Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 255 AM EDT Wed Apr 22 2020 Valid Apr 22/0000 UTC thru Apr 25/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough/closed low initially over the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in very good agreement with the details of the deep trough and closed low impacting the Northeast through Wednesday. The system should exit up across southeast Canada by Thursday. A general model blend will be preferred. ...Southern stream trough crossing the Southern Plains/Lower MS Valley through early Thursday... ...Associated energy and surface low crossing the OH Valley and Mid-Atlantic by Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z UKMET/ECMWF and 00Z GEFS/12Z ECENS mean blend Confidence: Average The models take the southern stream mid-level trough over the Southwest off to the east over the next couple of days, with the energy crossing the southern Plains on Wednesday and reaching the lower MS Valley by early Thursday. This energy along with a deepening surface low center will then advance northeast and cross the OH Valley and Mid-Atlantic region by Friday as an attendant cold front sweeps across the South. The system will exit offshore by Friday night. The 00Z NAM is the fastest solution with the trough and surface low. Considering the amplitude of the ejecting shortwave, the NAM appears too weak with its surface reflection. The 00Z GFS for its part may perhaps be episodically be a tad too fast, but the bigger concern may tend to be with the overall latitude of its surface low track involving the OH Valley/Mid-Atlantic, which is a little north of the generally well clustered 00Z non-NCEP solutions. However, it should be noted though that the 00Z CMC again appears to be a tad too weak with its surface low. Regarding timing and depth of the system, the 00Z UKMET and 00Z ECMWF tend to have better ensemble support (i.e. 00Z GEFS/12Z ECENS means). So, will favor a blend of the UKMET/ECMWF solutions and along with the ensemble means for the time being. ...Initial shortwave/low center across the Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models bring a northern stream shortwave and associated low center down from Canada and across the northern Plains on Wednesday which is expected to dampen out over the Midwest Wednesday night as the stronger southern stream system evolves across the southern Plains and lower MS Valley. A general model blend will be preferred with this system given very modest model mass field spread. ...Second shortwave/low center across the Northern Plains... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z CMC and 00Z ECMWF Confidence: Average The models bring a second northern stream shortwave and associated low center down from Canada and across the northern Plains on Thursday and then attempt to amplify it a bit over the Midwest on Friday. The 00Z GFS and 00Z UKMET end up being the strongest solutions with this energy, and while most of the models generally dampen out the low center, the UKMET actually holds on to a rather well-defined low center over the Midwest going into Saturday. The 00Z NAM, 00Z CMC and 00Z ECMWF are all weaker with the NAM overall the weakest. The 00Z GEFS mean and 12Z ECENS mean generally favor the CMC/ECMWF camp, and so a blend of these solutions will be preferred, but it should be noted that there are some GEFS members that do favor the stronger GFS, so a stronger evolution of this energy cannot be ruled out. ...Shortwave trough digging across the Intermountain West... ...Energy amplifying into the Lower MS Valley by Saturday... ...Associated deepening surface low... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z CMC/ECMWF and 12Z ECENS mean Confidence: Slightly below average The models bring yet another shortwave down across the Intermountain West which is then forecast to amplify across the southern Plains on Friday and cross the lower MS Valley by early Saturday. The models, especially the non-NCEP models, show the trough becoming negatively tilted by early Saturday and this will drive another deepening surface low center. The 00Z NAM and 00Z UKMET become weaker outlier solutions at the surface and aloft with the system, with the main difference being that the NAM is a bit faster, and also the UKMET is suggesting two low centers with over the lower MS Valley and one evolving over the Midwest by the end of the period given proximity of stronger northern stream shortwave energy lurking over the Midwest. The 00Z GFS appears to be a bit too progressive by Friday/Saturday and probably takes its energy a bit too far north, but it has agreement with the UKMET in having stronger northern stream energy nearby. The difference between the UKMET and GFS is that the GFS still has a more dominant southern stream shortwave trough and thus a dominant southern stream surface low. The GFS is supported by the 00Z CMC and 00Z ECMWF solutions with the idea of there being one consolidated low evolving through the lower MS Valley by the end of the period and a more dominant southern stream trough, but that is where the agreement ends as the CMC/ECMWF camp is farther south and slower with the surface low evolution. The CMC/ECMWF camp is generally supported by the 12Z ECENS mean, but the 00Z GEFS mean tends to favor a compromise between the GFS and CMC/ECMWF cluster. The preference for now will be toward a blend of the slower CMC/ECMWF and ECENS mean. However, given some of the uncertainties over how strong the nearby northern stream energy and related interaction will be, confidence is a bit limited in the Friday/Saturday time frame. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison