Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 139 AM EST Tue Feb 26 2019 Valid Feb 26/0000 UTC thru Mar 01/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low/trough over the Pacific Northwest... ...Undercutting shortwave arriving over northern CA Wed... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/GEFS mean Confidence: Slightly below average The guidance overall shows rather good agreement with the evolution of a slow-moving, positively tilted upper trough and associated closed low currently over the Pacific Northwest that should shift offshore on Tuesday underneath a strong deep layer ridge over the Gulf of Alaska and adjacent areas of northwest Canada. The closed low is expected to then begin shifting back to the east on Wednesday and is expected to open up into a progressive shortwave trough on Thursday that traverses the Intermountain West. In the meantime, there will be another system approaching the West Coast with a focus on northern CA by early Wednesday. This system will be the remnants of an upstream closed low that will weaken and undercut the aforementioned closed low offshore of the Pacific Northwest. A surface wave associated with this next system will move into northwest CA and then southern OR by late Wednesday. The 00Z ECMWF/CMC solutions are the farthest north with the low track of this system and suggest a surface wave riding up across western OR, but the remaining guidance including the 00Z NAM/GFS and 00Z UKMET are all clustered farther south toward far northern CA and then southern OR. Regarding the details of the closed low shifting back inland, the ECMWF and the 12Z ECENS mean are on their own in keeping the closed low offshore all the way through the period, although the ECMWF has trended a tad farther east. Every other model begins to shift the energy notably farther inland by the end of the period. The NAM is the fastest solution, followed then by the GFS. The UKMET is a little slower than the GFS, with the CMC a little slower and actually splitting the difference between the UKMET and ECMWF. The 00Z GEFS mean is actually a little faster than the GFS, and for the time being, this cluster will be preferred as a compromise. ...Shearing shortwave energy over the Midwest/OH Valley... ...Weak surface wave crossing the OH Valley/Mid-Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average A fast moving shortwave will work through the Upper Midwest and Great Lakes mid-week underneath a larger closed low over central Canada. The guidance at least with this feature are in good agreement, and so a general model blend will be preferred with this. ...Southern U.S./Gulf Coast Region... ...Surface wave over the Southeast by Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/UKMET Confidence: Average Broad zonal to slightly southwest flow aloft will persist through the forecast period across the southern U.S. and Gulf Coast region. Several subtle impulses will advance east within the fast zonal flow, with one weak shortwave by the end of the period actually favoring at least a weak surface low over the Southeast. Given concerns over the 00Z ECMWF/12Z ECENS mean upstream, these solutions will not be preferred at all over the entire Southern U.S., including the Gulf Coast states and the Southeast. The 00Z CMC/UKMET solutions both trended toward the flatter 00Z NAM/GFS camp and also with a bit more of a suppressed low track. There are concerns about the NAM though perhaps backing the mid level flow a little too much over the Southeast by Friday. Given the latest trends, a blend of the GFS and UKMET will be preferred. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison