Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 209 AM EST Wed Feb 27 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: General model blend...through 60 hours 00Z GEFS/12Z ECENS mean blend...after 60 hours Confidence: Slightly above average The models have come into very good agreement at least through about 60 hours 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. However, by later Friday, the 00Z non-NCEP guidance including the UKMET, CMC and ECMWF all begin to lag the 00Z NAM/GFS solution. There is some ensemble support from the 00Z GEFS ensemble suite for a somewhat slower evolution, but actually the 12Z ECENS suite tends to be a little more progressive. A general model blend should suffice through 60 hours, but based on the timing spread thereafter, a blend of the GEFS/ECENS mean will then 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 deep closed 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: 00Z GEFS/12Z ECENS mean/00Z ECMWF blend 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 00Z GFS tends to be on the somewhat on the southeast side of the model cluster at this point. The 00Z GEFS mean and 12Z ECENS mean both favor a closed low position a bit west of the GFS by the end of the period. The 00Z CMC is noted to be taking its closed low a little farther northeast of the model consensus. So, based on at least some modest model spread later in the period, a blend of the 00Z GEFS/12Z ECENS mean and 00Z ECMWF will be preferred which is also relatively well supported by the 00Z UKMET. ...Gulf Coast/Southeast/Mid-Atlantic... ...Surface wave activity over the Southeast Thu/Fri/Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend...first shortwave/surface low 00Z UKMET/CMC/ECMWF blend...second shortwave/surface low Confidence: Above average...first shortwave/surface low Below average...second shortwave/surface low 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 system and will be discounted. The 00Z GFS though is now appearing as if it is a bit too progressive as the 00Z GEFS mean is a little slower with the energy. The 00Z UKMET/CMC/ECMWF solutions are all slower than the GFS and better supported by the 12Z ECENS mean. So, with limited confidence, will prefer a solution toward the non-NCEP consensus with this second system. ...Southern stream trough/surface low approaching CA Sat... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend...through 72 hours 00Z UKMET/CMC/ECMWF blend...after 72 hours Confidence: Slightly 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. There is some timing spread that appears after 72 hours as the non-NCEP models begin to outrun the 00Z NAM/GFS solutions. Overall, it appears both the NAM and GFS could be a bit too strong at the end of the period, as the 00Z GEFS mean and 12Z ECENS mean both favor a solution a little flatter and faster by the end of the period. Will favor the non-NCEP model consensus after 72 hours, but a general model blend should suffice prior to this. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison