Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 252 AM EDT Thu Mar 19 2020 Valid Mar 19/0000 UTC thru Mar 22/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low impacting the West... ...Low pressure crossing the Central Plains into the Upper Great Lakes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM/ECMWF/UKMET blend Confidence: Average A potent shortwave in the southern stream pivoting around the main upper low over the Intermountain West is forecast to evolve into a closed low aloft over eastern Colorado by Thursday afternoon, and then become an open wave as it eventually phases with a northern stream shortwave reaching the northern Great Lakes by Friday afternoon. The result at the surface will be lee cyclogenesis over the western High Plains and then the surface low tracks northeastward to the Great Lakes region by Friday morning, with further deepening of the low thereafter as it lifts northward across Quebec. The 12Z UKMET is slower with the progression of the shortwave and northwest of the model consensus with the surface low over the central Plains and thus slower with the cold front passage. The GFS becomes faster and more amplified with the northern stream trough approaching the Great Lakes by Thursday night, but does not appear to have a major effect on the surface pressures. A blend of the 00Z NAM and 12Z ECMWF appears to best represent the evolution of this storm system. 7Z Update: The 00Z UKMET trended closer to the other models with regard to timing compared to its previous run. The 00Z GEFS mean trended closer to the amplified 00Z GFS solution with the northern trough. ...Second upper level trough to reach the northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z CMC/ECMWF/EC mean blend Confidence: Average The next short wave in the progressive northern stream flow crosses the northern Plains Friday night into Saturday morning, originating from the Northwest Territories of Canada. Model differences become more notable with this feature, as both the 18Z and 00Z NAM are slower and more amplified than the other guidance, and the 00Z GFS is slightly faster. The 18Z GEFS mean is also more pronounced with the amplitude compared to the EC mean. To resolve some of these differences, a blend of the EC mean, CMC, and ECMWF should suffice as a good starting point. 7Z Update: The UKMET is slightly weaker with this shortwave, and the NAM remains notably stronger. ...Mid level trough crossing Southwest on Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z CMC/12Z ECMWF/00Z NAM blend Confidence: Average The next southern stream shortwave to affect the Desert Southwest is progged to arrive by Saturday morning. Similar to the previous model evaluation, the UKMET remains the slowest model whilst the GFS is most progressive. A blend of the remaining guidance would represent the model consensus and thus a blend of the NAM, CMC, and ECMWF works well as a starting point. 7Z Update: No significant changes to previous discussion Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick