Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 100 PM EDT Tue Mar 24 2020 Valid Mar 24/1200 UTC thru Mar 28/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Shortwave tracking from the Central Plains to the East Coast on Wednesday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS/GEFS blend Confidence: Near average The southern stream trough exiting the Rockies and emerging over the Central Plains is forecast to remain intact as it reaches the eastern U.S on Wednesday. Surface cyclogenesis is in progress across northern Texas and Oklahoma, and this low reaches the central Appalachians and weakens by early Wednesday, with secondary cyclogenesis is likely off the Mid-Atlantic coast by Wednesday afternoon. The 12Z NCEP runs maintained decent run to run continuity...so the 24/12Z GFS and the 24/06Z GEFS mean were decidedly fast outliers. As a result, still preferred a non-GFS/non-GEFS mean model compromise. Longwave trough over the western U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-UKMET blend after 12Z Thursday Confidence: Average The amplified pattern over the eastern Pacific will end up producing a positively tilted longwave trough axis which will slowly progress down the West Coast, gradually move inland across the Desert Southwest by Friday morning and be about ready to cross the Southern Rockies by Friday evening. The 12Z NCEP guidance largely maintained continuity with respect to the timing and strength of the feature...leaving the UKMET a more amplified outlier than other guidance beginning on Thursday. The 24/12Z GFS was slower than the 24/00Z ECMWF, with the surface features reflecting the processes aloft, but not enough of a difference to be unusuable. Storm system crossing northern tier of the U.S. midweek ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM consensus Confidence: Average The 24/12Z run of the NAM got into much better agreement with other models in handling this system. The resulting agreement among the various global models was good...so a general compromise should work fine. The GFS heights at 700 mb may be a bit lower than other guidance by Wednesday afternoon over the Upper Midwest. Otherwise, details from any of the deterministic models could be used to reflect smaller scale details. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Bann