Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 300 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 model evaluation...Including final 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/ECMWF/UKMET blend Confidence: Average Generally good agreement exists regarding the surface low near the Oklahoma panhandle. Therefore, 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/ECMWF/UKMET 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. While the 00Z CMC sped up from its 12Z run, the 00Z CMC still 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 00Z UKMET adjusted toward the GFS/ECMWF, no longer toward the northern side with the leading shortwave energy and is now less aggressive with amplification of a subsequent shortwave amplifying toward New Mexico. The 00Z ECMWF adjusted faster with the leading shortwave and is now a little ahead of the GFS by Thursday morning. A blend of the reasonably similar 00Z GFS/ECMWF/UKMET 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: General model blend Confidence: Average Minor placement and strength differences exist with a weak surface low near the Great Lakes Tuesday. Aloft, the 00Z CMC adjusted quicker with the leading edge of the shortwave trough reaching the upper Mississippi valley on Tuesday but remains slightly slower than the remaining deterministic guidance and near the ensemble means. Enough agreement is now in place to support a general model blend. ...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/ECMWF/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 00Z 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/ECMWF/UKMET continues to split the larger differences seen with the 00Z CMC and 00Z NAM, with this blend also matching closely to the latest ensemble means. It should be noted that ensemble data does not completely discount the NAM or CMC, but better support exists for the GFS/ECMWF/UKMET. ...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 GFS/ECMWF/UKMET blend Confidence: Average The 00Z CMC remains a bit flatter and more northern with the shortwave as it amplifies into southwestern Canada. The other models show some differences with each other, and now with adjustments made by the 00Z UKMET, the 00Z NAM may be considered a bit too quick to bring the shortwave into the central Rockies. The slower/less aggressive 00Z UKMET, compared to its previous cycle, can be used along with the 00Z GFS and 00Z ECMWF. Despite some wobbles, the GFS and ECMWF have been fairly consistent and agree with ensemble trends and the latest scatter low plots. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto