Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1156 AM EST Fri Feb 23 2018 Valid Feb 23/1200 UTC thru Feb 27/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with latest model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface wave crossing the Great Lakes/northern New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with the ejecting the surface wave currently crossing the Great Lakes region that will clip portions of northern New England tonight. A general model orientation of the surface front across the South this period, and also with the details of the surface wave lifting up across upper Mississippi Valley and Great Lakes. A general model blend will be preferred. ...Strong shortwave over the Four Corners region today... ...Cyclogenesis over the Plains and lifting to the Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS, 00Z UKMET and 00Z ECMWF Confidence: Slight above average The models take a strong shortwave trough digging down across the Four Corners region today and eject it out across the Plains on Saturday where well-defined cyclogenesis will occur. An upper trough will then lift northeast across the upper Midwest by Saturday night and take on a negative tilt which will help to deepen surface low pressure as it lifts across the upper Great Lakes region by early Sunday. The 12Z NAM ends up again stronger aloft with its energy traversing the upper Midwest and places its surface low northwest of the model consensus as it nears the upper Midwest and upper Great Lakes. The 00Z CMC also is a bit deeper aloft like the NAM. However, the 12Z GFS, 00Z UKMET and 00Z ECMWF are not as strong with the height falls, but nevertheless show an energetic and negatively tilting upper trough with a rather strong surface low. The GFS, UKMET and ECMWF show good model clustering and ensemble support, and so a blend of these solutions will be preferred. ...Shortwave arriving over the Pacific Northwest on Saturday... ...Crossing the Four Corners/High Plains on Sunday... ...Ejecting east across the Mississippi/Ohio Valleys on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 00Z ECMWF Confidence: Average The next in a series of shortwaves to drop southeast down across western North America and into the Pacific Northwest will arrive on Saturday and then rapidly drop down into the Four Corners region on Sunday before rapidly ejecting east toward the mid Mississippi Valley and Ohio Valley on Monday. The models are in good agreement with their mass field details of this system until Sunday when the 00Z UKMET begins to lag the model consensus, and the 12Z GFS begins to outrun it just slightly. The 00Z CMC and 00Z ECMWF tend to favor the slower UKMET, with the 12Z NAM close to the GFS. The 06Z GEFS mean is close to the operational GFS, with the 00Z ECENS mean close to the operational ECMWF. The UKMET is slower than any of the model ensemble means though and will be discounted by Sunday and Monday. Accounting for the slower and faster camps, the preference will be to compromise by favoring a GFS and ECMWF blend. ...Shortwave arriving over the Pacific Northwest on Sunday... ...Larger scale trough evolution over the West by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Average The guidance brings another shortwave into the Pacific Northwest on Sunday along with a progressive cold front. The guidance is in good agreement with the arrival of the shortwave energy and the evolution of the height falls digging down across California and the Great Basin on Monday which will lead to a larger scale trough evolution aiming for the Southwest. Given the good larger scale agreement among the guidance with this energy at this point, a general model blend will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison