM into Ohio Valley by Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z CMC blend Confidence: Slightly above average ...07Z update... The 00Z UKMET slowed down while the 00Z CMC remained about the same compared to their previous 12Z cycles. The 00Z ECMWF edged slightly faster than its previous 12Z cycle, but is relatively similar. Given these changes, have added the 00Z UKMET into the preference, leaving out the 00Z CMC given it likely remains too slow. ...previous discussion follows... As the closed low near the Four Corners Sunday morning translates eastward into the Southern/Central Plains Sunday night, it is expected to open up and weaken toward the Ohio Valley through Monday night. Minor strength differences remain but timing differences are more significant. The 12Z UKMET ends up the fastest, while the 12Z CMC is the slowest of the deterministic guidance. The 00Z GFS is the second fastest model, behind the 12Z UKMET with the 00Z NAM/12Z ECMWF similar to one another and in the middle. Given the differences among the 00Z NAM, 00Z GFS and 12Z ECMWF are relatively minor, a 3-way blend of these models will be preferred, falling within the middle of the spread and slightly ahead of the 12Z ECMWF mean. The 12Z ECMWF mean has been very consistent over its past 3 12/00Z cycles, but a nudge ahead in the direction of the 00Z GFS/00Z NAM is warranted given often times the ECMWF will trend in the direction of the latest NAM/GFS when the verifying time is within the first 24-48 hours. ...Mid-level shortwave crossing the Pacific Northwest Sunday, digging into Northern/Central Plains Mon... ...Closed low likely crossing the Mississippi River Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: near the 00Z ECMWF Confidence: Slightly below average ...07Z update... Relative to their previous 12Z cycles, the 00Z UKMET/CMC sped up toward the previous preference of the 12Z ECMWF. However, the 700-500 mb low from the 00Z CMC remains slower and for the 00Z UKMET, weaker. The 00Z ECMWF remains similar to its previous run until Tuesday night when it speeds up the timing of the mid-level trough slightly. Overall thinking remains the same, as does the preference which is now near the 00Z ECMWF, given the timing adjustments made by the ECMWF were considered to be favorable...or a nudge toward the 00Z GFS. ...previous discussion follows... Differences with this system become notable on Monday as models struggle to handle the timing of the leading edge of the shortwave energy as it enters the Great Plains. The 00Z NAM is quickest, while the 12Z CMC is slowest. From Tuesday into Wednesday morning, The timing differences amplify with the 12Z CMC and 00Z NAM on the edges of the ensemble spread regarding a likely closed low crossing the Mississippi River Valley. Trends in the ensembles, looking back at the past 4 12/00Z cycles, have jumped around a bit, with slower followed by faster trends noted. The middle of the average of the recent ensemble cycles seems to be near the 12Z ECMWF mean and the 12Z ECMWF. However, recent verification of upper troughs moving through the central U.S. have tended to verify between the faster GFS and slower ECMWF. For this reason, a slight nudge ahead toward the 00Z GFS is recommended to account for future adjustments in the guidance. ...Mid-level shortwave trough/surface cold front clipping the Pacific Northwest on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average ...07Z update... Only minor trends were observed from the 00Z non-NCEP guidance, and they were convergent upon a common middle ground. Little difference now exists with this system, but given the 3-day outlook and potential for future adjustments, confidence is only average. ...previous discussion follows... There is reasonable agreement with a shortwave as it tracks into a mid-level ridge situated along the British Columbia/Pacific Northwest coastline Tuesday morning. While the 12Z ECMWF is flattest with the trough as it moves inland, there is relatively good agreement at least through the end of the short range period (12Z/26). A general model blend will be recommended at this point 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