Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 304 AM EST Sun Dec 09 2018 Valid Dec 09/0000 UTC thru Dec 12/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation...with Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Central Gulf and Southeast storm... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Slightly above average With the bulk of the storm now in the 24-36 hour time frame, model solutions have largely converged on a similar track and speed with the surface low developing in the northern Gulf of Mexico then jumping off the southeast US coast as it lifts northeast past Cape Hatteras. The speed has picked up a bit and this allows for a slight jog to the north with the precipitation shield seen in almost of the available guidance. Overall with respect to the QPF, the NAM and ECMWF are most similar with the deformation band axis lingering across south-central into southeastern VA the longest while the GFS and UKMET are lightest as it pulls away from the coast earlier. Thermally, all of the guidance has trended a bit warmer with the warm nose aloft. While there are mesoscale banding differences, in the general on the large scale with the synoptic and mass fields, the models are in good agreement and a general model blend is preferred. ...North, Great Lakes and Northeast Mon/Tues... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z GFS, 00z UKMET blend Confidence: Slightly above average 08z update: With the secondary trough axis moving across the northern Plains and Upper Midwest Tuesday night, the ECMWF is stronger and closes off a 500 mb low and also digs deeper compared to the GFS. Both models take this feature and becomes more negatively titled by the end of the forecast period however. The 00z CMC offered an uncharacteristic solution and overall was thrown out as outlier. ---previous discussion--- A trough will swing through the northern Great Lakes region through this forecast period. In general, model similarity is good, except for the 12z ECMWF which is much stronger/deeper with the trough as it pivots into the Northeast US Tuesday evening. It is also much sharper with a secondary trough in its wake. The GFS/NAM/CMC all show similar solutions and the UKMET seems to be an outlier. ...West into Rockies... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00z NAM/GFS and 12z ECMWF/ECENS mean blend Confidence: Below average 08z update: The ECMWF and CMC are still slower and lead to a cut-off low in the southwest US by Tuesday evening compared to the more open GFS and UKMET. There is above average uncertainty with more model spread, so overall lower confidence in the preferred blend. ---previous discussion--- Neutrally titled trough axis will begin to move onshore the Pacific Northwest over the next 24-48 hours where model agreement and similarity is high. Beyond that, upstream and downstream influences/model differences dominate a departure from best agreement and the trough shears/elongates. As the trough slows across southern California, some of the models forecast a cut-off low developing (12z ECMWF, 00z NAM) while the other guidance keeps this as open wave as it skirts through the Southwest US. The NAM pinches off this energy and drops it into Mexico, while the GFS holds it north into western Texas. The ECMWF has the feature completely cut off, stalling south of California. Finally, the CMC and UKMET are in the middle of the model spread, but vary on strength quite a bit. The trend seems to be to keep the feature open. A secondary trough pushes into the Pacific Northwest Tuesday night into Wednesday. Here, the CMC seems uncharacteristically deep/strong compared to the GFS/NAM/UKMET/ECMWF solutions. As such, for this cycle, will prefer a blend of the 00z GFS, 00z NAM with some weight toward the ECMWF/ECENS blend. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Taylor