Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1258 AM EDT Mon Mar 26 2018 Valid Mar 26/0000 UTC thru Mar 29/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS evaluation...Including preliminary preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Southern stream portion of positively tilted amplified trough over the West, slowly moving east to the Plains by Wednesday... ...Surface low over the Southern Plains through Monday, getting overtaken by a cold front on Monday Night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF blend Confidence: Average Regarding the surface low near the Oklahoma panhandle, a general model blend is preferred to iron out smaller scale differences before a cold front overtakes the low Monday night...with a weak, northeastward moving, surface low discussed in the below section. At least through 12Z/29, a 00Z GFS/12Z ECMWF blend will work for the southern stream portion of the upper trough over the West. Ensembles and deterministic guidance continue to show convergence in the previously faster GEFS and previously slower ECMWF ensemble members. The 12Z CMC looks to be a near slower outlier by 00Z/29 across the southern High Plains. The 00Z NAM is excluded as it is faster and farther north with vorticity in the leading shortwave approaching the lower Mississippi valley Thursday morning. The 12Z UKMET is toward the northern side with the energy and more aggressive with amplification of a subsequent shortwave amplifying toward New Mexico. A blend of the slightly quicker 00Z GFS and slower 12Z ECMWF is most fitting toward the ensemble means. ...Northern stream portion of the trough in the West, kicking east into the Great Lakes Tuesday and Wednesday... ...Faster eastward motion of northern portion of surface cold front with possible weak surface low in the Great Lakes early Tuesday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z CMC blend Confidence: Average Minor placement and strength differences exist with a weak surface low near the Great Lakes Tuesday. However, aloft, the 12Z CMC is notably slower with the leading edge of the shortwave trough, reaching the upper Mississippi valley on Tuesday. Outside of the 12Z CMC, there is broad agreement in line with an average of the latest ensemble means. Confidence would be higher if it weren't for relatively high run to run differences in the deterministic guidance. ...Slow moving closed low setting up in the western Atlantic, south-southeast of Nova Scotia today into Tuesday... ...Accelerated development of a surface low in the vicinity of Bermuda... ...Associated strong surface high settling into New England... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS, 12Z ECMWF and 12Z UKMET blend Confidence: Average Differences with this system are minor until Wednesday morning at which point some latitude differences with the closed low begin to develop as well as some strength differences. The ensemble means show a middle ground between the more southern/weaker 12Z CMC and more northern 00Z GFS/NAM. The NAM is weakest with the 500 mb low just south of Nova Scotia Wednesday morning. Sensible weather impacts are small, but a 00Z GFS/12Z ECMWF/12Z UKMET splits the larger differences seen with the 12Z CMC and 00Z NAM, with this blend also matching closely to the latest ensemble means. ...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 and Great Lakes Thursday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z NAM, 00Z GFS and 12Z ECMWF blend Confidence: Average The 12Z CMC is flattest and most northern with the shortwave as it amplifies into southwestern Canada. The other models show some differences, perhaps the 12Z UKMET stands out next with a farther north surface low. Ensemble trends and the latest scatter low plots support a blend of the 00Z NAM, 00Z GFS and 12Z ECMWF. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto