Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 1203 AM EST Thu Jan 02 2020 Valid Jan 02/0000 UTC thru Jan 05/1200 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 00Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Upper low over Mexico shearing to the northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average The models show good agreement in lifting the southern stream closed low over Mexico off to the northeast over the next 24 hours with the system shearing out across the lower Rio Grande Valley as it become embedded in deep layer southwest flow ahead of an amplifying trough over the southern High Plains. A general model blend will be preferred. ...Amplifying longwave trough across the central U.S. ...Surface low from the Lower MS Valley to the Northeast... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: 00Z GFS/12Z ECMWF/18Z GEFS/12Z ECENS blend Confidence: Average A split flow upper trough with several small scale shortwave impulses will eject out across the Plains going through the end of the week, with initially the dominant amplification occurring down over the southern High Plains. However, by late Friday, as multiple pieces in the northern stream will dig down across the Midwest and lead to a more dominant northern stream trough and closed low evolution which will pick up the southern stream energy. This will lead to surface low over the lower MS Valley which will lift northeast toward the OH Valley by Saturday. This system will cross the northern Mid-Atlantic by Saturday evening with low pressure redeveloping near southeast New England by early Sunday. The 00Z GFS has trended closer to the 12Z ECMWF and GEFS/ECENS mean cluster regarding the low and and mid-level trough evolution. Toward the end of the period, the 12Z CMC is likely too progressive and too far south with the low center, with the 00Z NAM/12Z UKMET solutions perhaps closer to the GFS/ECMWF cluster, but just a tad more progressive. The preference with the energy from the Plains to the Easy Coast will toward a blend of the GFS/ECMWF and ensemble means. ...Shortwave trough/low impacting the Pacific Northwest... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-ECMWF blend Confidence: Average There remain some timing differences with respect to energy approaching Vancouver Island and the Pacific Northwest Thursday and Friday. Model agreement is actually rather good with the first shortwave and attendant surface low that aims for central British Columbia by late Thursday which will help drive a warm front up across western WA Thursday night. As this system, fast upstream Pacific flow will drive another shortwave and strong surface low eastward to near the northern end of Vancouver Island by Friday night. A cold front associated with this will then cross the Pacific Northwest by early Saturday. The 12Z ECMWF is a tad south of the model consensus with the second system, with the remaining guidance clustered farther north and supported by the latest GEFS mean and ECENS mean. Will prefer a non-ECMWF consensus for the time being. ...Split flow trough near the Pacific Northwest by Sun... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 18Z GEFS mean/12Z ECENS mean Confidence: Average The models show a new split flow upper trough and attendant front approaching the Pacific Northwest by Sunday. The 00Z NAM/GFS and 12Z UKMET are a bit faster than the 12Z CMC/ECMWF solutions with the northern portion of the trough. Meanwhile, the 12Z CMC and 12Z UKMET are slow outliers with the southern portion of the trough. For now, a blend of the ensemble means will be preferred since this cluster appears to have a reasonable handle on both portions of the split flow trough. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison