Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1151 PM EST Mon Feb 25 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/18Z 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 12Z ECMWF is the farthest north with the low track of this system and suggests a surface wave riding up across western OR, but the remaining guidance is all clustered farther south toward far northern CA and then southern OR. Regarding the details of the closed low shifting back inland, the 12Z ECMWF and the 12Z ECENS mean are on their own in keeping the closed low offshore all the way through the period. Every other model begins to shift the energy inland. The 00Z NAM is the fastest solution, followed then by the 00Z GFS. The 12Z UKMET is a little slower than the 00Z GFS, with the 12Z CMC even slower and actually splitting the difference between the UKMET and ECMWF. The 18Z GEFS mean favors the 00Z GFS, and for the time being, this cluster will be preferred since these solutions are close to the overall model consensus. ...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 and 18Z GEFS mean Confidence: Slightly below average Broad zonal to slightly southwest flow aloft will persist through the forecast period across the southern US 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 12Z ECMWF/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. There are concerns that the 12Z CMC/UKMET solutions may be a little too far north with the surface wave by Friday, and at this point the UKMET also looks way too strong considering the zonal flow pattern. A more suppressed/flatter shortwave and surface low evolution will be preferred for the time being which is what the 00Z GFS/18Z GEFS mean and 00Z NAM all favor, although there are concerns about the NAM perhaps backing the mid level flow a little too much over the FL Peninsula by Friday. Thus, a solution toward the GFS/GEFS mean camp will be the choice for now. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison