Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1213 PM EST Sat Feb 08 2020 Valid Feb 08/1200 UTC thru Feb 12/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Weak shortwave crossing the OH Valley/Appalachians today/tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Deep trough/cyclone crossing the Northwest today... ...Downstream troughing over the northern Plains by Sunday with related surface low tracking into the Upper Midwest with trailing cold front across the Mississippi Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 00Z CMC blend Confidence: Average The 12Z GFS shows up as strongest with the 850 mb reflection of this system Sunday morning with the 12Z NAM a close second. The GEFS supports the stronger GFS while the 00Z ECMWF/UKMET/CMC are supported by the 00Z EC mean through Monday. Given the nearly even split and short term nature of the forecast, a blend of the two camps is recommended. This equates to a 12Z NAM/GFS and 00Z ECMWF/UKMET blend, excluding the 00Z CMC as its surface low deviates from the remaining model guidance later Sunday night near the lower Great Lakes region. ...Digging mid-level trough over the Great Basin/Southwest by Sunday, evolving into a strong closed low near southern California on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z NAM, 00Z ECMWF, 00Z CMC blend Confidence: Slightly above average Similar differences exist with this system as what was seen on Friday with the 12Z GFS faster than all of the deterministic guidance and almost all of the latest ensemble guidance. The 00Z UKMET trended slower however, and is now on the slower side of the deterministic guidance. Ensemble spaghetti heights from 500 mb at 558 dam support a middle ground but the envelope of solutions has trended quicker compared to its previous 3 cycles valid Tuesday. The 12Z NAM (slightly faster) blended with the 00Z ECMWF/CMC are recommended for this system at this time with the 12Z GFS considered very unlikely to verify. ...Northern stream trough/front over the Midwest by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z NAM blend Confidence: Slightly above average Timing differences show up with the 500 mb reflection of this shortwave early on Tuesday with the 12Z NAM fastest followed by the 00Z UKMET and 00Z CMC. The 12Z GFS is slowest while the 00Z ECMWF is in the middle. Differences through the end of the short range period (00Z/12) are relatively minor so a general model blend will be preferred for this system. ...Quasi-stationary front over the Gulf Coast states by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z CMC/ECMWF blend Confidence: Average Some latitude differences develop with this frontal boundary due to some differences aloft with the position of a strong ridge over the western Caribbean and an upstream closed low over the Southwest. As discussed above, the 12Z GFS is considered too fast with the ejection of the southwestern closed low and this impacts the orientation of the front downstream by Tuesday. The 12Z NAM showed some differences in wind convergence over the Gulf Coast states on Tuesday but the 00Z CMC/ECMWF appear similar enough to each other and are preferred with surrounding synoptic scale features to warrant use for the nearly stationary front across the Gulf Coast states through Tuesday. ...Mid-level shortwave potentially reaching the British Columbia coast Monday night and advancing into the Northwest for Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS Confidence: Below average Large uncertainty exists with a shortwave analyzed south of the western Aleutian Islands at 12Z this morning, and how it interacts and evolves downstream toward North America Monday and Tuesday. The 00Z ECMWF was fastest with this feature. Trends have been inconclusive with the deterministic guidance and ensemble guidance shows only weak support for a stronger compact shortwave as seen in the 12Z NAM and 00Z CMC. The 12Z GFS appears to be a favorable middle ground regarding timing and strength with this feature but poor run to run consistency and poor model agreement leads to below average confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto