Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 245 PM EDT Thu Apr 09 2020 Valid Apr 09/1200 UTC thru Apr 13/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation...with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep cyclone impacting the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Above average An anomalously deep closed low crossing the Great Lakes will deepen and take on a negative tilt as it approaches the Northeast this afternoon/evening. Meanwhile, low pressure crossing the interior of NY state and New England will consolidate over coastal areas of Maine this evening and deepen into an intense low center. The 12Z GFS is overall a tad deeper than the 12Z NAM and the 12Z non-NCEP solutions. The GFS also tracks its surface low a tad farther inland over Maine versus the more concentrated low center evolution along the Maine coast that the remaining guidance favors. This results in the GFS having a somewhat stronger warm nose wrapping farther inland. The preference will be toward a non-GFS blend at this time. ...Slow-moving closed low across the Southwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-GFS blend Confidence: Slightly above average The models gradually eject the large, slow-moving cut-off southern stream low over southern California off to the east over the next couple of days. The energy is expected to open up into a progressive shortwave trough over the southern Plains by Saturday which will then lift northeast and go negative tilt over lower MS Valley and Mid-South by Sunday as it comes under the influence of stronger northern stream height falls dropping down over the Midwest. The 12Z GFS, just like its previous runs, continues to be the fastest solution as the energy ejects out across the South. With its faster height fall progression, the GFS is also faster with its surface frontal progression and wave activity, and actually ends up with a somewhat stronger surface low compared to the other models by Sunday. The 12Z non-NCEP models did trend a tad more progressive with this cycle (at least mass field wise), but still tend to be a little slower than the GFS. The 12Z NAM overall tends to be close to the model consensus. Given the latest trends, a mass field preference toward a non-GFS blend will still be maintained, but overall at least guidance does cluster together a bit better. ...Upper level trough/cold front reaching the Northwest... ...Dropping through the northern Plains/Midwest on Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...led by 12Z GEFS/00Z ECENS Confidence: Average Shortwave energy along the southern coast of Alaska will progress eastward to the Yukon territory, and with the accelerating/exiting jet, the upstream ridge will break down and allow for greater propagation east and then southward across southwestern Canada. The height-falls will overspread the lee of the Canadian Rockies and then the northern High Plains, and support a surface cold front dropping southeastward across the northern Plains and Midwest by Sunday. The 12Z NAM and 12Z GFS both tend to be a little faster to advance their height-falls toward the Midwest and as such appear to be a little fast in advancing the cold front down to the southeast. The 12Z non-NCEP solutions are all just a tad slower. The 00Z ECENS and 12Z CMCE suites tend to favor the modestly slower camp, but the 12Z GEFS is a tad faster. So, based on the latest trends, a general model blend weighted toward a blend of the 12Z GEFS mean and 00Z ECENS mean will be preferred as a compromise. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison