Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1211 AM EST Wed Nov 13 2019 Valid Nov 13/0000 UTC thru Nov 16/1200 UTC ..See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z NAM/GFS Evaluation with Preliminary Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Shortwave tracking from the Northwest to the Plains by Wed and Northeast on Thu... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average The models show similarly with this system. ...Mid-level shortwave reaching the Lower Mississippi Valley late Thursday interacting with a weakening closed low crossing southern Texas around the same time... ...Closed low development over the Southeast by late Fri... ...Cyclogenesis off the Southeast Coast on Fri... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 50% 00Z GFS, 25/25% 12Z ECMWF/UKMET blend Confidence: Average Two shortwaves are expected to come rather close to one another along the central Gulf Coast Thursday night. One originates from northern Mexico while the other is a northern stream wave from the southern Plains and Lower Mississippi Valley. The 12Z CMC shows a different timing with a slower southern wave and faster northern wave. Meanwhile, the 00Z NAM begins to show stronger with the mid-level wave and winds up developing a surface low along a coastal frontal boundary and tracking the low well north of the available ensemble/deterministic guidance through the western Atlantic. The timing of the 12Z ECMWF's 500 mb shortwave is on the slow side of the ensemble spread, but does not look completely unreasonable, especially when blended with the similar 12Z UKMET position. The resulting surface low off of the Southeast U.S. is strongest in the 12Z UKMET and weakest in the 12Z ECMWF with the 00Z GFS in the middle. A 3-way blend of the 00Z GFS/12Z ECMWF/12Z UKMET is considered best at this time with more weight toward the 00Z GFS. ...Strong northern stream trough brushing the Northeast by Fri evening... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Despite some minor timing/depth differences, the models show similarly with this system. ...Mid-level shortwaves approaching the West Coast on Thu into Fri... ...Mid-level trough reaching the northern Rocky Mountains Saturday morning... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend, transitioning to a 12Z ECMWF/CMC blend by 12Z/16 Confidence: Slightly above average The models show good agreement with a relatively weak mid-level shortwave forecast to reach the Oregon/California coasts on Thursday. A second shortwave to the north, forecast to reach Washington early Friday, shows some greater differences. The 12Z UKMET/CMC are faster with the timing of this weave to reach the Pacific Northwest. Downstream, however, the 12Z CMC slows down with this system by Saturday morning while the 12Z UKMET remains faster. Meanwhile, the 00Z NAM/GFS show greater amplification into the West by Saturday morning resulting in colder temperatures compared to the agreeable ensemble means and 12Z ECMWF/CMC. Therefore, the overall preference will transition to a 12Z ECMWF/CMC blend by 12Z/16. ...Closed low development offshore southern California Fri night... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: non 12Z UKMET blend Confidence: Average The models show moderate differences with the timing of a closed low offshore of southern California by Saturday morning. The 12Z UKMET stands out with a slower track compared to the remaining guidance, so a non 12Z UKMET blend will be recommended at this time. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Otto