Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1148 AM EST Thu Mar 07 2019 Valid Mar 07/1200 UTC thru Mar 11/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preference and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Closed low in Pacific the Northwest, breaking into two with eastward progression... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/CMC, 12z GFS blend Confidence: Average A closed low over the Pacific Northwest will begin to break down in the next 24 hours. Two pieces of energy then will split, one of which is expected to become absorbed with a system tracking through Alberta/Saskatchewan. There is rather good model agreement on that scenario of the forecast. Differences on that other piece of energy are more substantial and it is more complex with the other approaching trough from the eastern Pacific. Some models shear it out, taking even smaller pieces eastward across the northern Rockies while others stall/close off more then eventually wait for the west coast trough to absorb it. It seems the consensus for the latter solution, which would favor the ECMWF/CMC more though the 12z GFS does show this happening somewhat as well. ...Upper Midwest Deepening Surface Low This Weekend... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/CMC, 12z GFS blend Confidence: Slightly below average A positively tilted shortwave will enter the Southwest tonight and will track across the southern Rockies late Friday, emerging as a negatively tilted shortwave in the Central Plains for Saturday with a developing surface low. As the cyclone deepens toward the Upper Midwest, a swath of heavy precipitation will develop across portions of the Dakotas, MN, and WI Saturday into Sunday. Overall, model agreement is fair though there are still spatial differences in the low track that will introduce precipitation type differences across IA/MN/WI. The GFS and NAM are on the northern/northwest side of the forecast envelope, with its low position at 10.00z across southeast Minnesota and also is a bit faster compared to the rest of the models. Meanwhile, the UKMET is the southern solution, having its low across southern IA at the same time. The 00z ECMWF/CMC remain in the middle, though are slightly tilted toward the northern solutions at this time. The cyclone then quickly moves into the UP of MI. The UKMET upper level trough is the most different compared to the rest of the deterministic and ensemble guidance. Based on this, a blend of the ECMWF/CMC with some inclusion of the GFS is preferred at this time. ...Next Pacific trough and surface low nearing Central West Coast Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z ECMWF/UKMET, 12z GFS blend Confidence: Average Several pieces of energy coming out of the eastern Pacific will eventually carve out a deeper trough over the west coast late in the weekend. In the larger scale sense, the models are in pretty good agreement with the evolution though there are some differences noted with the individual shortwaves as well as how much energy closes off over California. The GFS/NAM remain closest to the coast with the main upper level low and also close off the feature while the CMC/UKMET are further offshore/open and further removed from the northern stream energy. At the surface, a low approaches the northern California coast by Saturday afternoon then stalls out before dropping down the coast. Through 09.18z models are in good agreement but diverge quite a bit after that with the low track. The NAM/GFS take it more onshore while the ECMWF/UKMET/CMC are further offshore, especially the CMC which is an outlier in this case. As such, will lean on a ECMWF/UKMET/GFS blend at this point, noting that there is increasing model spread Sunday onward. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor