Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 142 PM EST Fri Feb 07 2020 Valid Feb 07/1200 UTC thru Feb 11/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Powerful surface low exiting from the Northeast Friday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system as a deepening surface low quickly races off toward the northeast, away from the New England coast. No significant changes were noted with the 12Z ECMWF/UKMET/CMC for this system. ...Weak shortwave crossing the OH Valley and Mid-Atlantic throughout the day/night on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average There are only minor amplitude/timing differences with this system, but a general model blend looks reasonable for this system. No significant changes were noted with the 12Z ECMWF/UKMET/CMC for this system. ...Deep trough/cyclone crossing the Pacific Northwest Saturday... ...Downstream troughing over the northern Plains by Sunday and related surface low tracking through the Upper Midwest with trailing cold front into the Lower Mississippi Valley... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z NAM blend Confidence: Slightly above average ...19Z update... Only minor changes were made with the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles, translating into continuing the preference for a non 12Z NAM blend with this system. ...previous discussion follows... As a potent mid-level shortwave reaches the Pacific Northwest late Friday, it will track into interior portions of the Northwest breaking into two components. A southern component of this system will track southward along the West Coast, likely closing off a low near southern California. This southern portion of the shortwave is discussed in the section below. The northern portion of the system is expected to track through the central to northern Great Plains Saturday night into the Upper Midwest on Sunday. A relatively weak surface low will accompany the upper system across the Upper Midwest and Great Lakes, with a trailing cold front into the Lower Mississippi Valley. The 12Z NAM's shortwave is stronger than the remaining model consensus and also a bit faster. There are some minor timing differences among the remaining guidance with the 00Z ECMWF a bit slower and 12Z GFS a bit faster. A blend between the 12Z GFS and 00Z ECMWF is preferred as it fits well within the middle of the latest ensemble spread. ...Digging mid-level trough over the Great Basin/Southwest by Sunday, evolving into a strong closed low near southern California on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/ECMWF/CMC Confidence: Slightly above average ...19Z update... The 12Z UKMET slowed down its timing a little from its previous 00Z cycle, but the 12Z cycle still outpaces the better ensemble clustering. Only minor adjustments were noted with the 12Z ECMWF/CMC, so the preference remains a ECMWF/CMC/NAM blend. ...previous discussion follows... Ensemble spaghetti plots at 500 mb for the 558 dam height support the 12Z NAM, 00Z ECMWF and 00Z CMC as energy aloft slides down the West Coast and allows a closed low to form over California by Monday morning. The 12Z GFS does not amplify the positively tilted mid-level trough as far back to the west as the remaining deterministic/ensemble consensus Saturday night into Sunday. This difference in the 12Z GFS continues through Monday evening with the 500 mb energy less closed off and separated from the northern stream westerlies than the remaining model guidance. The 00Z UKMET looks similar in the way it closes off the mid-level energy to the model consensus but the ensembles would suggest that the 00Z UKMET is too fast. This results in the 00Z UKMET's position falling out of alignment with the preference by Monday evening. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto