Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1245 PM EDT Sun Mar 29 2020 Valid Mar 29/1200 UTC thru Apr 2/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Closed low over Great Lakes and New England with surface cyclogenesis near the coast ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average There is very good synoptic scale agreement on the evolution of the parent upper low over the Upper Great Lakes that progresses eastward to New England by Monday night. This will support the development of a coastal low near southeast New England that is forecast to track slowly eastward roughly near 40 degrees north. In regard to the developing surface low, there are minor placement differences that develop, with the 00z UKMET slightly closer to the coast and the CMC a tad farther to the south, but still close enough to merit a deterministic multi-model blend. Southwest shortwave spurring southern Plains cyclogenesis Mon-Tues, sliding through South early in the week ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z NAM/GFS and 00z ECMWF Confidence: Average Shortwave currently along the CA coast will progress eastward across the southern tier states through early week. The 00z CMC is already out of phase, a bit south, and more compact than other guidance and is quickly dismissed from preference. The remaining difference initially through Tuesday across the Southern Plains and into the southern MS Valley is in depth and timing, with the UKMET and GFS a tad weaker than the ECMWF/NAM; which leads to slightly different placement of the deeper moisture/unstable environment ahead of it. The weaker/faster solutions suggest a slower transport north and stronger convective response farther south near the Gulf. This seems logical at this time of year, but continuity and overall forcing/mass fields suggest northward shift. The 00z UKMET is much flatter than the ensemble/continuity and is more dramatically so on Day 3 across the southeast. While this is plausible, it is more dramatic than the GFS/GEFS which will represent the uncertainty with its incorporation over the UKMET in a preferred blend. Still, the uncertainty here is going to be mesoscale convective placement and its upscale influence. So the preference will be near a 12z GFS/NAM and 00z ECMWF blend at average confidence. Closed low and upper level trough approaching Pacific Northwest through Monday...then the Northern Rockies/High Plains by late Wed. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12z GFS/00z UKMET with some 00z ECMWF/CMC at lower weight Confidence: Average Broad trof developing over the Gulf of AK will continue to press southeastward with upstream shortwave energy swinging through to press height-falls/triple point and cold front through Vancouver Island and the Pac NW by early Monday. This undercutting shortwave will swing across the Northern Rockies and the southern Canadian Rockies by early Tuesday, supporting a western High Plains surface cyclone. Here the 12z NAM is very strong/quick as it rotates eastward. This will overall shift the core of the upper low farther east than has been/currently is suggested by the ensemble suite and trends. The 12z GFS and 00z UKMET are as fast as the NAM but much weaker overall, so these would be generally be favored over the NAM. The slower solutions of the ECMWF/CMC, by late Tuesday/Wed, both suggest a greater influence/tug on the shortwave lifting across the Canadian Rockies from the Arctic stream, drawing both north and west, and strengthening them. The ECMWF is more so, including against its ensemble suite members. This does not seem to play much of a role in the remaining upstream energy/jet streak that presses through the Pacific NW late Tuesday into Wed; so from a CONUS perspective, the ECMWF is viable in preferred blends. The CMC is a tad weaker but may be viable as well if desired. So all in all, a Non-NAM solution is preferred across the Northwest/Northern Rockies and the Northern Plains, though with greater weighting to the GFS/UKMET. Confidence in the overall pattern is high, but with solid differences in timing/strength of the key internal shortwaves and their influence on surface cyclone depth/orientation, confidence remains average in this blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Gallina/Hamrick