Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 132 PM EST Mon Mar 04 2019 Valid Mar 04/1200 UTC thru Mar 08/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation Including Preference and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep trough over the Great Lakes/Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average There is generally good large scale agreement with the models on the deep trough that will be evolving over the Great Lakes region and adjacent areas of the Northeast going through midweek. A couple of shortwave impulses will be digging through the base of the trough with impacts on the Midwest/OH Valley, but the guidance shows only very modest differences with these features. A general model blend will be preferred as a result. ...Deep closed low center near 32N 143W... ...Arriving across CA by Wed... ...Shearing downstream across the central Plains on Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-GFS blend after 60 hours Confidence: Above average The models take a deep closed low near 32N 143W and eject it progressive east into CA by Wednesday as an open shortwave trough as the energy gets caught up underneath larger scale and stronger height falls dropping south offshore the Pacific Northwest. The guidance shows good agreement as the energy crosses CA on Wednesday, but then on Thursday as the energy ejects out across the central Plains, the 12Z GFS becomes a stronger outlier solution which helps to bring a wave of low pressure a bit farther northeast up across southeast KS and southwest MO along with a downstream warm front that is farther north across the mid-MS Valley. The remaining guidance agrees with a relatively flatter evolution which makes more sense considering the downstream confluent flow aloft over the Midwest that this energy will be encountering. Will recommend a general model blend as the energy initially advances inland, but after about 60 hours, a non-GFS blend will be preferred. ...Deep closed low near the Pacific Northwest... ...Undercutting shortwave trough approaching CA on Thurs... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average A rather deep closed low will be positioned near the Pacific Northwest for the next few days as shortwave energy drops down around the west side of the height falls and undercuts the base of the trough with a trajectory toward the West Coast and an emphasis on CA. Differences with the closed low itself are quite modest through the period, and have clustered together a bit better this cycle. Regarding the shortwave undercutting the closed low and approaching CA by Thursday, the 12Z NAM becomes a bit of a stronger outlier compared to the global models. Will prefer a non-NAM blend at this point considering the better overall clustering seen now with the global models. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison