Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1242 PM EDT Wed Apr 01 2020 Valid Apr 01/1200 UTC thru Apr 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Preliminary Model Evaluation ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Western Atlantic closed low and offshore surface low through Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Any of the operational models A maturing large scale closed trough, with intense surface low pressure dipping down to near or below 980 mb, will affect the east coast and western Atlantic with strong winds. The general circulation pattern now features this and another developing high amplitude, closed trough over the Intermountain West / Northern Plains. So the pattern is slowing down, and the intense cyclone off the coast will be slow to exit. The global models are in strong agreement in their handling of this system. ...Intermountain West / Great Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS / 00Z ECMWF...emphasis on the ECMWF after 04/00Z As a large scale closed trough develops over the mountains and parts of the Plains, elongated low pressure will slip out through the Plains and Upper Midwest along a cold front, with wintry weather impacts felt across the northern Rockies to the Upper Midwest. There has been quite a bit of trending of mesoscale details, and it does not yet appear that any particular model has this event nailed down. Earlier the 00Z ECMWF/UKMET looked like a good starting point, but the 12Z GFS has become more viable and now replaces the UKMET - which appears too slow, especially aloft over the Northern Plains on Day 2. THE GFS and ECMWF do look quite similar through the duration, as the low along the font eventually becomes more consolidated and settles in beneath a ridge in Canada on Day 3. In broader terms, however, we would recommend less weight on the GFS over the mountain region and central U.S. on Day 3, as the GFS upper air pattern turns a little out of phase given some upstream problems over the eastern Pacific. Regarding the NAM... its solution over the northern Plains is mostly in step with the ECMWF/GFS until about 03/12Z, so only 48 hours into the forecast. But even then the solution is slightly fast and with a weaker pressure gradient along the front. It then becomes more unrealistic in how it significantly erodes the southern flank of the Canadian ridge. We also note that QPF intensity drops off with southern extent. In fact, on Day 3 the synoptics look favorable for return moisture to encounter a fair amount of deep layer forcing over Texas, so the very dry NAM solutions there is not recommended. ...West Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z ECMWF/UKMET Challenging pattern on the back side of the developing larger scale trough over the Intermountain West. Two noteworthy shortwave troughs come into play along the west coast. The first into California shows the telltale signs of a remarkably fast GFS solution that stands out as an outlier. The second, larger wave shows a tendency to form a closed circulation and expand its influence as it approaches Washington/Oregon on Day 3. The NCEP guidance is more bullish in strengthening this feature and driving it farther south and west offshore. This is especially true of the NAM. Spaghetti plot show that this farther south and west position has lost favor in the ensembles over time. Consensus definitely points toward the ECMWF/UKMET solutions, although some further deepening, more the flavor of the GFS rather than NAM, is within reason. Overall the GFS problems with the lead wave into California make it less desirable along the west coast, and our preference remains with the EC/UK, pending the 12Z runs. But if one wanted to include the NAM for the California wave and GFS for the WA/OR wave, they may have some utility. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Burke