Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 201 PM EST Sat Mar 10 2018 Valid Mar 10/1200 UTC thru Mar 14/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z model evaluation with final preferences ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low weakening in the vicinity of New Brunswick and Nova Scotia tonight... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Shortwave(s) dropping southeastward across the Plains today and Mississippi valley on Sunday... ...Surface low tracking across the Gulf Coast States on Sunday with redevelopment off of the Southeast coast Sunday night before tracking north-northeastward on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z UKMET blend Confidence: Below average Significant model spread and poor run to run continuity remains regarding the main shortwave trough axis and mid-level vorticity max as it reaches the Southeast. However some clarity appears to be appearing with the 12Z deterministic modwls which show the 12Z GFS is likely at least a little too far north with its mid-level vorticity center 12Z/12 over the southern/central Appalachians. The non 12Z GFS models generall agree through this time frame with a more southern position. As the vorticity max continues eastward toward the Mid-Atlantic or Southeast coastline, a surface low is expected to develop and intensify in the western Atlantic. There are still differences with the latest deterministic guidance, but the 12Z UKMET appears to have shifted away from the consensus toward the south and now lies on the southern end of the deterministic and ensemble spread. The previously south 00Z CMC came north with its 12Z run to be closer to the 12Z NAM/GFS/ECMWF. Valid 00Z/13, among the non-12Z UKMET models, the 12Z ECMWF/cmc are farthest east, while the 12Z GFS if farthest north while both the 12Z NAM/GFS are more to the west with their low tracks. A preferred position would be just west of the agreeable 09Z SREF mean, 12Z GEFS mean and 00Z ECMWF mean, which is near a 4-way blend of the 12Z NAM, 12Z GFS, 12Z ECMWF and 12Z CMC. WPC thanks that the 12Z UKMET is too far displaced to the south/east given recent deterministic trends. This preference continues through 00Z/14 with models trading places with which one is closest to the coast or farther north. Therefore, a 4-way blend will be the preference, excluding the 12Z UKMET. Just to reiterate, the ensemble spread and poor run to run consistency lowers confidence with this storm. ...Closed mid-level low reaching the Great Lakes Monday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Differences are not too large here, and with the 12Z UKMET joining the remaining consensus, enough agreement is in place among the 12Z deterministic models to support a general model blend. This blend is in line with the latest ensemble spaghetti height plots at 500 mb. ...Low amplitude shortwave approaching California from the west later today... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non 12Z CMC blend Confidence: Above average Despite some minor differences, models have converged on a similar solution here. The 12Z CMC, however, remains a bit slower at the surface and weaker aloft with the shortwave. Therefore, a non 12Z CMC blend is recommended with this system. No significant changes were noted with the 12Z ECMWF/UKMET/CMC compared to their previous 00Z cycles. ...Large closed low off of the West Coast Monday night... ...Surface cyclone strengthening off of the Pacific Northwest coast Monday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 12Z GFS/12Z ECMWF/12Z UKMET blend Confidence: Average The ensemble scatter low plots support a 12Z GFS/12Z ECMWF/12Z UKMET blend with surface low forecast to develop near 40N, between 300 and 400 miles west of the northern California coast Monday evening. The 12Z NAM appears a bit too aggressive and eastward with the formation of a closed low, embedded within the larger scale closed low off of the West Coast Monday night. The 12Z CMC shows displacement from the above blend and when compared to the ensemble scatter low plots, currently lying toward the edge of the ensemble envelope. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto