Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 157 PM EST Tue Feb 18 2020 Valid Feb 18/1200 UTC thru Feb 22/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall Pattern Across the CONUS ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 48 hours; 06Z GEFS, 00Z ECMWF/ECENS blend thereafter Confidence: Average to slightly above average, except below average for NC/VA coastal system day 3 19Z update: No significant differences noted with the 12Z guidance through 48 hours but there remains discrepancy with the guidance on day 3 across the mid-atlantic and southeast US. The non-NCEP guidance still favors a coastal low suppressed and further offshore, keeping any deep moisture from not pulling back into portions of NC/VA. Given the lower confidence and forecast uncertainty, the preference is to lean toward the ensemble means on Day 3 for that area. Otherwise, the rest of the CONUS is in good shape with a general model blend. Positively tilted trough axis currently across portions of the central/eastern US is expected to slowly advance eastward through the next couple of days as a northern stream shortwave drops from the Canadian Rockies into the Great Lakes region by Day 2. Upstream ridging will build across the western US and interior Rockies for day 2 into portions of day 3 before a closed low slides down offshore the west coast. The surface pattern will be reflected by a large dome of Arctic high pressure over the central/eastern US. Toward the end of day 3, a low pressure may form off the NC coast. Through 48 hours, a general model blend is preferred as for the large scale mass fields there is relatively little spread seen from a deterministic perspective and the ensemble spread is fairly low. For Day 3, the most notable model spread lies across the southeastern US and where a potential low forms (and its implications for winter weather across NC/VA). For now, the NAM and GFS were considered less useful and not included in the preferred blend due to its bias for deeper moisture being pulled back to NW. The best consensus approach favored the 06Z GEFS mean and 00Z ECMWF/ECENS mean. Though it's important to point out that the day 3 forecast for the southeast is a low confidence forecast. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor