Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 248 AM EDT Thu Apr 23 2020 Valid Apr 23/0000 UTC thru Apr 26/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Initial Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Overall pattern across the continental U.S. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Saturday, then 00Z ECMWF/12Z EC mean blend for most areas Confidence: Moderate 7Z Update: The 00Z ECMWF trended northward with the surface low crossing the Ohio Valley this weekend with a slightly less amplified 500mb trough across the Deep South compared to its 12Z run. The UKMET trended a little less amplified with the shortwave exiting the East Coast Friday evening, a little stronger and farther south with the next storm system across the Midwest, and faster with the Pacific system approaching British Columbia. The CMC is now a little slower with the trough crossing the southern U.S. on Saturday. Overall, there are still significant model differences with the weekend storm system across the Ohio Valley, and given the model fluctuations over the past 24 hours, it is still prudent to incorporate some of the EC ensemble mean to mitigate these differences. ------------------ A split flow pattern will initially be over the central and eastern portions of the U.S. with a strong southern stream shortwave tracking eastward across the Deep South and then exiting the East Coast by Friday evening. This will sustain a surface low that will track from the Ozarks to the northern Mid-Atlantic region, and the CMC becomes slightly weaker with this disturbance by Friday, but not out of the realm of possibility, so a general model blend should suffice for this storm system given the overall decent model agreement. The next system arrives across the Midwest by Friday night as a shortwave amplifies in a northwest flow type pattern. This will support a surface low and cold front crossing the central Plains and Midwest states, and then the low crosses the Ohio Valley and eventually the Northeast states. This is where the models are differing the most, with the GFS becoming more amplified by Friday morning with the shortwave across the western High Plains, and continues going into the weekend. The NAM becomes slower than the model consensus by late Friday and the CMC is stronger with the southern portion of the trough across the Mid-South by Saturday morning. By the end of the forecast period, the UKMET is between the GEFS and EC means, and would be a good deterministic model to use along with the EC mean. Across the western U.S., an upper level ridge axis briefly builds in across the region through Friday ahead of the next system arriving from the north Pacific. The main surface low will likely impact the British Columbia coast, with a cold front reaching Washington and Oregon on Saturday. The GFS is slightly slower with the arrival of this front, and the CMC is slightly more amplified. There is enough agreement among the NAM, ECMWF, and UKMET to merit a blend of those models. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Hamrick