Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 136 PM EST Wed Feb 07 2018 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/Confidence... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Gradually Developing Cyclone Moving Quickly Northeast to near Labrador by Thursday, with Trailing Cold Front Sweeping Through the East Coast of the US... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General Model Blend Confidence: Above Average ---18Z UPDATE--- The 12Z CMC has moved into much better agreement with the other models, and a general model blend is now preferred. ---PREV. DISCUSSION--- Models are generally in good agreement with this system through the next 36 hours, at which point its related impacts should have spread offshore of the eastern US. There are minor differences in the mass fields, but these do not appear to be substantial or coherent enough to prefer one model over another on the synoptic scale. The 00Z CMC is a slight exception, as it shows higher heights aloft through much of the eastern US trough than other models, and as a result has a weaker surface low. Therefore, the preference is for a general blend that excludes the 00Z CMC. ...Gradual Deepening of a Broad Trough with Several Digging Waves Across the Northern Tier of States Thursday to Saturday... ...Southward Progression of an Arctic High into Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC Blend Confidence: Slightly Above Average ---18Z UPDATE--- The 12Z CMC has flipped the bias from the previous run, and now shows higher heights through the trough across the western and central US, more than other available models. While it is overall in better agreement, will continue to exclude it from the preference as it is showing run-to-run inconsistency. Other models remained fairly well clustered. ---PREV. DISCUSSION--- Over the past couple model cycles, models have come into better agreement with the slowly evolving trough over the CONUS. It continues to look like this will happen as the result of several digging shortwaves around the back side of the large mid-upper level low near Hudson Bay. One will shift across the Great Lakes on Friday, spreading a band of precipitation across the region, while the other will dig through the Intermountain West. The 00Z CMC shows lower heights through much of the West in the early hours of its forecast, eventually showing a much sharper and more amplified (positive tilt) trough across the West. The preference is to lean away from this solution as it seems to have an initial bias and is not supported by other models. Otherwise, model agreement is fairly good. There are slight differences -- for example, with the Great Lakes shortwave the 12Z NAM and GFS show a little more amplification of the trough and slower timing than the 00Z ECMWF and UKMET. However, these are small differences overall, and some of the differences could represent a new trend on the 12Z cycle. Therefore, a general blend is preferred with the exclusion of the 00Z CMC. ...Developing Front From the Gulf Coast States Northeastward to the Northeast Coast on Saturday and Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 12Z GFS/NAM, 00Z ECMWF Confidence: Average ---18Z UPDATE--- No change to the preliminary preference. The 12Z UKMET has slightly backed off its depiction of a sharper surface trough and lower pressures associated with the front, but continues to be the strongest in that regard. ---PREV. DISCUSSION--- As the broad trough slowly takes shape in the central US, an associated low-level front is expected to develop in advance of the upper level trough. Given the initial height field biases in the 00Z CMC, described in the discussions for other systems, confidence is low in incorporating that here. The 00Z UKMET is more similar to the other models with its height fields aloft, but sharpens the surface trough much faster with lower pressures than other available models. Given the lack of a sharp trough aloft, or potent shortwave ejecting in the flow around the trough, the overall evolution of the front is expected to be more gradual, and thus the preference would be toward the 12Z GFS/NAM and 00Z ECMWF which are reasonably similar. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Lamers