Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1201 AM EST Sun Mar 11 2018 Valid Mar 11/0000 UTC thru Mar 14/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z model evaluation...with model preferences and confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Surface low weakening over the southeast Canadian maritimes... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models are in good agreement with the details of this system weakening and moving east over the next 24 to 36 hours. A general model blend will be preferred. ...Shortwave energy crossing the MS/TN Valleys through Sunday... ...Surface low tracking across the Gulf Coast States on Sunday... ...Strong surface low redevelopment offshore the East Coast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/00Z GEM-REG...through 36 hours 00Z GFS/12Z ECMWF blend...after 36 hours Confidence: Average The models are gradually coming into better agreement with the details of the digging shortwave trough across the middle Mississippi Valley and its evolution across the Tennessee Valley on Sunday. Also, there are trends finally toward better model clustering with the surface low evolution across the Gulf Coast states and the strong redevelopment of low pressure Monday and Tuesday offshore the East Coast. The mass field spread through the latest day 1 period (12Z Monday) is noted with the 00Z NAM being a tad slower and farther south with the track of its 500/700 mb low center/vorticity versus the 00Z GFS which is a little more progressive and farther north. The 12Z UKMET/12Z CMC and 12Z ECMWF are all a little weaker than the NAM/GFS camp, but their placement through 12Z Monday is generally in between the NAM and GFS. The 00Z GEM regional model favored a stronger solution like the NAM and GFS, with its solution close to the model consensus. The 12Z GFS though has more support from the 18Z GEFS mean and to some extent the 12Z ECENS mean. The main concern is that the non-NCEP guidance appears too weak through the day 1 period, and as a result the preference will be toward a blend of the GFS and GEM-regional for the day 1 period. After 36 hours, the models all agree on a lead surface wave ejecting northeast off the southern Mid-Atlantic region and then a strong redevelopment of low pressure east of the Mid-Atlantic coast Monday night. This then lifts north-northeast offshore southeast New England on Tuesday before crossing over Nova Scotia by early Wednesday. The 00Z GFS is on the western side of the model spread, with the 12Z ECMWF just a little east of the GFS. The 12Z CMC and 12Z UKMET are the farthest east with the surface low track, with the UKMET also slower and farther south compared to the model consensus. The 18Z GEFS mean and 12Z ECENS mean are a tad east of the GFS and close to the ECMWF. Based on a collective westward trend generally seen in the guidance, outside of the UKMET solution, but especially with the NAM, GFS and ECMWF, the preference will be to weight toward the western side of the model spread. Therefore, will be leaning toward a GFS and ECMWF after 36 hours, with a tad more weighting suggested toward the GFS solution. ...Deep closed low dropping down over the Great Lakes region... ...Arriving over the Northeast through Tuesday/Wednesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS and 12Z ECMWF Confidence: Average The models all agree in dropping strong height falls with an amplifying trough and closed low down over the Great Lakes region through Monday and then the Northeast through Tuesday and into Wednesday. Toward the end of the period the 00Z NAM tends to become a stronger solution relative to the remaining guidance. The 12Z CMC appears to be shifting its height falls a little southeast of the model consensus. The better model clustering is towards the GFS and ECMWF, and a blend of these solutions will be preferred. ...Shortwave crossing the West Coast and into the Great Basin... ...Energy shearing southeast across the High Plains by Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The models all take a shortwave trough across the West Coast through Sunday and into the Great Basin through Monday. Thereafter, the guidance takes the energy around the crest of the large scale ridge axis developing over the West and drops the energy down over the High Plains where it will gradually shear out. The models show decent agreement with timing and depth outside of the 12Z CMC which appears to be too weak by Monday. Will prefer a non-CMC blend at this point with the energy. ...Large closed low off of the West Coast Monday night... ...Surface cyclone strengthening off of the Pacific Northwest coast Monday night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 00Z GFS/12Z ECMWF...through 60 hours 00Z GFS/18Z GEFS mean/12Z ECENS mean blend...thereafter Confidence: Slightly below average A large deep layer closed low offshore the West Coast will be moving east over the next few days and will approach the West Coast by Tuesday and then begin to spread height falls inland on Wednesday as multiple shortwaves rotate around the base of the trough and lift northeast. This will bring surface low pressure up off the Pacific Northwest on Monday, and then with a new area of low pressure attempting to consolidate by Wednesday offshore as additional energy digs into the base of the trough. The better model clustering resides with the 00Z GFS and 12Z ECMWF through Monday, but thereafter the ECMWF appears to be too ill-defined with the next surface low evolution off the West Coast, with the GFS having support from the 18Z GEFS mean and 12Z ECENS mean with a stronger low offshore by Wednesday. The 00Z NAM supports this idea as well. So, will prefer a blend of the GFS and ECMWF through 60 hours, and then lean toward a blend of the GFS, GEFS mean and ECENS mean thereafter. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison