Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 127 PM EST Thu Feb 22 2018 Valid Feb 22/1200 UTC thru Feb 26/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation...with latest model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Front stretching from the Mid-Atlantic to southeast Texas... ...Surface wave crossing the upper MS Valley/Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in reasonably good agreement with the 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. ...Shortwave initially over the Pacific Northwest... ...Dropping into the Four Corners region on Friday... ...Cyclogenesis over the Plains and lifting to the Midwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Average The models take rather strong shortwave trough digging down across the Pacific Northwest and drop it quickly into the Four Corners region on Friday. Model spread is minimal until the system ejects out into the Plains by Saturday where well-defined cyclogenesis will occur and the system lifts northeast toward the Midwest. The 12Z NAM ends up stronger aloft with its energy traversing the upper Midwest. The 12Z GFS is also quite energetic, especially with its degree of negative tilt and strong vort energy, but does not have quite the degree of height falls as the NAM. The 12Z UKMET, 12Z CMC and 12Z ECMWF all show a somewhat weaker system. However, there is some degree of ensemble support from the GEFS and the ECENS for a somewhat stronger low center to evolve with a negatively tilted trough that lifts northeast out of the central Plains and across the upper Midwest. Additionally, there was some trend collectively from the CMC, UKMET and ECMWF toward a somewhat stronger solution, but still not to the extent of the NAM aloft, or the GFS at the surface. For now, will suggest a compromise in mass fields from the GFS and ECMWF which makes for a model cluster more closely representing the model consensus at this time. ...Shortwave arriving over the Pacific Northwest on Saturday... ...Crossing the Four Corners/High Plains on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS consensus 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. The models are in good agreement with the mass field details of this system until Sunday when the 12Z UKMET begins to lag the model consensus, and the 12Z GFS begins to outrun it. The 12Z CMC and 12Z ECMWF tend to favor the slower UKMET, with the 12Z NAM more in between the GFS and NAM. There is a bit better ensemble support for the slower consensus including the GEFS mean and ECENS mean as the energy begins to eject out into the southern High Plains by late Sunday. Will prefer the slower consensus away from the GFS for now, led by the non-NCEP guidance. ...Shortwave arriving over the Pacific Northwest on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 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 relatively good agreement although the 12Z NAM appears to be perhaps just a tad more progressive. A blend of the 12Z GFS and 12Z ECMWF best approximates the model consensus at this time, and so a blend of these solutions will be preferred for now. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison