Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1247 AM EDT Mon Apr 06 2020 Valid Apr 06/0000 UTC thru Apr 09/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Initial Preferences and Confidence A well defined split flow pattern will continue to dominate North America over the next several days. The southern stream component to the split will continue to be anchored by the anomalously strong closed low moving very slowly southeast day 1 along the central California coast, swinging more east southeastward day 2 toward the northern Baja Peninsula and then east northeastward into the Southwest during day 3. The northern stream flow will be comprised of an omega block with an amplifying upper trof across central Canada days 1-2 and moving into the upper Great Lakes day 3, an amplifying closed low over northeast Canada and a closed upper high in between over far north central Canada. In between the two closed low components of the omega block, shortwave energy pushing east from the Upper Mississippi Valley into the Lower Lakes and the Mid-Atlantic days 1 and 2 will enhance lift over a northwest to southeast oriented warm front lying from the Lower Great Lakes into the Upper Ohio Valley and Mid-Atlantic. With respect to the above mentioned features in both the northern and southern streams, the NAM, GFS and ECMWF are showing good continuity over their respective past three runs. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Slow moving southern stream closed low. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend through 12Z Wednesday. Slower ECMWF for day 3. Confidence: Moderate-High Through the first two days, there is little in the way of differences at mid levels. During day 3...timing differences begin with the GFS on the more progressive side into the Southwest, while the EC and EC mean are the slowest and the NAM in between. The older (1200 utc Sun 4/5) of the CMC and UKMET were closer to the EC. The GFS tends to be too progressive and given the split in the flow and the strong nature of this closed low, favor the slower solutions by day 3. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Surface low moving from the Upper Mississippi Valley, across the Lower Lakes into the Mid-Atlantic days 2-3. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Model blend with speed of surface low Confidence: Low to Moderate. Higher for moderate to heavy precip There are timing differences with areas of low pressure moving east along the warm frontal boundary draped from the Lower Lakes into the Mid-Atlantic. This part of the overall flow across the U.S. is comprised of fast moving shortwaves. Low confidence in which speed is correct. However...there is better overall agreement for moderate to heavy precip in the vicinity of this boundary late day 1 into day 2 from the Lower Lakes, Upper Ohio Valley into the Central Appalachians and Mid-Atlantic. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~ Upper trof amplifying across the north central tier late day 2 into day 3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~ Preference: Toward the more progressive non-GFS solutions. Confidence: Moderate There are timing differences that develop late day 2 into day 3 with the amplifying northern stream trof across south central Canada and the north central U.S. The GFS is the slowest here, while the non GFS guidance is clustering faster. At the moment, we will favor the majority faster solution with this amplifying upper trof and the associated east southeast of the cold front from the Plains through the Mississippi Valley and into the Ohio Valley and Central Appalachians. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Oravec