Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 258 AM EDT Sun Mar 25 2018 Valid Mar 25/0000 UTC thru Mar 28/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation...including final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Amplification of the western U.S. trough with eventual evolution into northern and southern stream components by Tuesday morning... ...Lee cyclogenesis over the Plains today and Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 2/3 12/00Z ECMWF...1/3 00Z UKMET blend Confidence: Average A complex evolution aloft across the western U.S. continues to make a challenging forecast given multiple shortwave facets to consider. By Tuesday morning, a northern and southern stream trough component are evident, with the northern stream trough axis over the north-central U.S. while a mid-level trough/closed low sets up over the Southwest. The 00Z NAM/GFS remain a bit faster with the northern stream component compared to the ensemble means and remaining deterministic model consensus. Meanwhile down south, the 00Z UKMET remains a little slower with a shortwave moving across northern Utah which causes the southern stream wave to close off and be slightly slower than the ensemble consensus, evident in the 500 mb 558 dam spaghetti height plots Monday evening. The 00Z GFS slowed down some with its southern stream component since Saturday, but it remains faster, like the GEFS mean which is significantly ahead of the ECMWF and CMC members. While some convergence has been noted over the past 24 hours of model cycles between the slower and faster camps, the large amplified flow pattern would tend to favor a slower progression to the east than seen by the GEFS and even the 00Z GFS to some degree. The 00Z ECMWF slowed slightly with the southern stream and trended a bit faster with the northern stream wave compared to its previous cycle but a combination of the 00Z and 12Z ECMWF is considered best of the deterministic models for both northern and southern locations. The 00Z UKMET is considered the next best, although some component of the 00Z GFS could be considered usable across the South as well. Farther north, a weak surface low will move eastward through Kansas into the Midwest late Monday into, with ensemble scatter low plots quite varied in placement. However, the faster 00Z NAM/GFS are considered less likely than the 00Z ECMWF/UKMET given the ECMWF/UKMET have a more favorable upper evolution matching closer to the relatively consistent ECMWF mean. ...Shortwave weakening toward the Southeast U.S. today... ...Weakening associated surface low transferring to the Carolinas coastline by Sunday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The 00Z CMC trended stronger with a shortwave over the Midwest early in the forecast period compared to its previous cycle and is nearer to the remaining model consensus. The surface low that strengthens into the open Atlantic Sunday night is now comparable with the latest 00Z model suite, though the 00Z CMC is slightly weaker/slower. Agreement is close enough for a general model compromise. ...Closed low developing off the Northeast today and Monday... ...More accelerated development of the Carolinas coastal low well offshore on Monday and Tuesday... ...Associated strong surface high settling into New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Only minor differences remain with the closed low moving into the western Atlantic today/tonight with the 00Z CMC a little weaker than the consensus, the 00Z ECMWF and 00Z UKMET are on the western side of the deterministic/ensemble spread and the 00Z GFS is slightly faster/east than the consensus. All in all, the differences are minor and have little to no impact on the strength and position of the strong surface ridge settling into New England on Monday. A general model compromise can be used for this system. ...Shortwave rounding a Pacific ridge through the Gulf of Alaska on Monday and digging into the Northern Rockies Tuesday... ...Surface low developing over Alberta and Saskatchewan Tuesday with trailing cold front reaching the north-central U.S. Tuesday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 00Z UKMET blend Confidence: Slightly above average The 00Z UKMET remains the most amplified with a mid-level shortwave as it reaches southwestern Canada and eventually Montana Tuesday night. The resulting surface low in the 00Z UKMET is much deeper over Canada than the remaining model consensus. Outside of the 00Z UKMET, the model spread is small and the non 00Z UKMET consensus agrees well with the latest ensemble means. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto