Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1157 PM EST Tue Feb 26 2019 Valid Feb 27/0000 UTC thru Mar 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low/trough impacting the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-CMC blend Confidence: Above average The models have come into very good agreement with the details of the closed low offshore the Pacific Northwest that is expected to shift back east and open up into a progressive shortwave over the Intermountain West going through Friday. Although the 12Z CMC is the most progressive solution overall and outruns every other piece of guidance as the energy moves inland. A non-CMC blend will be preferred. ...Shearing shortwave energy over the Midwest/OH Valley... ...Weak surface wave crossing the OH Valley/Mid Atlantic... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The latest model guidance is in good agreement with the shortwave as it shears across the Northern Plains and Upper Great Lakes under a closed mid-level low over central Canada. Very modest differences are noted with the surface wave activity over the OH Valley and Mid-Atlantic, and based on the degree of clustering, a general model blend will again be preferred. ...Deep closed low/trough over southern Canada... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 60 hours Non-GFS blend...after 60 hours Confidence: Slightly above average All of the models bring a deep closed low and an elongated west/east trough axis over southern Canada by Friday and Saturday. These height falls will also spread south across the northern tier of the CONUS. The guidance is generally in good agreement with the mass field details, but the 00Z GFS is displaced a tad east of the model consensus with its closed low by the end of the period. A general model blend would be good through 60 hours, followed by a non-GFS blend thereafter. ...Gulf Coast/Southeast/Mid-Atlantic... ...Surface wave activity over the Southeast Thu/Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...first shortwave/surface low 00Z GFS/18Z GEFS mean/12Z UKMET blend...second shortwave/surface low Confidence: Average...through 60 hours Below average...after 60 hours The guidance allows for a pair of shortwave impulses to impact the Gulf Coast region, Southeast and Mid-Atlantic region from late Thursday through early Saturday. A lead shortwave shearing across the mid-MS Valley on Thursday will favor a weak surface wave developing over the Southeast Thursday night and early Friday. The global model consensus along with the GEFS/ECENS member suites overwhelmingly favor a more suppressed and weaker surface low versus the 00Z NAM which is more amplified, and farther north/stronger with its surface low. A non-NAM blend will be preferred with the initial shortwave/low center. A second shortwave will move across the Gulf Coast states/Southeast on Friday and through early Saturday which may result in a new weak area of low pressure across the Southeast coastal plain. The 00Z NAM again is a tad more amplified with this, but so is the 12Z ECMWF which happens to be the slowest solution. The remaining guidance is flatter/weaker, although the 12Z CMC tries to being more low pressure (albeit weak) farther north into the Mid-Atlantic region. The 00Z GFS and 12Z UKMET, along with the 18Z GEFS mean tend to align more closely with the model consensus, and a blend of these solutions will be preferred with this second shortwave and associated wave activity. Confidence becomes limited by the end of the period. ...Southern stream trough/surface low approaching CA Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The model guidance agrees in gradually deamplifying a southern stream closed low offshore of CA by later Friday, and thus support progressive shortwave and associated surface low approaching the state by early Saturday. Given reasonably good model clustering with timing and depth, a general model blend will be preferred with this system. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison