Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 155 AM EST Thu Jan 30 2020 Valid Jan 30/0000 UTC thru Feb 02/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with Final Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Primary Mid-level trough over the Four Corners now, crossing south Texas Thursday and the Southeast Friday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of 29/12Z ECMWF/UKMET with some 29/12Z CMC and 30/00Z GFS Confidence: Average A leading shortwave trough off a ridge over the interior Pacific Northwest early this evening will swing across northern Mexico through Thursday then south Texas on Thursday night. A secondary trough digs in behind Thursday night, weakening the mid-level energy as it crosses the Southeast Friday. The 30/00Z NAM had decent run to run consistency, but that left the NAM on the slower side of the envelope of solutions. ...Evolution of Trough over Eastern Half of the U.S. Friday into Saturday ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~ Preference: Blend of 30/00Z ECMWF/GFS/NAM Confidence: Below Average Complex interaction of several streams leads to a below average confidence forecast from Thursday night/Friday morning through Saturday. At jet-stream level, the flow pattern seems straight forward enough with the nose of a 110 to 130 kt upper level jet topping the western U.S. ridge and nosing into the Upper Midwest and western Great Lakes region...with the axis of 130 to 150 kt upper level jet oriented from southwest to northeast from the Gulf of Mexico into the Mid Atlantic region and approaching southern New England. Part of the jet energy drops southward across the middle of the country, with the 30/00Z NCEP guidance forming a trough which drops south into the Central/Southern Plains in the wake of the system mentioned above...while the non-NCEP guidance was more inclined to have a more unified flow with little mid-level development within the flow. Focus is greatest here considering its impacts on the development of a surface low along the Southeast coast that would clip parts of the Mid-Atlantic and Northeast U.S on Days 2/3. With the 30/00Z ECMWF moving towards the idea of a split between northern and southern stream...suspect there was a slow convergence on a common solution. However, there was still disagreement on how deep/strong the southern stream will be...with the NCEP guidance some 60 meters to 80 meters deeper than the ECMWF. For now, think starting with the NCEP guidance and tempering the depth of the system with the ECMWF should be a reasonable first guess. The UKMET started to show a split flow but not nearly to the extent while the Canadian held its ground on a more unified flow. Farther to the north, there remains some disagreement in terms of how quickly the northern stream wave will propagate eastward towards the Northeast U.S...but a blend of the ECMWF/GFS should provide a decent first guess that minimizes the differences. ...Longwave trough approaching the west coast of Canada Friday night/Saturday and downstream atmospheric river into the Pacific Northwest late Thursday into Saturday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 30/00Z ECMWF/UKMET/ECENS/NAM Confidence: Average The passage of a shortwave and accompanying cold front into British Columbia on Thursday will bring initially zonal flow into western Canada that amplifies as ridging increases ahead of an upstream shortwave Friday. Given reasonably good run-to-run consistency in the 30/00Z NCEP guidance, deterministic consensus and ensembles continue to favor a 30/00Z ECMWF/UKMET/NAM for the trough position and the downstream atmospheric river moving into the Pacific Northwest. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Bann