Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 142 AM EST Tue Feb 25 2020 Valid Feb 25/0000 UTC thru Feb 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation Including Final Preferences and Forecast Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low and its interaction with an upstream amplifying northern stream wave across Plains/Great Lakes through Tuesday... ...Associated surface low crossing the Mississippi River and into the Great Lakes Tue/Wed... ...Developing East Coast low Wed night.... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z CMC blend Confidence: Average ...07Z update... Run to run consistency continues to be below average for the deterministic guidance with the 00Z ECMWF/UKMET/CMC cycles trending slightly faster at 500 mb with the main shortwave tracking from the Mississippi River Valley Wednesday morning and into the Northeast as a negatively titled feature Thursday morning. Given some of the recent changes in the 00Z guidance, the 00Z NAM appears slightly slower. However, the differences are small enough and given some of the run to fun differences, a general model blend is preferred to come up with an average middle ground. The one exception is with the 00Z CMC which continues to differ from Thursday into Friday with the upstream shortwave over the upper Great Lakes in that the 00Z CMC shows greater separation between two 850 mb low centers with the secondary low to the east displaced eastward, while the primary low is displaced westward of the remaining model consensus. ...previous discussion follows... A complex interaction of several mid-level vorticity maxima will evolve into a broad trough covering the eastern 2/3 of the nation by Thursday morning. The main feature of interest will be a shortwave which is currently diving south through the High Plains and is forecast to reach the Mississippi River Valley Wednesday morning. The ensembles, which had been trending faster through Sunday's runs have reversed course and begin trending slower again with the shortwave trough axis over the middle Mississippi River Valley Wednesday morning. The good news is that the spread among all of the ensemble members has been decreasing and confidence has increased to near average for this system. The 00Z GFS continues to look too fast with the aforementioned shortwave and is also the strongest with the low level low through Wednesday evening. The 12Z CMC becomes the slowest by Wednesday evening leaving the 00Z NAM, 12Z ECMWF and 12Z UKMET as a reasonable compromise. By Thursday into Friday, as the parent surface low tracks into Ontario and Quebec, secondary low development is expected along the coast of Maine. There is reasonable agreement among the most recent deterministic guidance with the secondary low, although the 00Z NAM is on the weaker side, 00Z GFS a bit north of the ensemble cluster of lows, and 12Z UKMET a bit stronger. However, the 12Z CMC is slower and much deeper with the secondary low along the coast of Maine. There is less support for the 12Z CMC solution and given its 500 mb low differs significantly west of the better consensus Thursday evening, the 12Z CMC is not preferred. This is due to a differing interaction aloft with a shortwave dropping south across the upper Great Lakes which affects the closed low position at 500 mb in the CMC. Therefore, by Thursday into Friday, a non 12Z CMC blend is preferred as the 00Z GFS moves into better agreement with the remaining deterministic and ensemble guidance. ...Remainder of the CONUS... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average ...07Z update... No significant changes were noted across the remainder of the lower 48 regarding the 00Z CMC/UKMET/ECMWF compared to their previous 12Z cycles. ...previous discussion follows... The remainder of the lower 48 is expected to be fairly quiet through Friday morning as a +1 to +1.5 standardized height anomaly at 500 mb remains situated along the West Coast. A number of fast moving shortwaves will moving across British Columbia and dive southeastward into the Great Plains. These features are fairly low amplitude as the cross the ridge and the latest models are in fair agreement. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto