Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 244 PM EDT Tue May 01 2018 Valid May 01/1200 UTC thru May 05/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation including preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low/surface low departing from the Northeast today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Surface wave near the upper MS valley this morning tracking through Ontario/Quebec through tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Model spread is very modest with the timing and depth of the ejecting surface low out of the upper Mississippi Valley and its evolution downstream. A general model blend will be preferred. ...Ejecting low-amplitude shortwave/jet-max from the central Rockies this morning off to the northeast and across the Midwest today through early Wednesday... ...Shearing downwind across northern New England by late Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 24 hours 12Z NAM/12Z GFS/12Z ECMWF blend...after 24 hours Confidence: Above average, becoming average GOES-16 1-minute WV suite shows a well-defined shortwave impulse ejecting northeast across the central Rockies and immediate High Plains this morning. This energy will lift northeast across the Midwest later this afternoon, overnight and into early Wednesday while interacting with a very slow-moving frontal zone draped over the central to northern Plains. Most of the global models and the hires CAM guidance favors the idea of an elongated wave of low pressure and possibly multiple centers developing along the front this evening which will be at least partially influenced by convective processes. At least a modest wave will lift toward the upper Great Lakes region early Wednesday in association with the low-amplitude energy. By late Wednesday, the models show the wave lifting across far northern New England. Model mass field spread is limited through 24 hours, but thereafter the CMC and UKMET appear to track their surface waves a tad too far north and north of the NAM, GFS and ECMWF solutions which have a bit better hires-CAM support for a track a little farther south that would drive somewhat stronger impacts across northern New England Wednesday afternoon and evening. While initially a general model blend will be fine through about 24 hours, a blend of the NAM, GFS and ECMWF will be preferred thereafter. ...Shortwave crossing south-central Canada and the northern Plains on Wednesday... ...Energy shearing downstream across Ontario/Quebec through Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models take a shortwave east-southeast across south-central Canada by early Wednesday and a portion of it also crossing the northern Plains. By Thursday, this energy will begin to shear downstream across Ontario and Quebec given the arrival of additional upstream shortwave energy that will be digging southeast from south-central Canada down across the Midwest and Great Lakes later Thursday and Friday. Model spread is limited with this particular shortwave impulse, so a general model blend will be preferred. ...Ejecting Southwest U.S. upper trough crossing the central Plains and upper Midwest through Thursday... ...Phasing with northern stream energy from south-central Canada on Friday... ...Surface low lifting from the central Plains Thursday to the lower Great Lakes on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z GFS and 12Z ECMWF Confidence: Slightly above average, becoming below average The models take a large portion of the Southwest U.S. upper trough/closed low and lift it northeast across the central Plains and upper Midwest through Thursday which will then gradually phase with the arrival of northern stream shortwave energy from south-central Canada on Friday. This will allow low pressure riding northeast by along a front to cross the central Plains and then attempt to deepen over the lower Great Lakes on Friday depending on how much phasing actually occurs. The 12Z non-NCEP guidance led by the ECMWF, CMC and especially the UKMET promote stronger phasing and a somewhat slower low evolution. The 12Z NAM and 12Z GFS are a bit more progressive with the low and less phased. Overall, the NAM is the most progressive solution. Will lean somewhat toward a more progressive solution at this time, but out of respect for the relatively consistent non-NCEP guidance, a blend of the GFS and ECMWF will be preferred. This means essentially downplaying the progressive NAM and slower/deeper CMC/UKMET solutions. ...Lingering trough over the Southwest on Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average The models maintain a portion of the Southwest U.S. trough/closed low going through Friday. The CMC and UKMET have come into considerably better agreement with the NAM, GFS and ECMWF solutions overall. There remains some modest spread with depth of the troughing left behind, but at this point a general model blend will be preferred. ...Mid-level shortwave approaching British Columbia Friday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM and 12Z GFS Confidence: Below average The models bring a shortwave in off the Pacific on Friday and in across British Columbia. The 12Z UKMET and especially the 12Z ECMWF have trended weaker with this energy and are at least closer to the more modest 12Z NAM and 12Z GFS solutions. The 12Z CMC is also a little weaker and fairly close to the timing of the NAM/GFS camp. Overall, the support remains a bit more solid for the weaker NAM/GFS camp considering the downstream ridging that this energy will initially be encountering. The GEFS member spread certainly tends to favor the weaker NAM/GFS camp, and there is some European and Canadian ensemble member support for the weaker consensus too. Thus, will prefer a blend of the NAM and GFS for now, but with limited confidence. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison