Model Diagnostic Discussion NWS Weather Prediction Center College Park MD 151 PM EST Sat Jan 25 2020 Valid Jan 25/1200 UTC thru Jan 29/0000 UTC ...See NOUS42 KWNO (ADMNFD) for the status of the upper air ingest... 12Z Model Evaluation with latest Preferences and Confidence ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ...Deep closed low moving across the Northeast through Sunday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Above average Very good agreement persists in the evolution of a strong closed low currently across the Ohio Valley lifting northeast slowly through the weekend. The main core of this feature has good model consensus that it will drift through New England by Sunday and then over Atlantic Canada on Monday. The guidance at least through Monday is agreeable such that a general model blend can be preferred. ...Shortwave crossing the northern Plains through Sunday... ...Energy then digging through the Midwest/OH Valley on Monday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Non-NAM blend Confidence: Above average A shortwave currently over the northern High Plains will dive southeast across the Midwest and be racing across the OH Valley by late Monday. It will then reach the Mid-Atlantic coast Monday night. The 12Z NAM is a stronger outlier with this system, and so a non-NAM blend will be preferred. ...Shortwave crossing the Great Lakes late Monday... ...Dropping down across the OH Valley on Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z UKMET/ECMWF Confidence: Average In the wake of the shortwave on Monday, a new northern stream shortwave will drop southeast and cross the OH Valley on Tuesday. The 12Z CMC is a stronger and slower outlier solution with this energy. However, there have been some global model trends (especially with the non-NCEP solutions) to be stronger with this energy. In fact, the 12Z NAM is now suddenly among the weakest and most progressive solutions, with the 12Z GFS only a little slower/deeper. The 12Z UKMET and 12Z ECMWF are reasonably well clustered and tend to best approximate the model consensus in between the deep CMC and weaker NAM/GFS, so a blend of the UKMET and ECMWF will be preferred at this point. ...Split flow trough crossing the West coast on Sunday... ...Energy ejecting through the Southwest and Plains by Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: Blend of the 12Z NAM/GFS/ECMWF Confidence: Slightly below average The models all take a progressive split-flow trough across the West Coast on Sunday, with a southern stream portion of the energy then dropping down across the Southwest and amplifying into a closed low as it approaches the southern High Plains by early Tuesday. Meanwhile, the northern stream component of the trough will be over the northern High Plains. The 12Z CMC is an outlier with both northern and southern stream components as it is likely too strong/slow and too far north with the southern stream energy, and too slow with the energy in the northern stream. The 12Z UKMET also appears to be too slow/deep with its handling of the northern stream energy and like the CMC tends to support a bit more interaction between northern and southern stream troughs late in the period. The NAM/GFS and ECMWF all favor a bit more stream separation at least through this period with just some subtle northern/southern stream trough interaction at the very end of the period as the energy approaches the MS Valley. Will prefer a blend of the NAM/GFS and ECMWF with both streams at this time given they still tend to have the stronger ensemble support. ...Progressive upper trough over the Pacific Northwest Tuesday... ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Preference: General model blend Confidence: Average Yet another in a series of Pacific shortwave troughs will arrive on Tuesday across the Pacific Northwest. Overall, the guidance has tended to trend a little stronger with this system, but there is better agreement on timing and depth. Will prefer a general model blend at this point. Model trends at www.wpc.ncep.noaa.gov/html/model2.shtml 500 mb forecasts at www.wpc.ncep.noaa.gov/h5pref/h5pref.shtml Orrison